http://www.vitaminforum.net/ Tue, 06 Jan 2009 13:17:54 -0600 MyBB http://www.vitaminforum.net/thread-15.html Sat, 27 Dec 2008 20:53:40 -0600 slimgirl http://www.vitaminforum.net/thread-15.html but she didn't say what it did exactly. Does anyone know about this or is it just a myth??]]> but she didn't say what it did exactly. Does anyone know about this or is it just a myth??]]> http://www.vitaminforum.net/thread-14.html Mon, 15 Dec 2008 05:34:32 -0600 dragon117 http://www.vitaminforum.net/thread-14.html Calcium: It's a mineral not a vitamin but you still need it for strong and healthy bones. You get lots of calcium from milk, cheese, and eggs. It's also in cereals, veg and bread.
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Iron: This one's also a mineral, it's needed to produce the red blood cells that make up most of our blood.]]> Calcium: It's a mineral not a vitamin but you still need it for strong and healthy bones. You get lots of calcium from milk, cheese, and eggs. It's also in cereals, veg and bread.
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Iron: This one's also a mineral, it's needed to produce the red blood cells that make up most of our blood.]]> http://www.vitaminforum.net/thread-12.html Mon, 15 Dec 2008 05:31:08 -0600 dragon117 http://www.vitaminforum.net/thread-12.html Vitamin C: Helps your body to fight infection, so eat lots of fruit and veg if you don't want to end up with a cold like this bloke.
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Vitamin D: You need this to help your teeth grow strong and stay that way. It's found in very few foods e.g. oily fish and margarine.]]> Vitamin C: Helps your body to fight infection, so eat lots of fruit and veg if you don't want to end up with a cold like this bloke.
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Vitamin D: You need this to help your teeth grow strong and stay that way. It's found in very few foods e.g. oily fish and margarine.]]> http://www.vitaminforum.net/thread-11.html Mon, 24 Nov 2008 23:17:14 -0600 Ineffable http://www.vitaminforum.net/thread-11.html Why should I take FOS supplements? What can they do for me? How will they help my health?

Let’s start with what FOS stands for. FOS stands for fructo-oligosaccharides. This is a highfaluting way of referring to good old fruit sugars, such as you’ll find in many fruit and vegetables. You may be more familiar with its common name of fructose. FOS, along with GOS (galacto-oligosaccharides, or galactose), can only be partly digested by the human body. The same applies to inulin (not to be confused with insulin), which is a polysaccharide and a form of fiber.

The immediate question to ask here is if we can only partially digest FOS, GOS and inulin, why take them as supplements? The answer is that while we don’t digest them, the friendly flora living in your gut do. These bacteria (rather them than me) live inside the bowel and aid in good health and digestion. Some of these friendly bacteria are the lactobacillus and the bifidus species. These bacteria help keep toxic bacteria out of your system. If you’ve ever been on antibiotics and have suffered a yeast infection or a slightly upset tummy, this is why: the antibiotics have killed of your friendly bacteria, so replacing them (live yoghurt is the easiest way) plus giving them a beneficial environment to live in with FOS, GOS and inulin supplements.

Now the other great thing about FOS, GOS and inulin supplements is that they can possibly help in lowering blood sugar levels (although studies are still attempting to confirm this). This is good news for those who have Type 2 diabetes (non-insulin dependent or adult-onset diabetes), as they need to get their blood sugar levels down and reduce the amount of insulin (insulin, not inulin this time) in their system (producing too much insulin means that your cells become insensitive to it and won’t respond to it so the sugars in the bloodstream can be turned into energy, so the sugar just stays in the bloodstream). As inulin in particular has no effect at all on blood sugar (blood glucose), it can help in managing Type 2 diabetes (and probably is no bad thing for Type 1 diabetics either, if blood sugar management through diet rather than insulin dosage is an issue). Several scientific studies so far have shown that in people with raised triglyceride levels (either through pre-diabetes or full-blown Type 2 diabetes), taking inulin supplementation at a rate of 10 g a day for 8 weeks lowered their triglyceride levels and got their fasting blood sugar levels down significantly and also lowered insulin concentration.

While it is possible to get a reasonable intake of FOS, GOS and inulin through certain vegetables, it’s also true that these vegetables are a bit oddball and not to everyone’s taste; the list includes Jerusalem artichoke (which isn’t the same as the globe artichoke at all – they just taste similar), onions, leeks, garlic, burdock, chicory and asparagus, and even some other common plants like dandelions. Taking a FOS and/or inulin supplement is much easier than trying to munch your way through dandelions like a rabbit, trying to find a good supply of Jerusalem artichokes or having the bad breath that comes from eating garlic.
One more thing in the trivia department: inulin may play a big role in the future in fighting the fuel crisis and global warming, as it can be converted into ethanol, which is a biofuel gasoline subsitute. Good for your insides and good for the planet!
Ineffable
EBGREEN Marketing
Powerhouse Supplements]]> Why should I take FOS supplements? What can they do for me? How will they help my health?

Let’s start with what FOS stands for. FOS stands for fructo-oligosaccharides. This is a highfaluting way of referring to good old fruit sugars, such as you’ll find in many fruit and vegetables. You may be more familiar with its common name of fructose. FOS, along with GOS (galacto-oligosaccharides, or galactose), can only be partly digested by the human body. The same applies to inulin (not to be confused with insulin), which is a polysaccharide and a form of fiber.

The immediate question to ask here is if we can only partially digest FOS, GOS and inulin, why take them as supplements? The answer is that while we don’t digest them, the friendly flora living in your gut do. These bacteria (rather them than me) live inside the bowel and aid in good health and digestion. Some of these friendly bacteria are the lactobacillus and the bifidus species. These bacteria help keep toxic bacteria out of your system. If you’ve ever been on antibiotics and have suffered a yeast infection or a slightly upset tummy, this is why: the antibiotics have killed of your friendly bacteria, so replacing them (live yoghurt is the easiest way) plus giving them a beneficial environment to live in with FOS, GOS and inulin supplements.

Now the other great thing about FOS, GOS and inulin supplements is that they can possibly help in lowering blood sugar levels (although studies are still attempting to confirm this). This is good news for those who have Type 2 diabetes (non-insulin dependent or adult-onset diabetes), as they need to get their blood sugar levels down and reduce the amount of insulin (insulin, not inulin this time) in their system (producing too much insulin means that your cells become insensitive to it and won’t respond to it so the sugars in the bloodstream can be turned into energy, so the sugar just stays in the bloodstream). As inulin in particular has no effect at all on blood sugar (blood glucose), it can help in managing Type 2 diabetes (and probably is no bad thing for Type 1 diabetics either, if blood sugar management through diet rather than insulin dosage is an issue). Several scientific studies so far have shown that in people with raised triglyceride levels (either through pre-diabetes or full-blown Type 2 diabetes), taking inulin supplementation at a rate of 10 g a day for 8 weeks lowered their triglyceride levels and got their fasting blood sugar levels down significantly and also lowered insulin concentration.

While it is possible to get a reasonable intake of FOS, GOS and inulin through certain vegetables, it’s also true that these vegetables are a bit oddball and not to everyone’s taste; the list includes Jerusalem artichoke (which isn’t the same as the globe artichoke at all – they just taste similar), onions, leeks, garlic, burdock, chicory and asparagus, and even some other common plants like dandelions. Taking a FOS and/or inulin supplement is much easier than trying to munch your way through dandelions like a rabbit, trying to find a good supply of Jerusalem artichokes or having the bad breath that comes from eating garlic.
One more thing in the trivia department: inulin may play a big role in the future in fighting the fuel crisis and global warming, as it can be converted into ethanol, which is a biofuel gasoline subsitute. Good for your insides and good for the planet!
Ineffable
EBGREEN Marketing
Powerhouse Supplements]]> http://www.vitaminforum.net/thread-10.html Thu, 13 Nov 2008 13:53:34 -0600 Christian http://www.vitaminforum.net/thread-10.html
In general if you have a healthy diet you really don't need to take a lot of extra vitamins.]]>
In general if you have a healthy diet you really don't need to take a lot of extra vitamins.]]> http://www.vitaminforum.net/thread-9.html Thu, 13 Nov 2008 09:50:21 -0600 Christian http://www.vitaminforum.net/thread-9.html
But if I have a cold, I have found that making hot tea with Red Zinger or another citrus tea makes a great treatment if you add 1,000 mg of vitamin c. It really helps me, but I make SURE I drink lots of water to flush out the exta c.]]>
But if I have a cold, I have found that making hot tea with Red Zinger or another citrus tea makes a great treatment if you add 1,000 mg of vitamin c. It really helps me, but I make SURE I drink lots of water to flush out the exta c.]]> http://www.vitaminforum.net/thread-7.html Wed, 29 Oct 2008 22:01:29 -0500 Christian http://www.vitaminforum.net/thread-7.html http://www.vitaminforum.net/thread-6.html Wed, 29 Oct 2008 21:54:47 -0500 Christian http://www.vitaminforum.net/thread-6.html
I did it for a while and then stopped before the cut was healed. It turned out that the scar was small, and I think that if I had kept using it the scar would be even smaller and less noticible than it is.

Has anyone else used vitamin E for something like this?]]>
I did it for a while and then stopped before the cut was healed. It turned out that the scar was small, and I think that if I had kept using it the scar would be even smaller and less noticible than it is.

Has anyone else used vitamin E for something like this?]]> http://www.vitaminforum.net/thread-5.html Tue, 28 Oct 2008 16:07:46 -0500 Christian http://www.vitaminforum.net/thread-5.html Vitamin C

Vitamin C or L-ascorbate is an essential nutrient for a large number of higher primate species, a small number of other mammalian species (notably guinea pigs and bats), a few species of birds, and some fish.

The presence of ascorbate is required for a range of essential metabolic reactions in all animals and plants. It is made internally by almost all organisms, humans being the most well-known exception. It is widely known as the vitamin whose deficiency causes scurvy in humans. It is also widely used as a food additive.

The pharmacophore of vitamin C is the ascorbate ion. In living organisms, ascorbate is an anti-oxidant, since it protects the body against oxidative stress, and is a cofactor in several vital enzymatic reactions.

The uses and the daily requirement amounts of vitamin C are matters of on-going debate. People consuming diets rich in ascorbate from natural foods, such as fruits and vegetables, are healthier and have lower mortality from a number of chronic illnesses. However, a recent meta-analysis of 68 reliable antioxidant supplementation experiments involving a total of 232,606 individuals concluded that consuming additional ascorbate from supplements may not be as beneficial as thought.

Biological significance
Vitamin C is purely the L-enantiomer of ascorbate; the opposite D-enantiomer has no physiological significance. Both forms are mirror images of the same molecular structure. When L-ascorbate, which is a strong reducing agent, carries out its reducing function, it is converted to its oxidized form, L-dehydroascorbate. L-dehydroascorbate can then be reduced back to the active L-ascorbate form in the body by enzymes and glutathione.

L-ascorbate is a weak sugar acid structurally related to glucose which naturally occurs either attached to a hydrogen ion, forming ascorbic acid, or to a metal ion, forming a mineral ascorbate.

In humans, vitamin C is a highly effective antioxidant, acting to lessen oxidative stress, a substrate for ascorbate peroxidase, as well as an enzyme cofactor for the biosynthesis of many important biochemicals. Vitamin C acts as an electron donor for eight different enzymes:

* Three participate in collagen hydroxylation. These reactions add hydroxyl groups to the amino acids proline or lysine in the collagen molecule (via prolyl hydroxylase and lysyl hydroxylase), thereby allowing the collagen molecule to assume its triple helix structure and making vitamin C essential to the development and maintenance of scar tissue, blood vessels, and cartilage.

* Two are necessary for synthesis of carnitine. Carnitine is essential for the transport of fatty acids into mitochondria for ATP generation.

* The remaining three have the following functions:

o dopamine beta hydroxylase participates in the biosynthesis of norepinephrine from dopamine.
o another enzyme adds amide groups to peptide hormones, greatly increasing their stability.
o one modulates tyrosine metabolism.

Biological tissues that accumulate over 100 times the level in blood plasma of vitamin C are the adrenal glands, pituitary, thymus, corpus luteum, and retina. Those with 10 to 50 times the concentration present in blood plasma include the brain, spleen, lung, testicle, lymph nodes, liver, thyroid, small intestinal mucosa, leukocytes, pancreas, kidney and salivary glands.

Biosynthesis
The vast majority of animals and plants are able to synthesize their own vitamin C, through a sequence of four enzyme-driven steps, which convert glucose to vitamin C. The glucose needed to produce ascorbate in the liver (in mammals and perching birds) is extracted from glycogen; ascorbate synthesis is a glycogenolysis-dependent process. In reptiles and birds the biosynthesis is carried out in the kidneys.

Among the animals that have lost the ability to synthesise vitamin C are simians (specifically the suborder haplorrhini), guinea pigs, a number of species of passerine birds (but not all of them), and in apparently many major families of bats and perhaps all of them. Humans have no enzymatic capability to manufacture vitamin C. The cause of this phenomenon is that the last enzyme in the synthesis process, L-gulonolactone oxidase, cannot be made by the listed animals because the gene for this enzyme, Pseudogene ΨGULO, is defective. The mutation has not been lethal because vitamin C is abundant in their food sources. It has been found that species with this mutation (including humans) have adapted a vitamin C recycling mechanism to compensate.

Most simians consume the vitamin in amounts 10 to 20 times higher than that recommended by governments for humans. This discrepancy constitutes the basis of the controversy on current recommended dietary allowances.

It has been noted that the loss of the ability to synthesize ascorbate strikingly parallels the evolutionary loss of the ability to break down uric acid. Uric acid and ascorbate are both strong reducing agents. This has led to the suggestion that in higher primates, uric acid has taken over some of the functions of ascorbate. Ascorbic acid can be oxidised (broken down) in the human body by the enzyme ascorbic acid oxidase.

An adult goat, a typical example of a vitamin C-producing animal, will manufacture more than 13,000 mg of vitamin C per day in normal health and the biosynthesis will increase "many fold under stress". Trauma or injury has also been demonstrated to use up large quantities of vitamin C in humans. Some microorganisms such as the yeast Saccharomyces cerevisiae have been shown to be able to synthesize vitamin C from simple sugars.

Vitamin C Deficiency
Scurvy is an avitaminosis resulting from lack of vitamin C, since without this vitamin, the synthesised collagen is too unstable to perform its function. Scurvy leads to the formation of liver spots on the skin, spongy gums, and bleeding from all mucous membranes. The spots are most abundant on the thighs and legs, and a person with the ailment looks pale, feels depressed, and is partially immobilized. In advanced scurvy there are open, suppurating wounds and loss of teeth and, eventually, death. The human body can store only a certain amount of vitamin C, and so the body soon depletes itself if fresh supplies are not consumed.

It has been shown that smokers who have diets poor in vitamin C are at a higher risk of lung-borne diseases than those smokers who have higher concentrations of Vitamin C in the blood.

History of human understanding
James Lind, a British Royal Navy surgeon who, in 1747, identified that a quality in fruit prevented the disease of scurvy in what was the first recorded controlled experiment.

The need to include fresh plant food or raw animal flesh in the diet to prevent disease was known from ancient times. Native peoples living in marginal areas incorporated this into their medicinal lore. For example, spruce needles were used in temperate zones in infusions, or the leaves from species of drought-resistant trees in desert areas. In 1536, the French explorer Jacques Cartier, exploring the St. Lawrence River, used the local natives' knowledge to save his men who were dying of scurvy. He boiled the needles of the arbor vitae tree to make a tea that was later shown to contain 50 mg of vitamin C per 100 grams.

Throughout history, the benefit of plant food to survive long sea voyages has been occasionally recommended by authorities. John Woodall, the first appointed surgeon to the British East India Company, recommended the preventive and curative use of lemon juice in his book "The Surgeon's Mate", in 1617. The Dutch writer, Johann Bachstrom, in 1734, gave the firm opinion that "scurvy is solely owing to a total abstinence from fresh vegetable food, and greens; which is alone the primary cause of the disease."

While the earliest documented case of scurvy was described by Hippocrates around the year 400 BC, the first attempt to give scientific basis for the cause of this disease was by a ship's surgeon in the British Royal Navy, James Lind. Scurvy was common among those with poor access to fresh fruit and vegetables, such as remote, isolated sailors and soldiers. While at sea in May 1747, Lind provided some crew members with two oranges and one lemon per day, in addition to normal rations, while others continued on cider, vinegar, sulfuric acid or seawater, along with their normal rations. In the history of science this is considered to be the first occurrence of a controlled experiment comparing results on two populations of a factor applied to one group only with all other factors the same. The results conclusively showed that citrus fruits prevented the disease. Lind published his work in 1753 in his Treatise on the Scurvy.
Citrus fruits were one of the first sources of vitamin C available to ship's surgeons.

Lind's work was slow to be noticed, partly because he gave conflicting evidence within the book, and partly because the British admiralty saw care for the well-being of crews as a sign of weakness. In addition, fresh fruit was very expensive to keep on board, whereas boiling it down to juice allowed easy storage but destroyed the vitamin (especially if boiled in copper kettles). Ship captains assumed wrongly that Lind's suggestions didn't work because those juices failed to cure scurvy.

It was 1795 before the British navy adopted lemons or lime as standard issue at sea. Limes were more popular as they could be found in British West Indian Colonies, unlike lemons which weren't found in British Dominions, and were therefore more expensive. This practice led to the American use of the nickname "limey" to refer to the British. Captain James Cook had previously demonstrated and proven the principle of the advantages of carrying "Sour krout" on board, by taking his crews to the Hawaiian Islands and beyond without losing any of his men to scurvy. For this otherwise unheard of feat, the British Admiralty awarded him a medal.

The name "antiscorbutic" was used in the eighteenth and nineteenth centuries as general term for those foods known to prevent scurvy, even though there was no understanding of the reason for this. These foods included but were not limited to: lemons, limes, and oranges; sauerkraut, cabbage, malt, and portable soup.

In 1907, Axel Holst and Theodor Frølich, two Norwegian physicians studying beriberi contracted aboard ship's crews in the Norwegian Fishing Fleet, wanted a small test mammal to substitute for the pigeons they used. They fed guinea pigs their test diet, which had earlier produced beriberi in their pigeons, and were surprised when scurvy resulted instead. Until that time scurvy had not been observed in any organism apart from humans, and had been considered an exclusively human disease.

Discovery of ascorbic acid
Albert Szent-Györgyi, pictured here in 1948, was awarded the 1937 Nobel Prize in Medicine for the discovery of vitamin C

In 1912, the Polish-American biochemist Casimir Funk, while researching deficiency diseases, developed the concept of vitamins to refer to the non-mineral micro-nutrients which are essential to health. The name is a portmanteau of "vital", due to the vital role they play biochemically, and "amines" because Funk thought that all these materials were chemical amines. One of the "vitamines" was thought to be the anti-scorbutic factor, long thought to be a component of most fresh plant material.

In 1928 the Arctic anthropologist Vilhjalmur Stefansson attempted to prove his theory of how the Eskimos are able to avoid scurvy with almost no plant food in their diet, despite the disease striking European Arctic explorers living on similar high-meat diets. Stefansson theorised that the natives get their vitamin C from fresh meat that is minimally cooked. Starting in February 1928, for one year he and a colleague lived on an exclusively minimally-cooked meat diet while under medical supervision; they remained healthy. (Later studies done after vitamin C could be quantified in mostly-raw traditional food diets of the Yukon, Inuit, and Métís of the Northern Canada, showed that their daily intake of vitamin C averaged between 52 and 62 mg/day, an amount approximately the dietary reference intake (DRI), even at times of the year when little plant-based food were eaten.)

From 1928 to 1933, the Hungarian research team of Joseph L Svirbely and Albert Szent-Györgyi and, independently, the American Charles Glen King, first isolated the anti-scorbutic factor, calling it "ascorbic acid" for its vitamin activity. Ascorbic acid turned out not to be an amine, or even to contain any nitrogen. For their accomplishment, Szent-Györgyi was awarded the 1937 Nobel Prize in Medicine.

Between 1933 and 1934, the British chemists Sir Walter Norman Haworth and Sir Edmund Hirst and, independently, the Polish chemist Tadeus Reichstein, succeeded in synthesizing the vitamin, making it the first to be artificially produced. This made possible the cheap mass-production of what was by then known as vitamin C. Only Haworth was awarded the 1937 Nobel Prize in Chemistry for this work, but the "Reichstein process" retained Reichstein's name.

In 1934 Hoffmann–La Roche became the first pharmaceutical company to mass-produce synthetic vitamin C, under the brand name of Redoxon.

In 1957 the American J.J. Burns showed that the reason some mammals were susceptible to scurvy was the inability of their liver to produce the active enzyme L-gulonolactone oxidase, which is the last of the chain of four enzymes which synthesize vitamin C. American biochemist Irwin Stone was the first to exploit vitamin C for its food preservative properties. He later developed the theory that humans possess a mutated form of the L-gulonolactone oxidase coding gene.

Daily requirements for vitamin C
The North American Dietary Reference Intake recommends 90 milligrams per day and no more than 2 grams per day (2000 milligrams per day). Other related species sharing the same inability to produce vitamin C and requiring exogenous vitamin C consume 20 to 80 times this reference intake. There is continuing debate within the scientific community over the best dose schedule (the amount and frequency of intake) of vitamin C for maintaining optimal health in humans. It is generally agreed that a balanced diet without supplementation contains enough vitamin C to prevent scurvy in an average healthy adult, while those who are pregnant, smoke tobacco, or are under stress require slightly more.

High doses (thousands of milligrams) may result in diarrhea in healthy adults. Proponents of alternative medicine (specifically orthomolecular medicine) claim the onset of diarrhea to be an indication of where the body’s true vitamin C requirement lies, though this has yet to be clinically verified.

United States vitamin C recommendations
====================================================
Recommended Dietary Allowance (adult male) 90 mg per day
Recommended Dietary Allowance (adult female) 75 mg per day
Tolerable Upper Intake Level (adult male) 2,000 mg per day
Tolerable Upper Intake Level (adult female) 2,000 mg per day

Government recommended intakes

Recommendations for vitamin C intake have been set by various national agencies:

* 40 milligrams per day: the United Kingdom's Food Standards Agency
* 45 milligrams per day: the World Health Organization
* 60 mg/day: Health Canada 2007
* 60–95 milligrams per day: United States' National Academy of Sciences

The United States defined Tolerable Upper Intake Level for a 25-year-old male is 2,000 milligrams per day.

Alternative recommendations on intakes
Some independent researchers have calculated the amount needed for an adult human to achieve similar blood serum levels as vitamin C synthesising mammals as follows:

* 400 milligrams per day: the Linus Pauling Institute.
* 500 milligrams per 12 hours: Professor Roc Ordman, from research into biological free radicals.
* 3,000 milligrams per day (or up to 300,000 mg during illness): the Vitamin C Foundation.
* 6,000–12,000 milligrams per day: Thomas E. Levy, Colorado Integrative Medical Centre.
* 6,000–18,000 milligrams per day: Linus Pauling's personal use.

Vitamin C high dose arguments
Vitamin C megadosage, Megavitamin therapy, and Orthomolecular medicine. Although there is a strong advocacy movement for large doses of vitamin C based on in vitro and retrospective studies, large, randomized clinical trials on the effects of high doses on the general population have never taken place.

Many pro-vitamin C organizations promote usage levels well beyond the current Dietary Reference Intake (DRI). The movement is led by scientists and doctors such as Robert Cathcart, Ewan Cameron, Steve Hickey, Irwin Stone, Dr. Matthias Rath and twice Nobel Prize laureate, the late Linus Pauling. Pauling's 1986 book, How to Live Longer and Feel Better, was a bestseller that advocated taking many grams per day orally. There is some scientific literature critical of governmental agency dose recommendations.

The biological halflife for vitamin C is fairly short, about 30 minutes in blood plasma, a fact which high dose advocates say mainstream researchers have failed to take into account. The Institute of Medicine of the National Academy of Sciences decided upon the current DRI based upon tests conducted 12 hours (24 half lives) after consumption.

Vitamin C fights off the effects of having high cholesterol. Cholesterol repairs micro-fractures of blood vessel walls, when this happens the sticky nature of cholesterol when filling in these micro-fractures promotes the buildup of more cholesterol at these areas of blood vessel walls. With the supplementation of Vitamin C in higher dosages the micro-fractures of blood vessels is repaired by the vitamin C and thus the buildup of cholesterol and subsequent blockages of blood vessels will not occur.

Genetic rationales for high doses of vitamin C
Four gene products are necessary to manufacture vitamin C from glucose. The loss of activity of the gene for the last step, Pseudogene ΨGULO (GLO) the terminal enzyme responsible for manufacture of vitamin C, has occurred separately in the history of several species. The loss of this enzyme activity is responsible of inability of guinea pigs to synthesize vitamin C enzymatically, but this event happened independently of the loss in the haplorrhini suborder of primates, including humans. The remains of this non-functional gene with many mutations, is however still present in the genome of the guinea pigs and in primates, including humans. GLO activity has also been lost in all major families of bats, regardless of diet. In addition, the function of GLO appears to have been lost several times, and possibly re-acquired, in several lines of passerine birds, where ability to make vitamin C varies from species to species.

Loss of GLO activity in the primate order supposedly occurred about 63 million years ago, at about the time it split into the suborders haplorrhini (which lost the enzyme activity) and the more primitive strepsirrhini (which retained it). The haplorrhini ("simple nosed") primates, which cannot make vitamin C enzymatically, include the tarsiers and the simians (apes, monkeys and humans). The suborder strepsirrhini (bent or wet-nosed prosimians) which are still able to make vitamin C enzymatically, include lorises, galagos, pottos, and to some extent, lemurs.

Stone and Pauling calculated, based on the diet of our primate cousins (similar to what our common ancestors are likely to have consumed when the gene mutated), that the optimum daily requirement of vitamin C is around 2,300 milligrams for a human requiring 2,500 kcal a day.

The established RDA has been criticized by Pauling to be one that will prevent acute scurvy, and is not necessarily the dosage for optimal health.

Vitamin C Therapeutic uses
Since its discovery vitamin C has been considered by some enthusiastic proponents a "universal panacea", although this led to suspicions by others of it being over-hyped. Other proponents of high dose vitamin C consider that if it is given "in the right form, with the proper technique, in frequent enough doses, in high enough doses, along with certain additional agents and for a long enough period of time," it can prevent and, in many cases, cure, a wide range of common and/or lethal diseases, notably the common cold and heart disease, although the NIH considers there to be "fair scientific evidence against this use." Some proponents issued controversial statements involving it being a cure for AIDS, bird flu, and SARS.

Probably the most controversial issue, the putative role of ascorbate in the management of AIDS, is still unresolved, more than 16 years after a study published in the Proceedings of National Academy of Sciences (USA) showing that non toxic doses of ascorbate suppress HIV replication in vitro. Other studies expanded on those results, but still, no large scale trials have yet been conducted.

In an animal model of lead intoxication, vitamin C demonstrated "protective effects" on lead-induced nerve and muscle abnormalities In smokers, blood lead levels declined by an average of 81% when supplemented with 1000 mg of vitamin C, while 200 mg were ineffective, suggesting that vitamin C supplements may be an "economical and convenient" approach to reduce lead levels in the blood. The Journal of the American Medical Association published a study which concluded, based on an analysis of blood lead levels in the subjects of the Third National Health and Nutrition Examination Survey, that the independent, inverse relationship between lead levels and vitamin C in the blood, if causal, would "have public health implications for control of lead toxicity".

Vitamin C has limited popularity as a treatment for autism spectrum symptoms. A 1993 study of 18 children with ASD found some symptoms reduced after treatment with vitamin C, but these results have not been replicated. Small clinical trials have found that vitamin C might improve the sperm count, sperm motility, and sperm morphology in infertile men, or improve immune function related to the prevention and treatment of age-associated diseases.However, to date, no large clinical trials have verified these findings.

A preliminary study published in the Annals of Surgery found that the early administration of antioxidant supplementation using α-tocopherol and ascorbic acid reduces the incidence of organ failure and shortens ICU length of stay in this cohort of critically ill surgical patients. More research on this topic is pending.

Dehydroascorbic acid, the main form of oxidized Vitamin C in the body, was shown to reduce neurological deficits and mortality following stroke, due to its ability to cross the blood-brain barrier, while "the antioxidant ascorbic acid (AA) or vitamin C does not penetrate the blood-brain barrier". In this study published by the Proceedings of the National Academy of Sciences in 2001, the authors concluded that such "a pharmacological strategy to increase cerebral levels of ascorbate in stroke has tremendous potential to represent the timely translation of basic research into a relevant therapy for thromboembolic stroke in humans". No such "relevant therapies" are available yet and no clinical trials have been planned.

In January 2007 the US Food and Drug Administration approved a Phase I toxicity trial to determine the safe dosage of intravenous vitamin C as a possible cancer treatment for "patients who have exhausted all other conventional treatment options." Additional studies over several years would be needed to demonstrate whether it is effective.

In February 2007, an uncontrolled study of 39 terminal cancer patients showed that, on subjective questionnaires, patients reported an improvement in health, cancer symptoms, and daily function after administration of high-dose intravenous vitamin C. The authors concluded that "Although there is still controversy regarding anticancer effects of vitamin C, the use of vitamin C is considered a safe and effective therapy to improve the quality of life of terminal cancer patients".

Vitamin C has been shown to lower IOP in glaucoma patients when taken in massive amounts according to the September 2007 issue of GLEAMS.

In an August, 2008 article in the Proceedings of the National Academy of Sciences Mark Levine and colleagues at the National Institute of Diabetes and Digestive and Kidney Diseases found that direct injection of high doses of vitamin C reduced tumor weight and growth rate by about 50 percent in mouse models of ovarian, brain, and pancreatic cancers. No human therapies have yet been developed using this technique.

A Cochrane Review in 2008 found no evidence to support any increase in lifespan as a result of vitamin C supplementation. As opposed to supplementation with vitamin A, vitamin E, and beta-carotene, vitamin C was not linked with a decrease in lifespan.

Testing for ascorbate levels in the body
Simple tests use DCPIP to measure the levels of vitamin C in the urine and in serum or blood plasma. However these reflect recent dietary intake rather than the level of vitamin C in body stores. Reverse phase high performance liquid chromatography is used for determining the storage levels of vitamin C within lymphocytes and tissue.

It has been observed that while serum or blood plasma levels follow the circadian rhythm or short term dietary changes, those within tissues themselves are more stable and give a better view of the availability of ascorbate within the organism. However, very few hospital laboratories are adequately equipped and trained to carry out such detailed analyses, and require samples to be analyzed in specialized laboratories.

Adverse effects

Common side-effects
Relatively large doses of vitamin C may cause indigestion, particularly when taken on an empty stomach.

When taken in large doses, vitamin C causes diarrhea in healthy subjects. In one trial, doses up to 6 grams of ascorbic acid were given to 29 infants, 93 children of preschool and school age, and 20 adults for more than 1400 days. With the higher doses, toxic manifestations were observed in five adults and four infants. The signs and symptoms in adults were nausea, vomiting, diarrhea, flushing of the face, headache, fatigue and disturbed sleep. The main toxic reactions in the infants were skin rashes. On the other hand, Cathcart has demonstrated that sick patients, with influenza and cancer for example, do not suffer any adverse effects whatsoever until the dosage is raised to fairly high levels such as 100 grams or higher.

Possible side-effects
As vitamin C enhances iron absorption, iron poisoning can become an issue to people with rare iron overload disorders, such as haemochromatosis. A genetic condition that results in inadequate levels of the enzyme glucose-6-phosphate dehydrogenase (G6PD), can cause sufferers to develop hemolytic anemia after ingesting specific oxidizing substances, such as very large dosages of vitamin C.

There is a longstanding belief among the mainstream medical community that vitamin C causes kidney stones, which is based on little science. Although some individual recent studies have found a relationship there is no clear relationship between excess ascorbic acid intake and kidney stone formation.

In a study conducted on rats, during the first month of pregnancy, high doses of vitamin C may suppress the production of progesterone from the corpus luteum. Progesterone, necessary for the maintenance of a pregnancy, is produced by the corpus luteum for the first few weeks, until the placenta is developed enough to produce its own source. By blocking this function of the corpus luteum, high doses of vitamin C (1000+ mg) are theorized to induce an early miscarriage.

In a group of spontaneously aborting women at the end of the first trimester, the mean values of vitamin C were significantly higher in the aborting group. However, the authors do state: 'This could not be interpreted as an evidence of causal association.'

However, in a previous study of 79 women with threatened, previous spontaneous, or habitual abortion, Javert and Stander (1943) had 91% success with 33 patients who received vitamin C together with bioflavinoids and vitamin K (only three abortions), whereas all of the 46 patients who did not receive the vitamins aborted.

Chance of vitamin C overdose
As discussed previously, vitamin C exhibits remarkably low toxicity. The LD50 (the dose that will kill 50% of a population) in rats is generally accepted to be 11.9 grams per kilogram of body weight when taken orally. The LD50 in humans remains unknown, owing to medical ethics that preclude experiments which would put patients at risk of harm. However, as with all substances tested in this way, the LD50 is taken as a guide to its toxicity in humans and no data to contradict this has been found.

Natural and artificial dietary sources
Rose hips are a particularly rich source of vitamin C. The richest natural sources are fruits and vegetables, and of those, the camu camu fruit and the Kakadu plum contain the highest concentration of the vitamin. It is also present in some cuts of meat, especially liver. Vitamin C is the most widely taken nutritional supplement and is available in a variety of forms, including tablets, drink mixes, crystals in capsules or naked crystals.

Vitamin C is absorbed by the intestines using a sodium-ion dependent channel. It is transported through the intestine via both glucose-sensitive and glucose-insensitive mechanisms. The presence of large quantities of sugar either in the intestines or in the blood can slow absorption.

Plant sources
While plants are generally a good source of vitamin C, the amount in foods of plant origin depends on: the precise variety of the plant, the soil condition, the climate in which it grew, the length of time since it was picked, the storage conditions, and the method of preparation.

The following table is approximate and shows the relative abundance in different raw plant sources. As some plants were analyzed fresh while others were dried (thus, artifactually increasing concentration of individual constituents like vitamin C), the data are subject to potential variation and difficulties for comparison. The amount is given in milligrams per 100 grams of fruit or vegetable and is a rounded average from multiple authoritative sources:

Plant source Amount(mg / 100g)
Kakadu plum 3100
Camu Camu 2800
Rose hip 2000
Acerola 1600
Seabuckthorn 695
Jujube 500
Indian gooseberry 445
Baobab 400
Blackcurrant 200
Red pepper 190
Parsley 130
Guava 100
Kiwifruit 90
Broccoli 90
Loganberry 80
Redcurrant 80
Brussels sprouts 80
Wolfberry (Goji) 73 †
Lychee 70
Cloudberry 60
Elderberry 60
Persimmon 60

† average of 3 sources; dried

Plant source Amount(mg / 100g)
Papaya 60
Strawberry 60
Orange 50
Lemon 40
Melon, cantaloupe 40
Cauliflower 40
Garlic 31
Grapefruit 30
Raspberry 30
Tangerine 30
Mandarin orange 30
Passion fruit 30
Spinach 30
Cabbage raw green 30
Lime 30
Mango 28
Blackberry 21
Potato 20
Melon, honeydew 20
Cranberry 13
Tomato 10
Blueberry 10
Pineapple 10

Plant source Amount(mg / 100g)
Pawpaw 10
Grape 10
Apricot 10
Plum 10
Watermelon 10
Banana 9
Carrot 9
Avocado 8
Crabapple 8
Cherry 7
Peach 7
Apple 6
Beetroot 5
Chokecherry 5
Pear 4
Lettuce 4
Cucumber 3
Eggplant 2
Fig 2
Bilberry 1
Horned melon 0.5
Medlar 0.3


Animal sources
Goats, like almost all animals, make their own vitamin C. An adult goat will manufacture more than 13,000 mg of vitamin C per day in normal health and levels manyfold higher when faced with stress. The overwhelming majority of species of animals and plants synthesise their own vitamin C, making some, but not all, animal products, sources of dietary vitamin C.

Vitamin C is most present in the liver and least present in the muscle. Since muscle provides the majority of meat consumed in the western human diet, animal products are not a reliable source of the vitamin. Vitamin C is present in mother's milk and, in lower amounts, in raw cow's milk, with pasteurized milk containing only trace amounts. All excess vitamin C is disposed of through the urinary system.

The following table shows the relative abundance of vitamin C in various foods of animal origin, given in milligram of vitamin C per 100 grams of food:

Animal Source Amount(mg / 100g)
Calf liver (raw) 36
Beef liver (raw) 31
Oysters (raw) 30
Cod roe (fried) 26
Pork liver (raw) 23
Lamb brain (boiled) 17
Chicken liver (fried) 13

Animal Source Amount(mg / 100g)
Lamb liver (fried) 12
Lamb heart (roast) 11
Lamb tongue (stewed) 6
Human milk (fresh) 4
Goat milk (fresh) 2
Cow milk (fresh) 2


Food preparation
Vitamin C chemically decomposes under certain conditions, many of which may occur during the cooking of food. Normally, boiling water at 100°C is not hot enough to cause any significant destruction of the nutrient, which only decomposes at 190°C, despite popular opinion. However, pressure cooking, roasting, frying and grilling food is more likely to reach the decomposition temperature of vitamin C. Longer cooking times also add to this effect, as will copper food vessels, which catalyse the decomposition.

Another cause of vitamin C being lost from food is leaching, where the water-soluble vitamin dissolves into the cooking water, which is later poured away and not consumed. However, vitamin C doesn't leach in all vegetables at the same rate; research shows broccoli seems to retain more than any other. Research has also shown that fresh-cut fruits don't lose significant nutrients when stored in the refrigerator for a few days.

Vitamin C supplements
Vitamin C is widely available in the form of tablets and powders. The Redoxon brand, launched in 1934 by Hoffmann-La Roche, was the first mass-produced synthetic vitamin C.

Vitamin C is the most widely taken dietary supplement. It is available in many forms including caplets, tablets, capsules, drink mix packets, in multi-vitamin formulations, in multiple antioxidant formulations, and crystalline powder. Timed release versions are available, as are formulations containing bioflavonoids such as quercetin, hesperidin and rutin. Tablet and capsule sizes range from 25 mg to 1500 mg. Vitamin C (as ascorbic acid) crystals are typically available in bottles containing 300 g to 1 kg of powder (a teaspoon of vitamin C crystals equals 5,000 mg).

Artificial modes of synthesis
Vitamin C is produced from glucose by two main routes. The Reichstein process, developed in the 1930s, uses a single pre-fermentation followed by a purely chemical route. The modern two-step fermentation process, originally developed in China in the 1960s, uses additional fermentation to replace part of the later chemical stages. Both processes yield approximately 60% vitamin C from the glucose feed.

Research is underway at the Scottish Crop Research Institute in the interest of creating a strain of yeast that can synthesise vitamin C in a single fermentation step from galactose, a technology expected to reduce manufacturing costs considerably.

World production of synthesised vitamin C is currently estimated at approximately 110,000 tonnes annually. Main producers have been BASF/Takeda, DSM, Merck and the China Pharmaceutical Group Ltd. of the People's Republic of China. China is slowly becoming the major world supplier as its prices undercut those of the US and European manufacturers. By 2008 only the DSM plant in Scotland remained operational outside the strong price competition from China. The world price of vitamin C rose sharply in 2008 partly as a result of rises in basic food prices but also in anticipation of a stoppage of the two Chinese plants, situated at Shijiazhuang near Beijing, as part of a general shutdown of polluting industry in China over the period of the Olympic games.

Vitamins (A11)

Fat soluble
A: Retinol - Beta-carotene - Tretinoin - Alpha-carotene
D3: 7-Dehydrocholesterol → Previtamin D3 → Cholecalciferol (D3) → Calcidiol → Calcitriol (active form) → Calcitroic acid
D2: Ergosterol → Ergocalciferol (D2)
D analogues: Dihydrotachysterol - Calcipotriol - Tacalcitol
D4: Dihydroergocalciferol
E: Tocopherol - Tocotrienol
K: Naphthoquinone - Phylloquinone/K1 - Menatetrenone/K2
Water soluble: B vitamins
B1 (Thiamine) - B2 (Riboflavin) - B3 (Niacin, Nicotinamide) - B5 (Pantothenic acid, Dexpanthenol, Pantethine) - B6 (Pyridoxine, Pyridoxal phosphate, Pyridoxamine) - B7 (Biotin) - B9 (Folic acid, Folinic acid) - B12 (Cyanocobalamin, Hydroxocobalamin, Methylcobalamin, Cobamamide)
Water soluble: other
C (Ascorbic acid) - Choline
see also enzyme cofactors]]> Vitamin C

Vitamin C or L-ascorbate is an essential nutrient for a large number of higher primate species, a small number of other mammalian species (notably guinea pigs and bats), a few species of birds, and some fish.

The presence of ascorbate is required for a range of essential metabolic reactions in all animals and plants. It is made internally by almost all organisms, humans being the most well-known exception. It is widely known as the vitamin whose deficiency causes scurvy in humans. It is also widely used as a food additive.

The pharmacophore of vitamin C is the ascorbate ion. In living organisms, ascorbate is an anti-oxidant, since it protects the body against oxidative stress, and is a cofactor in several vital enzymatic reactions.

The uses and the daily requirement amounts of vitamin C are matters of on-going debate. People consuming diets rich in ascorbate from natural foods, such as fruits and vegetables, are healthier and have lower mortality from a number of chronic illnesses. However, a recent meta-analysis of 68 reliable antioxidant supplementation experiments involving a total of 232,606 individuals concluded that consuming additional ascorbate from supplements may not be as beneficial as thought.

Biological significance
Vitamin C is purely the L-enantiomer of ascorbate; the opposite D-enantiomer has no physiological significance. Both forms are mirror images of the same molecular structure. When L-ascorbate, which is a strong reducing agent, carries out its reducing function, it is converted to its oxidized form, L-dehydroascorbate. L-dehydroascorbate can then be reduced back to the active L-ascorbate form in the body by enzymes and glutathione.

L-ascorbate is a weak sugar acid structurally related to glucose which naturally occurs either attached to a hydrogen ion, forming ascorbic acid, or to a metal ion, forming a mineral ascorbate.

In humans, vitamin C is a highly effective antioxidant, acting to lessen oxidative stress, a substrate for ascorbate peroxidase, as well as an enzyme cofactor for the biosynthesis of many important biochemicals. Vitamin C acts as an electron donor for eight different enzymes:

* Three participate in collagen hydroxylation. These reactions add hydroxyl groups to the amino acids proline or lysine in the collagen molecule (via prolyl hydroxylase and lysyl hydroxylase), thereby allowing the collagen molecule to assume its triple helix structure and making vitamin C essential to the development and maintenance of scar tissue, blood vessels, and cartilage.

* Two are necessary for synthesis of carnitine. Carnitine is essential for the transport of fatty acids into mitochondria for ATP generation.

* The remaining three have the following functions:

o dopamine beta hydroxylase participates in the biosynthesis of norepinephrine from dopamine.
o another enzyme adds amide groups to peptide hormones, greatly increasing their stability.
o one modulates tyrosine metabolism.

Biological tissues that accumulate over 100 times the level in blood plasma of vitamin C are the adrenal glands, pituitary, thymus, corpus luteum, and retina. Those with 10 to 50 times the concentration present in blood plasma include the brain, spleen, lung, testicle, lymph nodes, liver, thyroid, small intestinal mucosa, leukocytes, pancreas, kidney and salivary glands.

Biosynthesis
The vast majority of animals and plants are able to synthesize their own vitamin C, through a sequence of four enzyme-driven steps, which convert glucose to vitamin C. The glucose needed to produce ascorbate in the liver (in mammals and perching birds) is extracted from glycogen; ascorbate synthesis is a glycogenolysis-dependent process. In reptiles and birds the biosynthesis is carried out in the kidneys.

Among the animals that have lost the ability to synthesise vitamin C are simians (specifically the suborder haplorrhini), guinea pigs, a number of species of passerine birds (but not all of them), and in apparently many major families of bats and perhaps all of them. Humans have no enzymatic capability to manufacture vitamin C. The cause of this phenomenon is that the last enzyme in the synthesis process, L-gulonolactone oxidase, cannot be made by the listed animals because the gene for this enzyme, Pseudogene ΨGULO, is defective. The mutation has not been lethal because vitamin C is abundant in their food sources. It has been found that species with this mutation (including humans) have adapted a vitamin C recycling mechanism to compensate.

Most simians consume the vitamin in amounts 10 to 20 times higher than that recommended by governments for humans. This discrepancy constitutes the basis of the controversy on current recommended dietary allowances.

It has been noted that the loss of the ability to synthesize ascorbate strikingly parallels the evolutionary loss of the ability to break down uric acid. Uric acid and ascorbate are both strong reducing agents. This has led to the suggestion that in higher primates, uric acid has taken over some of the functions of ascorbate. Ascorbic acid can be oxidised (broken down) in the human body by the enzyme ascorbic acid oxidase.

An adult goat, a typical example of a vitamin C-producing animal, will manufacture more than 13,000 mg of vitamin C per day in normal health and the biosynthesis will increase "many fold under stress". Trauma or injury has also been demonstrated to use up large quantities of vitamin C in humans. Some microorganisms such as the yeast Saccharomyces cerevisiae have been shown to be able to synthesize vitamin C from simple sugars.

Vitamin C Deficiency
Scurvy is an avitaminosis resulting from lack of vitamin C, since without this vitamin, the synthesised collagen is too unstable to perform its function. Scurvy leads to the formation of liver spots on the skin, spongy gums, and bleeding from all mucous membranes. The spots are most abundant on the thighs and legs, and a person with the ailment looks pale, feels depressed, and is partially immobilized. In advanced scurvy there are open, suppurating wounds and loss of teeth and, eventually, death. The human body can store only a certain amount of vitamin C, and so the body soon depletes itself if fresh supplies are not consumed.

It has been shown that smokers who have diets poor in vitamin C are at a higher risk of lung-borne diseases than those smokers who have higher concentrations of Vitamin C in the blood.

History of human understanding
James Lind, a British Royal Navy surgeon who, in 1747, identified that a quality in fruit prevented the disease of scurvy in what was the first recorded controlled experiment.

The need to include fresh plant food or raw animal flesh in the diet to prevent disease was known from ancient times. Native peoples living in marginal areas incorporated this into their medicinal lore. For example, spruce needles were used in temperate zones in infusions, or the leaves from species of drought-resistant trees in desert areas. In 1536, the French explorer Jacques Cartier, exploring the St. Lawrence River, used the local natives' knowledge to save his men who were dying of scurvy. He boiled the needles of the arbor vitae tree to make a tea that was later shown to contain 50 mg of vitamin C per 100 grams.

Throughout history, the benefit of plant food to survive long sea voyages has been occasionally recommended by authorities. John Woodall, the first appointed surgeon to the British East India Company, recommended the preventive and curative use of lemon juice in his book "The Surgeon's Mate", in 1617. The Dutch writer, Johann Bachstrom, in 1734, gave the firm opinion that "scurvy is solely owing to a total abstinence from fresh vegetable food, and greens; which is alone the primary cause of the disease."

While the earliest documented case of scurvy was described by Hippocrates around the year 400 BC, the first attempt to give scientific basis for the cause of this disease was by a ship's surgeon in the British Royal Navy, James Lind. Scurvy was common among those with poor access to fresh fruit and vegetables, such as remote, isolated sailors and soldiers. While at sea in May 1747, Lind provided some crew members with two oranges and one lemon per day, in addition to normal rations, while others continued on cider, vinegar, sulfuric acid or seawater, along with their normal rations. In the history of science this is considered to be the first occurrence of a controlled experiment comparing results on two populations of a factor applied to one group only with all other factors the same. The results conclusively showed that citrus fruits prevented the disease. Lind published his work in 1753 in his Treatise on the Scurvy.
Citrus fruits were one of the first sources of vitamin C available to ship's surgeons.

Lind's work was slow to be noticed, partly because he gave conflicting evidence within the book, and partly because the British admiralty saw care for the well-being of crews as a sign of weakness. In addition, fresh fruit was very expensive to keep on board, whereas boiling it down to juice allowed easy storage but destroyed the vitamin (especially if boiled in copper kettles). Ship captains assumed wrongly that Lind's suggestions didn't work because those juices failed to cure scurvy.

It was 1795 before the British navy adopted lemons or lime as standard issue at sea. Limes were more popular as they could be found in British West Indian Colonies, unlike lemons which weren't found in British Dominions, and were therefore more expensive. This practice led to the American use of the nickname "limey" to refer to the British. Captain James Cook had previously demonstrated and proven the principle of the advantages of carrying "Sour krout" on board, by taking his crews to the Hawaiian Islands and beyond without losing any of his men to scurvy. For this otherwise unheard of feat, the British Admiralty awarded him a medal.

The name "antiscorbutic" was used in the eighteenth and nineteenth centuries as general term for those foods known to prevent scurvy, even though there was no understanding of the reason for this. These foods included but were not limited to: lemons, limes, and oranges; sauerkraut, cabbage, malt, and portable soup.

In 1907, Axel Holst and Theodor Frølich, two Norwegian physicians studying beriberi contracted aboard ship's crews in the Norwegian Fishing Fleet, wanted a small test mammal to substitute for the pigeons they used. They fed guinea pigs their test diet, which had earlier produced beriberi in their pigeons, and were surprised when scurvy resulted instead. Until that time scurvy had not been observed in any organism apart from humans, and had been considered an exclusively human disease.

Discovery of ascorbic acid
Albert Szent-Györgyi, pictured here in 1948, was awarded the 1937 Nobel Prize in Medicine for the discovery of vitamin C

In 1912, the Polish-American biochemist Casimir Funk, while researching deficiency diseases, developed the concept of vitamins to refer to the non-mineral micro-nutrients which are essential to health. The name is a portmanteau of "vital", due to the vital role they play biochemically, and "amines" because Funk thought that all these materials were chemical amines. One of the "vitamines" was thought to be the anti-scorbutic factor, long thought to be a component of most fresh plant material.

In 1928 the Arctic anthropologist Vilhjalmur Stefansson attempted to prove his theory of how the Eskimos are able to avoid scurvy with almost no plant food in their diet, despite the disease striking European Arctic explorers living on similar high-meat diets. Stefansson theorised that the natives get their vitamin C from fresh meat that is minimally cooked. Starting in February 1928, for one year he and a colleague lived on an exclusively minimally-cooked meat diet while under medical supervision; they remained healthy. (Later studies done after vitamin C could be quantified in mostly-raw traditional food diets of the Yukon, Inuit, and Métís of the Northern Canada, showed that their daily intake of vitamin C averaged between 52 and 62 mg/day, an amount approximately the dietary reference intake (DRI), even at times of the year when little plant-based food were eaten.)

From 1928 to 1933, the Hungarian research team of Joseph L Svirbely and Albert Szent-Györgyi and, independently, the American Charles Glen King, first isolated the anti-scorbutic factor, calling it "ascorbic acid" for its vitamin activity. Ascorbic acid turned out not to be an amine, or even to contain any nitrogen. For their accomplishment, Szent-Györgyi was awarded the 1937 Nobel Prize in Medicine.

Between 1933 and 1934, the British chemists Sir Walter Norman Haworth and Sir Edmund Hirst and, independently, the Polish chemist Tadeus Reichstein, succeeded in synthesizing the vitamin, making it the first to be artificially produced. This made possible the cheap mass-production of what was by then known as vitamin C. Only Haworth was awarded the 1937 Nobel Prize in Chemistry for this work, but the "Reichstein process" retained Reichstein's name.

In 1934 Hoffmann–La Roche became the first pharmaceutical company to mass-produce synthetic vitamin C, under the brand name of Redoxon.

In 1957 the American J.J. Burns showed that the reason some mammals were susceptible to scurvy was the inability of their liver to produce the active enzyme L-gulonolactone oxidase, which is the last of the chain of four enzymes which synthesize vitamin C. American biochemist Irwin Stone was the first to exploit vitamin C for its food preservative properties. He later developed the theory that humans possess a mutated form of the L-gulonolactone oxidase coding gene.

Daily requirements for vitamin C
The North American Dietary Reference Intake recommends 90 milligrams per day and no more than 2 grams per day (2000 milligrams per day). Other related species sharing the same inability to produce vitamin C and requiring exogenous vitamin C consume 20 to 80 times this reference intake. There is continuing debate within the scientific community over the best dose schedule (the amount and frequency of intake) of vitamin C for maintaining optimal health in humans. It is generally agreed that a balanced diet without supplementation contains enough vitamin C to prevent scurvy in an average healthy adult, while those who are pregnant, smoke tobacco, or are under stress require slightly more.

High doses (thousands of milligrams) may result in diarrhea in healthy adults. Proponents of alternative medicine (specifically orthomolecular medicine) claim the onset of diarrhea to be an indication of where the body’s true vitamin C requirement lies, though this has yet to be clinically verified.

United States vitamin C recommendations
====================================================
Recommended Dietary Allowance (adult male) 90 mg per day
Recommended Dietary Allowance (adult female) 75 mg per day
Tolerable Upper Intake Level (adult male) 2,000 mg per day
Tolerable Upper Intake Level (adult female) 2,000 mg per day

Government recommended intakes

Recommendations for vitamin C intake have been set by various national agencies:

* 40 milligrams per day: the United Kingdom's Food Standards Agency
* 45 milligrams per day: the World Health Organization
* 60 mg/day: Health Canada 2007
* 60–95 milligrams per day: United States' National Academy of Sciences

The United States defined Tolerable Upper Intake Level for a 25-year-old male is 2,000 milligrams per day.

Alternative recommendations on intakes
Some independent researchers have calculated the amount needed for an adult human to achieve similar blood serum levels as vitamin C synthesising mammals as follows:

* 400 milligrams per day: the Linus Pauling Institute.
* 500 milligrams per 12 hours: Professor Roc Ordman, from research into biological free radicals.
* 3,000 milligrams per day (or up to 300,000 mg during illness): the Vitamin C Foundation.
* 6,000–12,000 milligrams per day: Thomas E. Levy, Colorado Integrative Medical Centre.
* 6,000–18,000 milligrams per day: Linus Pauling's personal use.

Vitamin C high dose arguments
Vitamin C megadosage, Megavitamin therapy, and Orthomolecular medicine. Although there is a strong advocacy movement for large doses of vitamin C based on in vitro and retrospective studies, large, randomized clinical trials on the effects of high doses on the general population have never taken place.

Many pro-vitamin C organizations promote usage levels well beyond the current Dietary Reference Intake (DRI). The movement is led by scientists and doctors such as Robert Cathcart, Ewan Cameron, Steve Hickey, Irwin Stone, Dr. Matthias Rath and twice Nobel Prize laureate, the late Linus Pauling. Pauling's 1986 book, How to Live Longer and Feel Better, was a bestseller that advocated taking many grams per day orally. There is some scientific literature critical of governmental agency dose recommendations.

The biological halflife for vitamin C is fairly short, about 30 minutes in blood plasma, a fact which high dose advocates say mainstream researchers have failed to take into account. The Institute of Medicine of the National Academy of Sciences decided upon the current DRI based upon tests conducted 12 hours (24 half lives) after consumption.

Vitamin C fights off the effects of having high cholesterol. Cholesterol repairs micro-fractures of blood vessel walls, when this happens the sticky nature of cholesterol when filling in these micro-fractures promotes the buildup of more cholesterol at these areas of blood vessel walls. With the supplementation of Vitamin C in higher dosages the micro-fractures of blood vessels is repaired by the vitamin C and thus the buildup of cholesterol and subsequent blockages of blood vessels will not occur.

Genetic rationales for high doses of vitamin C
Four gene products are necessary to manufacture vitamin C from glucose. The loss of activity of the gene for the last step, Pseudogene ΨGULO (GLO) the terminal enzyme responsible for manufacture of vitamin C, has occurred separately in the history of several species. The loss of this enzyme activity is responsible of inability of guinea pigs to synthesize vitamin C enzymatically, but this event happened independently of the loss in the haplorrhini suborder of primates, including humans. The remains of this non-functional gene with many mutations, is however still present in the genome of the guinea pigs and in primates, including humans. GLO activity has also been lost in all major families of bats, regardless of diet. In addition, the function of GLO appears to have been lost several times, and possibly re-acquired, in several lines of passerine birds, where ability to make vitamin C varies from species to species.

Loss of GLO activity in the primate order supposedly occurred about 63 million years ago, at about the time it split into the suborders haplorrhini (which lost the enzyme activity) and the more primitive strepsirrhini (which retained it). The haplorrhini ("simple nosed") primates, which cannot make vitamin C enzymatically, include the tarsiers and the simians (apes, monkeys and humans). The suborder strepsirrhini (bent or wet-nosed prosimians) which are still able to make vitamin C enzymatically, include lorises, galagos, pottos, and to some extent, lemurs.

Stone and Pauling calculated, based on the diet of our primate cousins (similar to what our common ancestors are likely to have consumed when the gene mutated), that the optimum daily requirement of vitamin C is around 2,300 milligrams for a human requiring 2,500 kcal a day.

The established RDA has been criticized by Pauling to be one that will prevent acute scurvy, and is not necessarily the dosage for optimal health.

Vitamin C Therapeutic uses
Since its discovery vitamin C has been considered by some enthusiastic proponents a "universal panacea", although this led to suspicions by others of it being over-hyped. Other proponents of high dose vitamin C consider that if it is given "in the right form, with the proper technique, in frequent enough doses, in high enough doses, along with certain additional agents and for a long enough period of time," it can prevent and, in many cases, cure, a wide range of common and/or lethal diseases, notably the common cold and heart disease, although the NIH considers there to be "fair scientific evidence against this use." Some proponents issued controversial statements involving it being a cure for AIDS, bird flu, and SARS.

Probably the most controversial issue, the putative role of ascorbate in the management of AIDS, is still unresolved, more than 16 years after a study published in the Proceedings of National Academy of Sciences (USA) showing that non toxic doses of ascorbate suppress HIV replication in vitro. Other studies expanded on those results, but still, no large scale trials have yet been conducted.

In an animal model of lead intoxication, vitamin C demonstrated "protective effects" on lead-induced nerve and muscle abnormalities In smokers, blood lead levels declined by an average of 81% when supplemented with 1000 mg of vitamin C, while 200 mg were ineffective, suggesting that vitamin C supplements may be an "economical and convenient" approach to reduce lead levels in the blood. The Journal of the American Medical Association published a study which concluded, based on an analysis of blood lead levels in the subjects of the Third National Health and Nutrition Examination Survey, that the independent, inverse relationship between lead levels and vitamin C in the blood, if causal, would "have public health implications for control of lead toxicity".

Vitamin C has limited popularity as a treatment for autism spectrum symptoms. A 1993 study of 18 children with ASD found some symptoms reduced after treatment with vitamin C, but these results have not been replicated. Small clinical trials have found that vitamin C might improve the sperm count, sperm motility, and sperm morphology in infertile men, or improve immune function related to the prevention and treatment of age-associated diseases.However, to date, no large clinical trials have verified these findings.

A preliminary study published in the Annals of Surgery found that the early administration of antioxidant supplementation using α-tocopherol and ascorbic acid reduces the incidence of organ failure and shortens ICU length of stay in this cohort of critically ill surgical patients. More research on this topic is pending.

Dehydroascorbic acid, the main form of oxidized Vitamin C in the body, was shown to reduce neurological deficits and mortality following stroke, due to its ability to cross the blood-brain barrier, while "the antioxidant ascorbic acid (AA) or vitamin C does not penetrate the blood-brain barrier". In this study published by the Proceedings of the National Academy of Sciences in 2001, the authors concluded that such "a pharmacological strategy to increase cerebral levels of ascorbate in stroke has tremendous potential to represent the timely translation of basic research into a relevant therapy for thromboembolic stroke in humans". No such "relevant therapies" are available yet and no clinical trials have been planned.

In January 2007 the US Food and Drug Administration approved a Phase I toxicity trial to determine the safe dosage of intravenous vitamin C as a possible cancer treatment for "patients who have exhausted all other conventional treatment options." Additional studies over several years would be needed to demonstrate whether it is effective.

In February 2007, an uncontrolled study of 39 terminal cancer patients showed that, on subjective questionnaires, patients reported an improvement in health, cancer symptoms, and daily function after administration of high-dose intravenous vitamin C. The authors concluded that "Although there is still controversy regarding anticancer effects of vitamin C, the use of vitamin C is considered a safe and effective therapy to improve the quality of life of terminal cancer patients".

Vitamin C has been shown to lower IOP in glaucoma patients when taken in massive amounts according to the September 2007 issue of GLEAMS.

In an August, 2008 article in the Proceedings of the National Academy of Sciences Mark Levine and colleagues at the National Institute of Diabetes and Digestive and Kidney Diseases found that direct injection of high doses of vitamin C reduced tumor weight and growth rate by about 50 percent in mouse models of ovarian, brain, and pancreatic cancers. No human therapies have yet been developed using this technique.

A Cochrane Review in 2008 found no evidence to support any increase in lifespan as a result of vitamin C supplementation. As opposed to supplementation with vitamin A, vitamin E, and beta-carotene, vitamin C was not linked with a decrease in lifespan.

Testing for ascorbate levels in the body
Simple tests use DCPIP to measure the levels of vitamin C in the urine and in serum or blood plasma. However these reflect recent dietary intake rather than the level of vitamin C in body stores. Reverse phase high performance liquid chromatography is used for determining the storage levels of vitamin C within lymphocytes and tissue.

It has been observed that while serum or blood plasma levels follow the circadian rhythm or short term dietary changes, those within tissues themselves are more stable and give a better view of the availability of ascorbate within the organism. However, very few hospital laboratories are adequately equipped and trained to carry out such detailed analyses, and require samples to be analyzed in specialized laboratories.

Adverse effects

Common side-effects
Relatively large doses of vitamin C may cause indigestion, particularly when taken on an empty stomach.

When taken in large doses, vitamin C causes diarrhea in healthy subjects. In one trial, doses up to 6 grams of ascorbic acid were given to 29 infants, 93 children of preschool and school age, and 20 adults for more than 1400 days. With the higher doses, toxic manifestations were observed in five adults and four infants. The signs and symptoms in adults were nausea, vomiting, diarrhea, flushing of the face, headache, fatigue and disturbed sleep. The main toxic reactions in the infants were skin rashes. On the other hand, Cathcart has demonstrated that sick patients, with influenza and cancer for example, do not suffer any adverse effects whatsoever until the dosage is raised to fairly high levels such as 100 grams or higher.

Possible side-effects
As vitamin C enhances iron absorption, iron poisoning can become an issue to people with rare iron overload disorders, such as haemochromatosis. A genetic condition that results in inadequate levels of the enzyme glucose-6-phosphate dehydrogenase (G6PD), can cause sufferers to develop hemolytic anemia after ingesting specific oxidizing substances, such as very large dosages of vitamin C.

There is a longstanding belief among the mainstream medical community that vitamin C causes kidney stones, which is based on little science. Although some individual recent studies have found a relationship there is no clear relationship between excess ascorbic acid intake and kidney stone formation.

In a study conducted on rats, during the first month of pregnancy, high doses of vitamin C may suppress the production of progesterone from the corpus luteum. Progesterone, necessary for the maintenance of a pregnancy, is produced by the corpus luteum for the first few weeks, until the placenta is developed enough to produce its own source. By blocking this function of the corpus luteum, high doses of vitamin C (1000+ mg) are theorized to induce an early miscarriage.

In a group of spontaneously aborting women at the end of the first trimester, the mean values of vitamin C were significantly higher in the aborting group. However, the authors do state: 'This could not be interpreted as an evidence of causal association.'

However, in a previous study of 79 women with threatened, previous spontaneous, or habitual abortion, Javert and Stander (1943) had 91% success with 33 patients who received vitamin C together with bioflavinoids and vitamin K (only three abortions), whereas all of the 46 patients who did not receive the vitamins aborted.

Chance of vitamin C overdose
As discussed previously, vitamin C exhibits remarkably low toxicity. The LD50 (the dose that will kill 50% of a population) in rats is generally accepted to be 11.9 grams per kilogram of body weight when taken orally. The LD50 in humans remains unknown, owing to medical ethics that preclude experiments which would put patients at risk of harm. However, as with all substances tested in this way, the LD50 is taken as a guide to its toxicity in humans and no data to contradict this has been found.

Natural and artificial dietary sources
Rose hips are a particularly rich source of vitamin C. The richest natural sources are fruits and vegetables, and of those, the camu camu fruit and the Kakadu plum contain the highest concentration of the vitamin. It is also present in some cuts of meat, especially liver. Vitamin C is the most widely taken nutritional supplement and is available in a variety of forms, including tablets, drink mixes, crystals in capsules or naked crystals.

Vitamin C is absorbed by the intestines using a sodium-ion dependent channel. It is transported through the intestine via both glucose-sensitive and glucose-insensitive mechanisms. The presence of large quantities of sugar either in the intestines or in the blood can slow absorption.

Plant sources
While plants are generally a good source of vitamin C, the amount in foods of plant origin depends on: the precise variety of the plant, the soil condition, the climate in which it grew, the length of time since it was picked, the storage conditions, and the method of preparation.

The following table is approximate and shows the relative abundance in different raw plant sources. As some plants were analyzed fresh while others were dried (thus, artifactually increasing concentration of individual constituents like vitamin C), the data are subject to potential variation and difficulties for comparison. The amount is given in milligrams per 100 grams of fruit or vegetable and is a rounded average from multiple authoritative sources:

Plant source Amount(mg / 100g)
Kakadu plum 3100
Camu Camu 2800
Rose hip 2000
Acerola 1600
Seabuckthorn 695
Jujube 500
Indian gooseberry 445
Baobab 400
Blackcurrant 200
Red pepper 190
Parsley 130
Guava 100
Kiwifruit 90
Broccoli 90
Loganberry 80
Redcurrant 80
Brussels sprouts 80
Wolfberry (Goji) 73 †
Lychee 70
Cloudberry 60
Elderberry 60
Persimmon 60

† average of 3 sources; dried

Plant source Amount(mg / 100g)
Papaya 60
Strawberry 60
Orange 50
Lemon 40
Melon, cantaloupe 40
Cauliflower 40
Garlic 31
Grapefruit 30
Raspberry 30
Tangerine 30
Mandarin orange 30
Passion fruit 30
Spinach 30
Cabbage raw green 30
Lime 30
Mango 28
Blackberry 21
Potato 20
Melon, honeydew 20
Cranberry 13
Tomato 10
Blueberry 10
Pineapple 10

Plant source Amount(mg / 100g)
Pawpaw 10
Grape 10
Apricot 10
Plum 10
Watermelon 10
Banana 9
Carrot 9
Avocado 8
Crabapple 8
Cherry 7
Peach 7
Apple 6
Beetroot 5
Chokecherry 5
Pear 4
Lettuce 4
Cucumber 3
Eggplant 2
Fig 2
Bilberry 1
Horned melon 0.5
Medlar 0.3


Animal sources
Goats, like almost all animals, make their own vitamin C. An adult goat will manufacture more than 13,000 mg of vitamin C per day in normal health and levels manyfold higher when faced with stress. The overwhelming majority of species of animals and plants synthesise their own vitamin C, making some, but not all, animal products, sources of dietary vitamin C.

Vitamin C is most present in the liver and least present in the muscle. Since muscle provides the majority of meat consumed in the western human diet, animal products are not a reliable source of the vitamin. Vitamin C is present in mother's milk and, in lower amounts, in raw cow's milk, with pasteurized milk containing only trace amounts. All excess vitamin C is disposed of through the urinary system.

The following table shows the relative abundance of vitamin C in various foods of animal origin, given in milligram of vitamin C per 100 grams of food:

Animal Source Amount(mg / 100g)
Calf liver (raw) 36
Beef liver (raw) 31
Oysters (raw) 30
Cod roe (fried) 26
Pork liver (raw) 23
Lamb brain (boiled) 17
Chicken liver (fried) 13

Animal Source Amount(mg / 100g)
Lamb liver (fried) 12
Lamb heart (roast) 11
Lamb tongue (stewed) 6
Human milk (fresh) 4
Goat milk (fresh) 2
Cow milk (fresh) 2


Food preparation
Vitamin C chemically decomposes under certain conditions, many of which may occur during the cooking of food. Normally, boiling water at 100°C is not hot enough to cause any significant destruction of the nutrient, which only decomposes at 190°C, despite popular opinion. However, pressure cooking, roasting, frying and grilling food is more likely to reach the decomposition temperature of vitamin C. Longer cooking times also add to this effect, as will copper food vessels, which catalyse the decomposition.

Another cause of vitamin C being lost from food is leaching, where the water-soluble vitamin dissolves into the cooking water, which is later poured away and not consumed. However, vitamin C doesn't leach in all vegetables at the same rate; research shows broccoli seems to retain more than any other. Research has also shown that fresh-cut fruits don't lose significant nutrients when stored in the refrigerator for a few days.

Vitamin C supplements
Vitamin C is widely available in the form of tablets and powders. The Redoxon brand, launched in 1934 by Hoffmann-La Roche, was the first mass-produced synthetic vitamin C.

Vitamin C is the most widely taken dietary supplement. It is available in many forms including caplets, tablets, capsules, drink mix packets, in multi-vitamin formulations, in multiple antioxidant formulations, and crystalline powder. Timed release versions are available, as are formulations containing bioflavonoids such as quercetin, hesperidin and rutin. Tablet and capsule sizes range from 25 mg to 1500 mg. Vitamin C (as ascorbic acid) crystals are typically available in bottles containing 300 g to 1 kg of powder (a teaspoon of vitamin C crystals equals 5,000 mg).

Artificial modes of synthesis
Vitamin C is produced from glucose by two main routes. The Reichstein process, developed in the 1930s, uses a single pre-fermentation followed by a purely chemical route. The modern two-step fermentation process, originally developed in China in the 1960s, uses additional fermentation to replace part of the later chemical stages. Both processes yield approximately 60% vitamin C from the glucose feed.

Research is underway at the Scottish Crop Research Institute in the interest of creating a strain of yeast that can synthesise vitamin C in a single fermentation step from galactose, a technology expected to reduce manufacturing costs considerably.

World production of synthesised vitamin C is currently estimated at approximately 110,000 tonnes annually. Main producers have been BASF/Takeda, DSM, Merck and the China Pharmaceutical Group Ltd. of the People's Republic of China. China is slowly becoming the major world supplier as its prices undercut those of the US and European manufacturers. By 2008 only the DSM plant in Scotland remained operational outside the strong price competition from China. The world price of vitamin C rose sharply in 2008 partly as a result of rises in basic food prices but also in anticipation of a stoppage of the two Chinese plants, situated at Shijiazhuang near Beijing, as part of a general shutdown of polluting industry in China over the period of the Olympic games.

Vitamins (A11)

Fat soluble
A: Retinol - Beta-carotene - Tretinoin - Alpha-carotene
D3: 7-Dehydrocholesterol → Previtamin D3 → Cholecalciferol (D3) → Calcidiol → Calcitriol (active form) → Calcitroic acid
D2: Ergosterol → Ergocalciferol (D2)
D analogues: Dihydrotachysterol - Calcipotriol - Tacalcitol
D4: Dihydroergocalciferol
E: Tocopherol - Tocotrienol
K: Naphthoquinone - Phylloquinone/K1 - Menatetrenone/K2
Water soluble: B vitamins
B1 (Thiamine) - B2 (Riboflavin) - B3 (Niacin, Nicotinamide) - B5 (Pantothenic acid, Dexpanthenol, Pantethine) - B6 (Pyridoxine, Pyridoxal phosphate, Pyridoxamine) - B7 (Biotin) - B9 (Folic acid, Folinic acid) - B12 (Cyanocobalamin, Hydroxocobalamin, Methylcobalamin, Cobamamide)
Water soluble: other
C (Ascorbic acid) - Choline
see also enzyme cofactors]]> http://www.vitaminforum.net/thread-4.html Mon, 27 Oct 2008 12:49:28 -0500 slimgirl http://www.vitaminforum.net/thread-4.html
This forum looks new, is it?

Well, I'm looking to learn more about vitamins and health.

Bye!]]>
This forum looks new, is it?

Well, I'm looking to learn more about vitamins and health.

Bye!]]> http://www.vitaminforum.net/thread-2.html Sun, 19 Oct 2008 22:56:27 -0500 nimda http://www.vitaminforum.net/thread-2.html Vitamin A

Vitamin A refers to a family of similarly shaped molecules: the retinoids. Its important part is the retinyl group, which can be found in several forms. In foods of animal origin, the major form of vitamin A is an ester, primarily retinyl palmitate, which is converted to an alcohol (retinol) in the small intestine. Vitamin A can also exist as an aldehyde (retinal), or as an acid (retinoic acid). Precursors to the vitamin (provitamins) are present in foods of plant origin as some of the members of the carotenoid family of compounds.

All forms of vitamin A have a Beta-ionone ring to which an isoprenoid chain is attached. This structure is essential for vitamin activity. The orange pigment of carrot - Beta-carotene - can be represented as two connected retinyl groups. The retinyl group, when attached to a specific protein, is the only primary light absorber in visual perception, and the compound name is related to the retina of the eye.

Vitamin A can be found in various forms:

* retinol, the form of vitamin A absorbed when eating animal food sources, is a yellow, fat-soluble, vitamin with importance in vision and bone growth. Since the alcohol form is unstable, the vitamin is usually produced and administered in a form of retinyl acetate or palmitate.

* other retinoids, a class of chemical compounds that are related chemically to vitamin A, are used in medicine.

Contents

* 1 Discovery of vitamin A
* 2 Equivalencies of retinoids and carotenoids (IU)
* 3 Recommended daily intake
* 4 Sources of vitamin A
* 5 Metabolic functions of vitamin A
o 5.1 Vision
o 5.2 Gene transcription
o 5.3 Dermatology
* 6 Deficiency
* 7 Toxicity
* 8 See also
* 9 References
* 10 Further reading
* 11 External links

Discovery of vitamin A

The discovery of vitamin A stemmed from research dating back to 1906, indicating that factors other than carbohydrates, proteins, and fats were necessary to keep cattle healthy. By 1917 one of these substances was independently discovered by Elmer McCollum at the University of Wisconsin-Madison, and Lafayette Mendel and Thomas Osborne at Yale University. Since "water-soluble factor B" (Vitamin B) had recently been discovered, the researchers chose the name "fat-soluble factor A" (vitamin A). Vitamin A was first synthesized in 1947 by two Dutch chemists, David Adriaan van Dorp and Jozef Ferdinand Arens.

Equivalencies of retinoids and carotenoids (IU)

Since some carotenoids can be converted into vitamin A, attempts have been made to determine how much of them in the diet is equivalent to a particular amount of retinol, so that comparisons can be made of the benefit of different foods. Unfortunately the situation is confusing because the accepted equivalences have changed. For many years, a system of equivalencies was used in which an international unit (IU) was equal to 0.3 micrograms of retinol, 0.6 μg of β-carotene, or 1.2 μg of other provitamin-A carotenoids. Later, a unit called retinol equivalent (RE) was introduced. 1 RE corresponded to 1 μg retinol, 2 μg β-carotene dissolved in oil (as in supplement pills), 6 μg β-carotene in normal food (because it is not absorbed as well as from supplements), and 12 μg of either α-carotene or β-cryptoxanthin in food.

However, new research showed that the absorption of provitamin-A carotenoids was only half as much as previously thought, so in 2001 the US Institute of Medicine recommended a new unit, the retinol activity equivalent (RAE). 1 μg RAE corresponds to 1 μg retinol, 2 μg of β-carotene in oil, 12 μg of "dietary" beta-carotene, or 24 μg of other dietary provitamin-A carotenoids.
Substance and its chemical environment Micrograms of retinol equivalent per microgram of the substance
retinol 1
beta-carotene, dissolved in oil 1/2
beta-carotene, common dietary 1/12
alpha-carotene, common dietary 1/24
beta-cryptoxanthin, common dietary 1/24

Because the production of retinol from provitamins by the human body is regulated by the amount of retinol available to the body, the conversions apply strictly only for vitamin A deficient humans. The absorption of provitamins also depends greatly on the amount of lipids ingested with the provitamin; lipids increase the uptake of the provitamin.

The conclusion that can be drawn from the newer research is that fruits and vegetables are not as useful for obtaining vitamin A as was thought--in other words, the IU's that they were reported to contain were worth much less than the same number of IU's of fat-dissolved supplements. This is important for vegetarians. (Night blindness is prevalent in countries where little meat or vitamin A-fortified foods are available.) A sample vegan diet for one day that provides sufficient vitamin A has been published by the Food and Nutrition Board (page 120). On the other hand, reference values for retinol or its equivalents, provided by the National Academy of Sciences, have decreased. The RDA (for men) of 1968 was 5000 IU (1500 μg retinol). In 1974 the RDA was set to 1000 RE (1000 μg retinol), whereas now the Dietary Reference Intake is 900 RAE (900 μg or 3000 IU retinol). This is equivalent to 1800 μg of β-carotene supplement (3000 IU) or 10800 μg of β-carotene in food (18000 IU).

Sources of vitamin A

Vitamin A is found naturally in many foods:

* liver (beef, pork, chicken, turkey, fish) (6500 μg 722%)
* carrots (835 μg 93%)
* Broccoli leaves (800 μg 89%) - Acc. to USDA database. Broccoli florets supposedly have much less - see note.
* sweet potatoes (709 μg 79%)
* kale (681 μg 76%)
* butter (684 μg 76%)
* spinach (469 μg 52%)
* leafy vegetables
* pumpkin (369 μg 41%)
* collard greens (333 μg 37%)
* cantaloupe melon (169 μg 19%)
* eggs (140 μg 16%)
* apricots (96 μg 11%)
* papaya (55 μg 6%)
* mango (38 μg 4%)
* peas (38 μg 4%)
* broccoli (31 μg 3%)
* winter squash

Note: bracketed values are retinol equivalences and percentage of the adult male RDA per 100g.

Conversion of carotene to retinol varies from person to person and bioavailability of carotene in food varies.

Metabolic functions of vitamin A

Vitamin A plays a role in a variety of functions throughout the body, such as:

* Vision
* Gene Transcription
* Immune Function
* Embryonic Development and Reproduction
* Bone Metabolism
* Haematopoiesis
* Skin Health
* Reducing Risk of Heart Disease and Cancer
* Antioxidant Activity

Vision

The role of vitamin A in the vision cycle is specifically related to the retinal form. Within the eye, 11-cis-retinal is bound to rhodopsin (rods) and iodopsin (cones) at conserved lysine residues. As light enters the eye the 11-cis-retinal is isomerized to the all-"trans" form. The all-"trans" retinal dissociates from the opsin in a series of steps called bleaching. This isomerization induces a nervous signal along the optic nerve to the visual center of the brain. Upon completion of this cycle, the all-"trans"-retinal can be recycled and converted back to the 11-"cis"-retinal form via a series of enzymatic reactions. Additionally, some of the all-"trans" retinal may be converted to all-"trans" retinol form and then transported with an interphotoreceptor retinol-binding protein (IRBP) to the pigment epithelial cells. Further esterification into all-"trans" retinyl esters allow this final form to be stored within the pigment epithelial cells to be reused when needed. The final conversion of 11-cis-retinal will rebind to opsin to reform rhodopsin in the retina. Rhodopsin is needed to see black and white as well as see at night. It is for this reason that a deficiency in vitamin A will inhibit the reformation of rhodopsin and lead to night blindness.

Gene transcription

Vitamin A, in the retinoic acid form, plays an important role in gene transcription. Once retinol has been taken up by a cell, it can be oxidized to retinal (by retinol dehydrogenases) and then retinal can be oxidized to retinoic acid (by retinal oxidase). The conversion of retinal to retinoic acid is an irreversible step, meaning that the production of retinoic acid is tightly regulated, due to its activity as a ligand for nuclear receptors. Retinoic acid can bind to two different nuclear receptors to initiate (or inhibit) gene transcription: the retinoic acid receptors (RARs) or the retinoid "X" receptors (RXRs). RAR and RXR must dimerize before they can bind to the DNA. RAR will form a heterodimer with RXR (RAR-RXR), but it does not readily form a homodimer (RAR-RAR). RXR, on the other hand, readily forms a homodimer (RXR-RXR) and will form heterodimers with many other nuclear receptors as well, including the thyroid hormone receptor (RXR-TR), the Vitamin D3 receptor (RXR-VDR), the peroxisome proliferator-activated receptor (RXR-PPAR) and the liver "X" receptor (RXR-LXR). The RAR-RXR heterodimer recognizes retinoid acid response elements (RAREs) on the DNA whereas the RXR-RXR homodimer recognizes retinoid "X" response elements (RXREs) on the DNA. The other RXR heterodimers will bind to various other response elements on the DNA. Once the retinoic acid binds to the receptors and dimerization has occurred, the receptors undergo a conformational change that causes co-repressors to dissociate from the receptors. Coactivators can then bind to the receptor complex, which may help to loosen the chromatin structure from the histones or may interact with the transcriptional machinery. The receptors can then blind to the response elements on the DNA and upregulate (or downregulate) the expression of target genes, such as cellular retinol-binding protein (CRBP) as well as the genes that encode for the receptors themselves.

Dermatology

Vitamin A appears to function in maintaining normal skin health. The mechanisms behind retinoid's therapeutic agents in the treatment of dermatological diseases are being researched. For the treatment of acne, the most effective drug is 13-cis retinoic acid (isotretinoin). Although its mechanism of action remains unknown, it is the only retinoid that dramatically reduces the size and secretion of the sebaceous glands. Isotretinoin reduces bacterial numbers in both the ducts and skin surface. This is thought to be a result of the reduction in sebum, a nutrient source for the bacteria. Isotretinoin reduces inflammation via inhibition of chemotatic responses of monocytes and neutrophils. Isotretinoin also has been shown to initiate remodeling of the sebaceous glands; triggering changes in gene expression that selectively induces apoptosis. Isotretinoin is a teratogen and its use is confined to medical supervision.

Deficiency

Vitamin A deficiency is estimated to affect millions of children around the world. Approximately 250,000-500,000 children in developing countries become blind each year owing to vitamin A deficiency, with the highest prevalence in Southeast Asia and Africa. According to the World Health Organization (WHO), vitamin A deficiency is under control in the United States, but in developing countries vitamin A deficiency is a significant concern. With the high prevalence of vitamin A deficiency, the WHO has implemented several initiatives for supplementation of vitamin A in developing countries. Some of these strategies include intake of vitamin A through a combination of breast feeding, dietary intake, food fortification, and supplementation. Through the efforts of WHO and its partners, an estimated 1.25 million deaths since 1998 in 40 countries due to vitamin A deficiency have been averted.

Vitamin A deficiency can occur as either a primary or secondary deficiency. A primary vitamin A deficiency occurs among children and adults who do not consume an adequate intake of yellow and green vegetables, fruits and liver. Early weaning can also increase the risk of vitamin A deficiency. Secondary vitamin A deficiency is associated with chronic malabsorption of lipids, impaired bile production and release, low fat diets, and chronic exposure to oxidants, such as cigarette smoke. Vitamin A is a fat soluble vitamin and depends on micellar solubilization for dispersion into the small intestine, which results in poor utilization of vitamin A from low-fat diets. Zinc deficiency can also impair absorption, transport, and metabolism of vitamin A because it is essential for the synthesis of the vitamin A transport proteins and the oxidation of retinol to retinal. In malnourished populations, common low intakes of vitamin A and zinc increase the risk of vitamin A deficiency and lead to several physiological events. A study in Burkina Faso showed major reduction of malaria morbidity with combined vitamin A and zinc supplementation in young children.

Since the unique function of retinyl group is the light absorption in Retinylidene protein, one of the earliest and specific manifestations of vitamin A deficiency is impaired vision, particularly in reduced light - Night blindness. Persistent deficiency gives rise to a series of changes, the most devastating of which occur in the eyes. Some other ocular changes are referred to as xerophthalmia. First there is dryness of the conjunctiva (xerosis) as the normal lacrimal and mucus secreting epithelium is replaced by a keratinized epithelium. This is followed by the build-up of keratin debris in small opaque plaques (Bitot's spots) and, eventually, erosion of the roughened corneal surface with softening and destruction of the cornea (keratomalacia) and total blindness. Other changes include impaired immunity, hypokeratosis (white lumps at hair follicles), keratosis pilaris and squamous metaplasia of the epithelium lining the upper respiratory passages and urinary bladder to a keratinized epithelium. With relations to dentistry, a deficiency in Vitamin A leads to enamel hypoplasia.

Adequate supply of Vitamin A is especially important for pregnant and breastfeeding women, since deficiencies cannot be compensated by postnatal supplementation.

Toxicity

Hypervitaminosis A

As vitamin A is fat-soluble, disposing of any excesses taken in through diet is much harder than with water-soluble vitamins B and C. As such, vitamin A toxicity can result. This can lead to nausea, jaundice, irritability, anorexia (not to be confused with anorexia nervosa, the eating disorder), vomiting, blurry vision, headaches, muscle and abdominal pain and weakness, drowsiness and altered mental status.

Acute toxicity generally occurs at doses of 25,000 IU/kg of body weight, with chronic toxicity occurring at 4,000 IU/kg of body weight daily for 6-15 months. However, liver toxicities can occur at levels as low as 15,000 IU per day to 1.4 million IU per day, with an average daily toxic dose of 120,000 IU per day. In people with renal failure 4000 IU can cause substantial damage. Additionally excessive alcohol intake can increase toxicity. Children can reach toxic levels at 1500IU/kg of body weight.

In chronic cases, hair loss, drying of the mucous membranes, fever, insomnia, fatigue, weight loss, bone fractures, anemia, and diarrhea can all be evident on top of the symptoms associated with less serious toxicity.

It has been estimated that 75% of people may be ingesting more than the RDA for vitamin A on a regular basis in developed nations. Intake of twice the RDA of preformed vitamin A chronically may be associated with osteoporosis and hip fractures. High vitamin A intake has been associated with spontaneous bone fractures in animals. Cell culture studies have linked increased bone resorption and decreased bone formation with high vitamin A intakes. This interaction may occur because vitamins A and D may compete for the same receptor and then interact with parathyoid hormone which regulates calcium.

Toxic effects of vitamin A have been shown to significantly affect developing fetuses. Therapeutic doses used for acne treatment have been shown to disrupt cephalic neural cell activity. The fetus is particularly sensitive to vitamin A toxicity during the period of organogenesis.

These toxicities only occur with preformed (retinoid) vitamin A (such as from liver). The carotenoid forms (such as beta-carotene as found in carrots), give no such symptoms, but excessive dietary intake of beta-carotene can lead to carotenodermia, which causes orange-yellow discoloration of the skin.

A study by Siri Forsmo et al. shows a correlation between low bone mineral density and too high intake of vitamin A.

Researchers have succeeded in creating water-soluble forms of vitamin A, which they believed could reduce the potential for toxicity. However, a 2003 study found that water-soluble vitamin A was approximately 10 times as toxic as fat-soluble vitamin. A 2006 study found that children given water-soluble vitamin A and D, which are typically fat-soluble, suffer from asthma twice as much as a control group supplemented with the fat-soluble vitamins.

Chronically high doses of Vitamin A can produce the syndrome of "pseudotumor cerebri". This syndrome includes headache, blurring of vision and confusion. It is associated with increased intracerebral pressure.


From Wikipedia, the free encyclopedia
]]> Vitamin A

Vitamin A refers to a family of similarly shaped molecules: the retinoids. Its important part is the retinyl group, which can be found in several forms. In foods of animal origin, the major form of vitamin A is an ester, primarily retinyl palmitate, which is converted to an alcohol (retinol) in the small intestine. Vitamin A can also exist as an aldehyde (retinal), or as an acid (retinoic acid). Precursors to the vitamin (provitamins) are present in foods of plant origin as some of the members of the carotenoid family of compounds.

All forms of vitamin A have a Beta-ionone ring to which an isoprenoid chain is attached. This structure is essential for vitamin activity. The orange pigment of carrot - Beta-carotene - can be represented as two connected retinyl groups. The retinyl group, when attached to a specific protein, is the only primary light absorber in visual perception, and the compound name is related to the retina of the eye.

Vitamin A can be found in various forms:

* retinol, the form of vitamin A absorbed when eating animal food sources, is a yellow, fat-soluble, vitamin with importance in vision and bone growth. Since the alcohol form is unstable, the vitamin is usually produced and administered in a form of retinyl acetate or palmitate.

* other retinoids, a class of chemical compounds that are related chemically to vitamin A, are used in medicine.

Contents

* 1 Discovery of vitamin A
* 2 Equivalencies of retinoids and carotenoids (IU)
* 3 Recommended daily intake
* 4 Sources of vitamin A
* 5 Metabolic functions of vitamin A
o 5.1 Vision
o 5.2 Gene transcription
o 5.3 Dermatology
* 6 Deficiency
* 7 Toxicity
* 8 See also
* 9 References
* 10 Further reading
* 11 External links

Discovery of vitamin A

The discovery of vitamin A stemmed from research dating back to 1906, indicating that factors other than carbohydrates, proteins, and fats were necessary to keep cattle healthy. By 1917 one of these substances was independently discovered by Elmer McCollum at the University of Wisconsin-Madison, and Lafayette Mendel and Thomas Osborne at Yale University. Since "water-soluble factor B" (Vitamin B) had recently been discovered, the researchers chose the name "fat-soluble factor A" (vitamin A). Vitamin A was first synthesized in 1947 by two Dutch chemists, David Adriaan van Dorp and Jozef Ferdinand Arens.

Equivalencies of retinoids and carotenoids (IU)

Since some carotenoids can be converted into vitamin A, attempts have been made to determine how much of them in the diet is equivalent to a particular amount of retinol, so that comparisons can be made of the benefit of different foods. Unfortunately the situation is confusing because the accepted equivalences have changed. For many years, a system of equivalencies was used in which an international unit (IU) was equal to 0.3 micrograms of retinol, 0.6 μg of β-carotene, or 1.2 μg of other provitamin-A carotenoids. Later, a unit called retinol equivalent (RE) was introduced. 1 RE corresponded to 1 μg retinol, 2 μg β-carotene dissolved in oil (as in supplement pills), 6 μg β-carotene in normal food (because it is not absorbed as well as from supplements), and 12 μg of either α-carotene or β-cryptoxanthin in food.

However, new research showed that the absorption of provitamin-A carotenoids was only half as much as previously thought, so in 2001 the US Institute of Medicine recommended a new unit, the retinol activity equivalent (RAE). 1 μg RAE corresponds to 1 μg retinol, 2 μg of β-carotene in oil, 12 μg of "dietary" beta-carotene, or 24 μg of other dietary provitamin-A carotenoids.
Substance and its chemical environment Micrograms of retinol equivalent per microgram of the substance
retinol 1
beta-carotene, dissolved in oil 1/2
beta-carotene, common dietary 1/12
alpha-carotene, common dietary 1/24
beta-cryptoxanthin, common dietary 1/24

Because the production of retinol from provitamins by the human body is regulated by the amount of retinol available to the body, the conversions apply strictly only for vitamin A deficient humans. The absorption of provitamins also depends greatly on the amount of lipids ingested with the provitamin; lipids increase the uptake of the provitamin.

The conclusion that can be drawn from the newer research is that fruits and vegetables are not as useful for obtaining vitamin A as was thought--in other words, the IU's that they were reported to contain were worth much less than the same number of IU's of fat-dissolved supplements. This is important for vegetarians. (Night blindness is prevalent in countries where little meat or vitamin A-fortified foods are available.) A sample vegan diet for one day that provides sufficient vitamin A has been published by the Food and Nutrition Board (page 120). On the other hand, reference values for retinol or its equivalents, provided by the National Academy of Sciences, have decreased. The RDA (for men) of 1968 was 5000 IU (1500 μg retinol). In 1974 the RDA was set to 1000 RE (1000 μg retinol), whereas now the Dietary Reference Intake is 900 RAE (900 μg or 3000 IU retinol). This is equivalent to 1800 μg of β-carotene supplement (3000 IU) or 10800 μg of β-carotene in food (18000 IU).

Sources of vitamin A

Vitamin A is found naturally in many foods:

* liver (beef, pork, chicken, turkey, fish) (6500 μg 722%)
* carrots (835 μg 93%)
* Broccoli leaves (800 μg 89%) - Acc. to USDA database. Broccoli florets supposedly have much less - see note.
* sweet potatoes (709 μg 79%)
* kale (681 μg 76%)
* butter (684 μg 76%)
* spinach (469 μg 52%)
* leafy vegetables
* pumpkin (369 μg 41%)
* collard greens (333 μg 37%)
* cantaloupe melon (169 μg 19%)
* eggs (140 μg 16%)
* apricots (96 μg 11%)
* papaya (55 μg 6%)
* mango (38 μg 4%)
* peas (38 μg 4%)
* broccoli (31 μg 3%)
* winter squash

Note: bracketed values are retinol equivalences and percentage of the adult male RDA per 100g.

Conversion of carotene to retinol varies from person to person and bioavailability of carotene in food varies.

Metabolic functions of vitamin A

Vitamin A plays a role in a variety of functions throughout the body, such as:

* Vision
* Gene Transcription
* Immune Function
* Embryonic Development and Reproduction
* Bone Metabolism
* Haematopoiesis
* Skin Health
* Reducing Risk of Heart Disease and Cancer
* Antioxidant Activity

Vision

The role of vitamin A in the vision cycle is specifically related to the retinal form. Within the eye, 11-cis-retinal is bound to rhodopsin (rods) and iodopsin (cones) at conserved lysine residues. As light enters the eye the 11-cis-retinal is isomerized to the all-"trans" form. The all-"trans" retinal dissociates from the opsin in a series of steps called bleaching. This isomerization induces a nervous signal along the optic nerve to the visual center of the brain. Upon completion of this cycle, the all-"trans"-retinal can be recycled and converted back to the 11-"cis"-retinal form via a series of enzymatic reactions. Additionally, some of the all-"trans" retinal may be converted to all-"trans" retinol form and then transported with an interphotoreceptor retinol-binding protein (IRBP) to the pigment epithelial cells. Further esterification into all-"trans" retinyl esters allow this final form to be stored within the pigment epithelial cells to be reused when needed. The final conversion of 11-cis-retinal will rebind to opsin to reform rhodopsin in the retina. Rhodopsin is needed to see black and white as well as see at night. It is for this reason that a deficiency in vitamin A will inhibit the reformation of rhodopsin and lead to night blindness.

Gene transcription

Vitamin A, in the retinoic acid form, plays an important role in gene transcription. Once retinol has been taken up by a cell, it can be oxidized to retinal (by retinol dehydrogenases) and then retinal can be oxidized to retinoic acid (by retinal oxidase). The conversion of retinal to retinoic acid is an irreversible step, meaning that the production of retinoic acid is tightly regulated, due to its activity as a ligand for nuclear receptors. Retinoic acid can bind to two different nuclear receptors to initiate (or inhibit) gene transcription: the retinoic acid receptors (RARs) or the retinoid "X" receptors (RXRs). RAR and RXR must dimerize before they can bind to the DNA. RAR will form a heterodimer with RXR (RAR-RXR), but it does not readily form a homodimer (RAR-RAR). RXR, on the other hand, readily forms a homodimer (RXR-RXR) and will form heterodimers with many other nuclear receptors as well, including the thyroid hormone receptor (RXR-TR), the Vitamin D3 receptor (RXR-VDR), the peroxisome proliferator-activated receptor (RXR-PPAR) and the liver "X" receptor (RXR-LXR). The RAR-RXR heterodimer recognizes retinoid acid response elements (RAREs) on the DNA whereas the RXR-RXR homodimer recognizes retinoid "X" response elements (RXREs) on the DNA. The other RXR heterodimers will bind to various other response elements on the DNA. Once the retinoic acid binds to the receptors and dimerization has occurred, the receptors undergo a conformational change that causes co-repressors to dissociate from the receptors. Coactivators can then bind to the receptor complex, which may help to loosen the chromatin structure from the histones or may interact with the transcriptional machinery. The receptors can then blind to the response elements on the DNA and upregulate (or downregulate) the expression of target genes, such as cellular retinol-binding protein (CRBP) as well as the genes that encode for the receptors themselves.

Dermatology

Vitamin A appears to function in maintaining normal skin health. The mechanisms behind retinoid's therapeutic agents in the treatment of dermatological diseases are being researched. For the treatment of acne, the most effective drug is 13-cis retinoic acid (isotretinoin). Although its mechanism of action remains unknown, it is the only retinoid that dramatically reduces the size and secretion of the sebaceous glands. Isotretinoin reduces bacterial numbers in both the ducts and skin surface. This is thought to be a result of the reduction in sebum, a nutrient source for the bacteria. Isotretinoin reduces inflammation via inhibition of chemotatic responses of monocytes and neutrophils. Isotretinoin also has been shown to initiate remodeling of the sebaceous glands; triggering changes in gene expression that selectively induces apoptosis. Isotretinoin is a teratogen and its use is confined to medical supervision.

Deficiency

Vitamin A deficiency is estimated to affect millions of children around the world. Approximately 250,000-500,000 children in developing countries become blind each year owing to vitamin A deficiency, with the highest prevalence in Southeast Asia and Africa. According to the World Health Organization (WHO), vitamin A deficiency is under control in the United States, but in developing countries vitamin A deficiency is a significant concern. With the high prevalence of vitamin A deficiency, the WHO has implemented several initiatives for supplementation of vitamin A in developing countries. Some of these strategies include intake of vitamin A through a combination of breast feeding, dietary intake, food fortification, and supplementation. Through the efforts of WHO and its partners, an estimated 1.25 million deaths since 1998 in 40 countries due to vitamin A deficiency have been averted.

Vitamin A deficiency can occur as either a primary or secondary deficiency. A primary vitamin A deficiency occurs among children and adults who do not consume an adequate intake of yellow and green vegetables, fruits and liver. Early weaning can also increase the risk of vitamin A deficiency. Secondary vitamin A deficiency is associated with chronic malabsorption of lipids, impaired bile production and release, low fat diets, and chronic exposure to oxidants, such as cigarette smoke. Vitamin A is a fat soluble vitamin and depends on micellar solubilization for dispersion into the small intestine, which results in poor utilization of vitamin A from low-fat diets. Zinc deficiency can also impair absorption, transport, and metabolism of vitamin A because it is essential for the synthesis of the vitamin A transport proteins and the oxidation of retinol to retinal. In malnourished populations, common low intakes of vitamin A and zinc increase the risk of vitamin A deficiency and lead to several physiological events. A study in Burkina Faso showed major reduction of malaria morbidity with combined vitamin A and zinc supplementation in young children.

Since the unique function of retinyl group is the light absorption in Retinylidene protein, one of the earliest and specific manifestations of vitamin A deficiency is impaired vision, particularly in reduced light - Night blindness. Persistent deficiency gives rise to a series of changes, the most devastating of which occur in the eyes. Some other ocular changes are referred to as xerophthalmia. First there is dryness of the co