VITAMIN C

Vitamin C or L-ascorbic acid is an essential nutrient for humans, 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. Ascorbate (an ion of ascorbic acid) is required for a range of essential metabolic reactions in all animals and plants. It is made internally by almost all organisms, humans being a notable exception. It is widely known that a deficiency in this vitamin 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. Scurvy has been known since ancient times. People in many parts of the world assumed it was caused by a lack of fresh plant foods. The British Navy started giving sailors lemon juice to prevent scurvy in 1795Ascorbic acid was finally isolated by 1933 and synthesized in 1934. The uses and recommended daily intake of vitamin C are matters of on-going debate. 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

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 glutathioneDuring this process semidehydroascorbic acid radical is formed. Ascorbate free radical reacts poorly with oxygen, and thus, will not create a superoxide. Instead two semidehydroascorbate radicals will react and form one ascorbate and one dehydroascorbate. With the help of glutathione, dehydroxyascorbate is converted back to ascorbate. The presence of Glutathione is crucial since it spares ascorbate and improves antioxidant capacity of blood. Without it dehydroxyascorbate could not convert back to ascorbate.

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. 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.