Treatment for low bone density depends on how strong your bones are - not the name of the disease.

Like their names suggest, osteopenia and osteoporosis are related diseases. Both are varying degrees of bone loss, as measured by bone mineral density, a marker for how strong a bone is and the risk that it might break. If you think of bone mineral density as a slope, normal would be at the top and osteoporosis at the bottom. Osteopenia, which affects about half of Americans over age 50, would fall somewhere in between.

Measuring bone mineral density

The main way to determine your bone density is to have a painless, noninvasive test called dual-energy x-ray absorptiometry (DXA) that measures the mineral content of bone. The measurements, known as T-scores, determine which category - osteopenia, osteoporosis, or normal - a person falls into (see graphic).

Fracture risk increases as bone mineral density declines. A study published in the Journal of the American Medical Association in 2001 reported that a 50-year-old white woman with a T-score of -1 has a 16% chance of fracturing a hip, a 27% chance with a -2 score, and a 33% chance with a -2.5 score.

But there isn't a huge difference between, say, a -2.3 T-score and -2.5, although the former would be labeled osteopenia and the latter, osteoporosis. "The label matters less than the number. These distinctions are to some extent arbitrary lines in the sand," says Dr. Maureen Connelly, a preventive medicine expert at Harvard Medical School. Regardless of your exact score, if you fall into the osteopenia category, your doctors will probably schedule you for a bone mineral density test every two to five years.

Osteopenia Prevention

Everybody's bones get weaker as they get older. But certain choices and habits accelerate the process. They include:

• not getting enough calcium and vitamin D
• smoking
• drinking too much alcohol
• using certain medications, such as corticosteroids and anticonvulsants
• not getting enough weight-bearing exercise (at least 30 minutes on most days). If your feet touch the ground during an exercise, it's probably weight bearing. Running and walking are weight bearing. Swimming and biking are not.

Women are far more likely to have low bone density than men, but it's no longer viewed as solely a women's condition. About a third of white and Asian men over age 50 are affected. The percentages for Hispanics (23%) and blacks (19%) are lower, but still sizable.

Osteopenia treatments

Osteopenia can be treated either with exercise and nutrition or with medications. But some doctors are increasingly wary about overmedicating people with osteopenia. The fracture risk is low to begin with, and research has shown that medication may not reduce it that much. We also don't know if the medications might have some long-term effects. So if your T-score is closer to -1, you're better off getting more weight-bearing exercise, calcium, and vitamin D. If you're closer to -2.5, you're more likely to be prescribed alendronate (Fosamax), risedronate (Actonel), or raloxifene (Evista). Estrogen (Premarin, Estrace, other brands) is still FDA-approved for prevention of osteoporosis, but only women who've had a hysterectomy would take estrogen by itself, because it increases the risk of uterine cancer. And the combination of estrogen with progestin (Prempro) is now primarily used for relief of short-term menopausal symptoms like hot flashes because it has been found to increase the risk of breast cancer, heart attacks, strokes, and blood clots in the legs and lungs.

Further reading: Osteoporosis drugs: Which one is right for you?

(This article was first printed in the October, 2003 issue of the Harvard Health Letter. For more information or to order, please go to http://health.harvard.edu/health.)