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What You Should Know About Quercetin

Let’s talk about quercetin. Maybe you’ve heard it mentioned in discussions about cancer or COVID-19. This natural ingredient can help your overall health. But how much, exactly?

We talked to Bryan Kuhn, PharmD, a poison education specialist at Banner Poison & Drug Information Center, about what quercetin is, what it can treat and what it can’t treat. Like many natural ingredients, quercetin can be helpful but ultimately has its limits.

What is quercetin?

Quercetin is in a class of metabolites known as “flavonoids,” a natural ingredient that can be found in many different fruits, vegetables and plants. Here’s where you’ll find it:

  • Apples
  • Berries
  • Grapes
  • Onions
  • Shallots
  • Capers
  • Tomatoes
  • Honeys
  • Seeds
  • Nuts
  • Flowers
  • Barks
  • Leaves
  • Wines
  • Teas

Basically, if you consume a lot of organic foods that sprout from the earth, you’ll get a lot of quercetin. In countries like Spain, where the cuisine is heavy in fruits and vegetables, people have shown high daily intakes of quercetin. (Mediterranean diet, anyone?) Quercetin is also available in medicinal botanicals like ginkgo biloba, and as a dietary supplement.

How does quercetin work?

As a flavonoid, quercetin is also an antioxidant. And antioxidants like quercetin attack “free radicals,” or unstable atoms in your cells that cause illness and aging.

Ailments usually cause inflammation, and antioxidants can decrease this inflammation — but antioxidants by themselves don’t cure inflammation, Dr. Kuhn said. Ibuprofen can be just as (or more) effective in treating inflammation and have more predictable results.

“Antioxidants work in concert with many other elements of your diet, but antioxidants alone may not be as effective,” he explained. Quercetin and other antioxidants are simply part of a healthy diet.

According to the National Library of Medicine’s quercetin summary, “Extracts of quercetin have been used to treat or prevent diverse conditions including heart disease, hypercholesterolemia, rheumatic diseases, infections and cancer but have not been shown to be effective in clinical trials for any medical condition.”

Currently, there’s no data to support that higher dosages of quercetin (500-1000mg daily) will protect you any better than a healthy diet would. (And yes, there is such a thing as too many vitamins.)

Be careful, and be realistic

As with any supplement, consult your physician or pharmacist before taking quercetin supplements, Dr. Kuhn advised. These supplements can interact with your other medications or existing conditions, perhaps in ways you don’t expect.

Also note: Quercetin by itself doesn’t prevent coronavirus transmission or its serious side effects. One of COVID-19’s most dangerous side effects is severe inflammatory pneumonia, so excessive inflammation is a big risk factor. Because of this, substances that reduce inflammation can be helpful overall. While quercetin is becoming a subject of more COVID-19 research, there’s no evidence yet to confirm or even suggest that it aids in the prevention and treatment of COVID-19.

Finding help

If you have additional questions about taking quercetin or any other supplements, don’t hesitate to speak with your health care provider. To find a Banner Health specialist in your area, visit bannerhealth.com.

If you’d like to learn more about how antioxidants impact health, check out these helpful articles written with help from Banner Health experts.

COVID-19 Nutrition Wellness