VITAMIN A GETS A MINUS
People need less vitamin A for good health than previously thought, according to a panel of experts that sets the Recommended Dietary Allowances (RDA guidelines) for vitamins and minerals, a mainstay for health-conscious Americans since 1941.
The panel from the Institute of Medicine, an arm of the prestigious National Academy of Sciences, also weighed in on vitamin K and a dozen other nutrients, from chromium to zinc. Adult men need 900 micrograms of vitamin A per day and women need 700 micrograms, according to the panel, 100 micrograms less than earlier recommended.
Vitamin A is important for normal vision and immune function. However, recent research shows that too much vitamin A may increase the risk of liver damage and birth defects. As a result, the Institute of Medicine panel set a ceiling or "upper level" for vitamin A at 3,000 micrograms a day for adults. People should bear in mind the limit when picking out a dietary supplement.
Surprisingly, the panel also found that tried and true sources of vitamin A such as carrots, sweet potatoes and broccoli actually supply the body with half as much vitamin A as previously believed. "People need to take this into consideration and make sure they select enough carotene-rich fruit and vegetables to meet their daily vitamin A requirement,' said Robert Russell, professor of medicine and nutrition, Tufts University School of Medicine, and chairman of the panel. "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," he added.
How Much is Too Much?
The latest report is the fifth in a series that updates and expands on the RDA guidelines. Along with setting new Dietary Reference Intakes (DRI) that will gradually replace the RDA guidelines, it sets Upper Intake Levels (ULs) a ceiling and Adequate Intake (AI) levels the amount of a nutrient that healthy people should aim for each day when there isn't enough scientific evidence to determine an RDA.
The panel gave vitamin K, which helps blood clot and is found in leafy, green veggies, an AI of 120 micrograms for men and 90 micrograms for women. It didn't put a ceiling on vitamin K because no adverse effects have been reported.
The panel changed the RDA for iron to eight milligrams a day for men and post-menopausal women, lower than before. But it hiked the RDA for pre-menopausal women to 18 milligrams and said pregnant women should take even more. The RDA for pregnant women is 27 milligrams. Also, vegetarians need to consume twice as much iron since the body absorbs less from plant food than from animal food. The UL for iron is 45
milligrams for adults.
The panel shaved the RDA for zinc to 11 milligrams a day for men and eight for women but noted, like iron, vegetarians may need to consume more. A UL of 40 milligrams was set based on studies that show high levels of zinc adversely affect copper absorption in the body.