In Your 20s

Be watchful of weight watching. If you’re dieting, be sure to exercise, too. Studies show that dieting without exercise can lead to bone loss.

Exercise smartly. Regular exercise that puts pressure on your bones (20 to 30 minutes a day is ideal), such as running and lifting weights, will help preserve bone density by encouraging the formation of osteoblasts. But don’t overdo it: If you exercise excessively, your period can become irregular or cease, which may increase your risk of premature bone loss.

Pay attention to your periods. Infrequent periods (fewer than six to eight a year) are associated with low estrogen levels and often with low body weight, “which can be a double whammy for bones,” says Felicia Cosman, M.D., the clinical director of the National Osteoporosis Foundation and a professor of medicine at Columbia University. Estrogen is your bones’ best ally because it tends to slow the rate of bone loss. So if you’re not having regular periods, speak with your gynecologist.

Think carefully about contraception. The estrogen in oral contraceptives may increase bone mass. But using Depo-Provera, the once-a-month injectable contraceptive, for more than two years has been shown to suppress estrogen production and lead to bone loss in young women, Cosman warns.