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Recommended daily allowances (RDAs).
They were introduced as a standard for the daily amounts of vitamins and minerals needed by a healthy person. Unfortunately, the amounts they came up with is normally only the bare minimum required to ward off deficiency diseases such as beriberi, rickets, scurvy, and night blindness. Not enough to assure and maintain maximum health, but rather borderline health. The relatively few studies that have explicitly investigated the role of vitamin and mineral supplements in promoting health and preventing disease have generally found benefits from the supplements. In fact, evidence is increasing rapidly for a beneficial role of supplementation with a number of nutrients, including vitamins B6, C, and E; beta-carotene and other carotenes; folic acid; calcium; magnesium; and other factors.
Although there is little dispute about the importance and functions of many vitamins and nutrients, questions arise regarding the levels necessary to produce optimum health. Many contend that the optimal levels of these compounds can be obtained in a normal diet and that the effect of additional amounts is negligible.
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