BONE-MINERAL DENSITY AND RISK OF BREAST-CANCER IN OLDER WOMEN - THE STUDY OF OSTEOPOROTIC FRACTURES

Objective.-To test the hypothesis that bone mineral density (BMD) is a ssociated with the risk of developing breast cancer in older women. De sign.-Prospective cohort study with mean (SD) follow-up of 3.2 (1.6) y ears. Setting.-Four clinical centers, one each located in the followin g areas: Baltimore, Md; Minneapolis, Minn; Portland, Ore; and the Mono ngahela Valley in Pennsylvania. Participants.-A total of 6854 nonblack women who were 65 years of age or older and enrolled in the Study of Osteoporotic Fractures. Measurements.-Radius and calcaneus BMD by sing le photon absorptiometry at baseline; hip and spine BMD by dual-energy x-ray absorptiometry 2 years later. Main Outcome Measure.-Breast canc er confirmed by medical record review. Results.-A total of 97 women de veloped breast cancer. In the multivariate model, adjusting for age, t he degree of obesity, and other important covariates, the risk of brea st cancer was about 30% to 50% higher per 1 SD increase in BMD (relati ve risk, distal radius BMD=1.50; 95% confidence interval, 1.16-1.95), The age-adjusted incidence rate of breast cancer per 1000 person-years among women in the lowest quartile of distal radius BMD was 2.46, com pared with 5.99 among women with the highest BMD. Women with BMD above the 25th percentile were at 2.0 to 2.5 times increased risk of breast cancer compared with women below the 25th percentile. Results were co nsistent across all BMD sites. Conclusions.-Bone mineral density predi cts the risk of breast cancer in older women. The magnitude of the ass ociation is similar to that observed between BMD and all fractures. Ou r findings suggest a link between 2 of the most common conditions affe cting a woman's health, Identifying a common denominator for these con ditions should substantially improve our understanding of their etiolo gy and prevention.