Who is at risk?

Although most osteoporotic women are older than 50 and well into menopause, women in their 30s—or even younger—can develop the condition if they have a history of anorexia or bulimia (which may cause amenorrhea and low calcium levels as a result of vomiting, purging and poor nutrition); if they are athletes training hard enough to become amenorrheic; or if they have low estrogen levels. Because osteoporosis is usually asymptomatic, it can sneak up on women, many of whom aren't diagnosed until they actually break a bone. For this reason it's called a "silent disease."

7 major risk factors

1. Eating disorders Since their nutrition is so poor, anorexics and bulimics deprive their bodies of calcium, bone's major building block. Anorexics often don't have enough body fat to menstruate, so their estrogen levels drop, too, increasing bone breakdown. This double whammy occurs when bone density should be still rising, so these women may never attain a normal peak bone mass.

2. Body size It is believed that thin women with small frames have lower bone mineral density (BMD), a measure of bone health.

3. Family history Researchers aren't sure osteoporosis is genetic, but it does seem to run in families. Having a mother or sister with it puts you at increased risk. White and Asian women have a higher risk as well.

4. Erratic periods/early menopause (whether from natural causes or a hysterectomy) Irregular periods translates into a lack of progesterone, a hormone needed along with estrogen for bone health. Estrogen reduces the rate of bone loss, while progesterone, when in the presence of estrogen, stimulates new bone formation. Athletes beware: Rigorous training and low body fat can trigger irregular periods or amenorrhea.

5. Some diseases Conditions like hyperthyroidism, hyperparathyroidism and chronic kidney, lung and gastrointestinal disorders are risk factors.

6. Long-term use of certain medications The number one culprit: corticosteroids to suppress inflammation. Steroid drugs prescribed for diseases like epilepsy, severe asthma, severe allergies and autoimmune diseases like lupus can also have an effect (nonsteroidal drugs prescribed for these diseases do not pose problems in terms of bone loss).

7. Excessive doses of thyroid hormone Normal replacement dosages for hypothyroid patients are perfectly safe, although super high doses prescribed by a doctor in certain rare circumstances can have an effect if prolonged.