Quercetin is a natural antioxidant derived from plants with the ability to reduce illness and maintain mental performance in physically stressed test subjects. Quercetin is a flavonol, one of a class of bioflavonoids found in fruits, vegetables, leafy greens and grains. Plants produce these chemical compounds to protect themselves against parasites, bacteria and cell injury and to preserve vitamins. 

Definition of A Flavonoid

Flavonoid is a scientific word for a group of substances that plants make. Flavonoids are vitamin-like substances that aren't essential for life but have been shown to decrease the rate of arterial aging and immune-system aging. Flavonoids help your immune system fight bacteria and viruses that cause illness. Many fruits and vegetables are rich sources of flavonoids. Quercetin is an anti-inflammatory flavonoid, a natural antihistamine and can increase your exercise performance. It’s also an energy boost for your cells. It increases the mitochondria in your muscles. That’s good news for your body’s hardest-working muscle, the heart. 

Free Radical Damage

Quercetin, like other antioxidants, eliminates free radicals. These are unstable molecules in the body that can damage nearby cells, leading to aging effects, heart disease and even cancer. Quercetin helps protect cell membranes against destruction by free radicals. Free radicals are atoms that contain unpaired electrons, which can easily bond with other atoms or molecules, causing oxidative damage and degenerative changes. These particularly affect the heart muscle, nerve cells and immune factors. Things that contribute to the proliferation of free radicals include radiation exposure, smoking, air pollution and a diet high in fried foods. 


If you mix quercetin with just about any virus or bacteria, it stops their replication early on. The U.S. Department of Defense conducted some studies to see if quercetin could help buoy soldiers’ immunity. They simulated the fatigue soldiers’ experience during a three-day war mission and followed up with a series of muscle biopsies and blood analyses and found infections in only 5 percent of the quercetin group compared with 45 percent of the placebo group. 

Improved Exercise Stamina

A preliminary study by the University of South Carolina showed that eating foods rich in quercetin improved endurance and oxygen capacity in active but untrained men and women. Other studies at the University of Pepperdine and Appalachian State University have shown similar results. This improvement in athletic ability is thought to be because quercetin has a positive effect on the energy processors of the cell, the mitochondria. This positive effect, plus the activity of quercetin as a sort of antioxidant (like vitamin C), boosts the immune system and may lead to a general improvement in health.

Help For Arthritis

Quercetin acts similarly to an anti-inflammatory drug like ibuprofen, which makes it a strong help for those suffering from arthritis. It is thought that quercetin may limit the swelling and pain that occurs in joints as a result of arthritis. According to the University of Maryland Medical Center, there are reports that a diet changed from the typical Western diet to one more centered on fruits and vegetables that contain quercetin, has improved symptoms of arthritis. That being said, the reports also point out that there is no direct evidence that quercetin supplements will improve symptoms. So eating the foods high in quercetin is recommended.

Eye Disorders

Many eye disorders like macular degeneration and cataracts are in some part caused by free radicals – particles that can cause cell damage in the body. Since quercetin acts like an antioxidant, which helps to stop free radicals from damaging the cells, taking it in the form of blueberries, blackberries and dark cherries may help to limit eye problems. According to Herbs 2000, studies have shown that quercetin can limit the progression of cataracts in animals.

Foods High In Quercetin

The highest concentrations of quercetin are found in capers, lovage – a hardy perennial herb with ribbed stalks that resemble celery and is used as an addition to salads, soups and stews – berries, apples, green and chamomile tea, raisins, red grapes, asparagus, green beans, red leaf lettuce and onions. Elderberries, of all the berries, are very rich in quercetin, but blueberries—and all other berries—also contain substantial amounts of quercetin. So, while the average American consumes only 20 milligrams of quercetin per day, vegetarians who eat a lot of apples, onions, berries have been found to get 100 to 200 milligrams daily. People with high quercetin intake have a 60 percent reduction in lung-cancer death rates. They have a third less incidence of heart disease and research shows that they have less pancreatic and colon cancer as well. If people increase their intake of quercetin rich food over the long term they should experience lower rates for various types of cancer and heart disease.