The use of various dietary supplements, including vitamins, to prevent or delay disease or aging rests for the most part on epidemiological associations. It does appear from these data that a diet rich in vitamins is associated with a tendency to improved health; however, the results from controlled trials are dismal. The discrepancy between different types of studies is probably explained by the fact that dietary composition and supplement use is a component in a cluster of healthy behaviors. An alternative hypothesis is that there are as-yet-unknown essential organic compounds in certain foods. The most prudent approach is to recommend a daily intake of fruits and vegetables as a likely source of essential nutrients. Failing compliance with a natural source of essential nutrients, and in populations at high risk of vitamin deficiency, vitamin supplements should be encouraged.