Quercetin: Fact Sheet for Consumers (Evidence Based)

Quercetin is a type of flavonoid present in many fruits, vegetables, and grains.

It’s one of the most abundant antioxidants in the diet and plays an important role in helping your body combat free radical damage, which is linked to chronic diseases.

In addition, its antioxidant properties may help reduce inflammation, allergy symptoms, and blood pressure.

Related: Can Quercetin Help Against Coronavirus?

This article explores quercetin’s uses, benefits, side effects and dosage.



What is quercetin?

Quercetin is a pigment that belongs to a group of plant compounds called flavonoids.

Flavonoids are present in vegetables, fruits, grains, tea, and wine. They have been linked to several health benefits, including reduced risks of heart disease, cancer, and degenerative brain disorders (Trusted Source, Trusted Source).

The beneficial effects of flavonoids like quercetin come from their ability to function as antioxidants inside your body (Trusted Source).

Antioxidants are compounds that can bind to and neutralize free radicals.

Free radicals are unstable molecules that may cause cellular damage when their levels become too high. Damage caused by free radicals has been linked to numerous chronic conditions, including cancer, heart disease, and diabetes (Trusted Source).

Quercetin is the most abundant flavonoid in the diet. It’s estimated that the average person consumes 10–100 mg of it daily through various food sources (Trusted Source).

Foods that commonly contain quercetin include onions, apples, grapes, berries, broccoli, citrus fruits, cherries, tea, and capers (Trusted Source).

It’s also available as a dietary supplement in powder and capsule form.

People take this supplement for several reasons, including to boost immunity, fight inflammation, combat allergies, aid exercise performance, and maintain general health.

Health benefits of quercetin

Research has linked quercetin’s antioxidant properties to various potential health benefits.
Here are some of its top science-based ones.

May reduce inflammation

Free radicals may do more than simply damage your cells. Research shows that high levels of free radicals may help activate genes that promote inflammation. Thus, high levels of free radicals may lead to an increased inflammatory response (Trusted Source).

While a little inflammation is necessary to help your body heal and fight infections, persistent inflammation is linked to health problems, including certain cancers, as well as heart and kidney diseases (Trusted Source).

Studies show that quercetin may help reduce inflammation.

An 8-week study in 50 women with rheumatoid arthritis observed that participants who took 500 mg of quercetin experienced significantly reduced early-morning stiffness, morning pain, and after-activity pain (Trusted Source).

May lower your risk of chronic brain disorders

Coffee is a popular beverage that has been linked to a lower risk of Alzheimer’s disease. In fact, research shows that quercetin, not caffeine, is the primary compound in coffee that is responsible for its potential protective effects against this illness (Trusted Source).

May reduce blood pressure

High blood pressure affects one in three American adults. It raises your risk of heart disease — the leading cause of death in the United States (Trusted Source).

A review of 9 human studies in 580 people found that taking more than 500 mg of quercetin in supplement form daily reduced systolic and diastolic blood pressure by an average of 5.8 mm Hg and 2.6 mm Hg, respectively (Trusted Source).

Although these findings are promising, more human studies are needed to determine whether the compound could be an alternative therapy for high blood pressure levels.

May help in cancer treatment

Quercetin is a well-known plant flavonoid that is reported to have anticancer actions in vitro and in vivo. Studies suggest that quercetin binds to several receptors that play important roles in carcinogenesis, regulates expression of various genes, induces epigenetic changes, and interferes with enzymes that metabolize chemical carcinogens. In addition, it also elicits anti-inflammatory and antiviral effects. The ability of quercetin to induce apoptosis of cancer cells without affecting non-cancer cells has been documented using various cell lines. Quercetin also has antiangiogenic and antimetastatic properties. When used in combination with chemotherapy and radiotherapy, quercetin can act as a sensitizer and protect non-cancer cells from the side effects of currently used cancer therapies. The safety and potential usefulness of quercetin for the prevention and treatment of cancer have been documented in both animal experiments and a phase I clinical trial.

Other potential benefits

Here are several other potential benefits of quercetin:
  • May aid exercise performance. A review of 11 human studies found that taking quercetin may slightly improve endurance exercise performance (Trusted Source).
  • May aid blood sugar control. Human and animal research indicates that the compound may reduce fasting blood sugar levels and protect against complications of diabetes (Trusted Source, Trusted Source, Trusted Source).
Food sources and dosage

Quercetin is found naturally in many plant-based foods, particularly in the outer layer or peel (USDA).

Good food sources include (USDA, Trusted Source):
  • capers
  • peppers — yellow and green
  • onions — red and white
  • shallots
  • asparagus — cooked
  • cherries
  • tomatoes
  • red apples
  • red grapes
  • broccoli
  • kale
  • red leaf lettuce
  • berries — all types, such as cranberries, blueberries, and raspberries
  • tea — green and black
Note that the amount of quercetin in foods may depend on the conditions in which the food was grown. For example, organic tomatoes appear to have up to 79% more quercetin than commercially grown ones (Trusted Source).

Quercetin supplements

You can purchase quercetin as a dietary supplement online and from health food stores. It’s available in several forms, including capsules and powders.

Typical dosages range from 500–1,000 mg per day (Trusted Source, Trusted Source).

On its own, quercetin has a low bioavailability, which means your body absorbs it poorly (Trusted Source, Trusted Source).

That’s why the supplements may include other compounds, such as vitamin C or digestive enzymes like bromelain, as they may increase absorption (PubChem, Food and Nutrition Journal).

Additionally, some research indicates that quercetin has a synergistic effect when combined with other flavonoid supplements, such as resveratrol, genistein, and catechins (Trusted Source, Trusted Source, Trusted Source).

Safety and side effects 

Quercetin is found in many fruits and vegetables and is safe to consume.

As a supplement, it appears to be generally safe with little to no side effects.

In some instances, taking more than 1,000 mg of quercetin per day may cause mild symptoms like headaches, stomach aches, or tingling sensations (Trusted Source).

When consumed in food, quercetin is safe for pregnant and breastfeeding women. However, studies on the safety of quercetin supplements for pregnant and breastfeeding women are lacking, so you should consult your healthcare provider before taking it (Trusted Source).

As with any supplement, consult your healthcare provider before taking quercetin, as it can interact with some medications, including antibiotics and blood pressure medications (Trusted Source).

Conclusion

Quercetin is the most abundant dietary flavonoid.

It has been linked to improved exercise performance and reduced inflammation, blood pressure, and blood sugar levels. Plus, it may have brain-protective, anti-allergy, and anticancer properties.

Though its benefits seem promising, more human research is needed.


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