Association of vitamin B(6), vitamin B(12) and methionine with risk of breast cancer: a dose–response meta-analysis

BACKGROUND: Epidemiological studies evaluating the association of vitamin B(6), vitamin B(12) and methionine with breast cancer risk have produced inconsistent results. METHODS: Pertinent studies were identified by a search in PubMed and Web of Knowledge. Random-effect model was used. Dose–response relationship was assessed by restricted cubic spline. RESULTS: The combined relative risk (95% confidence interval) of breast cancer for the highest vs lowest category of serum pyridoxal 5′-phosphate (PLP, active form of vitamin B(6)) levels and dietary methionine intake was 0.80 (0.66–0.98, P=0.03) and 0.94 (0.89–0.99, P=0.03), respectively, and the associations of breast cancer with higher serum PLP levels and dietary methionine intake were significant among post-menopausal women, but not among pre-menopausal women. The inverse association between breast cancer risk and dietary vitamin B(6) intake, serum vitamin B(12) levels and dietary vitamin B(12) intake was not significant overall. Linear dose–response relationship was found, and the risk of breast cancer decreased by 23% (P<0.00) for every 100 pmol ml(−1) increment in PLP levels and 4% (P=0.05) for every 1 g per day increment in dietary methionine intake, respectively. CONCLUSION: Serum PLP levels and methionine intake might be inversely associated with breast cancer risk, especially among postmenopausal women, which need to be confirmed.