The A Train: Some Fruits and Veggies Have Half the Vitamin A Once Thought

From the WebMD Archives

Jan. 9, 2001 (Washington) -- A scientific panel that sets nutrition standards has discovered something that could change the way we eat: Dark-colored fruits and vegetables contain only half the vitamin A previously thought. That means strict vegetarians may need to consume more carrots, green asparagus, or even mangoes and papaya.

"What we're saying is that people who depend on fruits and vegetables for their vitamin A ... [have] to be more concerned about their choice of fruits or vegetables," Robert Russell, MD, tells WebMD. Russell is chair of the food and nutrition board at the Institute of Medicine, a part of the National Academy of Sciences that offers advice to government agencies.

Over the past five years, the board has been setting standards for the vitamins and minerals necessary for a healthy diet. The report, released Tuesday, reviews a number of key nutrients in an effort to establish what are called Dietary Reference Intakes (DRIs) for substances ranging from vitamin A to iron. These scientifically calibrated amounts are a more informative form of the commonly known Recommended Dietary Allowances (RDAs).

Also, for the first time, the board set "tolerable upper intake levels." Known as ULs, they represent the largest safe amount a person can take. For vitamin A, the UL is 3,000 mcg per day. The RDA is 900 mcg for men and 700 for women -- which is a bit less than previously recommended. However, less than 5% of the U.S. population runs the risk of not getting enough vitamin A, Russell says.

Using a new measuring technique, the panel determined that fruits and green leafy vegetables contain only half the anticipated carotenoids that are converted into vitamin A. That means one new unit of vitamin A amounts to only six molecules of carotenoid instead of 12.

"That doesn't mean that fruit and vegetable consumption must double," Russell says. Among the alternatives, he says, are liver, fish rich in oil, and dairy products. Also, he says, a standard regimen of five servings of fruits and vegetables will suffice, or half-a-cup of cooked carrots.

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On the other hand, some people are taking megadoses of vitamin A that could damage the liver or cause birth defects in pregnant women. Generally, the body protects itself from too much vitamin A, but eating too much liver has proved fatal in children.

Besides vitamin A, the board examined the nutritional value of 13 additional vitamins and minerals, and most of the recommendations for minerals were slightly lower than in the past. In one exception, the recommended dose of vitamin K, essential for blood clotting, went up slightly to 120 mcg for men and 90 for women.

For iron, another crucial mineral, the board suggested slightly raising the amount for women and slightly lowering the dose for men. Postmenopausal women and men should get 8 mg a day, while premenopausal women (who lose blood during menstruation) should get 18 mg daily. The panel says pregnant women should get 27 mg daily and establishes an upper limit for adults at 45 mg daily, which is considered safe for all but those with the genetic disease known as hemochromatosis.

For a variety of other vitamins and minerals, the board recommended doses based on the average consumption of American adults. For chromium, for example, they found that harmful side effects are rare from too much chromium in food and based its daily recommendations of 35 mcg for men and 25 mcg for women on average diets.

The RDA for the popular supplement zinc was set at 11 and 8 mg a day for men and women, respectively, with an upper limit of 40 mg. The scientists say that vegetarians may need about 50% more than nonvegetarians, and infants between 7 and 12 months old will not get adequate amounts of zinc from mother's milk and would need to get it from other foods or formula.

Other recommendations:

  • The new RDA for copper is 900 mcg a day for both men and women, with an upper limit of 10 mg a day.
  • The new RDA for iodine is 150 mcg a day for both men and women, with an upper limit of 1.1 mg a day.
  • The new RDA for manganese is 2.3 mg for men and 1.8 mg for women, daily, with an upper limit of 11 mg a day.
  • The new RDA for molybdenum is 45 mcg a day for both men and women, with an upper limit of 2 mg a day.

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The report did not make any recommendations on daily intake levels for arsenic, boron, nickel, silicon, and vanadium, but did warn that at high doses these elements were likely to be toxic.

The report says that in almost all cases, it's possible to get the necessary nutrients without taking dietary supplements. The report goes to the FDA, and that agency will decide how to implement the recommendations. In the case of vitamin A, Russell says foods containing the nutrient will need a label change reflecting a reduced amount in the product.

The board expects to finish its work next year.

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