Berkeley Wellness Alerts
November 23, 2012 | Comments: 1
Vitamin A and Your Bones
Vitamin A is essential for good health. But high doses are toxic and can cause bone loss and other health problems.
More than a decade ago, the Nurses' Health Study, a famous Harvard study of 70,000 female nurses, found that a daily consumption of 6,600 IU or more of vitamin A from food and supplements (not much more than the 5,000 IU found in most multivitamins then) may actually weaken postmenopausal women's bones. Several other studies have supported this finding. The message traveled fast, and in response many vitamin manufacturers lowered the amount of vitamin A in their formulas.
High doses of vitamin A can also cause liver damage. And pregnant women are advised to avoid high doses because of the risk of birth defects.
"Preformed" vitamin A comes only from animal products, fortified foods, and supplements. It is measured in International Units (IU) or sometimes in micrograms. The Recommended Dietary Allowance (RDA) for vitamin A is 2,333 IU daily for women (3,000 IU for men). Confusingly, the labels on foods use a different number for the "Daily Value" for A, which is 5,000 IU. The Institute of Medicine has set 10,000 IU as the safe upper limit for vitamin A, especially for pregnant women.
Not all vitamin A comes preformed. Beta carotene (found in plant foods, especially dark green and highly colored vegetables and fruits) is converted to vitamin A as needed in our bodies. You can't get dangerous levels of vitamin A by consuming beta carotene.
What you should do
It's a good idea to avoid consuming a lot of preformed vitamin A, especially if you are a postmenopausal woman at risk for bone loss. Keep in mind:
- Liver is a rich source of vitamin A. Beef liver has about 24,000 IU in 3 ounces (cooked); chicken liver, 12,000 IU. If you eat liver, do so sparingly and occasionally. It is also very high in cholesterol.
- There is no evidence that beta carotene weakens bones. Keep your intake of carotene-rich fruits and vegetables high. The body carefully regulates the conversion of beta carotene into vitamin A.
- If you take a multivitamin, check the label. It should have no more than 3,000 IU of preformed vitamin A. If the label says "Vitamin A, 5,000 IU (50% as beta carotene)," that is okay, since that means the preformed A content is only 2,500 IU.
- If you eat highly fortified foods, such as some breakfast cereals, check the labels for vitamin A content. Milk is fortified with 300 to 500 IU of vitamin A per cup, an amount you need not worry about.
- Don't take cod liver oil, unless the label says its vitamin A has been reduced.
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