Get enough calcium.
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You've been hearing that calcium builds strong bones since those Got Milk? mustache ads started popping up some 20 years ago – and for good reason. "Calcium is the major element of bone," says Dr. Robert Recker, president of the National Osteoporosis Foundation. "Bone contains 100 times, maybe even 1,000 times more calcium than the rest of the body. But when you don't get the recommended 1 to 1.5 grams per day, calcium gets pulled from the bones to support rest of the body." The result: brittle bones.

Since you're always losing calcium through sweat and urine, you really need to keep refilling the tank. Recker says dairy is far and away the best calcium source. "Drink skim milk – an 8-ounce glass has 300 mg of calcium," he suggests. "Yogurt is great. too, but not cottage cheese, because the calcium has been taken out." If you don't do dairy, Recker recommends supplementing up to 1.5 grams of calcium per day. "Take supplements with meals, and don't do more than 500 to 600 mg at one time, because after that, absorption tapers off."