Quercetin is a plant pigment, also known as a flavonoid, found in raw red onions, kale, tomatoes, raw asparagus and capers. The pigment is taken to treat health issues such allergies, vessel and heart complications, and infections of the prostate.
The effectiveness of quercetin on vessel and heart disease is highly debated, as some studies suggest that consuming foods containing the plant pigment can decrease the overall risk of heart-related fatalities in males, whereas other studies fail to yield the same results. There are also studies which show that taking quercetin orally might lower discomfort from prostate infections.
Athletes use quercetin in an effort to improve their performance and endurance. Although there are studies that show such effects are possible with animals, there is not as much evidence to suggest the same effects with humans. Additionally, more research is needed to prove that the flavonoid can decrease the risk of cancer.
Most evidence suggests that quercetin is safe when taken as a food, but only in normal amounts for a short period of time. There is a chance that consuming the plant pigment can lead to headaches and tingling in the limbs. There is also a chance the kidneys may become damaged from extreme amounts of quercetin.