Quercetin is a naturally-occurring flavonoid found in many common foods. Flavonoids are water-soluble plant pigments and are often referred to as “nature’s biological response modifiers” because of their ability to modify the body’s reaction to allergens, viruses, and carcinogens. Like many other flavonoids, quercetin show anti-allergic, anti-inflammatory, and anti-cancer activity.
Numerous studies have found quercetin to be the most active of flavonoids; many medicinal plants owe much of their activity to their high content in quercetin. Because it is capable of directly inhibiting the initial process of inflammation, quercetin has demonstrated substantial anti-inflammatory activity. It also hinders the release of histamines and other allergic mediators, making it a superb anti-allergic supplement. In addition, it exerts potent antioxidant activity and enhances vitamin C absorption. Quercetin may also have positive effects in fighting or help in preventing cancer, prostatitis, heart disease, cataracts and respiratory diseases such as bronchitis and asthma. It has also been claimed that quercetin may have anti-depressant properties. However, no solid test results have yet confirmed its anti-depressant abilities.
Foods rich in quercetin are generally dark-pigmented. For example, capers, apples, tea, red grapes, tomatoes cherries, raspberries, red wine and red onions all contain high levels of quercetin. On the other hand, quercetin is also found in other non-dark pigmented fruits and vegetables such as broccoli, citrus fruits and leafy greens.
Since quercetin is not considered an essential nutrient, there is no set Recommended Daily Allowance. It is suggested that a dosage of 50 – 150mg per day is reasonable. Various studies of quercetin have been carried out and none so far have indicated any issues of toxicity. However, it is still not recommended to consume quercetin in mega-doses (500mg or above per day).
References: (1) http://en.wikipedia.org/wiki/Quercetin (2) http://ezinearticles.com/?Discover-the-Health-Benefits-of-Quercetin&id=154044 (3) http://www.puritan.com/pages/healthnotes.asp?languri=eng&ContentID=
