Experts agree that more research on vitamin supplementation is necessary. But what is known–the finding that comes up again and again–is that when vitamins and minerals are consumed in food, they are just about always good for you. In pill form, however, particularly with high doses, vitamins should be used with caution.

One of the difficulties of pill supplementation is in calculating dosage. How much of any vitamin a person needs varies–age, sex, stage of life, and specific individual needs all factor into correct dosage. There is no single level of any vitamin or mineral that can be considered the optimum intake for everyone.

In addition, despite the possible healing properties of supplemental vitamins (unproven at this point), there are risks when nutrients are taken separately from foods containing them and in doses much greater than the body is designed to process.

Specific vitamin overdoses can cause known problems:

Too much vitamin A can cause headaches from increased brain pressure, liver and bone damage, hair loss, skin disorders, psychiatric symptoms and, when taken in early pregnancy, birth defects. Too much B6 can damage nerves. Too much vitamin C can interfere with tests for blood in the stool. Large amounts of calcium can limit the absorption of iron. Iron supplements can be deadly to small children, and the most common cause of poisoning deaths among children is not from caustics or aspirin–but from iron supplements intended for adult use.

Again, for the average healthy person who consumes a variety of foods, there is scant evidence that vitamin and mineral supplements are beneficial. Even for segments of the population who may need more vitamins–smokers, people who are ill or poorly nourished, the elderly and pregnant women–the long-term benefits are unclear at best. According to a 13-year study of 10,758 Americans, people who took vitamins did not live longer or suffer fewer cancer deaths than those who did not take vitamins.

Americans are heavier than ever, but not necessarily well nourished. However, nutrition experts, even those who believe in vitamin supplements, don’t believe vitamin pills can compensate for dietary deficiencies. They emphasize that there are many health-promoting substances in foods other than vitamins and minerals. Their best advice: eat a balanced and varied diet that is low in fat and high in fruits and vegetables and complex carbohydrates.