Quercetin: An Antioxidant and Synergistic Supplement

Quercetin is a flavonoid found in fruits and vegetables, and has the advantage of being relatively well studied. On its own, quercetin is a modestly effective supplement. Like other flavonoids, it is an antioxidant, anti-inflammatory molecule, and appears to enhance the immune system. It may also lower blood sugar, reduce blood pressure, protect against cancer and improve lipid profile (lowers LDL cholesterol while increasing HDL cholesterol).

Multiple systematic review and meta analyses support the benefits of quercetin: a review of 13 studies found a significant reduction in blood glucose with quercetin supplementation. Another meta analysis suggested that quercetin improved lipid profiles (after 8 weeks of supplementation) and reduced blood pressure.

In addition to these effects, quercetin may also improve the absorption of other supplements. Quercetin inhibits the activity of sulfurotransferases in the intestines and liver – enzymes that metabolise compounds such as resveratrol and limit their availability. Thus, supplementation with quercetin may improve the effectiveness of other supplements.

Among the numerous studies investigating quercetin supplementation in humans, side effects have rarely been found, and those that have are mild in nature. However, there is little data on the effects of quercetin supplementation lasting longer than 12 weeks. Some animal studies also suggest that quercetin may worsen kidney disease.