Consumption of quercetin and kaempferol in free-living subjects eating a variety of diets.

Quercetin and related flavonoids are anticarcinogenic in rats, but little is known about human intakes. The intake of five major flavonols and flavones was calculated using 1-day dietary records of 17 volunteers from 14 countries, and using both 3-day records and a food frequency questionnaire of eight Dutch adults. Total consumption (+/- SD) was 27.6 +/- 19.5 mg/day in the international subjects, 34.1 +/- 31.2 mg/day in the Dutch adults according to 3-day records, and 41.9 +/- 23.7 mg/day according to questionnaires. Quercetin contributed 68-73%, and kaempferol 22-29%, the major sources being tea and onions. A brief food frequency questionnaire may be a suitable method for ranking individuals by flavonol intake.