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.