Quercetin, a member of the flavonoids family, is one of the most prominent dietary antioxidants. Plants containing flavonoids have a long history of use in traditional medicines in many cultures, but flavonoids themselves were not discovered until the 1930s.

Quercetin first gained attention several decades ago when it was found to cause DNA mutations in bacteria, a sign that it might actually contribute to causing cancer. It is ubiquitously present in foods including vegetables, fruit, tea and wine as well as countless food supplements and is claimed to exert beneficial health effects. 

Research in recent years has focused on several possible helpful effects of quercetin, including its potential role in preventing cancer. 

This includes protection against various diseases such as osteoporosis, certain forms of cancer, pulmonary and cardiovascular diseases but also against aging. Especially the ability of quercetin to scavenge highly reactive species such as peroxynitrite and the hydroxyl radical is suggested to be involved in these possible beneficial health effects. Consequently, numerous studies have been performed to gather scientific evidence for these beneficial health claims as well as data regarding the exact mechanism of action and possible toxicological aspects of this flavonoid.

Quercetin is said to have a number of uses, but most of these are based on early findings from laboratory studies. Some proponents claim it can help stabilize small blood vessels and may help protect against heart attacks and strokes.

Most of the research on quercetin and cancer has been done in cell culture or animal studies. These types of studies can suggest possible helpful effects, but they do not provide proof that such effects can be achieved in humans. It is still unclear how well quercetin is absorbed by the human body when taken by mouth. Controlled clinical trials are needed to show whether quercetin has helpful properties in humans.

Recent studies suggest that quercetin can slow the growth of cancer cells and can help foster apoptosis, a form of natural cell death that doesn't happen in most cancer cells. Some studies in animals have shown that quercetin may help protect against certain types of cancer, particularly colon cancer.

Until conclusive clinical research findings emerge, it is reasonable to include foods that contain quercetin as part of a balanced diet with an emphasis on fruits, vegetables, legumes, and whole grains. The interaction between certain phytochemicals and the other compounds in foods is not well understood, but it is unlikely that any single compound offers the best protection against cancer. A balanced diet that includes 5 or more servings a day of fruits and vegetables, along with foods from a variety of other plant sources such as nuts, seeds, whole grain cereals, and beans, is likely to be more effective in reducing cancer risk than eating one particular phytochemical in large amounts.

News of the disease-protective and longevity benefits of red wine has grabbed headlines around the world during the past few years. Red wine contains a number of beneficial polyphenols, such as the much-publicized resveratrol as well as quercetin-a compound that is now also making news of its own.

While quercetin can be obtained through red wine and other dietary sources such as apples, onions, grapefruit, tea, green vegetables, and beans,6 highly purified supplements make it possible to acquire the bio-logically meaningful doses that have shown promise in tightly controlled studies. In the words of the German nutrition expert Professor Stephan C.

Despite being the most common and best studied of the polyphenols, quercetin has been largely neglected in the public eye until recently, as new research has revealed its astonishing potential as a health-promoting, disease-preventing supplement.

Quercetin’s powerful antioxidant effects directly reduce tissue damage and have now been shown to prevent diseases such as cancer and cardiovascular disease.

Independent effects of quercetin directly reduce fat tissue growth and development, and even reduce the bulk of body fat stores, promoting health through weight reduction.

Quercetin shows promise in fighting the numerous components of the metabolic syndrome, including hypertension, insulin resistance, and adverse lipid profiles.

Quercetin’s antioxidant effects lead to anti-inflammatory and anti-allergy effects, augmenting its role in chronic disease prevention and treatment.