Waist circumference, body mass index, and postmenopausal breast cancer incidence in the Cancer Prevention Study-II Nutrition Cohort

Abstract

Purpose: High body mass index (BMI) is an established risk factor for postmenopausal breast cancer. However, less is known about associations with waist circumference. In particular, it is unclear whether a larger waist circumference is associated with risk more than would be expected based solely on its contribution to BMI. Methods: We examined the associations of BMI and waist circumference with risk of postmenopausal breast cancer, with and without mutual adjustment, in the Cancer Prevention Study-II Nutrition Cohort. Analyses included 28,965 postmenopausal women who reported weight and waist circumference on a questionnaire in 1997 and were not taking menopausal hormones. Results: During a median follow-up of 11.58 years, 1,088 invasive breast cancer cases were identified. Hazard ratios (HR) and 95 % confidence intervals (CI) were estimated from multivariable-adjusted Cox proportional hazard regression models. Without adjustment for BMI, a larger waist circumference was associated with higher risk of breast cancer (per 10 cm increase in waist circumference, HR = 1.13, 95 % CI 1.08-1.19). However, adjustment for BMI eliminated the association with waist circumference (per 10 cm HR = 1.00, 95 % CI 0.92-1.08). BMI was associated with risk unadjusted for waist circumference (per 1 kg/m2 HR = 1.04, 95 % CI 1.03-1.05) and adjusted for waist circumference (per 1 kg/m2 HR = 1.04, 95 % CI 1.02-1.06). Conclusions: Our study of predominantly white women provides evidence that a larger waist circumference is associated with higher risk of postmenopausal breast cancer, but not beyond its contribution to BMI. © 2014 Springer International Publishing Switzerland.