In Your 30s

Protect your bones during pregnancy. If you skimp on calcium while pregnant, your growing baby will take the calcium it needs from your bones. But if you get the recommended 1,000 milligrams a day, your body will absorb even more of the bone-fortifying mineral than usual. Afterward, breast-feeding for more than a year can adversely affect your bones, Cosman says, “but bone mass, for the most part, can be regained later if you get the requisite amount of calcium and vitamin D.”

Identify risky medications. The use of corticosteroids (to treat asthma, inflammatory bowel disease, rheumatoid arthritis, or lupus), anticonvulsants (for seizure disorders), or GnRH agonists (for endometriosis) can lead to fairly rapid bone loss, says David Hamerman, M.D., the director of the Center for Bone Health at Montefiore Medical Center, in New York City. High doses of proton pump inhibitors, which are used to treat acid reflux, may harm bones by interfering with the absorption of calcium. If you are taking one of these medications, consult with your doctor. She might choose to put you on bisphosphonates, a type of drug that counteracts bone loss, says Hamerman.

Get a grip on stress. Stress hormones, like cortisol, can inhibit bone growth and accelerate bone breakdown. Depression can have similarly harmful effects on bones.