Quercetin is a natural pigment 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.
This article explores quercetin’s uses, benefits, side effects, and dosage.
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 (1, 2).
The beneficial effects of flavonoids like quercetin come from their ability to function as antioxidants inside your body (3).
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 (4).
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 (5).
Foods that commonly contain quercetin include onions, apples, grapes, berries, broccoli, citrus fruits, cherries, tea, and capers (5).
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.
Summary Quercetin is a plant pigment with potent antioxidant properties. It’s present in many common foods, such as onions, apples, grapes, and berries. It can also be purchased as a dietary supplement for a variety of uses.
Research has linked quercetin’s antioxidant properties to various potential health benefits.
Here are some of its top science-based ones.
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 (3).
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 (6).
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 (9).
They also had reduced markers of inflammation, such as TNFα, compared with those who received a placebo (9).
While these findings are promising, more human research is needed to understand the compound’s potential anti-inflammatory properties.
Quercetin’s potential anti-inflammatory properties may provide allergy symptom relief.
For example, one study showed that taking quercetin supplements suppressed peanut-related anaphylactic reactions in mice (13).
Still, it’s unclear whether the compound has the same effect on allergies in humans, so more research is needed before it can be recommended as an alternative treatment.
Because quercetin has antioxidant properties, it may have cancer-fighting properties (14).
In a review of test-tube and animal studies, quercetin was found to suppress cell growth and induce cell death in prostate cancer cells (15).
Though these findings are promising, human studies are needed before quercetin can be recommended as an alternative treatment for cancer.
Research suggests that quercetin’s antioxidant properties may help protect against degenerative brain disorders, such as Alzheimer’s disease and dementia (20).
In one study, mice with Alzheimer’s disease received quercetin injections every two days for three months. By the end of the study, the injections had reversed several markers of Alzheimer’s and the mice performed much better on learning tests (21).
In another study, a quercetin-rich diet reduced markers of Alzheimer’s disease and improved brain function in mice at the early-middle stage of the condition. However, the diet had little to no effect on animals with middle-late stage Alzheimer’s (22).
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 (23).
Though these findings are promising, more research in humans is needed.
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 (24).
When mice with high blood pressure were given quercetin daily for 5 weeks, their systolic and diastolic blood pressure values (the upper and lower numbers) decreased by an average of 18% and 23%, respectively (27).
Similarly, 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 (28).
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.
Here are several other potential benefits of quercetin:
Summary Quercetin may improve inflammation, blood pressure, exercise performance, and blood sugar control. In addition, it may have brain-protective, anti-allergy and anticancer properties. Still, more research in humans is needed.
Quercetin is found naturally in many plant-based foods, particularly in the outer layer or peel (36).
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 (38).
You can purchase quercetin as a dietary supplement online and from health food stores. It’s available in several forms, including capsules and powders.
Summary Quercetin is present in many commonly consumed foods and is available as a dietary supplement. Typical doses range from 500–1,000 mg per day.
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 (48).
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 (48).
As with any supplement, consult your healthcare provider before taking quercetin, as it can interact with some medications, including antibiotics and blood pressure medications (48).
Summary Quercetin appears to be generally safe with little to no side effects. However, it may interact with various medications and may be unsuitable for pregnant and breastfeeding women, so speak with your healthcare provider before using it.
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.