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

Objective: 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.
Methods: 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.
Results: 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.
Conclusions: 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.