The disease, if it is a disease, afflicts most middle-aged and elderly women, and a large segment of men. But it has no symptoms, it is not clear what patients should do about it and it is being diagnosed more and more often.
The condition is osteopenia, or low bone density. Many doctors consider it to be a first step toward osteoporosis, a serious disorder that leaves bone density extremely low and makes bones porous and prone to shatter.
But researchers say that while bone density predicts fracture risk, more is involved, including age, family history and a poorly understood factor known as bone quality.
Those nuances may be lost, researchers say, as patients fixate on a number (bone density) and a diagnosis (osteopenia) and fear that unless they act their fates are sealed.
Doctors tell women to find out their bone density as soon as they go through menopause. Younger women and middle-aged men are also being tested.
The tests are easy to come by. Special X-ray machines can be found in hospitals, medical centers and screening centers, offering scans for about $125. Portable bone density testing machines are turning up in doctors' offices and in shopping centers.
But the painless screening test and quick diagnosis by no means offer patients and doctors a simple answer. Osteopenia, it turns out, is yet another diagnosis that strikes at the core of debates emblematic of modern medicine, when screening can get ahead of treatment, or even the understanding of a condition, medical experts say.
One estimated conservatively that osteopenia afflicted 13 million to 17 million women and 1 million to 2 million men in the United States.
Opinions range from dismissing the condition as largely an invented problem to urging that nearly everyone who has it to start treatment.
"We have medicalized a nonproblem," said Dr. Michael McClung, director of the Oregon Osteoporosis Center. Most people with the condition, he said, have bone densities that are below average but not below normal. "Only in Lake Wobegon is everyone above average," he said. While some women may need treatment, many more do not, he added.
Dr. James Simon, president of the North American Menopause Society, begs to differ. Once bone starts being lost, it is time to think about taking action, he said, with the only question being how low should bone density go before consideration of treatment begins. He added that, in his opinion, if the drugs were free, "the argument would largely go away."