Flavonoid Friday: A Guide to Quercetin Health Benefits, Foods, and Effects

Flavonoid Friday: A Guide to Quercetin Health Benefits, Foods, and Effects

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So many aspects of life can impact your immune system, from lack of sleep to stress to junk food. And even when you prioritize healthy habits, you might find it difficult to incorporate every vitamin you need into your daily diet.

If you’re like most, you probably can’t begin to fathom the countless nutrients your body craves to help it maintain balance. For instance, did you know about the immune-boosting abilities of the flavonoid, quercetin?

Let’s take a look at what this super flavonoid can do for you!

What is Quercetin?

Quercetin is a flavonoid found in cannabis as well as fruits and vegetables, chocolate, red wine, and olive oil, to name a few. Also referred to as vitamin P, flavonoids like quercetin are responsible for various flavors and colors in plants. To date, scientists have identified over 5000 flavonoids, which they attribute to significant health benefits.

Quercetin, in particular, is garnering extra attention for its potent anti-inflammatory and immune-boosting powers. But that’s just one beneficial aspect of this super flavonoid. There’s so much you’ll want to explore.

Antioxidant Properties of Quercetin

Quercetin is a polyphenol, which is a term that describes the molecular structure of the compound. Its structure allows it to donate an electron or hydrogen atom to neutralize free radicals, which are unstable molecules in the body that can damage cells and cause illness and aging. This process is known as “antioxidant” activity and is why polyphenols like quercetin are popular dietary supplements.

Quercetin Effects on Inflammation and Immune Function

Free radical generating substances like sugar and alcohol can exist in the food we eat, the air we breathe, and the substances we take–leading to inflammation. But antioxidants help hunt down and neutralize disease-producing free radicals. And as a flavonoid antioxidant, quercetin can play a significant role in your wellness regime.

  • One study published in the American College of Nutrition Journal looked at 50 women with rheumatoid arthritis. The researchers found that 500 mg of quercetin each day over eight weeks helped reduce stiffness and pain.
  • Another study published in the European Journal of Clinical Nutrition found that taking 500 mg of quercetin a day can help lower the inflammatory biomarker c-reactive protein (CRP) levels, which becomes elevated in conditions like diabetes, heart disease, and rheumatoid arthritis.

Quercetin also seems to act as an immune modulator and can prevent viral entry into cells and inhibit viral replication. It can treat and prevent many viral infections, including the common cold, flu, and upper respiratory tract infections.

  • A study published in the Journal of Clinical & Experimental Cardiology found that 1000 mg of quercetin a day can help reduce upper respiratory tract infections after intense exercise in the winter. Quercetin can also act synergistically with other immune-boosting nutrients like zinc to help mitigate viral replication.
  • The Front Line Covid-19 Critical Care Alliance group recently published a Covid-19 prevention and treatment protocol that consists of at least 250 mg per day. The Alliance notes that quercetin’s virucidal properties against various viruses, including SARS-CoV-2 as well as its antioxidant and anti-inflammatory powers, is a crucial aspect of why it's so effective. Moreover, quercetin binds zinc and synergizes with vitamin C to enhance its overall benefits.

What Foods are High in Quercetin?

Quercetin and Apples

Apples contain several different valuable phytochemicals like quercetin, along with a beneficial fiber called pectin. To reap the benefits of quercetin from apples, eat them unpeeled. And keep in mind that apple juice doesn’t provide the same benefits as the whole fruit.  

Quercetin and Chocolate

You may have heard that dark chocolate contains powerful antioxidants. The free-radical-fighting power of this delicious treat comes in the form of flavanols and two types of flavonoids -- one of which is quercetin.

Quercetin and Onions

All varieties of onions contain quercetin, but since quercetin is a pigment, colorful onions like red and yellow varieties have the most. To maximize the quercetin, remove as few of the outer layers as possible.

Quercetin and Cannabis

While flavonoids exist in a variety of fruits and vegetables, you can also get them from cannabis. The deep purple cannabis strains owe their coloring to antioxidant flavonoids like kaempferol and quercetin.

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What is the Best Form of Quercetin?

Because quercetin occurs naturally in so many healthy foods, it is estimated to account for 75% of our flavonoid intake. And the best way to increase your quercetin intake is to eat more of these foods.

Quercetin amounts in milligrams per 100-gram serving:

  • Lovage leaves: 170 mg
  • Capers: 180 mg
  • Red onions: 32 mg
  • Buckwheat: 23 mg
  • Apples: 4 mg
  • Blueberries: 3 mg
  • Red Grapes: 3.5 mg
  • Black tea: 2 mg

If you commit to eating many foods that contain quercetin, you will easily consume around 100 to 300 mg of quercetin daily. But most clinical studies show results with a dose of 500 to 1000 mg a day, so if you are looking to use quercetin to support immunity or help fight allergies, you may want to add a supplement to your quercetin-filled diet.

How the Body Processes Quercetin

While studies can confirm the powerful health benefits of quercetin, science is still working to understand how well it absorbs in the body. One study showed the bioavailability of quercetin in humans at around 45%, while another reported it from 0 to 50%. Outside of the laboratory in nature, most flavonoids occur in plants as glycosides.

This means they bind to a sugar molecule, making them more water-soluble and more easily absorbed.

While quercetin’s exact absorption rate is unclear, we know the body metabolizes it in the small intestine, colon, and liver. Once absorbed, human gut enzymes begin to break the bond between quercetin and the attached sugar. But the majority of quercetin continues through the GI tract to the colon, where microbiota converts it in various ways that affect human health.

How Often Should I Take Quercetin?

The most common oral dose of quercetin is 500 mg twice a day. But people have achieved good results with smaller amounts as well. Keep in mind that there are no established optimal doses of quercetin for any specific condition.

Quercetin is generally considered safe, and a 2017 review paper showed that participants rarely reported adverse side effects using servings up to 1000 mg per day.

Bottom Line

Quercetin is an antioxidant that has proven beneficial for overall wellness because it supports immunity, prevents viral entry, and acts as an anti-inflammatory. It is also one of the most versatile flavonoids found in the cannabis plant. You can get quercetin in an array of food sources that also contain various other beneficial nutrients.

However, if you want to help manage a specific issue, you may need to supplement with 500 to 1000 mg per day. But keep in mind, as with any supplement, it’s essential to check with your doctor about questions or concerns.

At ACS Laboratory we test for 16 flavonoids including Quercetin. Because we are a CLIA licensed laboratory, we can also do human trials (research studies) aka PK studies (Pharmacokinetic Studies) aka bioavailability studies. Research studies on bioavailability are an integral part of the pharmacokinetics paradigm.

Pharmacokinetics is the study of drug movement through the body. These studies allow us to draw conclusions that are based on actual, not anecdotal research.