Dairy Consumption in Adolescence and Early Adulthood and Risk of Breast Cancer.

Background: Carcinogenic exposure in early life may be critical for subsequent breast cancer risk. Dairy consumption was examined during adolescence and early adulthood in relation to incident breast cancer in the Nurses' Health Study II cohort.
Methods: For the analyses of early adulthood dairy consumption, we included 90,503 premenopausal women ages 27 to 44 years in 1991 who reported dairy consumption using a validated food-frequency questionnaire. From 1991 to 2013, 3,191 invasive breast cancer cases were identified. In 1998, 44,264 women recalled adolescent dairy consumption. This subgroup of women was followed up from 1998 to 2013; 1,318 invasive breast cancer cases were identified. Multivariate hazard ratios (HRs) and 95% confidence intervals (CIs) were estimated using the Cox proportional hazard regression.
Results: Adolescent and early adulthood total dairy consumption was not associated with overall breast cancer risk (each serving/day during adolescence, total dairy HR = 1.02, 95% CI, 0.97-1.07; for early adulthood total dairy HR = 1.01, 95% CI, 0.97-1.04), as were intakes of calcium, vitamin D, and lactose. Adolescent consumption of total and high-fat dairy was associated with higher risk of estrogen and progesterone receptor negative (each serving/day: total dairy HR = 1.11, 95% CI, 1.00-1.24; high-fat dairy HR = 1.17, 95% CI, 1.04-1.31). However, higher adolescent high-fat dairy consumption was associated with lower risk of estrogen and progesterone receptor positive tumors (each serving/day HR = 0.91, 95% CI, 0.86-0.97).Conclusions: Our results suggest no overall association between dairy consumption during adolescence or early adulthood and breast cancer risk, but the findings may differ by hormone receptor status of tumors.Impact: Dairy consumption in adolescence or early adulthood may not be a significant predictor of breast cancer incidence. Cancer Epidemiol Biomarkers Prev; 27(5); 575-84. ©2018 AACR. ©2018 American Association for Cancer Research.