Quercetin: Benefits, Uses, Sources, and Risks

Reviewed by Dr. Michael Kessler, DC — Quercetin is an antioxidant compound that helps give foods their color. It is a member of the flavonoid family, which means that it is a phytonutrient, or plant chemical. As such, quercetin benefits are wide-ranging.

Quercetin, like many other flavonoids, is found in virtually every fruit, vegetable, and other plant-based food. It is one of the most abundant antioxidants available, and can play an important role protecting your body from harmful free radicals.

Free radicals are compounds in the body that can damage cells to trigger illness. Antioxidants like quercetin fight the “oxidative” stress caused by free radicals to encourage better health and potentially prevent disease.

Quercetin may aid in limiting inflammation, combating allergy symptoms, boosting immune strength, and more.

Quercetin Benefits and Uses

People use supplemental quercetin for a variety of reasons. Although there isn’t always sufficient evidence that it will produce results, it is generally an affordable form of treatment that is enticing for many.

That said, quercetin supplementation is not always safe and should only be taken under your doctor’s advice.

If you’re interested in the following potential benefits of quercetin, look to increase your intake through dietary measures.

May Limit Inflammation

Free radicals can lead to inflammation that quercetin can help silence. Studies have shown that quercetin may help reduce inflammation—which may not be surprising, given it is found in anti-inflammatory fruits and vegetables.

One study showed that women with rheumatoid arthritis, an inflammatory condition that causes severe joint pain and stiffness, reported less stiffness and pain than those on a placebo. They also had lower levels of inflammatory markers after taking 500 milligrams (mg) of quercetin a day for eight weeks.

These results are promising, but it was a small study and much more work is required to uncover any specific medical anti-inflammatory uses for quercetin.

May Relieve Allergy Symptoms

There is some research to suggest that quercetin’s potential anti-inflammatory capabilities could also help ease allergy symptoms.

Some test-tube and animal studies have shown that quercetin may:

• Block enzymes involved in inflammation
• Suppress chemicals that promote inflammation

One chemical that promotes inflammation is histamine, a common compound involved in local immune response. It is responsible for the itching and sneezing during an allergic reaction.

More research is required to determine if quercetin can help tame allergic reactions in humans.

May Influence Alzheimer’s and Dementia Risk

An antioxidant-rich diet is also associated with improved cognition and a lower risk for Alzheimer’s and dementia. Studies on mice suggest that quercetin may improve learning and brain function in the early-middle stages of Alzheimer’s disease.

The lack of human studies means that taking quercetin for cognitive function is not currently recommended. However, eating a nutritious, plant-based diet, which would feature plenty of quercetin, is.

May Help Lower Blood Pressure

There is also some research highlighting quercetin’s potential effect on blood pressure.

A review of nine human studies found that taking more than 500 mg of quercetin per day could help reduce systolic and diastolic blood pressure by an average of 5.8 millimeters of mercury (mm Hg) and 2.5 mm Hg, respectively.

Any blood-pressure-lowering benefits offered by quercetin are surely due to its potential anti-inflammatory capabilities.

Quercetin is found in a variety of foods that fit perfectly into a heart-healthy diet.

The Best Sources of Quercetin

Some of the best quercetin foods are:

• Red apples
• Red grapes
• Capers
• Onion
• Figs
• Red leaf lettuce
• Yellow and green peppers
• Shallots
• Cooked asparagus
• Cherries
• Tomatoes
• Broccoli
• Kale
• Berries (including cranberries, blackberries, blueberries, raspberries, etc.)
• Green and black tea

Food is the best source of quercetin. The benefits mentioned above are synonymous with those of a healthy diet featuring an array of colorful fruits and vegetables that are rich in healthful flavonoids, vitamins, and minerals.

Quercetin is also available as a supplement in highly concentrated doses. You can purchase it in capsule or powder form, and dosages generally range between 500 and 1,000 mg per day.

Although supplemental doses are high, quercetin is not highly bioavailable on its own. That means it is not well-absorbed by the body. Estimates suggest only three percent to 17% is absorbed.

You will get the most out of quercetin in its natural state. Consuming it through foods allows quercetin to work synergistically with other flavonoids for optimal absorption.

Quercetin Side Effects and Risks

Quercetin is safe to consume when it’s derived from natural food sources. Supplements are generally safe, but can lead to symptoms or risks in certain situations.

Taking more than 1,000 mg per day may lead to headaches, stomachaches, and tingling in the extremities.

Very high doses may cause kidney damage. It’s also possible that quercetin supplementation may make kidney problems worse.

There is also little work examining the potential long-term effects of taking quercetin supplements.

Talking to your doctor before beginning any supplement regimen for any reason is always recommended.

Eat Your Quercetin for Best Results

Instead of focusing your attention on one specific flavonoid like quercetin, it may be more beneficial to focus on eating more nutritious foods. Quercetin is found in a wide array of colorful fruits and vegetables that are packed with plenty of antioxidants that promote health in a number of ways.

Simply eating more of these foods and limiting your intake of refined and processed foods can likely add to any benefit you’re looking for. The more total nutrition in your diet, the better.