Weight cycling and risk of endometrial cancer.

BACKGROUND Obesity, as measured by body mass index (BMI), is an established risk factor for endometrial cancer in postmenopausal women. Weight cycling, which consists of repeated cycles of weight loss followed by regain, occurs frequently in overweight and obese women. It is unclear whether weight cycling is associated with risk of endometrial cancer independent of BMI. METHODS This analysis included 38,148 postmenopausal women enrolled in the Cancer Prevention Study II Nutrition Cohort, of whom 559 were diagnosed with endometrial cancer between enrollment in 1992 and June 30, 2007. Number of lifetime weight cycles was determined from questions on the baseline questionnaire asking how many times 10 or more pounds were intentionally lost and later regained. Multivariable-adjusted hazard rate ratios (RR) and 95% confidence intervals (CI) were estimated using Cox proportional hazards regression. RESULTS Weight cycling was positively associated with endometrial cancer incidence (RR, 2.13; 95% CI, 1.63-2.78 for 10+ weight cycles vs. no weight cycles; P(trend) < 0.0001). However, after adjustment for BMI in 1992, this association was null (RR, 1.05; 95% CI, 0.77-1.42; P(trend) = 0.82). Weight cycling was not associated with endometrial cancer in analyses stratified by BMI or by weight change after adjustment for BMI. CONCLUSIONS After adjustment for BMI, weight cycling was not associated with the risk of endometrial cancer. IMPACT These findings suggest that weight loss with subsequent regain is unlikely to increase risk of endometrial cancer. Therefore, weight loss for better health should be encouraged.