What You Need to Know: Few foods inherently contain vitamin D, and some of us may not spend enough time in the sun for our bodies to produce sufficient amounts on their own. But unless your doctor recommends this supplement to treat a deficiency or to reduce your risk of osteoporosis, you should probably skip it, says Patsy Brannon, R.D., Ph.D., professor of nutritional science at Cornell University and a member of the panel of the Institute of Medicine (IOM). In fact, some studies suggest too much D may increase the risk of pancreatic cancer. If you do need it, check the label for D3, which may be more effective than D2, the other type used in supplements.
Who Should Take It: Postmenopausal women at risk for osteoporosis due to family history, small frame size, sedentary lifestyle or low calcium intake.
What to Watch Out For: Megadoses of vitamin D can cause high blood calcium (hypercalcemia) and excessive calcium in the urine (hypercalciuria), both of which put you at risk for damaging your kidneys and bones.
Get It Naturally: Fortified foods (including breads, cereals and orange juice) can have more vitamin D and calcium than milk. Fatty fish, like tuna and salmon, and canned light tuna are also good sources.