Does dietary folate intake modify effect of alcohol consumption on breast cancer risk? Prospective cohort study.

OBJECTIVE To evaluate the effect of dietary folate intake on the relation between alcohol consumption and breast cancer risk. DESIGN Prospective cohort study. SETTING Melbourne, Australia. PARTICIPANTS 17,447 Anglo-Australian women resident in Melbourne, aged 40-69 years at recruitment in 1990-4, and followed up until 31 December 2003. MAIN OUTCOME MEASURE Invasive breast cancers diagnosed during follow-up and ascertained through the Victorian cancer registry. RESULTS 537 invasive breast cancers were diagnosed. Compared with lifetime abstainers, the hazard ratio for breast cancer in women who consumed an average of 40 g or more of alcohol daily at baseline was 1.41 (95% confidence interval 0.90 to 2.23). No direct association was found between dietary folate intake and risk of breast cancer, but a high folate intake mitigated the excess risk associated with alcohol. The estimated hazard ratio of an alcohol consumption of 40 g/day or more was 2.00 (1.14 to 3.49) for women with intakes of 200 mug/day of folate and 0.77 (0.33 to 1.80) for 400 mug/day of folate (P = 0.04 for interaction between alcohol and folate). CONCLUSIONS An adequate dietary intake of folate might protect against the increased risk of breast cancer associated with alcohol consumption.