Quercetin: The Hidden Power in Your Pantry

by Erica Stephanopoulos, MPH, MBA
October 23, 2020

With the COVID-19 virus still a top headline in the news, most people are impatiently awaiting a cure, looking for preventative measures to avoid getting sick, and searching for possible treatments for symptoms from pharmacies and doctors alike. On top of this, cold and allergy season is just around the corner, which carries its own threat of infection and hospitalization rates. Thankfully, researchers and medical experts have been busy unpacking (and putting to use) some natural solutions. One treatment that is being explored is the healing properties of a compound called Quercetin, which can be found in many foods in your pantry.

red onions are a great source of quercetin

What is Quercetin?

Before we dive into how Quercetin can help you fight off infections, let’s look at what it is and how it is found naturally in our everyday environments. Quercetin is a plant pigment or flavonoid generally found in a variety of different foods and plants. It’s also used widely in traditional Chinese and botanical medicine. 


Flavonoids, in general, are phytonutrients found in plants and other compounds that give fruits and vegetables their vibrant colors. As polyphenols, flavonoids like Quercetin also have properties that support our health in various ways.

Where is Quercetin found naturally?

To find a natural source of Quercetin, all you need to do is turn to the produce aisle. Quercetin is in many fruits, vegetables, seeds, nuts, and medicinal plants. Here is a list of some common foods containing Quercetin:

  • Fruits: apples, kiwis, citrus fruits, berries, grapes, tomatoes
  • Vegetables: asparagus, green pepper, lettuce, potatoes, celery, eggplant, onions, shallots, cruciferous vegetables (like broccoli, cabbage, kale, etc.)
  • Legumes: beans
  • Medicinal plants: St. John’s wort, Elderflower, and Ginkgo biloba
  • Other sources: Nuts, seeds, beans, and honey

Onions are particularly rich in Quercetin. In fact, one of the highest concentrations of Quercetin is found in the onion’s outermost skin, closest to the root. This is why many medicinal supplements are made from onion skin powder. There is also evidence that organic fruits and vegetables may contain higher concentrations of Quercetin. This 2016 study showed that organic tomatoes contained as much as 79% greater amounts of Quercetin versus non-organic tomatoes.

How does Quercetin work?

As an antioxidant, Quercetin binds to free radicals and neutralizes them to reduce oxidative stress and inflammation in the body. In this way, Quercetin has antioxidant and anti-inflammatory effects which could potentially help reduce inflammation, kill cancer cells, control blood sugar, help fight infections, reduce sinus inflammation, help prevent heart disease and much more.

Can Quercetin help with respiratory inflammation?

Quercetin has promising antiviral and anti-inflammatory properties, which researchers are finding may be useful in helping treat early and late pulmonary phases of COVID-19 symptoms. Research into this topic (like many treatments) is in its early stage, but a few research studies investigating Quercetin have been reported. The studies find that the compound may have the ability to:

  • Act as a long-lasting anti-inflammatory substance that possesses strong anti-inflammatory capacities.
  • Exert antiviral effects on the novel coronavirus by inhibiting a protease’s function called 3CLpro in SARS-CoV-2, the virus that causes COVID-19.
  • Block entry of the virus into host cells, which could play a key role in both the prevention and treatment of COVID-19.

Due to this preliminary research, some healthcare providers are using Quercetin as part of their medical treatment protocol for COVID-19 patients. Medical protocols from Eastern Virginia Medical School recommend that antiviral drug therapy with Quercetin begin at the Early Pulmonary Phase (after both disease incubation and symptomatic phases), and to escalate this treatment in the Late Pulmonary Phase).

How does Quercetin help with allergies?

Quercetin has shown to play a significant role in managing allergies. Clinical studies show that Quercetin prevents immune cells from releasing histamines, the chemicals that cause allergic reactions.

Because of this, Quercetin is the key ingredient in one of our top allergy-relief products, Aller-Aid. This 100% natural supplement can help you find relief from allergy symptoms without the side effects your get from over-the-counter medicines such as drowsiness, dry mouth and more.

Should you take a supplement with Quercetin?

As we highlighted earlier, there are many reasons people take Quercetin supplements. The anti-inflammatory and immune-boosting properties of the flavonoid alone are two great reasons. Quercetin also offers some other health benefits. Research indicates that Quercetin may help:

  • Improve mental performance
  • Reduce the risk of cancer
  • Reduce inflammation
  • Reduce viruses’ ability to replicate (antiviral)
  • Reduce lipid peroxidation and blood clotting
  • Reduce capillary permeability
  • Improve mental and physical performance
  • Reduce one’s risk for infections

Furthermore, clinical studies show that Quercetin may potentially reduce blood pressure, reduce the risk for cardiovascular disease and help combat diabetes.


With this list of health benefits, it’s no wonder that scientists are looking for a connection with Quercetin and how it can help our bodies fight off illnesses in this season. However, before beginning any new treatment regimens, you should check with your doctor to find the best treatment for you.

How much Quercetin should you consume?

Access to and global consumption of foods rich in Quercetin varies widely throughout the world. In the US, the average adult consumes about 10 mg of Quercetin daily from food sources. But we also know that on average, across the globe, of the flavonoids ingested from food consumption, 75% is Quercetin. Fruits, vegetables, and tea are typically the biggest players when it comes to people consuming Quercetin naturally.


As for how much Quercetin you should aim to consume daily, the optimal amount of Quercetin has not been determined and various studies show different impacts. For example, one scientific study identified 162 mg/day as a “supra-nutritional” dose. While other medical practitioners have suggested that short-term “medicinal” doses could be as much as 500 mg twice daily.

Does Quercetin have any side effects?

When Quercetin is consumed naturally through food, various sources agree that there is no evidence of side effects. However, when Quercetin is taken as a medicinal supplement, there may be some mild side effects such as headache, stomachache, or tingling of the arms and legs. The risk of more serious side effects from higher dosage Quercetin supplements is undetermined.


Some sources say there are no serious side effects from Quercetin. Other sources say that if high doses (500-1000 mg/day) are taken for longer than 12 weeks, there may be a risk of kidney damage and suggest that those who are pregnant or breastfeeding do not take Quercetin supplements. Further, these sources suggest that Quercetin may interact with, alter the effects of, or increase the risk of side effects if taken along with antibiotics, cyclosporine, warfarin, or other drugs that affect or rely on liver function.

Final Thoughts on Quercetin

Quercetin shows promise to treat a host of inflammatory conditions including allergies. Most recently, it has been used on the front lines of the COVID-19 pandemic. However, you should talk to your doctor before beginning any new treatment regimens.

Erica Stephanopoulos, MPH, MBA
Erica Stephanopoulos, MPH, MBA

Erica has a longstanding passion and involvement with healthcare philanthropy and global health, specifically looking at how malnutrition and lack of key nutrients relate to infectious disease. She’s helped establish clinics and research projects across the globe in her work with Stanford Research Institute, Airbel Impact Lab, World Pediatric Project, and the International Rescue Committee. She’s also written for numerous publications to help educate others on the importance of nutrition and their overall health. Before setting out to make her mark on the world, Erica studied Biochemistry and International Relations. Just to shake things up, she then went on to get her Masters in Public Health and M.B.A. When she isn’t working, she is an avid runner, reader, and (very) amateur chef.

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