Bone mineral density and risk of breast cancer in postmenopausal women.

High bone mineral density (BMD) has been associated with increased breast cancer in prospective studies of postmenopausal women, but the real relationship is still controversial. Therefore, we undertook a meta-analysis to evaluate the association between BMD and the risk of breast cancer in postmenopausal women. We performed systematic searches on MEDLINE, EMBASE, and OVID. Data extraction was performed independently by two reviewers. For each study, we extracted the relative risks (RRs) and 95 % confidence intervals (CIs) for categorical variables and per standard deviation (SD) increases in BMD. Heterogeneity, publication bias, and subgroup analysis were performed. The analysis included 70,878 postmenopausal women from 10 studies with 1,889 breast cancers during a mean follow-up of 6 years (range 3.2-8.4 years). The summary RRs for the highest versus lowest categorical variable showed that higher BMD in the hip (RR 1.62; 95 % CI: 1.17-2.06) and in the spine (RR 1.82; 95 % CI: 1.07-2.57) were associated with a 62 and 82 % increased risk of breast cancer. Per SD, increase in hip BMD and spine BMD were also associated with a higher risk of breast cancer (RR for hip BMD 1.20; 95 % CI: 1.09-1.31 and RR for spine BMD 1.26; 95 % CI: 1.10-1.41). In this meta-analysis, a higher BMD was found to be associated with a significantly higher risk of breast cancer in postmenopausal women.