Chicago Almost 20 million American women, or nearly half of those past menopause, have thinning bones and don't know it, one of the largest osteoporosis studies to date suggests.
The study was funded by Merck & Co., which makes an osteoporosis drug.
Using a relatively inexpensive imaging technique on 200,160 healthy women 50 and older, researchers found full-fledged osteoporosis in 7 percent and low bone density in an additional 40 percent.
The women were then followed for a year to see how many broke bones.
The fracture rate in women with low bone density was nearly double that of women with normal bones and four times higher in women with osteoporosis.
The study shows not only that bone-thinning is "grossly underdiagnosed" in postmenopausal women but that bone density can be used to predict the risk of fractures in as little as a year, said Dr. Ethel Siris, a Columbia University professor of clinical medicine who led the study.
The study is published in today's Journal of the American Medical Assn.
Dr. Felicia Cosman, clinical director of the National Osteoporosis Foundation, said the findings are not surprising to osteoporosis experts. Previous estimates suggested that about 8 million American women have osteoporosis and 14 million more have low bone mass, she said. But she said the study underscores the need for postmenopausal women to take preventive measures such as exercise, good nutrition that includes calcium and vitamin D, and medication.
Fractures were found to be more common among women with risk factors such as smoking, older age and a family history of osteoporosis. But many other women thought to be at low risk also had broken bones.
The study included 18,000 black women, who previous studies have shown face a lower osteoporosis risk than whites. The prevalence of low bone mass and osteoporosis among them was still significant 32 percent and 4 percent respectively.