Spring 2001 Vol. 1 No. 1
For generations, parents have urged their children to eat all their carrots for good eyesight. They were right, of course, but recently scientists have discovered that carrots don't provide the body with as much vitamin A -- which prevents night blindness and other eye problems -- as previously thought.
Darkly colored fruits and vegetables, such as carrots, sweet potatoes, and broccoli, contain carotenoids that are converted to an active form of vitamin A in the body. But in its latest report on Dietary Reference Intakes (DRIs), the Institute of Medicine's Food and Nutrition Board says recent studies show that it takes twice as many carotenoids to yield the same amount of vitamin A that researchers believed were needed in 1989, when the board last issued recommendations for vitamin A.
The new findings mean people need to make especially sure they eat enough orange, red, green, and dark-yellow fruits and vegetables to meet their daily requirement for vitamin A, particularly if they are strict vegetarians. Meat eaters and vegetarians who eat egg and dairy products typically get plenty of vitamin A, since it is abundant in animal-derived foods. And while vitamin A deficiency is rarely observed in the United States, up to 500,000 children go blind each year in other parts of the world because of a lack of it.
Along with vitamin A, the report examines the nutritional value of vitamin K, arsenic, boron, chromium, copper, iodine, iron, manganese, molybdenum, nickel, silicon, vanadium, and zinc. It says the daily requirements for Americans and Canadians of these nutrients can, in almost all instances, be met without taking supplements.
DRIs are developed by U.S. and Canadian scientists, who base their recommendations on indicators of good health and the prevention of chronic disease. DRIs include not only Recommended Dietary Allowances (RDAs), but also adequate intakes (AIs), which are recommended when not enough evidence exists to set an RDA, and tolerable upper intake levels (ULs).
ULs are established in the report -- some for the first time -- for vitamin A, boron, copper, iodine, iron, manganese, molybdenum, nickel, vanadium, and zinc to help people avoid harm from taking too much of a nutrient. For example, while the RDA for vitamin A was set at 900 and 700 micrograms a day for men and women respectively, a UL also was set at 3,000 micrograms daily since excessive consumption may increase the risk of birth defects, liver abnormalities, and bulging of the skull where bone has not yet completely formed in infants and young children.
The report also includes either RDAs or AIs for vitamin K, chromium, copper, iodine, iron, manganese, molybdenum, and zinc. Whenever the data allows, recommendations are made for all age groups as well as for pregnant and lactating women. For instance, pregnant women need more iron, as do all women during pre-menopausal years when iron is lost through menstrual bleeding. In fact, surveys show that only half of all pregnant women who live in the United States consume adequate amounts of iron in their diets.
Although there is some evidence suggesting a beneficial role for arsenic, boron, nickel, silicon, and vanadium in human health, not enough data exist to set recommended intake levels. To fill in the gaps in what is known about these trace elements and the other nutrients, the report calls for more research specifically designed to estimate nutrient requirements and detect side effects from chronic overconsumption. -- Bill Kearney
Dietary Reference Intakes for Vitamin A, Vitamin K, Arsenic, Boron, Chromium, Copper, Iodine, Iron, Manganese, Molybdenum, Nickel, Silicon, Vanadium, and Zinc. Panel on Micronutrients, Food and Nutrition Board, Institute of Medicine (2001, approx. 650 pp.; ISBN 0-309-07279-4; available from National Academy Press, tel. 1-800-624-6242; $49.95 plus $4.50 shipping for single copies).
The panel was chaired by Robert Russell, professor of medicine and nutrition, School of Medicine, and associate director, Jean Mayer U.S. Department of Agriculture Human Nutrition Research Center on Aging, Tufts University, Boston. The study was funded by the U.S. Department of Health and Human Services; the National Institutes of Health; the Centers for Disease Control and Prevention; Health Canada; the Institute of Medicine; the Dietary Reference Intakes Private Foundation Fund, including the Dannon Institute and the International Life Sciences Institute; and the Dietary Reference Intakes Corporate Donors' Fund, which includes contributions from Roche Vitamins Inc., Mead Johnson Nutrition Group, Nabisco Foods Group, U.S. Borax, Daiichi Fine Chemicals Inc., Kemin Foods Inc., M&M/Mars, Weider Nutrition Group, and the Natural Source Vitamin E Association.