What Is Quercetin, and What Are the Antioxidant’s Health Benefits?
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There’s a reason plant-based diets get so much healthy hype. Loading up on fruits and vegetables has been linked with a lower risk of chronic disease and we’re well-aware plants are packed with tons of vitamins, minerals and nutrients that promote overall wellness. And it’s those plant-based pigments—like the beta-carotene in orange veggies or anthocyanins in purple fruits—get singled out for their powerful roles in fighting inflammation, stress, and diseases like diabetes, heart disease, and even cancer.
One flavonoid in particular is a standout due its potential ability to boost cardiovascular health and possibly even reduce cancer risk: Quercetin.
But what exactly is quercetin? And do you really need a pill to reap the benefits of the so-called plant-based powerhouse? Below, we dig into the research and consult with two registered dietitians and one certified nutrition specialist to find out.
What is quercetin?
“Quercetin is a flavonoid known for its antioxidant and anti-inflammatory health benefits,” explains Yasi Ansari, R.D.N., C.S.S.D., a registered dietitian in the Los Angeles and San Francisco areas. Numerous studies highlighted in research published in the journal Nutrients indicate that quercetin has anti-carcinogenic, anti-inflammatory and antiviral activities, says Josh Axe, D.N.M., C.N.S., D.C., founder of Ancient Nutrition.
“In fact, there isn’t much this powerful antioxidant compound can’t do, especially when combined with the health benefits of bromelain, an anti-inflammatory enzyme,” he states. Dr. Axe adds that while it’s possible to consume a substantial amount of quercetin in your diet, many people also opt to take a supplement “for even stronger anti-inflammatory effects.”
Uses of quercetin
According to the Icahn School of Medicine at Mount Sinai, quercetin may offer protection against heart disease and cancer. Furthermore, this compound could help stabilize the cells that release histamine in the body, creating an anti-inflammatory and antihistamine effect. Plus, quercetin might also slow down the aging process by reducing the effects oxidative stress (like chronic stress and anxiety, poor sleep habits, processed foods, pollution and exposure to chemicals) have on the body, explains Dr. Axe. “Overall, quercetin plays a role in regulating the immune system’s response to outside stressors through cell signaling pathways called kinases and phosphatases—two types of enzyme and membrane proteins needed for proper cellular function,” he says.
Potential health benefits of quercetin
Quercetin’s health benefits boil down to its ability to fight inflammation and its antioxidant properties, meaning it can neutralize damaging free radicals (a type of molecule in the body), which is a common precursor to several chronic diseases. Even though Dr. Axe adds that more studies on the power of quercetin supplements is needed since the majority of science focuses on quercetin-rich foods, here are some of the potential benefits of this antioxidant.
Inflammation
Research—which has mostly been done in animals and in labs—has suggested quercetin has both brain-protective and antidepressant effects and may reduce inflammation and oxidative stress, a condition in which free radicals cause damage to cells. “Studies now show us that inflammation is the root of most diseases, including heart disease, cancer, cognitive decline, some mental disorders and autoimmune disorders,” states Dr. Axe.
The findings from one study published in the Journal of Inflammation indicate that quercetin could become a remedy in treating life-threatening severe inflammation in COVID-19 patients.
Heart disease
Some studies show that quercetin may protect against the buildup of plaque in the arteries (also known as atherosclerosis), decreasing “bad” LDL levels, thus reducing risk of heart disease and high blood pressure, explains Ansari. Other research suggests that quercetin may help support people living with heart and blood vessel-related disorders, while a study published in the journal Mediators of Inflammation found it could be therapeutic in treating obesity and type 2 diabetes, says Dr. Axe.
“If you’ve ever heard that red wine is good for your heart, that’s because it’s a natural source of quercetin,” he states. “It’s one of the main active ingredients in red wine extract, which is associated with healthier heart function.”
Allergies
Quercetin has also shown some promise in relieving allergies as it stabilizes mast cells, which release histamine, says Robin Foroutan, R.D.N., an integrative medicine dietitian and spokesperson for the Academy of Nutrition and Dietetics. “Histamines are to blame for symptoms like seasonal allergies, so high doses of quercetin can be really helpful to reduce seasonal allergy and hay fever symptoms.”
While it may help reduce the severity of the symptoms, such as coughing, runny nose, watery eyes, hives and/or swollen lips and face, the evidence has not been conducted on humans, according to Mount Sinai.
Skin issues
Since quercetin may have an effect on mast cells that trigger allergic reactions, this compound has also been shown—like in research published in the journal PLoS One—to possibly play a role in protecting the skin from disorders, such as dermatitis and photosensitivity, states Dr. Axe.
“Flavonoids like quercetin block the release of many pro-inflammatory cytokines, which helps stop symptoms related to skin inflammation, even in people who don’t find relief from other conventional treatments or prescriptions,” he says.
Cancer
Some in vitro data (meaning the research was done outside of a living organism, like a culture dish) has even indicated that quercetin may help to decrease the formation of liver cancer cells and quantities of rectal tumors, explains Ansari. Mount Sinai reports that quercetin (along with other flavonoids) have been shown in animal and test tube studies to inhibit the growth of cancer cells from breast, colon, prostate, ovarian, endometrial, and lung tumors.
Dr. Axe points to a study published in the journal Oncology Reports, which found that quercetin may have chemo-preventive activity. “It might have a unique antiproliferative effect on cancerous cells, making it an effective addition to any natural cancer treatment approach.”
Unfortunately, though, there are few large-scale clinical studies in people and the ones that exist have shown varying effects of quercetin, according to the Memorial Sloan Kettering Cancer Center. Plus, it may even interfere with certain chemotherapy drugs because of its antioxidant properties.
“Although there is some level of decreased cancer incidence, there is no evidence that it is the activity of quercetin alone versus the combination of more than one antioxidant providing the health benefits,” says Ansari.
Foods high in quercetin
Some research indicates the quercetin found naturally in whole foods is more bioavailable to the body than capsule varieties. Certain studies suggest the quercetin from onions is more bioavailable than that from apples, for example, and that eating the antioxidant alongside heart-healthy fats can improve absorption, too.
However, more research in humans is needed to understand absorption from both supplementation and food. Ansari, favors a food-first approach.
“I think there is some evidence to suggest health benefits of quercetin supplementation for those suffering from high blood pressure and overall increased risk of chronic disease and inflammation,” says Ansari. “But it’s too early to tell as additional research is still needed on dosage, type and what to pair supplements with that would help increase absorption.”
Dr. Axe suggests placing more of these quercetin-rich foods on your plate:
Apples
Peppers
Red wine
Dark cherries and dark berries (like blueberries blackberries and bilberries
Raw, red onion
Olive oil
Capers
Parsley
Asparagus
Cruciferous vegetables
Leafy green vegetables
Citrus fruits
Black and green tea
Quercetin side effects and risks
As of now, there are no specific public health recommendations for quercetin intake, such as dietary reference intakes (DRIs) or daily value amounts (DV), from the Food and Drug Administration for the antioxidant, says Ansari.
According to Mount Sinai, quercetin is generally considered safe, yet pregnant and breastfeeding women and adults living with kidney disease should avoid taking this supplement. Typical side effects may include headache and upset stomach. Also, the integrated hospital system recommends taking periodical breaks from quercetin supplements since evidence suggests high doses may damage the kidneys.
Lastly, it’s important to know that quercetin supplements could interfere with prescription medications, including antibiotics, blood thinners, chemotherapy, corticosteroids and immunosuppressive drugs, as well as drugs that treat heart failure and liver conditions.
Disclaimer: Dietary supplements are products intended to supplement the diet. They are not medicines and are not intended to treat, diagnose, mitigate, prevent, or cure diseases. Be cautious about taking dietary supplements if you are pregnant or nursing and be sure to consult your doctor before taking new supplements (or providing them to a family member) in any situation, as they can interfere with medication.
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