title: The validity and reproducibility of food-frequency questionnaire-based total antioxidant capacity estimates in Swedish women.
abstract: BACKGROUND
  Total antioxidant capacity (TAC) provides an assessment of antioxidant activity and synergistic interactions of redox molecules in foods and plasma.
  
  
  OBJECTIVE
  We investigated the validity and reproducibility of food-frequency questionnaire (FFQ)-based TAC estimates assessed by oxygen radical absorbance capacity (ORAC), total radical-trapping antioxidant parameters (TRAP), and ferric-reducing antioxidant power (FRAP) food values.
  
  
  METHODS
  Validity and reproducibility were evaluated in 2 random samples from the Swedish Mammography Cohort. Validity was studied by comparing FFQ-based TAC estimates with one measurement of plasma TAC in 108 women (54-73-y-old dietary supplement nonusers). Reproducibility was studied in 300 women (56-75 y old, 50.7% dietary supplement nonusers) who completed 2 FFQs 1 y apart.
  
  
  RESULTS
  Fruit and vegetables (mainly apples, pears, oranges, and berries) were the major contributors to FFQ-based ORAC (56.5%), TRAP (41.7%), and FRAP (38.0%) estimates. In the validity study, whole plasma ORAC was correlated (Pearson) with FFQ-based ORAC (r = 0.35), TRAP (r = 0.31), and FRAP (r = 0.28) estimates from fruit and vegetables. Correlations between lipophilic plasma ORAC and FFQ-based ORAC, TRAP, and FRAP estimates from fruit and vegetables were 0.41, 0.31, and 0.28, and correlations with plasma TRAP estimates were 0.31, 0.30, and 0.28, respectively. Hydrophilic plasma ORAC and plasma FRAP values did not correlate with FFQ-based TAC estimates. Reproducibility, assessed by intraclass correlations, was 0.60, 0.61, and 0.61 for FFQ-based ORAC, TRAP, and FRAP estimates, respectively, from fruit and vegetables.
  
  
  CONCLUSIONS
  FFQ-based TAC values represent valid and reproducible estimates that may be used in nutritional epidemiology to assess antioxidant intake from foods. Further studies in other populations to confirm these results are needed.
authors.affiliation: Division of Nutritional Epidemiology, Institute of Environmental Medicine, Karolinska Institute, Stockholm, Sweden.
authors.forename: Susanne
authors.initials: S
authors.lastname: Rautiainen
authors.forename: Mauro
authors.initials: M
authors.lastname: Serafini
authors.forename: Ralf
authors.initials: R
authors.lastname: Morgenstern
authors.forename: Ronald L
authors.initials: RL
authors.lastname: Prior
authors.forename: Alicja
authors.initials: A
authors.lastname: Wolk
mesh_terms: D000368:Aged; D000975:Antioxidants / Q000032:analysis* / Q000378:metabolism*; D015331:Cohort Studies; D005260:Female; D005290:Ferric Compounds / Q000378:metabolism; D005638:Fruit / Q000378:metabolism*; D006801:Humans; D008875:Middle Aged; D010084:Oxidation-Reduction; D010949:Plasma / Q000737:chemistry / Q000378:metabolism; D017382:Reactive Oxygen Species / Q000378:metabolism; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D011795:Surveys and Questionnaires / Q000592:standards*; D013548:Sweden; D014675:Vegetables / Q000378:metabolism*
chemical_list: D000975:Antioxidants; D005290:Ferric Compounds; D017382:Reactive Oxygen Species