title: Relative validation of 24-h urinary hippuric acid excretion as a biomarker for dietary flavonoid intake from fruit and vegetables in healthy adolescents.
abstract: OBJECTIVE
  A biomarker for dietary flavonoid intake from fruit and vegetables (FlavFV) is needed to elucidate the relevance of flavonoids from these sources for the prevention of chronic diseases. Urinary hippuric acid (HA)-a major metabolite of flavonoids-is promising in this respect as it was shown to satisfyingly indicate fruit and vegetable consumption in different age groups. Therefore, we validated urinary HA as a biomarker for intake of FlavFV.
  
  
  METHODS
  Analyses included data from 287 healthy adolescents of the DONALD Study (aged 9-16 years) for whom a minimum of two pairs of HA measurements from 24-h urine samples (test method) and FlavFV intake estimated from 3-day weighed dietary records (reference method) existed. Agreement between both methods was assessed by Spearman correlation and cross-classification analyses. Possible confounders of the association were identified by linear regression models. Analyses were performed using a split-sample approach allowing for consecutive exploration (n = 192) and confirmation (n = 95) of results.
  
  
  RESULTS
  Agreement between urinary HA excretion and FlavFV intake was moderate according to correlation analysis in the exploratory sample (runadjusted= 0.47, P < 0.0001). Yet, 79 % of the subjects were classified into same/adjacent quartiles, and only 5 % were misclassified into opposite quartiles. These findings were corroborated by analyses in the confirmatory sample (runadjusted= 0.64; 88 % in same/adjacent vs. 4 % in opposite quartiles). Body surface area (BSA) was the only relevant covariate in the exploratory sample, and its adjustment improved cross-classification estimates in both subsamples.
  
  
  CONCLUSIONS
  BSA-adjusted 24-h urinary HA excretion represents a suitable biomarker of habitual FlavFV intake in healthy adolescents.
authors.affiliation: IEL - Nutritional Epidemiology, DONALD Study at the Research Institute of Child Nutrition, Rheinische Friedrich-Wilhelms-University Bonn, Heinstueck 11, 44225, Dortmund, Germany.
authors.forename: Katharina J
authors.initials: KJ
authors.lastname: Penczynski
authors.affiliation: IEL - Nutritional Epidemiology, DONALD Study at the Research Institute of Child Nutrition, Rheinische Friedrich-Wilhelms-University Bonn, Heinstueck 11, 44225, Dortmund, Germany.
authors.forename: Danika
authors.initials: D
authors.lastname: Krupp
authors.affiliation: IEL - Nutritional Epidemiology, DONALD Study at the Research Institute of Child Nutrition, Rheinische Friedrich-Wilhelms-University Bonn, Heinstueck 11, 44225, Dortmund, Germany.|Institute of Human Nutrition and Food Science, Christian-Albrechts-University Kiel, Duesternbrooker Weg 17, 24105, Kiel, Germany.
authors.forename: Anna
authors.initials: A
authors.lastname: Bring
authors.affiliation: IEL - Nutritional Epidemiology, DONALD Study at the Research Institute of Child Nutrition, Rheinische Friedrich-Wilhelms-University Bonn, Heinstueck 11, 44225, Dortmund, Germany.
authors.forename: Katja
authors.initials: K
authors.lastname: Bolzenius
authors.affiliation: IEL - Nutritional Epidemiology, DONALD Study at the Research Institute of Child Nutrition, Rheinische Friedrich-Wilhelms-University Bonn, Heinstueck 11, 44225, Dortmund, Germany.
authors.forename: Thomas
authors.initials: T
authors.lastname: Remer
authors.affiliation: IEL - Nutritional Epidemiology, DONALD Study at the Research Institute of Child Nutrition, Rheinische Friedrich-Wilhelms-University Bonn, Heinstueck 11, 44225, Dortmund, Germany. buyken@uni-bonn.de.
authors.forename: Anette E
authors.initials: AE
authors.lastname: Buyken
mesh_terms: D000293:Adolescent; D017195:Adolescent Nutritional Physiological Phenomena / Q000208:ethnology; D015415:Biomarkers / Q000652:urine; D001830:Body Surface Area; D002648:Child; D002664:Child Nutritional Physiological Phenomena / Q000208:ethnology; D015331:Cohort Studies; D015930:Diet Records; D000072001:Diet, Healthy / Q000208:ethnology; D005260:Female; D005419:Flavonoids / Q000008:administration & dosage*; D005638:Fruit / Q000737:chemistry; D005858:Germany; D006626:Hippurates / Q000652:urine*; D006801:Humans; D008137:Longitudinal Studies; D008297:Male; D015596:Nutrition Assessment; D010349:Patient Compliance / Q000208:ethnology; D012044:Regression Analysis; D065667:Renal Elimination; D014675:Vegetables / Q000737:chemistry
chemical_list: D015415:Biomarkers; D005419:Flavonoids; D006626:Hippurates; C030514:hippuric acid
keywords: 24-h Urine; Adolescents; Biomarker of intake; Flavonoids; Hippuric acid; Relative validation