Low bone mineral density is associated with breast cancer in postmenopausal women: a case–control study

Objective: To evaluate risk factors for low bone mineral density (BMD) in postmenopausal breast cancer survivors compared with postmenopausal women without breast cancer (controls). Method: In this study, 112 breast cancer survivors were compared to 224 women (controls). Inclusion criteria were amenorrhea ≥12 months, age 45–75 years, treated for breast cancer, and metastasis-free for at least 5 years. The control group consisted of women without breast cancer, matched by age and menopause status (in a proportion of 1: 2 as sample calculation). The risk factors for low BMD (osteopenia/osteoporosis) were assessed by interview. BMD was measured by dual-energy X-ray absorptiometry in the lumbar spine (L1–L4) and femoral neck. Logistic regression models (odds ratio, OR) were used to identify factors associated with low BMD. Results: The mean (standard deviation) age of breast cancer survivors was 61.3 (9.7) years, with a mean follow-up of 10.2 (3.9) years. These women had a higher incidence of osteopenia (45.1%) and osteoporosis (22.3%) in the femoral neck than controls (39.3% and 9.0%, respectively) (p = 0.0005). Lumbar spine BMD did not differ between groups (p = 0.332). Univariate analysis adjusted for age and time since menopause revealed that chemotherapy (OR 6.90; 95% confidence interval (CI) 5.57–9.77) was associated with a higher risk of low BMD. Contrarily, regular physical exercise (OR 0.24; 95% CI 0.06–0.98) and a body mass index ≥30 kg/m2 (OR 0.09; 95% CI 0.02–0.37) reduced the risk among breast cancer survivors. Conclusion: Postmenopausal breast cancer survivors had a higher incidence of osteopenia and osteoporosis in the femoral neck than women without breast cancer. A history of chemotherapy was a risk factor for low BMD, whereas regular physical activity and high body mass index reduced the risk among breast cancer survivors.