Long-term and baseline recreational physical activity and risk of endometrial cancer: the California Teachers Study

Background: Physical activity may be associated with decreasing endometrial cancer risk; it remains unclear whether the association is modified by body size. Methods: Among 93 888 eligible California Teachers Study participants, 976 were diagnosed with incident endometrial cancer between 1995-1996 and 2007. Cox proportional hazards regression methods were used to estimate relative risks (RRs) and 95% confidence intervals (CIs) for endometrial cancer associated with long-term (high school through age 54 years) and baseline (3 years prior to joining the cohort) strenuous and moderate recreational physical activity, overall and by body size. Results: Increased baseline strenuous recreational physical activity was associated with decreased endometrial cancer risk (P-trend-0.006) with approximately 25% lower risk among women exercising >3 h per week per year than among those exercising <1/2 h per week per year (RR, 0.76; 95% CI, 0.63-0.92). This inverse association was observed among overweight/obese women (body mass index >= 25 kg m(-2); P-trend=0.006), but not among thinner women (P-trend=0.12). Baseline moderate activity was associated with lower risk among overweight/obese women. Conclusion: Increasing physical activity, particularly strenuous activity, may be a lifestyle change that overweight and obese women can implement to reduce their endometrial cancer risk.