title: Association of vitamin B6, vitamin B12 and methionine with risk of breast cancer: a dose-response meta-analysis.
abstract: BACKGROUND
  Epidemiological studies evaluating the association of vitamin B6, vitamin B12 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 B6) 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 B6 intake, serum vitamin B12 levels and dietary vitamin B12 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.
  
  
  CONCLUSIONS
  Serum PLP levels and methionine intake might be inversely associated with breast cancer risk, especially among postmenopausal women, which need to be confirmed.
authors.affiliation: Department of Epidemiology and Health Statistics, Medical College of Qingdao University, Dongzhou Road, No. 38, Qingdao, Shandong 266021, China.
authors.forename: W
authors.initials: W
authors.lastname: Wu
authors.forename: S
authors.initials: S
authors.lastname: Kang
authors.forename: D
authors.initials: D
authors.lastname: Zhang
mesh_terms: D001943:Breast Neoplasms / Q000453:epidemiology*; D004032:Diet; D004305:Dose-Response Relationship, Drug; D005260:Female; D006801:Humans; D008715:Methionine / Q000008:administration & dosage*; D011732:Pyridoxal Phosphate / Q000097:blood*; D012306:Risk; D014805:Vitamin B 12 / Q000008:administration & dosage*; D025101:Vitamin B 6 / Q000008:administration & dosage*
chemical_list: D011732:Pyridoxal Phosphate; D025101:Vitamin B 6; D008715:Methionine; D014805:Vitamin B 12
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