Body mass index, height, and postmenopausal breast cancer mortality in a prospective cohort of US women.

Epidemiologic evidence suggests a positive association between body mass, adult height, and postmenopausal breast cancer. However, most studies have not been large enough to examine the association across a very wide range of body mass or height, and few studies have assessed the relationship between body mass or height and postmenopausal breast cancer mortality. The relation between body mass index (BMI) and height and postmenopausal breast cancer mortality was examined in the American Cancer Society's Cancer Prevention Study II (CPS-II), a large prospective mortality study of US adults enrolled in 1982. After 14 years of follow-up, 2852 breast cancer deaths were observed among 424,168 postmenopausal women who were cancer-free at interview. Cox proportional hazards modeling was used to estimate relative risks and to control for potential confounding. Breast cancer mortality rates increased continually and substantially with increasing BMI (rate ratio (RR) = 3.08, 95% confidence interval (CI) = 2.09-4.51 for BMI > 40.0 compared to BMI 18.5-20.49). If causal, the multivariate-adjusted RR estimates in this study correspond to approximately 30-50% of breast cancer deaths among postmenopausal women in the US population being attributable to overweight. Breast cancer mortality also increased with increasing height up to 66 inches with RR= 1.64, (95% CI = 1.23-2.18) in women 66 inches tall compared to those <60 inches. Postmenopausal obesity is an important and potentially avoidable predictor of fatal breast cancer in this study. These results underscore the importance of maintaining moderate weight throughout adult life.