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.