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By Steven Reinberg

NEW YORK (Reuters Health) – The results of a large US population-based study show that almost half of postmenopausal women have undiagnosed low bone mineral density (BMD), putting them at high risk of osteoporosis, osteopenia, and fractures.

"In the primary care setting women are not routinely being evaluated for the risk of osteoporosis," Dr. Ethel S. Siris from Columbia Presbyterian Medical Center, New York, told Reuters Health. "We found that 46% of real world women had low BMD or osteoporosis," she added.

Dr. Siris and colleagues collected data for 200,160 postmenopausal women 50 years of age or older, with no history of osteoporosis, who were seen in 4236 primary care practices in the US. The participants were enrolled in the National Osteoporosis Risk Assessment (NORA) study.

The study was started in 1997 and continued into 1999, with approximately 12 months of additional follow-up, according to the report in The Journal of the American Medical Association for December 12.

The researchers obtained BMD T scores and at the heel, finger or forearm. A BMD T score of 0 equals the mean peak BMD of a healthy population of premenopausal white women between the ages of 20 and 29 years, the researchers explain. Using a questionnaire, at baseline and after 12 months, they determined risk factors for low BMD and fracture rates.

Among the 163,979 women who provided follow-up data, 39.6% were diagnosed with osteopenia and 7.2% with osteoporosis. "I didn't think we were going to find that nearly half the women had low bone density," Dr. Siris said. This is probably an underestimate, she noted, because women already diagnosed with osteoporosis were excluded from the study.

Factors that made developing osteoporosis significantly more likely included age, personal or family history of fracture, being Asian or Hispanic, smoking, and using cortisone, the researchers found.

Having a high body mass index, being African-American, using estrogen or diuretics, regular exercise, and consuming alcohol were all associated with a significantly lower osteoporosis risk, Dr. Siris' team reports.

Women with osteoporosis had a fracture rate almost 4-fold greater than women with normal BMD (rate ratio 4.03) and women with osteopenia had a fracture rate 1.8-fold higher than women with normal BMD, the investigators add.

"There is a lot of low bone density out there in this population at risk," Dr. Siris said. "We need to get into a preventive mode to minimize the number of fractures we currently see," Dr. Siris said.

The NORA findings confirm "what many clinicians and osteoporosis researchers have long suspected, ie, that a significant number of postmenopausal women in primary care practices have clinically significant low BMD and that such women have increased risk of incident fracture within 1 year," Dr. Charles H. Chesnut III from the University of Washington Medical Center, Seattle, comments in a journal editorial.

"Based on the current study, strategies to identify, manage, and treat osteoporosis in primary care need to be established and implemented–hopefully, sooner rather than later."