title: Investigation of the reliability of 24 h urine excretion as a biomarker of isoflavone exposure over time and over a wide range of isoflavone intakes.
abstract: OBJECTIVE
  To study the variation in genistein + daidzein intake over a 6-month period and test the reliability of 24 h urinary isoflavones as a biomarker of exposure over time.
  
  
  METHODS
  Dietary genistein + daidzein intake was assessed at various time points throughout six months in 15 healthy subjects. Group 1 (n=8) followed nonsupplemented diets and Group 2 (n=7) took a 35 mg/d isoflavone supplement for 3 months and each subject provided a 24 h urine collection, validated with para-aminobenzoic acid, during weeks 7, 15 and 19. Urine was analysed for genistein and daidzein using LC-MS.
  
  
  RESULTS
  Isoflavone intake in Groups 1 and 2 ranged from 0.00 to 1.1 mg/d and 0.1 to 53.1 mg/d, respectively. Urine excretion for both groups ranged from 0.20 to 9.56 mg/d. The relationship between 24 h excretion and isoflavone intake is y=0.44 x +/- 0.03(standard deviation) + 1.57; r=0.89, P<0.001.
  
  
  CONCLUSIONS
  The 24 h urinary isoflavones can be used as biomarkers of isoflavone exposure over time.
authors.affiliation: Bute Medical School, University of St. Andrews, Fife, Scotland. mrr3@st-andrews.ac.uk
authors.forename: M R
authors.initials: MR
authors.lastname: Ritchie
authors.forename: M S
authors.initials: MS
authors.lastname: Morton
authors.forename: A M
authors.initials: AM
authors.lastname: Thompson
authors.forename: N
authors.initials: N
authors.lastname: Deighton
authors.forename: A
authors.initials: A
authors.lastname: Blake
authors.forename: J H
authors.initials: JH
authors.lastname: Cummings
authors.forename: C M
authors.initials: CM
authors.lastname: Steel
mesh_terms: D000328:Adult; D015415:Biomarkers / Q000652:urine; D018592:Cross-Over Studies; D019587:Dietary Supplements; D005260:Female; D019833:Genistein / Q000008:administration & dosage* / Q000652:urine*; D006801:Humans; D007529:Isoflavones / Q000008:administration & dosage* / Q000652:urine*; D008875:Middle Aged; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013997:Time Factors
chemical_list: D015415:Biomarkers; D007529:Isoflavones; C004742:daidzein; D019833:Genistein