Abstract
BACKGROUND: The impact of weight change, physical activity, and sedentary behavior on endometrial cancer risk among the Asian population is uncertain. We investigated the association of those factors with endometrial cancer risk among Japanese women with a low body mass index level. METHODS: We performed a large-scale nationwide cohort study consisting of 33,801 female participants aged 40-79 years. The Cox proportional hazards model was used to calculate the hazard ratios (HRs) and 95% confidence intervals (CIs) of incident endometrial cancer. RESULTS: The mean body mass index of participants was 22.8 kg/m(2). During a median follow-up of 14.8 years, 79 participants developed endometrial cancer. After adjustment for potential confounding factors, body mass index over 23.0 kg/m(2) was linearly associated with the risk of endometrial cancer. The HR per 5 kg/m(2) increase was 1.80 (95% CI, 1.28-2.54). Weight increment ≥+5 kg since age 20 was associated with an increased risk of endometrial cancer compared to a weight change of -5 to <+5 kg (multivariable HR 1.96; 95% CI, 1.12-3.40). Compared with females who were mainly sitting at the worksite, those who were mainly standing and moving were at lower risk; the multivariable HRs were 0.79 (95% CI, 0.39-1.59) and 0.46 (95% CI, 0.22-0.97), respectively (P for trend = 0.042). Hours of physical exercise, daily walking, and TV viewing were not associated with endometrial cancer risk. CONCLUSIONS: Overweight and weight gain were positively associated with the risk of endometrial cancer, while worksite physical activity was inversely associated with the risk.