Quercetin: What It Is, How Much You Need, and Where to Find It

Medically Reviewed
Quercetin Supplement
You can find quercetin in whole foods, but this antioxidant is also available as a supplement, which may provide certain health benefits.Eugeniusz Dudzin?ski/Adobe Stock

With the increased popular interest in fighting inflammation and preventing disease, you may be wondering how diet and supplementation can help you.

Quercetin — found in many foods and in supplement form — is an antioxidant that has recently garnered attention for these reasons.

“This antioxidant supports healthy cellular function, cardiovascular health, and circulation, and encourages a healthy immune response by neutralizing free radicals,” says Jessica Cho, MD, the founder of Wellness at Century City, her personal practice in Los Angeles. “Quercetin?may be beneficial for a wide range of conditions, including allergies, hay fever, asthma, heart disease, high cholesterol, hypertension, cancer, and inflammatory disorders, such as rheumatoid arthritis, interstitial cystitis, and prostatitis.”

While it’s generally best to get antioxidants from plant-based foods to combat inflammation and related diseases, you may be wondering if you would benefit from quercetin supplementation. Here, we ask the experts about quercetin and break down the latest research.

What Is Quercetin, and Why Do I Need It?

Quercetin is a type of flavonoid, or plant pigment, found in antioxidant-rich foods such as berries, apples, and green tea. Like other flavonoids, quercetin is rich in antioxidants and may have anti-inflammatory properties.

In this regard, antioxidants like quercetin may help to “clear dangerous free radicals from the body, which prevents the buildup of chronic inflammation,” says Natalie Rizzo, RD, of New York City, the founder of Greenletes. “Chronic inflammation is related to the development of serious diseases; therefore, it’s important to reduce inflammation in the body.”

Those diseases include cancer, heart disease, and diabetes.

While you can gain the potential anti-inflammatory benefits of this flavonoid via food, quercetin is also available in supplement form.

“Supplementing with quercetin might be warranted for someone who is trying to support their immune system, manage symptoms of allergies, or looking to optimize musculoskeletal recovery,” says?Bethany Tennant, ND, the founder of Natural Sports Medicine?in Portland, Oregon, which provides health advice and sells food, supplements, and beauty products.

While someone may observe those effects of quercetin supplements, strong scientific research doesn’t support many of the purported uses for quercetin supplements.

Common Questions & Answers

Who should (and should not) take quercetin?

You may consider taking quercetin supplements for fighting inflammation, ideally if your doctor or registered dietitian recommends them. You should not take quercetin if you’re pregnant or breastfeeding, or if you have kidney problems. Several prescription drugs and herbs may also interact with quercetin supplements.

What is the difference between quercetin and CoQ10?

Coenzyme Q10 (CoQ10) is an antioxidant that may help complement treatments for heart disease, high cholesterol, and diabetes. Unlike quercetin, CoQ10 is found naturally in your body, though the amounts decrease with age. It’s also found in different food sources: mainly nuts, meats, and fish.

How can quercetin affect immunity?

Quercetin has antioxidant effects. Through a chemical process, antioxidants neutralize free radicals in the body that may damage healthy cells. While antioxidants help your immune system fight harmful intruders, it’s not clear whether supplements can offer the same effects as those in your diet.

Which foods contain the most quercetin?

Quercetin is primarily found in fruits and vegetables. The best sources are berries, apples, and cherries, as well as red leaf lettuce, onions, and asparagus. Quercetin is also found in broccoli, green peppers, peas, and tomatoes, but at lower levels.

Is it safe to take quercetin every day?

Daily quercetin 1 gram (g) supplements have been proven safe in most people, but only when used on a short-term basis of up to 12 weeks. In some cases, your doctor may recommend you take these supplements for longer if they’re being used to treat a medical condition.

Uses of Quercetin

Quercetin is primarily used in the treatment of blood vessel and heart conditions, as well as for potential cancer prevention. Other possible uses include reducing inflammation caused by infections, arthritis, and high-intensity workouts. Another purported use is to control blood sugar in diabetes, but there’s not enough evidence in human studies to support its efficacy in all these conditions.

Due to the COVID-19 pandemic, people increasingly looked for ways in addition to diet and exercise to support their immune systems. While quercetin has potential anti-inflammatory effects, there’s currently no evidence that these supplements are suitable for preventing or treating COVID-19 infections.

Potential Health Benefits of Quercetin

Quercetin promotes antioxidant activity in the body, thereby reducing chronic inflammation that may contribute to a variety of ailments and diseases. Antioxidants, in general, may reduce your risk of heart disease, cancers, and diabetes.

Below are some of the potential benefits associated with quercetin, along with some of the limitations of the current research.

May help prevent heart disease?“Quercetin is a potent anti-inflammatory and antioxidant which can be cardioprotective,” says Dr. Tennant. “Research shows this flavonoid can protect against atherosclerosis, oxidative stress, endothelial cell dysfunction, and more.” Dr. Cho says quercetin may have cardioprotective effects, which “can also reduce oxidative and inflammatory damage and prevent atherosclerosis" (plaque buildup in arteries that can lead to heart attack or stroke).

One review of in vivo studies backs up these cardioprotective claims, suggesting that quercetin may help prevent heart disease.

Additionally, research suggests quercetin may have anti-hypertensive actions, reducing your risk of high blood pressure.

May help lower your blood sugar?A different review notes that flavonoids like quercetin may promote better blood sugar management in the body. At the same time, experts have not yet determined that quercetin is safe for diabetes management, because of a lack of human studies.

“Although the efficacy of quercetin in human diabetic patients is yet to be explored more, recent data has shown that quercetin is a strong potential therapy for diabetes because it modulates whole-body glucose levels by acting on many targets in the small intestine, pancreas, skeletal muscle, adipose tissue, and liver,” says Cho. “For diabetic patients, quercetin may enhance insulin function and improve glucose metabolism.”

May help prevent cancer Another review suggests quercetin may work by decreasing the loss of cell viability that could contribute to a variety of cancers, in vivo research suggests.

That said, human studies are lacking.
May help alleviate allergies?“Quercetin is a bioflavonoid found in onions, apples, black tea, and grapefruit that is a mast cell stabilizer, making it a great natural option for allergy support,” Tennant says. While the National Center for Complementary and Integrative Health doesn’t yet recommend quercetin for treating allergic rhinitis associated with seasonal allergies,

emerging research does support quercetin as having “anti-allergic” capabilities, such as reducing inflammation and inhibiting histamine production associated with allergies and allergic asthma.

May promote exercise recovery but not performance?“Recent research has shown that quercetin supplementation can improve recovery following eccentric exercise-induced muscle damage,” says Tennant. A small randomized controlled trial of 16 men in their twenties involving quercetin supplementation versus placebo for 14 days found improved muscle recovery after repeated intense exercise, and a reduction in exercise-induced weakness.

“Data shows that quercetin leads to an increase in plasma levels of the anabolic factors IGF-I and IGF-II,” explains Cho. This could help reduce injuries while promoting muscle recovery. That said, more studies are needed before quercetin can be recommended widely for this purpose.
The benefits of quercetin for exercise and athletic performance aren’t proven, either.

Furthermore, no evidence backs quercetin as a safe or effective body-building supplement.

May have neuroprotective effects?The antioxidant and anti-inflammatory mechanisms of quercetin have also led researchers to investigate its possible neuroprotective effects in in vivo animal and human studies. It’s thought that quercetin may play such a role because of its ability to counteract oxidative stress that may damage brain cells.

In turn, this may reduce the risk of developing types of dementia, including Alzheimer’s disease.

Foods With Quercetin

Quercetin is considered one of the most widely available flavonoids in the Western diet.

It’s found in a variety of fruits, vegetables, and other plant sources, such as:

  • Apples
  • Asparagus
  • Berries
  • Broccoli
  • Cherries
  • Green peppers
  • Onions
  • Peas
  • Red leaf lettuce
  • Tomatoes
A nutritious diet full of fruits and vegetables like these provides an average of 13 milligrams (mg) of quercetin per day.

National Institutes of Health Office of Dietary Supplements

For most people, a healthy diet full of foods high in quercetin is sufficient.

“Since the research on quercetin is limited and you get many other nutrients from the foods, like other antioxidants, fiber, vitamins, and minerals, I recommend eating a quercetin-rich food rather than using the supplement,” Rizzo says.

Take quercetin supplements only if your doctor or licensed nutritionist or health practitioner recommends them. These supplements may interact with other supplements, as well as certain herbs and medications, so check with your primary doctor before adding it to your health and wellness routine.

How Much Quercetin Should I Consume?

If your doctor thinks you might benefit from quercetin supplements, it’s important to follow the recommended dosage. Most often, quercetin supplements are taken in 250 to 1,000 mg doses. In some adults, 1 gram (g) daily doses may be safely used. The supplements are taken daily by mouth for up to 12 weeks at a time.

For therapeutic uses of quercetin, Tennant recommends using it more conservatively than the aforementioned recommendation: 500 mg, one to two times daily, and to talk with your doctor if you want to use quercetin supplements for longer than four weeks. “Safety in high doses for longer periods of time has not yet been determined,” she says.

Side Effects and Safety of Quercetin

While quercetin supplements may be recommended for some people, there are also potential risks to consider.

First, don’t take quercetin supplements if you currently have kidney problems, as these can worsen kidney disease.

If you have estrogen-dependent cancer, quercetin supplements could also promote tumor development, and should thus be avoided.

Also, while studies haven’t shown any adverse effects in athletes taking up to 1,000 mg quercetin per day for up to eight weeks, the National Institutes of Health cautions that there isn’t enough clinical evidence to say these supplements are entirely safe at this amount or length of time.

It’s unknown whether quercetin is safe for pregnant or lactating women. For this reason, you may consider avoiding quercetin supplements unless otherwise recommended by your doctor.

Quercetin Supplement and Drug Interactions

While quercetin isn’t known to interact with any foods, these supplements may make certain medications less effective.

There are several supplement and drug interactions to be aware of, including the following:

  • Anti-diabetes medications, which can cause sharp drops in blood sugar levels
  • Anti-hypertensive drugs, which can lead to low blood pressure
  • Cyclosporine
  • Diclofenac, a topical and oral medication used in the treatment of arthritis
  • Herbs or supplements that lower your blood sugar, such as chromium
  • Herbs or supplements that lower your blood pressure, such as L-arginine and niacin
  • Midazolam
  • Pravastatin
  • Quinolone antibiotics
  • Quetiapine
  • Warfarin

Summary

Quercetin is an antioxidant common in several plant foods that has anti-inflammatory effects on the body. “I would recommend eating a whole-food, plant-forward diet to reduce inflammation,” says Rizzo. “Antioxidants, like quercetin, are abundant in plant foods, so eating a variety of fruits and vegetables every day will help keep inflammation at bay.”

While it’s ideal to eat quercetin-containing foods first, your doctor may recommend supplements if your condition warrants them.

At the same time, taking quercetin supplements isn’t the only way to reduce disease-causing inflammation in the body. Tennant also recommends focusing on other inflammation-fighting strategies, such as stress management. “As always, finding a root cause of inflammation is key, such as addressing toxic burden from environmental exposures, mold, stealth infections, or chronic stress,” she says.

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