Relative validation of 24-h urinary hippuric acid excretion as a biomarker for dietary flavonoid intake from fruit and vegetables in healthy adolescents

Purpose 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 ( r unadjusted = 0.47, P