Objectives: To determine whether higher adiposity is associated with greater breast cancer risk in older postmenopausal women.
Design: Prospective cohort study with mean follow-up of 11.3 years.
Setting: Four U.S. clinical centers.
Participants: Seven thousand five hundred twenty-three women (mean age 73.5) enrolled in the Study of Osteoporotic Fractures.
Measurements: Weight, height, and waist and hip circumference were measured at baseline. Body composition was determined using bioelectrical impedance. Risk factor information was obtained by interview and questionnaire. Bone mineral density was measured using dual energy x-ray absorptiometry. The outcome was incident invasive breast cancer, confirmed using medical records.
Results: After adjustment for multiple risk factors, including bone density, women in the uppermost quartiles of weight, weight gain since age 25, body mass index, waist circumference, and percentage of body fat had higher breast cancer rates than women in the first quartiles of each measure. For example, breast cancer rates were 49% higher for women in the uppermost quartile of weight (hazard ratio (HR)=1.49, 95% confidence interval (CI)=1.05-2.10), 64% higher for women in the top quartile of weight gain since age 25 (HR=1.64, 95% CI=1.15-2.34), and 58% higher for women in the top quartile of percentage of body fat (HR=1.58, 95% CI=1.11-2.23) than for women in the lowest quartile of each measure. The associations between adiposity measures and breast cancer rates were not altered when the analyses were limited to very elderly women (> or = 70).
Conclusion: Higher adiposity is an independent risk factor for breast cancer in elderly women.