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by Philip Hagen, M.D.
DEAR MAYO CLINIC:
At my last checkup, my blood work showed a vitamin D deficiency. My doctor recommended a vitamin D supplement but didn't say how much to take. I'm a healthy 51-year-old woman and eat a well-balanced diet. How much vitamin D do I need?
Vitamin D has been in the headlines recently. Researchers are learning more about the many ways it benefits health -- and, as a result, increasing the recommendation for vitamin D intake.
It's well established that vitamin D helps with calcium absorption and helps keep bones strong. There's also evidence that vitamin D helps reduce the risk of common cancers, muscle and joint pain and perhaps even multiple sclerosis. Newer studies, including one published last year in the
In the same study, researchers looked at data on the prevalence of vitamin D deficiency. They found that half of American adults may be deficient.
Given the importance of vitamin D -- and the prevalence of vitamin D deficiency -- it's good your doctor checked your vitamin D levels. For adults, the current recommended daily allowance (RDA) for vitamin D ranges from 200 to 600 international units (IU), depending on your age. For someone who's 51, the recommendation is 400 IU. However, many experts now say that adults should consume 800 to 1,000 IU of vitamin D daily. But before taking more than the recommended daily allowance, double check with your doctor. Taking doses higher than 2,000 IU per day can be harmful except in unusual cases, for example, when a person can't absorb vitamin D well because of a medical condition or disease.
For some people, it's difficult to get these higher amounts of vitamin D from the usual sources, which are diet and sunshine. Vitamin D is called the sunshine vitamin because your body can produce it when you are exposed to the sun's ultraviolet rays. If you aren't outside much, have dark skin or live in a northern climate, the sunshine factor is not enough. If you live where there is year-round sun, wearing sunscreen -- still important because of skin cancer risk -- cuts down vitamin D production.
A few foods are good sources of vitamin D -- fortified dairy products as well as salmon, tuna and mackerel. A cup of fortified milk offers about 100 IU of vitamin D. Salmon (3.5 ounces) offers about 650 IU of vitamin D. Most people won't eat enough of these foods every day to reach the recommended amount. That's where supplements come in.
For your age and situation, a supplement that includes both calcium and vitamin D may be a good idea. Many women enter menopause in their early 50s, which is a time of more rapid bone loss. This is why the recommended daily allowance for calcium and vitamin D increases at age 50. Once you've gotten the OK from your doctor, consider a supplement that includes 500 to 600 milligrams of calcium and 400 IU of vitamin D and take it twice a day. The supplement plus your normal dietary vitamin D should keep you in a range that is safe and will raise your levels back to normal.
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