Dietary intake of B vitamins and methionine and breast cancer risk

Purpose: We investigated prospectively the relationship between dietary intakes of methionine and B vitamins associated with one-carbon metabolism and breast cancer risk, including modification by age, hormone receptor status and alcohol consumption. Interactions between different B vitamins and methionine were also examined. Methods: During follow-up of 20,756 women from the Melbourne Collaborative Cohort Study for an average of 16 years, we ascertained 936 incident breast cancers. Dietary intakes were estimated using a 121-item food frequency questionnaire. Hazard ratios (HR) and 95 % confidence intervals were estimated using Cox regression. Results: We found weak evidence for an inverse association between breast cancer risk and riboflavin intake (fourth versus first quartile, HR _{Q4 vs. Q1} = 0.84 (0.69, 1.01); p _{linear trend} = 0.05) and a positive association for vitamin B12 (HR _{Q4 vs. Q1} = 1.21 (1.00, 1.46); p _{linear trend} = 0.06). We did not find any significant interactions between alcohol consumption and any of the B vitamins or methionine intake (all p _interaction > 0.17) or between methionine or folate intake and any other B vitamins (all p _interaction > 0.07). No association varied by tumor hormone receptor status (all p _homogeneity > 0.14). Conclusions: We found weak evidence of an inverse association between breast cancer risk and riboflavin intake and a positive association with vitamin B12.