Quercetin levels in various berries.
Quercetin is one of a number of water-soluble plant pigments called bioflavonoids. Quercetin and the other bioflavonoids cannot be produced in the human body. They have been researched for a number of beneficial effects. Quercetin is found in many foods including apples, onions, tea, berries, grapes, broccoli, cauliflower, and cabbage, as well as many seeds and nuts.
Because quercetin is also an antioxidant, it can help prevent the oxidation or damage to cholesterol, thereby reducing the risk of developing atherosclerosis.1 This antioxidant activity may carry over to the treatment of cataracts and support of healthy vision. Studies suggest that quercetin may limit free radical damage to the eyes while inhibiting other factors that can damage vision.2
A study recently investigated the quercetin levels in berries. Twenty individuals ingested 100 grams of berries daily, which included black currants, lingonberries, and bilberries. A control group consumed a regular diet. Serum measurements were taken 2 weeks before the study, baseline, and 2, 4, and 8 weeks during the study. The results showed that quercetin levels were 32 to 51% higher in the berry group. During this study, the average quercetin levels in the berry group were between 21.4 and 25.3 mg/l. The authors of this study concluded that, "the berries used in this study are a good source of bioavailable quercetin."3
1. Negre-Salvayre A, et al. Quercetin Prevents the Cytotoxicity of Oxidized LDL on Lymphoid Cell Lines. Free Radic Biol Med. 1992;12(2):101-06.
2. Beyer-Mears A, et al. Diminished Sugar Cataractogenesis by Quercetin. Exp Eye Res. Jun1979;28(6): 709-16.
3. Erlund I, et al. Consumption of black currants, lingonberries and bilberries increases serum quercetin concentrations. Eur J Clin Nutr. Jan 2003;57:37-42.