Quercetin is a natural pigment present in 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.
What is quercetin?
Quercetin is a pigment that belongs to a group of plant compounds called flavonoids.
Flavonoids are present in:
They’ve been linked to several health benefits, including reduced risks of heart disease, cancer, and degenerative brain disorders.
The beneficial effects of flavonoids like quercetin come from their ability to function as antioxidants inside your body.
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.
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.
Foods that commonly contain quercetin include onions, apples, grapes, berries, broccoli, citrus fruits, cherries, green tea, coffee, red wine, and capers.
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
- 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.
Health benefits of quercetin
Research has linked quercetin’s antioxidant properties to various potential health benefits.
Here are some of its top science-based benefits.
Quercetin 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 increased inflammatory response.
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.
Studies show that quercetin may help reduce inflammation.
In test-tube studies, quercetin reduced markers of inflammation in human cells, including the molecules tumor necrosis factor-alpha (TNFα) and interleukin-6 (IL-6).
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.
They also had reduced markers of inflammation, such as TNFα, compared to those who received a placebo.
While these findings are promising, more human research is needed to understand the compound’s potential anti-inflammatory properties.
Quercetin may ease allergy symptoms
Quercetin’s potential anti-inflammatory properties may provide allergy symptom relief.
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Test-tube and animal studies found that it may block enzymes involved in inflammation and suppress inflammation-promoting chemicals, such as histamine.
For example, one study showed that taking quercetin supplements suppressed peanut-related anaphylactic reactions in mice.
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.
Quercetin may have anticancer effects
Because quercetin has antioxidant properties, it may have cancer-fighting properties.
In a review of test-tube and animal studies, quercetin was found to suppress cell growth and induce cell death in prostate cancer cells.
Other test-tube and animal studies observed that the compound had similar effects in liver, lung, breast, bladder, blood, colon, ovarian, lymphoid, and adrenal cancer cells.
Though these findings are promising, human studies are needed before quercetin can be recommended as an alternative treatment for cancer.
Quercetin may lower your risk of chronic brain disorders
Research suggests that quercetin’s antioxidant properties may help protect against degenerative brain disorders, such as Alzheimer’s disease and dementia.
In one study, mice with Alzheimer’s disease received quercetin injections every 2 days for 3 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.
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.
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Coffee is a popular beverage that has been linked to a lower risk of Alzheimer’s disease.
Research shows that quercetin, not caffeine, is the primary compound in coffee that’s responsible for its potential protective effects against this illness.
Though these findings are promising, more research in humans is needed.
Quercetin may reduce blood pressure
High blood pressure affects 1 in 3 American adults. It raises your risk of heart disease — the leading cause of death in the United States.
Research suggests that quercetin may help reduce blood pressure levels. In test-tube studies, the compound appeared to have a relaxing effect on blood vessels.
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.
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.
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.
Other potential benefits of quercetin
Here are several other potential benefits of quercetin:
- May help combat aging. Test-tube and animal research suggest that quercetin may help rejuvenate or eliminate aging cells and reduce markers of aging. However, more human research is needed.
- May aid exercise performance. A review of 11 human studies found that taking quercetin may slightly improve endurance exercise performance.
- 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.
Summary: Quercetin may improve inflammation, blood pressure, exercise performance, and blood sugar management. In addition, it may have brain-protective, anti-allergy, and anticancer properties. Still, more research on humans is needed.
Food sources and dosage of quercetin
Quercetin is found naturally in many plant-based foods, particularly in the outer layer or peel.
Good food sources include:
- peppers — yellow and green
- onions — red and white
- asparagus — cooked
- red apples
- red grapes
- 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, in one study, organic tomatoes appear to have up to 79% more quercetin than conventionally grown ones.
However, other studies point out differences between the quercetin content in various species of tomatoes regardless of the farming method. There was no difference in bell peppers, conventionally or organically grown.
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.
On its own, quercetin has a low bioavailability, which means your body absorbs it poorly.
That’s why the supplements may include other compounds, such as vitamin C or digestive enzymes like bromelain, as they may increase absorption.
Additionally, some research indicates that quercetin has a synergistic effect when combined with other flavonoid supplements, such as resveratrol, genistein, and catechins.
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.
Safety and side effects of quercetin
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.
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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 avoid taking quercetin if you’re pregnant or nursing.
As with any supplement, consult your healthcare provider before taking quercetin, as it can interact with some medications, including antibiotics and blood pressure medications.
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’s 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.