According to the U.S. Institute of Medicine, people should get between 200 and 400 international units of vitamin D a day. The best way to get vitamin D, naturally, is by being out in the sun.
As little as 10 to 15 minutes of sun a day can give you all a vitamin D you need. Vitamin D is also available in small quantities in foods such as fish and milk.
Preventing hip fracture is another good reason to keep your vitamin D levels up, Holick said. "To get vitamin D levels to where they need to be to reduce the risk of hip fracture, you need to be taking at least 1,000 international units of vitamin D a day from a supplement," he advised.
Dr. John Jacob Cannell, executive director of the nonprofit Vitamin D Council, agreed that most people are not getting enough of the nutrient.
"Women need to know their vitamin D status," Cannell said. "They need to ask their doctor for the right test," known as the 25 hydroxy D test. "Women should strive to keep your vitamin D levels above 125 nanomoles per liter, year round. To do that, they are going to require supplements."
Cannell recommends that before they get a blood test for vitamin D, women take 2,000 international units of vitamin D a day for three months.
For more about vitamin D, visit the U.S. National Institutes of Health.
SOURCES: John Jacob Cannell, M.D., executive director, Vitamin D Council, Atascadero, Calif.; Michael F. Holick, M.D., Ph.D., director, Vitamin D Skin and Bone Research Laboratory, Boston University; Aug. 19, 2008, Annals of Internal Medicine
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