SELF-CARE

Upper limit and adequate intake levels set for nutrients

The old adage "everything in moderation" seems to be more apt than ever, at least when it comes to taking vitamin A. So a panel of the National Academy of Sciences' Institute of Medicine (IOM) appears to warn in a new report on Dietary Reference Intakes (DRIs).

In an effort to help people avoid harm from taking too much of a nutrient, the panel has established "upper intake" levels (ULs). It also has recommended what it calls "adequate intake" levels (AI), based on diets known to be nutritionally adequate for the U.S. and Canadian populations when not enough evidence exists to set a Recommended Dietary Allowance (RDA).

The panel set a UL for vitamin A intake for both foods and supplements at 3,000 micrograms a day for adults. Excess vitamin A intake may increase the risk of physical birth defects, liver abnormalities in adults, and bulging of the skull where bone has not yet formed in infants and young children.

To ensure adequate stores of vitamin A in the body, the panel recommended that women should consume 700 micrograms a day and men should take 900 mcg daily.

Vitamin A is essential to maintain normal reproduction, vision, and immune function. It also plays a role in gene expression, embryonic development, and growth. A deficiency of vitamin A, although uncommon in North America, can result in vision impairment, especially night blindness.

Here are some other nutrient levels released in the new guidelines:

• The RDA for iron for adult men and postmenopausal women is 8 milligrams per day and 18 mg/day for premenopausal women. The RDA for pregnant women is 27 mg/day, which usually requires taking a small supplement. The RDA for women who breast-feed and who are not menstruating is 9 mg a day, and for adolescents who breast-feed, it is 10 mg daily. The UL for iron is set at 45 mg per day for adults, above which gastrointestinal distress may occur, especially when iron supplements are consumed on an empty stomach. Research has suggested a possible link between elevated iron stores and a higher incidence of heart disease and cancer.

• The RDA for zinc is set at 8 milligrams per day for women and 11 mg per day for men. A UL of 40 mg for adults was recommended, based on studies showing that zinc adversely affects copper absorption at high levels of intake.

• The panel recommended an AI of 120 micrograms of vitamin K for men and 90 mcg for women (no UL was established). There was insufficient data to establish an RDA. No adverse effects have been reported for vitamin K, so a UL was not established.

• An AI of 35 micrograms for men and 25 mcg for women was recommended for chromium (no UL was established). The RDA for chromium could not be established because not enough information exists to determine a relationship between a particular dose of the nutrient and insulin response. Few serious side effects have been associated with excess intake of chromium from food, and scarce data are available on the adverse effects resulting from chronically high intake of the chromium contained in supplements, so no UL was set.

• The new RDA for copper is 900 micrograms a day for both men and women. To protect against possible liver damage, the UL was set at 10 milligrams per day.

• An RDA of 150 micrograms a day was established for iodine for both men and women. To avoid overabsorption of iodine by the thyroid, adults should not consume more than a UL of 1.1 milligrams daily.

• The report set an adequate intake level for manganese at 2.3 milligrams per day for men and 1.8 mg per day for women. The nutrient is involved in bone formation and in protein, fat, and carbohydrate metabolism. The UL is set at 11 mg for adults, based on a new study showing that no adverse health effects occurred when this amount was consumed on a chronic basis. (No RDA was set for manganese, boron, vanadium or nickel.)

• The UL recommended for boron is 20 milligrams per day; for vanadium, 1.8 mg per day; and for nickel, 1 mg per day. Neither an RDA nor an AI was established for these nutrients.

• The new RDA for molybdenum is 45 micrograms per day for men and women. The UL was set at 2 milligrams, based on studies showing impaired reproduction and growth in animals at high levels of chronic intake. Molybdenum is a component of a limited number of enzymes in the body. Sources of this enzyme-enhancing nutrient in-clude legumes, grain products, and nuts.

IOM said the daily requirements for nutrients it examined can be met, in almost all instances, without taking supplements. One exception is pregnant women, who usually need iron supplements to meet their increased daily requirements.

Sandra Levy

Sandra Levy. Upper limit and adequate intake levels set for nutrients.

Drug Topics

2001;3:46.