BackgroundSeveral studies have determined that dietary intake of B vitamins may be associated with breast cancer risk as a result of interactions between 5,10-methylenetetrahydrofolate reductase (MTHFR) and methionine synthase (MTR) in the one-carbon metabolism pathway. However, the association between B vitamin intake and breast cancer risk in Brazilian women in particular has not yet been investigated.MethodsA case-control study was conducted in São Paulo, Brazil, with 458 age-matched pairs of Brazilian women. Energy-adjusted intakes of folate, vitamin B6, and vitamin B12 were derived from a validated Food Frequency Questionnaire (FFQ). Genotyping was completed for MTHFR A1298C and C677T, and MTR A2756G polymorphisms. A logistical regression model was used to calculate odds ratios (ORs) and 95% confidence intervals (95% CIs).ResultsNeither dietary intake of folate, vitamin B6, or vitamin B12 nor MTHFR polymorphisms were independently associated with breast cancer risk. Analysis stratified by menopausal status showed a significant association between placement in the highest tertile of folate intake and risk of breast cancer in premenopausal women (OR = 2.17, 95% CI: 1.23–3.83; Ptrend = 0.010). The MTR 2756GG genotype was associated with a higher risk of breast cancer than the 2756AA genotype (OR = 1.99, 95% CI = 1.01–3.92; Ptrend = 0.801), and statistically significant interactions with regard to risk were observed between the MTHFR A1298C polymorphism and folate (P = 0.024) or vitamin B6 (P = 0.043), and between the MTHFR C677T polymorphism and folate (P = 0.043) or vitamin B12 (P = 0.022).ConclusionMTHFR polymorphisms and dietary intake of folate, vitamin B6, and vitamin B12 had no overall association with breast cancer risk. However, increased risk was observed in total women with the MTR 2756GG genotype and in premenopausal women with high folate intake. These findings, as well as significant interactions between MTHFR polymorphisms and B vitamins, warrant further investigation.

We investigated the association of dietary intakes of folate, vitamin B-6, vitamin B-12, and methionine with the risk of colorectal cancer in a large prospective cohort study of middle-aged Japanese men and women. A total of 81,184 subjects (38,107 men and 43,077 women) who participated in the Japan Public Health Center-based Prospective Study were followed from 1995-1998 to the end of 2002, during which 526 cases of colorectal cancer (335 men, 191 women) were newly identified. Dietary intake of nutrients was calculated using a 138-item self-administered FFQ. We observed a significant inverse association between vitamin B-6 intake and colorectal cancer in men. Compared with the lowest quartile, the multivariate hazard ratio (95% [CI]) in the highest quartile of intake was 0.69 (0.48-0.98) (P(trend) = 0.03). Men who consumed 150 g/wk alcohol or more had twice the risk of colorectal cancer of those who drank less in the lowest quartile of vitamin B-6 intake, but risk due to alcohol intake was not higher in the highest quartile of vitamin B-6 intake. Vitamin B-6 intake and colorectal cancer were not associated in women. Folate and methionine intakes were not associated with colorectal cancer risk in men or women, but colorectal cancer risk tended to increase (P(trend) = 0.05) with increasing intake of vitamin B-12 in men. Our results support previous evidence that low vitamin B-6 intake is associated with an increased risk of colorectal cancer. In particular, a higher intake of vitamin B-6 appears beneficial in men with higher alcohol intake.