Too Much Vitamin A Dangerous

Report Sets Nutrient Guidelines

Lauran Neergaard / AP 9jan01

WASHINGTON -- Don't pop too many vitamin A supplements, because large amounts, particularly megadoses available from health-food stores, can be dangerous, the government says in guidelines that update how much of certain nutrients Americans should consume for good health.

Men need 900 micrograms of vitamin A a day and women 700, says Tuesday's report by the Institute of Medicine, which slightly lowers the ``recommended daily allowance,'' or RDA, of the nutrient.

Never eat more than 3,000 micrograms a day, because such high levels can cause severe liver disease and, in pregnant women, birth defects, the panel concluded.

Vitamin A is crucial for good vision, immune function and other bodily functions. In poor countries, vitamin A deficiency is a huge problem that blinds thousands.

Here, vitamin A deficiency is very rare, because Americans have so many foods chock full of the nutrient: meat, fish, eggs, vitamin-fortified breakfast cereals, and dark-colored fruits and vegetables like oranges, carrots and spinach.

It's easy for most Americans to get enough through diet alone, said Tufts University nutrition professor Robert Russell, who chaired the Institute of Medicine panel.

Vegetarians, however, may need to eat more dark-colored fruits and vegetables, because new research shows those foods actually yield half as much vitamin A as previously thought.

``We're not talking about eating mammoth amounts,'' Russell said. Half a cup of cooked carrots is enough. Cooking doubles the body's absorption of vitamin A, so people who prefer raw veggies need more.

But vitamin supplements -- even a regular multivitamin that contains three times the RDA -- can push people over safe levels, the report cautioned. Of most concern are megadoses sold in health food stores, often measured in confusing ``international units.'' Know that 10,000 international units is the same as 3,000 micrograms, a dangerous amount, Russell warned.

The institute is part of the National Academy of Sciences, a nonprofit organization that advises the federal government and has set the nation's RDAs for nutrients since 1941.

Other nutrient levels released Tuesday:

• Men and post-menopausal women need 8 milligrams a day of iron, vital to prevent anemia. Because iron is lost through bleeding, premenopausal women need 18 milligrams daily.
  
  Iron is found in many foods, especially meat. But pregnant women need an extra 27 milligrams daily for fetal growth, and thus require iron in prenatal vitamins.
  
  More than 45 milligrams a day will cause stomach upset. Also, men should not take iron supplements, the institute said. There's no benefit; some research suggests too much iron increases the risk of heart disease; and some people harbor a gene that makes their bodies dangerously overload iron.

• The RDA for zinc is 11 milligrams for men, 8 milligrams for women, a little lower than before because scientists have found the body stores zinc better than once thought. About 10 percent of Americans don't eat that much, a particular problem for children because zinc deficiency can stunt growth.
  
  The upper limit is 40 milligrams a day. That much can block the body's absorption of another vital nutrient, copper. As for those zinc supplements popular to fight colds, there's not yet proof they really work and the doses could exceed the upper limit, IOM cautioned.

• Chromium, widespread through the food supply, may stimulate insulin, a hormone important for converting blood sugar into energy. Consequently, chromium supplements have become popular among people worried about diabetes. But the IOM called chromium supplement studies inconclusive and couldn't set an RDA or a safe upper limit because so little is known about the nutrient. Americans today eat 25 to 35 micrograms daily.

• Men need 120 micrograms of vitamin K daily, 90 for women. Found in green leafy vegetables and certain oils, it's essential for blood clotting.

• Copper's new RDA is 900 micrograms; the upper limit is 10 milligrams daily, which can cause liver damage. Copper is found in organ meats, seafood and nuts.

• Eat 150 micrograms a day of iodine but never more than 1.1 milligrams a day. Found mostly in iodized salt but also some seafood and grains, it's important for proper thyroid gland function.

• http://www.nas.edu

• http://books.nap.edu/books/0309072794/html/65.html#pagetop Section for Vitamin A