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What Is Quercetin, and Can It Help Improve Athletic Performance?

Quercetin is an antioxidant tied to longevity, heart health, endurance, immunity, and more. Here's why you should add it to your diet.

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Have you ever wondered what makes a “superfood” super? Or what top superfoods like red wine, green tea, kale, and blueberries all have in common? The answer is quercetin, a natural compound tied to longevity, heart health, endurance, immunity, and more.

Considered one of the most abundant flavonoid antioxidants in the human diet, quercetin plays an important role in fighting free radical damage, the effects of aging, and inflammation, according to many studies. In fact, quercetin is considered to be the most widely distributed and extensively studied flavonoid, according to a 2018 review. Here are nine reasons to add quercetin-rich foods and supplements to your diet:

1. Lowers Inflammation

Flavonoids (aka bioflavonoids) including quercetin, are key anti-inflammatories that act as antioxidants, which means they fight the natural process of oxidation that takes place over time as we age. Quercetin can help stop damaging particles in the body known as free radicals, which negatively impact how cells work. It can also reduce expression of inflammatory genes such as interleukin.

Research now shows that inflammation is the root of most diseases, including heart disease, cancer, cognitive decline, some mental disorders, and autoimmune disorders. At this time, practitioners and patients report using quercetin to effectively fight a variety of conditions related to inflammation, including:

  • “Hardening of the arteries” (atherosclerosis)
  • High cholesterol
  • Heart disease and circulation problems
  • Insulin resistance and diabetes
  • Eye-related disorders, including cataracts
  • Allergies, asthma, and hay fever
  • Stomach ulcers
  • Cognitive impairment
  • Gout
  • Cancer
  • Viral infections
  • Chronic fatigue syndrome
  • Inflammation of the prostate, bladder, and ovaries
  • Chronic infections of the prostate
  • Skin disorders, including dermatitis and hives

Related: How to Reduce Inflammation Naturally

2. Fights Allergies

Some consider quercetin to be a natural antihistamine and an anti-inflammatory, possibly making it effective for lowering the effects of seasonal and food allergies, plus asthma and skin reactions. However, most research to date has been conducted on animals and not humans.

Histamines are chemicals that are released when the immune system detects an allergy or sensitivity. Quercetin can help stabilize their release from certain immune cells, which results in decreased symptoms such as coughs, watery eyes, runny noses, hives, swollen lips or tongue, and indigestion.

Quercetin has long been used in ancient Chinese herbal formulas to block allergies to certain foods (such as peanuts). Studies conducted on mice suggest that it may be as effective at fighting allergies as prescription medications, with little to no side effects.

3. Supports Heart Health

Because of its ability to lower inflammation and oxidative stress, quercetin seems to be beneficial for people with heart- and blood vessel-related disorders, according to a number of studies.

For example, eating lots of deeply colored fruits and veggies that contain flavonoids is linked to a lower risk of cardiovascular disease, and even death, in older adults. Quercetin has also been connected to reduced risk for type 2 diabetes and obesity, which have many of the same risk factors as heart disease.

Studies done on animals and some human populations show that various types of flavonoids (quercetin, resveratrol, and catechins, for example) can help reduce the risk of atherosclerosis, a buildup of plaque within the arteries that can reduce blood flow, one of the primary risk factors for heart attack and stroke. Some studies have also shown that people who eat the most flavonoid-rich foods typically have healthier and lower cholesterol levels, plus fewer incidences of hypertension and high blood pressure.

In fact, if you’ve ever heard that red wine is good for your heart, that’s because it’s a natural source of quercetin. It’s one of the main active ingredients in red wine extract, which is associated with healthier heart function.

4. Helps Fight Pain

Taking quercetin supplements may help lower pain associated with arthritis, as well as infections, including those of the prostate and respiratory tract. That’s because studies suggest quercetin reduces inflammatory pain. For example, there’s some evidence from several small studies that people experiencing bladder pains from infections (causing an urgent need to urinate, swelling, and burning) have fewer symptoms when taking quercetin supplements.

Flavonoids are also linked to reduced symptoms of prostatitis (inflammation of the prostate) and rheumatoid arthritis(RA). There’s evidence that when patients with RA switch from eating a “typical Western diet” to one higher in antioxidant-rich foods (like uncooked berries, fruits, vegetables, nuts, roots, seeds, and sprouts), they experience less pain and fewer recurring symptoms.

5. May Improve Energy and Endurance

Quercetin is added to some athletic supplements because it’s believed to help increase athletic performance and endurance, likely because of its positive effects on blood flow. Researchers from the School of Applied Physiology at the Georgia Institute of Technology found that, on average, “quercetin provides a statistically significant benefit in human endurance exercise capacity (VO2 max) and endurance exercise performance.”

Other studies show that quercetin helps increase immune function and prevents susceptibility to illnesses that can occur when someone trains intensely and experiences exhaustion. One study found evidence that taking a dosage of 500 mg of quercetin twice daily helped protect cyclers from exercise-induced respiratory infections.

Because it can boost energy, quercetin could affect sleep patterns. One study found evidence that it may alter the sleep-wake cycle partly through activation of GABA receptors. However, insomnia is generally not believed to be a common side effect of taking quercetin.

Related: The Fatigue Fix

6. Might Help Fight Cancer

A Boston University School of Medicine study published in the Journal of Biological Regulators and Homeostatic Agents shows a link between a nutrient-dense diet rich in quercetin and a lowered risk of cancer. Quercetin seems to have potential chemo-preventive activity and might have a unique antiproliferative effect on cancer cells, making it an effective addition to any natural treatment approach. Research shows that this may result from the modulation of either EGFR or estrogen-receptor pathways. Recent studies have also found that quercetin can help stop the processes involved in cell proliferation and mutation, the growth of tumors, and symptoms related to typical cancer treatments, such as radiation or chemotherapy.

At this time, the majority of studies done on quercetin’s effects on cellular functioning have involved animals, so more research is needed to reveal specific effects on human cancer cells.

7. Helps Protect Skin Health

Capable of blocking “mast cells,” which are immune cells critical in triggering allergic reactions, inflammatory disease, and autoimmune disease, quercetin can help protect skin from the effects of disorders like dermatitis and photosensitivity. Flavonoids like quercetin block the release of many proinflammatory cytokines, such as IL-8 and TNF, which helps stop symptoms related to skin inflammation, even in people who don’t find relief from other conventional treatments or prescriptions.

Studies have found that quercetin has antioxidant and anti-inflammatory effects that help fight allergic and inflammatory diseases as well as some prescriptions when taken in oral supplement form. For example, some people take quercetin for eczema since it can inhibit the secretion of histamine and pro-inflammatory markers.

8. Protects Liver Health

Recent research has shown that quercetin has protective effects when administered to rats with ethanol-induced acute liver injury. Researchers concluded that “quercetin, by multiple mechanisms interplay, demonstrates a hepatoprotective effect on liver injury induced by alcohol by increasing ethanol metabolizing enzyme activities, increasing antioxidant system activities against oxidative stress, and lowering the expressions of proinflammatory cytokines.”

A 2017 study found evidence indicating that quercetin attenuates liver inflammation and fibrosis in mice through inhibiting macrophages infiltration. Researchers believe it “holds promise as a potential therapeutic agent for human fibrotic liver disease,” a condition triggered by liver injury and inflammation.

9. Protects the Brain

There’s mounting evidence that quercetin offers neuroprotective benefits due to its ability to defend the brain against oxidation and inflammation, leading to potentially less risk for cognitive conditions such as Alzheimer’s disease and dementia.

A 2018 study concluded that “findings suggest a possible new protective role for dietary flavonoids on Alzheimer’s disease (AD).” The study found that quercetin helps ameliorate cognitive dysfunction and may help reduce the destruction of neurons.

Supplements and Dosage

Some of the most common forms of quercetin found in dietary supplements include quercetin 3, quercetin 3 glucoside, quercetin aglycone, isoquercetin, quercetin 7 rutinoside, and quercetin 3-O-rhamnoside. Some quercetin supplements are also labeled as quercetin dihydrate, which is mostly insoluble in water and may not be absorbed as well as other kinds.

There isn’t a daily recommended amount of quercetin intake, so dosage recommendations can vary depending on your health condition. Estimates show that most people typically get 5–40 mg of quercetin per day from eating common plant foods, but if you eat a nutrient-dense diet overall, you’re likely to take in as much as 500 mg daily according to some reports.

  • Optimal doses of quercetin haven’t been established by the FDA, so it’s up to you and your doctor to decide what amount works best for you.
  • Common oral dosages are 500 mg taken twice daily, but it’s also possible to experience benefits when taking lower doses.
  • Quercetin is often combined with other anti-inflammatory ingredients. For example, quercetin with bromelain (an enzyme found in pineapples) may be taken to help manage allergies.

Related: 7 Foods to Help Fight Seasonal Allergies

Side Effects, Risks, and Interactions

Because it’s derived from foods, quercetin poses few risks. Most studies have found little to no side effects in people eating diets high in quercetin or taking supplements short term. Amounts up to 500 mg taken twice daily for 12 weeks appear to be safe. If you plan to take it for longer, speak with your doctor first.

In very high doses, quercetin can produce side effects such as headaches and tingling of the arms and legs. It’s also possible that quercetin can impact the effectiveness of chemotherapy, antibiotics, and blood-thinners, so use caution if you currently take any of these.

Food Sources of Quercetin