USRDAs were devised by the Food and Drug Administration for
nutritional labeling. These are the lists on processed foods and vitamin products that
tell what percentage of each of 19 essential nutrients you get per serving or dose. It is
a rough guide because it doesn't differentiate among people of different ages and sex who
have different nutrient requirements.
The USRDAs, in turn, are based on the RDAs- Recommended Dietary
Allowances derived by a prestigious group of nutritional scientists who advise the
Food and Nutrition Board, a committee of the National Academy of Sciences-National
Research Council. Every five years or so, the board reviews and revises its
recommendations. As the board defines them, the RDAs are "the levels of intake of
essential nutrients considered, in the judgment of the Food and Nutrition Board on the
basis of available scientific knowledge, to be adequate to meet the known nutritional
needs of practically all healthy persons."
Except for vitamins A and D, it's not harmful to consume
two to three times the recommended levels of vitamins. Many people regularly do through
the foods they eat and especially if they take a multivitamin supplement.
There are some caveats regarding the RDAs. The board that
established them admits that scientific knowledge of nutritional requirements is far from
complete: that the requirements for many nutrients have not been established; that several
essential nutrients have only recently been discovered; and that in all likelihood other
nutrients will be found to be essential in years to come. Therefore, to be sure that as
yet undefined nutritional needs are met, it's important to eat a varied diet and not
depend on pills or processed foods artificially stoked with known micronutrients.
The RDAs should not be confused with nutritional
requirements. Requirements differ from individual to individual because of inherent
genetic differences, among other factors. Therefore, the RDAs represent estimates that
exceed the requirements of most people.
The RDAs were developed for healthy people under normal
circumstances (i.e., no illness, no genetic weaknesses, no environmental toxin exposure)
to prevent the development of overt deficiency diseases. They were not developed to serve
as a guide to determining optimal nutritional needs.
In addition, the studies that were used to determine the
level of a nutrient sufficient to prevent a nutritional deficiency were typically
conducted for six to nine months, only about 1% of the average human life span.
Nutritional studies with animals have shown that the amounts of some nutrients sufficient
to provide health and the prevention of a deficiency disease for short periods of time may
be totally inadequate to maintain the health of the animal over its entire lifespan.
of United States Recommended Daily Allowances (USRDA)
Allowances of Vitamins and Minerals
The Suggested Optimal Daily Nutritional Allowances
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