Alcohol, folate, methionine, and risk of incident breast cancer in the American Cancer Society Cancer Prevention Study II Nutrition Cohort.

Recent studies suggest that the increased risk of breast cancer associated with alcohol consumption may be reduced by adequate folate intake. We examined this question among 66,561 postmenopausal women in the American Cancer Society Cancer Prevention Study II Nutrition Cohort. A total of 1,303 incident cases had accrued during the first 5 years of follow-up. Cox proportional hazards models and stratified analysis were used to examine the relationship between alcohol, dietary and total folate intake, multivitamin use, dietary methionine, and breast cancer. We observed an increasing risk of breast cancer with increasing alcohol consumption (P for trend = 0.01). In the highest category of consumption (15 or more grams of ethanol/day), the risk of breast cancer was 1.26 (95% confidence interval, 1.04-1.53) compared with nonusers. We observed this association with higher alcohol consumption for in situ, localized, and regional disease. We found no association between risk of breast cancer and dietary folate, total folate, multivitamin use, or methionine intake. Furthermore, we found no evidence of an interaction between levels of dietary folate (P for interaction = 0.10) or total folate (P for interaction = 0.61) and alcohol. Nor did we find evidence of an interaction between alcohol consumption and recent or long-term multivitamin use (P for interaction = 0.27). Our results are consistent with a positive association with alcohol but do not support an association with folate or methionine intake or an interaction between folate and alcohol intake on risk of breast cancer.