VITAMIN-C (ASCORBIC-ACID) - NEW ROLES, NEW REQUIREMENTS

There is an enormous amount of literature on vitamin C intake and heal th in animals, cell cultures, and humans. Beyond its function in colla gen formation, ascorbic acid is known to increase absorption of inorga nic iron, to have essential roles in the metabolism of folic acid and of some amino acids and hormones, and to act as an antioxidant. In rec ent years, research has increasingly focused on this latter function, stimulated by suggestions that ''oxidative stress'' may be a causal fa ctor in the etiology of such diverse and important disorders of aging as cancer, cardiovascular disease, and cataract formations. The presen t evidence is strong enough to have convinced nutritionists that daily vitamin C intake should be many times higher than the amount needed t o protect against scurvy, and this is reflected in the present Recomme nded Dietary Allowances. Suggestions that the recommended levels shoul d be higher still are largely based on extrapolations from results of animal and tissue culture studies. How much ascorbic acid is necessary to achieve in humans the effects seen in animal studies is not clear. In general, the limited human studies have not been persuasive. The d ata are incomplete, and many of the studies have serious flaws. There are no toxicity studies of the type done for new compounds being consi dered for approval as therapy for major disease conditions. Interventi on studies will be difficult, but are essential, and methods for tissu e saturation measurement must be defined before new recommendations fo r the public are designed.