Alcohol and folate intake and breast cancer risk in the WHI Observational Study

Background Alcohol increases breast cancer risk. Epidemiological studies suggest folate may modify this relationship. Objective To examine the relationship among breast cancer, alcohol and folate in the Women’s Health Initiative-Observational Study (WHI-OS). Methods 88,530 postmenopausal women 50–79 years completed baseline questionnaires between October 1993 and December 1998, which addressed alcohol and folate intake and breast cancer risk factors. Cox proportional hazards analysis examined the relationship between self-reported baseline alcohol and folate intake and incident breast cancer. Results 1,783 breast cancer cases occurred over 5 years. Alcohol was associated with increased risk of breast cancer (RR = 1.005, 95%CI 1.001–1.009). Risk increased with consumption of alcohol (up to 5 g/d, adjusted HR = 1.10, 95%CI 0.96–1.32; >5–15 g/d HR = 1.14, 95%CI 0.99–1.31; and >15 g/d HR = 1.13 95%CI 0.96–1.32). We found no significant interaction between alcohol and folate in our adjusted model. Conclusions We found no evidence for folate attenuating alcohol’s effect on breast cancer risk in postmenopausal women. Our results may be due to misclassification of folate intake or the relatively short follow-up period.