Correlations between urinary concentrations and dietary intakes of flavonols in the European Prospective Investigation into Cancer and Nutrition (EPIC) study.

Purpose: In this study, we aimed to study the correlation between acute and habitual intakes of flavonols, their main food sources and their 24-h urinary concentrations in an European population.
Methods: A 24-h dietary recall (24-HDR) and 24-h urine samples were collected on the same day from a convenience subsample of 475 men and women from four countries (France, Italy, Greece and Germany) of the European Prospective Investigation into Cancer and Nutrition (EPIC) study. A standardized 24-HDR software and a country/centre-specific validated dietary questionnaire (DQ) were used to collect acute and habitual dietary data, respectively. The intake of dietary flavonols was estimated using the Phenol-Explorer database. Urinary flavonols (quercetin, isorhamnetin, and kaempferol) were analysed using tandem mass spectrometry with a previous enzymatic hydrolysis.
Results: Weak partial Spearman correlations between both dietary acute and habitual intake and urinary concentrations of quercetin (both R _partial  ~ 0.3) and total flavonols (both R _partial  ~ 0.2) were observed. No significant correlations were found for kaempferol and isorhamentin. Regarding flavonol-rich foods, weak correlations were found between urinary concentrations of quercetin and total flavonols and the acute intake of onions and garlics, fruits, tea, and herbal tea (all R _partial  ~ 0.2). For habitual intake, statistically significant correlations were only found between urinary quercetin concentration and herbal tea (R _partial  = 0.345) and between urinary total flavonol concentration and tea, and herbal tea consumption (R _partial  ~ 0.2).
Conclusions: Our results suggest that urinary quercetin level can be used as potential concentration biomarkers of both acute and habitual quercetin intake, while urinary concentrations of flavonols are unlikely to be useful biomarkers of individual flavonol-rich foods.