CHICAGO — Almost 20 million American women, or nearly half of those beyond 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., maker of an osteoporosis drug.
Using a relatively inexpensive imaging technique on 200,160 healthy women 50 and older, researchers found full-fledged osteoporosis in 7% and low bone density in an additional 40%.
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 post-menopausal women but also 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.
"The message to doctors is, when you look around your waiting rooms and make assumptions of who is at risk for osteoporosis, you really have no clue," Siris said.
Dr. Felicia Cosman, clinical director of the National Osteoporosis Foundation, said the findings are not surprising to osteoporosis experts. Previous estimates suggested 8 million American women have osteoporosis and 14 million more have low bone mass.
But she said the study underscores the need for post-menopausal women to exercise, eat a healthy diet that includes calcium and vitamin D, and consider medication.
Doctors should measure bone mass in all post-menopausal women who have had fractures or a family history of osteoporosis, and in all women 65 and older, Siris said.
Low-dose X-rays of the hip and spine are considered the best measurement of bone density and strength, but the technique requires large machines that may cost $75,000 or more. This study used smaller devices that may cost as little as $10,000 to measure bone density at the heel, forearm or finger.
While none of the participants in the study had been diagnosed with osteoporosis or low bone density, 11%--22,096 women--reported having had fractures after age 45, before the study began. Those fractures should have been a tip-off to doctors, the researchers said.
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% and 4%, respectively.