title: Development of a food frequency questionnaire for the assessment of quercetin and naringenin intake.
abstract: OBJECTIVE
  To measure the relationship between quercetin and naringenin intakes as estimated by food frequency questionnaire (FFQ), and the urinary excretion of quercetin and naringenin aglycones after their enzymatic hydrolysis in human volunteers.
  
  
  METHODS
  Volunteers were recruited via the Human Nutrition Unit volunteer databank at the Institute of Food Research, Norwich. Sixty-three volunteers were recruited into the study, of which 14 were excluded and 49 completed the study. A modified FFQ was developed and used to estimate daily intake of quercetin and naringenin in 49 healthy volunteers who also provided five 24-h urine samples over a 2-week period. Urinary excretion of quercetin and naringenin metabolites was determined by solid-phase extraction and high-pressure liquid chromatography.
  
  
  RESULTS
  The estimated mean intakes of quercetin and naringenin were 29.4 mg (s.d. 15.0) and 58.1 mg (s.d. 62.7) per day, respectively. Mean urinary excretion of quercetin was 60.1 microg (s.d. 33.1) and that of naringenin was 0.56 mg (s.d. 0.4). The correlation between FFQ estimated intake of quercetin and naringenin and levels excreted in the urine were r=0.82 (P<0.0001) and r=0.25 (P=0.05), respectively.
  
  
  CONCLUSIONS
  We observed a statistically significant correlation between the urinary excretion of quercetin and naringenin metabolites and their dietary intake as estimated by FFQ. Use of FFQs in epidemiological studies requiring an estimate of flavonoid intake seems justified.
authors.affiliation: Department of Surgery, Norfolk and Norwich University Hospital, Norwich, UK.
authors.forename: S
authors.initials: S
authors.lastname: Ranka
authors.forename: J M
authors.initials: JM
authors.lastname: Gee
authors.forename: L
authors.initials: L
authors.lastname: Biro
authors.forename: G
authors.initials: G
authors.lastname: Brett
authors.forename: S
authors.initials: S
authors.lastname: Saha
authors.forename: P
authors.initials: P
authors.lastname: Kroon
authors.forename: J
authors.initials: J
authors.lastname: Skinner
authors.forename: A R
authors.initials: AR
authors.lastname: Hart
authors.forename: A
authors.initials: A
authors.lastname: Cassidy
authors.forename: M
authors.initials: M
authors.lastname: Rhodes
authors.forename: I T
authors.initials: IT
authors.lastname: Johnson
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D015930:Diet Records; D004812:Epidemiologic Methods; D005260:Female; D044950:Flavanones / Q000008:administration & dosage* / Q000032:analysis / Q000652:urine; D006801:Humans; D008297:Male; D008875:Middle Aged; D009753:Nutritive Value; D011794:Quercetin / Q000008:administration & dosage* / Q000032:analysis / Q000652:urine; D011795:Surveys and Questionnaires
chemical_list: D044950:Flavanones; D011794:Quercetin; C005273:naringenin