title: Plasma isoflavone level and subsequent risk of breast cancer among Japanese women: a nested case-control study from the Japan Public Health Center-based prospective study group.
abstract: OBJECTIVE
  Because they have large variations in consumption, Asian countries are suitable settings for studies of the effect of relatively high-dose isoflavone intake on breast cancer risk. Nevertheless, no prospective study from Asia has assessed blood or urine levels as biomarkers of isoflavone intake.
  
  
  METHODS
  A total of 24,226 women ages 40 to 69 years in the Japan Public Health Center-based prospective study who responded to the baseline questionnaire and provided blood in 1990 to 1995 were observed to December 2002. During a mean 10.6 years of follow-up, 144 patients newly diagnosed with breast cancer were identified. Two matched controls for each patient were selected from the cohort. Isoflavone levels were assessed by plasma level and food frequency questionnaire, and the odds ratio of breast cancer according to isoflavone level was estimated using a conditional logistic regression model.
  
  
  RESULTS
  We found a statistically significant inverse association between plasma genistein and risk of breast cancer, but no association for plasma daidzein. Adjusted odds ratios for the highest versus lowest quartile of plasma level were 0.34 for genistein (95% CI, 0.16 to 0.74; P for trend, .02) and 0.71 for daidzein (95% CI, 0.35 to 1.44; P for trend, .54). Median plasma genistein values in the control group were 31.9 ng/mL for the lowest and 353.9 ng/mL for the highest quartile groups. Regarding dietary intake of isoflavones, nonsignificant inverse associations were observed for both genistein and daidzein.
  
  
  CONCLUSIONS
  This nested case-control study found an inverse association between plasma genistein and the risk of breast cancer in Japan.
authors.affiliation: Epidemiology and Prevention Division, Research Center for Cancer Prevention and Screening, National Cancer Center, 5-1-1 Tsukiji, Chuo-ku, Tokyo, 104-0045, Japan. moiwasak@gan2.res.ncc.go.jp
authors.forename: Motoki
authors.initials: M
authors.lastname: Iwasaki
authors.forename: Manami
authors.initials: M
authors.lastname: Inoue
authors.forename: Tetsuya
authors.initials: T
authors.lastname: Otani
authors.forename: Shizuka
authors.initials: S
authors.lastname: Sasazuki
authors.forename: Norie
authors.initials: N
authors.lastname: Kurahashi
authors.forename: Tsutomu
authors.initials: T
authors.lastname: Miura
authors.forename: Seiichiro
authors.initials: S
authors.lastname: Yamamoto
authors.forename: Shoichiro
authors.initials: S
authors.lastname: Tsugane
mesh_terms: D000328:Adult; D000368:Aged; D001943:Breast Neoplasms / Q000097:blood* / Q000453:epidemiology*; D016022:Case-Control Studies; D002851:Chromatography, High Pressure Liquid; D004032:Diet; D005260:Female; D019833:Genistein / Q000097:blood*; D006801:Humans; D007529:Isoflavones / Q000097:blood*; D007564:Japan / Q000453:epidemiology; D008875:Middle Aged; D012307:Risk Factors; D045730:Soy Foods; D011795:Surveys and Questionnaires
chemical_list: D007529:Isoflavones; C004742:daidzein; D019833:Genistein