Vitamin C is the L-ascorbic acid in man while the isomer D-ascorbic acid is biologically inactive. It is water soluble white in color and odorless substance with a sour taste. Ascorbic acid is easily destroyed by heat, oxidation and exposure to air especially in the presence of iron and copper ions. Alkalies also destroy it and therefore its absorption is decreased in achlorhydria. Its chemical names are ascorbic acid, and ascorbyl palmitate. Man and other animal cannot make vitamin C in their bodies and for this reason it is vitamin for them. The inability to produce this vitamin is due to lack of enzyme L-gluonolactone oxidase.
Fresh fruits and vegetables are effective sources of this vitamin; animal tissues are not a good source. Guava, citrus, fruit and tomatoes are the best sources. Other sources are green pepper, onion, spinach, cabbage, turnips, melons and potatoes. Milk is deficient in it, though human milk is richer than cow’s milk. One ounce of orange has about 22 mg of ascorbic acid which is sufficient for daily need of an infant.
- Hydroxylation of Proline: Ascorbic acid (vitamin C) is involved n the conversion of proline present in the procollagen to hydroxyproline. This hydroxylation of proline is essential because in its absence collagen cannot form the triply helix required for the normal tissue structure. It also participates in the hydroxylation of lysine of procollagen to hydroxylysine. It also stimulates collagen formation.
- Antioxidant: Vitamin C acts as an anti-oxidant and along with other antioxidants, e.g. β-carotene, vitamin E etc. It prevents tissue injury to the body tissues from the toxic oxidation products. Studies have shown it is beneficial in high doses for protecting against cancer, hypertension and coronary atherosclerosis.
- Steroidogenesis: It is present in large amount in glandular tissues especially adrenal cortex and corpus luteum; in these tissues it appears to take part in reducing reactions involved in the synthesis of steroid hormones.
- Help in Iron Absorption: Its help in reducing ferric to ferrous and helps in the absorption of iron from the intestine and in its utilization. It also takes part in the oxidation-reduction reaction systems coupled with glutathione, cytochrome and NAD+ etc. Due to its reducing properties ascorbic acid is of some use in the treatment of methemoglobinemia.
- Degradation of Tyrosine: It is also involved in the degradation of tyrosine to homogentisic acid.
- Its takes part in the processing of certain polypeptide hormones such as oxytocin and antidiuretic hormone. It promotes their activity here.
- Other reaction in which vitamin C is involved are the hydroxylation of dopamine to noradrenalin, synthesis of carnitine, formation of bile acids and microsomal drug metabolism.
The deficiency of vitamin C results in a condition called Scurvy. Scurvy is liable to occur in artificially fed infants because of low vitamin C content of cow’s milk and destruction of vitamin C on boiling and pasteurization. Breast fed infants rarely suffer from this disease. Other sections of people who are liable to suffer from scurvy include elderly people living alone, alcoholic and drug addicts.
Clinical Picture of Scurvy
There is disruption of layers of blood vessels leading to hemorrhages form the nose, mouth GIT tract, urinary tract, skin muscles and subperiosteal tissues. The most frequent site of lesion is the gums which become spongy and show redness, swelling and ulceration. Capillaries show increased fragility.
Its excess can interfere with the absorption of vitamin B12, cause uricosuria, raise blood level of exogenously administered estrogen and can lead to formation of urinary stones of oxalate type.