Alcohol Consumption and Breast Cancer Risk in Younger Women According to Family History of Breast Cancer and Folate Intake.

To evaluate the association between alcohol consumption and breast cancer risk in younger women, overall and by family history of breast cancer and folate intake, we prospectively followed 93,835 US women aged 27-44 years in Nurses' Health Study II who had alcohol consumption data in 1991. Alcohol consumption and folate intake were measured by food frequency questionnaire every 4 years. We documented 2,866 incident cases of invasive breast cancer between 1991 and 2011. Alcohol consumption was not associated with breast cancer risk overall (for intake of ≥10 g/day vs. nondrinking, multivariate hazard ratio = 1.07, 95% confidence interval: 0.94, 1.22). When the association was stratified by family history and folate intake, a positive association between alcohol consumption and breast cancer was found among women with a family history and folate intake less than 400 μg/day (multivariate hazard ratio = 1.82, 95% confidence interval: 1.06, 3.12; P-trend = 0.08). Alcohol consumption was not associated with breast cancer in other categories of family history and folate intake (P-interaction = 0.55). In conclusion, in this population of younger women, higher alcohol consumption was associated with increased risk of breast cancer among those with both a family history of breast cancer and lower folate intake.