Dairy food and nutrient intake in different life periods in relation to risk of ovarian cancer

High lactose intake has been suggested to increase epithelial ovarian cancer (EOC) risk. We evaluated the association between lactose consumed during specific life periods (high school, premenopause, and postmenopause) and later risk of EOC. We assessed the association of dairy food and nutrient intake with risk of EOC during 28 years of follow-up including 764 cases in the Nurses' Health Study (NHS) and NHSII. Cox proportional hazards regression was used to model the hazard ratios (HRs) and 95 % confidence intervals (CIs) for EOC across categories of dairy food or nutrient intake. We examined dietary intake in adulthood overall, as well as during premenopausal/postmenopausal years and high school. In analyses of the highest versus lowest cumulative average intake in adulthood, we observed a non-significant inverse association with skim milk intake (HR 0.76, 95 % CI 0.54-1.06, p (trend) = 0.05), a non-significant inverse association with lactose intake (HR 0.87, 95 % CI 0.69-1.11, p (trend) = 0.22) and no association with consumption of whole milk, dairy calcium, or dairy fat. Similar risk estimates were observed for dairy food/nutrient intake during high school, premenopause or postmenopause. Lactose intake in adulthood was inversely associated with risk of endometrioid EOC (HR 0.32, 95 % CI 0.16-0.65, p (trend) < 0.001). These findings do not support the hypothesis that higher lactose intake increases EOC risk. The inverse association with endometrioid tumors deserves further study.