Changes in plasma concentration of flavonoids after ingestion of a flavonoid-rich meal prepared with basic foodstuffs

Background: As flavonoids have a variety of functions, such as antioxidant activity, there is a growing interest in the development of flavonoid supplements. However, there have been reports of DNA damage due to exposure to flavonoids at high concentrations in rats, which could suggest that a habitual intake of flavonoid supplements may cause toxicity. Therefore, we considered that ingesting flavonoids from a typical meal combined with basic foodstuffs is safe because it is unlikely to result in high concentrations like supplements and focused on the intake of flavonoids from a typical meal. Thus, this study investigated the absorption of flavonoids in humans after the consumption of a typical meal. Methods: On the first 2 days of the study, seven healthy volunteers were provided with meals low in flavonoids (flavonoid content below the detection limit by HPLC: less than 0.24 mg/meal) three times a day as a washout. A flavonoid-rich meal (40.44 +/- 1.49 mg/meal) was then provided for breakfast on the third day. Blood was collected from all volunteers 0, 2, 3, 7, 8, and 9 h after the flavonoid-rich meal was consumed. After enzyme hydrolysis of the plasma, the plasma concentrations of flavonoids aglycone of quercetin, daidzein and genistein were measured using LC-MS. Urine was also collected and pooled 24 h after the flavonoid-rich meal was consumed. Thereafter, the urine was treated with enzyme hydrolysis, and the measurement of urinary flavonoids was performed. Results: Plasma flavonoid peaks were observed 8 h after consumption of the flavonoid-rich meal (quercetin: 4.29 +/- 1.46 mu M, daidzein: 0.51 +/- 0.41 mu M, genistein: 0.91 +/- 0.73 mu M). Furthermore, flavonoids were confirmed to be present in plasma even at 9 h after the intake meal. The urinary recovery of flavonoids was 3.43 +/- 1.50% for quercetin, 13.87 +/- 6.68% for daidzein, and 16.89 +/- 11.40% for genistein. Conclusion: These results suggest that consuming a typical meal that combines a variety of basic foodstuffs delays attainment of the plasma flavonoid peak compared with consuming a single type of food or supplements as previously reported. In addition, the flavonoid urinary recovery was also reduced compared with those previously reported.