Second Thoughts

"The problem is that this category lumps together some people with very high risk and others at very low risk," McClung said. "We should not be treating them all the same."

To some extent, losing bone mass, or bone density, is a normal part of aging. For both men and women, density peaks during our 20s and 30s and then falls throughout our remaining lives. Bone tissue constantly renews itself, shedding old cells and forming new. But, at some point, bone formation begins to lag behind bone loss. For women, bone mass drops steeply after menopause; men lose mass more steadily. Because women begin with less bone mass and lose it at a faster rate, at any age women have lower bone densities than men.

Other Risks

So, what -- besides bone mineral density -- are the risk factors for fractures?

Age is one. The fracture rates for both men and women rise rapidly after age 75; the average age for hip fracture, for example, is 82. One 1998 study showed that women 85 or older have about 100 times the rate of hip fractures of women ages 45 to 54. Nonetheless, prevention efforts often miss the elderly because a marketing strategy for osteoporosis drugs is to target younger women like my friends and me, according to McClung. My mother is a case in point. She was not treated with Fosamax until age 88, after several falls and two broken bones.

A history of fracture also increases risk. Several studies have shown that a woman who has had a fracture is about twice as likely to experience another one as a woman of the same age and bone density without a previous fracture. "If you are a woman 50 or older and have had a spine or hip fracture, you . . . should be treated," Siris added.

But don't count on your doctor to recommend it: Three-quarters of people who fracture bones after age 45 are never evaluated for osteoporosis, Siris said. "The medical profession is still not caught up with the idea that we should be treating this population."

And then there's bone mineral density. A DXA scan shows how many grams of calcium and other bone minerals are packed into a segment of bone at the hip, spine or wrist -- common fracture sites. The higher the mineral content, the denser the bone and the lower the fracture risk. Your T-score compares your reading to that of a 30-year-old (when bone mass peaks) of your sex. A score between zero and minus-1 is considered normal. Between minus-1 and minus-2.5 is defined as osteopenia. Anything lower than minus-2.5 is defined as osteoporosis; most medical societies recommend treating people in that category.

Other lifestyle factors that affect fracture risk include smoking, drinking (more than two drinks per day) and being skinny (weighing under 127 pounds or having a body mass index of less than 20). You're also at higher risk if your parents had a fracture, you use corticosteroids (including prednisone or hydrocortisone) or have rheumatoid arthritis.

Exercise, vitamin D and calcium also seem to influence risk. "There is good evidence in older adults that the combination of calcium and vitamin D, and probably vitamin D alone, reduces fall risk, bone loss and fracture incidence," McClung said. "While there is little evidence that weight-bearing exercise will effectively raise bone density in healthy adults, it seems to slow bone loss in older adults," he concluded. Weight-bearing exercises include walking, jogging, hiking, dancing, lifting weights and using elastic bands.

Finally, factors related to falling -- such as poor vision, frailty, reduced strength and mobility, poor balance and use of sedatives -- are useful for predicting fracture risk in the elderly. Ninety percent of hip fractures are caused by a simple fall from standing height or lower.

One Step at a Time

Although my mother is clearly at high risk of fractures -- two previous fractures, advanced age, poor vision, frail, poor balance -- my research suggests that my osteopenic friends and I are on the low-risk end of the spectrum. Of all the risk factors, the only one that applies to me is parental history.

So I've struck a bargain with my gynecologist to stop taking low-dose hormones and try a regimen of vitamin D and weight-bearing exercises for a year to see if I can maintain my bone density.

I'll postpone riskier treatment options for when I reach a higher risk category. ·

Nancy J. Nelson is a Washington area freelance writer. Comments:health@washpost.com.