Vitamins are a group of organic compounds occurring naturally in food and are necessary for good health. Lack of a
vitamin may lead to a specific deficiency syndrome, which may be primary (due to inadequate diet) or secondary (due to malabsorption or to increased metabolic need), and it is rational to use high-dose
vitamin supplementation in situations where these clinical conditions exist. However, pharmacological doses of
vitamins are claimed to be of value in a wide variety of conditions which have no, or only a superficial, resemblance to the classic
vitamin deficiency syndromes. The enormous literature on which these claims are based consists mainly of uncontrolled clinical trials or anecdotal reports. Only a few studies have made use of the techniques of randomisation and double-blinding. Evidence from such studies reveals a beneficial
therapeutic effect of
vitamin E in
intermittent claudication and
fibrocystic breast disease and of
vitamin C in
pressure sores, but the use of
vitamin A in
acne vulgaris,
vitamin E in
angina pectoris, hyperlipidaemia and enhancement of athletic capacity, of
vitamin C in advanced
cancer, and
niacin in
schizophrenia has been rejected. Evidence is conflicting or inconclusive as to the use of
vitamin C in the
common cold,
asthma and enhancement of athletic capacity, of
pantothenic acid in
osteoarthritis, and
folic acid (
folacin) in
neural tube defects. Most of the
vitamins have been reported to cause adverse effects when ingested in excessive doses. It is therefore worthwhile to consider the risk-benefit ratio before embarking upon the use of high-dose
vitamin supplementation for disorders were proof of efficacy is lacking.