Effect of Quercetin Supplements on Healthy Males: a Four-Week Randomized Cross-Over Trial

The main goal of the research is to determine the long term effects of daily supplementation of quercetin, a compound naturally and normally present in food, on the chemical composition (uric acid ii and glucose) of blood and urine and on blood pressure, of healthy males. Six of the volunteers will collect urine after consuming a standard meal made from fresh onion and after quercetin supplement intake, in the same way, with 3 days washout before each. The urine collected here will be analysed to check that the supplement is equivalent to the food. Stage 2 will only be conducted with supplement and placebo. Healthy male volunteers with higher (than average) blood uric acid will be selected and will be asked to consume a standard supplement/placebo added to their own diet for 4 weeks per phase. Two arms are separated by 4 weeks resting period: quercetin supplement and placebo. Blood and urine samples will be taken every other week to detect any changes of uric acid and other biomarkers. \----- i) Quercetin is found in a variety of foods including apples, berries, brassica vegetables, capers, grapes, onions, shallots, tea, and tomatoes, as well as many seeds, nuts, flowers, barks, and leaves. ii) Uric acid, a compound found in both in the human body and urine, is produced by the breakdown of purines, which are nitrogen-containing compounds in substances such as nucleic acids (DNA). They enter the circulation from digestion of certain foods, drinks (alcoholic beverages like beer and wine) or from normal breakdown and turnover of cells in the body. Most uric acid is removed by the kidneys and disposed of in the urine; the remainder is excreted in the stool.