January 12, 2001

Carotene-rich fruits and vegetables -- such as carrots, sweet potatoes, and broccoli -- provide the body with half as much vitamin A as previously thought, says the latest report on Dietary Reference Intakes (DRIs) from the National Academies' Institute of Medicine. This means people need to make sure they eat enough of these fruits and vegetables to meet their daily requirement for vitamin A, especially if they do not eat animal-derived foods, which serve as abundant sources of the nutrient for most people.

"Darkly colored fruits and vegetables are still good sources of vitamin A," said Robert Russell, professor of medicine and nutrition, Tufts University School of Medicine, Boston, and chair of the panel that wrote the report. "But new evidence shows that it takes twice as much of them to yield the same amount of vitamin A in the body as we previously understood. People need to take this into consideration and make sure they select enough carotene-rich fruits and vegetables to meet their daily vitamin A requirement. This is especially true for those who don't eat meats, fish, eggs, or vitamin A-fortified milk or cereal. They may need to significantly increase their consumption of such fruits and vegetables."

Three carotenoids -- alpha-carotene, beta-carotene, and beta-cryptoxanthin -- are present in certain orange, red, green, and dark-yellow fruits and vegetables. They are referred to as provitamin A carotenoids because they can be converted in the body to retinol, an active form of vitamin A. Based on a comprehensive review of recent research, the panel found that the amount of provitamin A carotenoids required to create a unit of retinol is twofold higher than the amount believed needed in 1989, when the National Academy of Sciences last issued recommendations for vitamin A.

In addition to vitamin A, the report examines the nutritional value of the micronutrients vitamin K, arsenic, boron, chromium, copper, iodine, iron, manganese, molybdenum, nickel, silicon, vanadium, and zinc. It sets a daily maximum level of intake for vitamin A as well as for boron, copper, iodine, iron, manganese, molybdenum, nickel, vanadium, and zinc. Specific recommended intakes are given for vitamins A and K, chromium, copper, iodine, iron, manganese, molybdenum, and zinc.

Based on national nutrition surveys, the report says that daily requirements for the nutrients it examined can be met, in almost all instances, without taking supplements. One exception, however, is that pregnant women usually need iron supplements to meet their increased daily requirements. In fact, surveys in the United States show that only half of all pregnant women who live here consume adequate amounts of iron in their diets.