Quercetin: Health Benefits, Sources, Supplements, and Doses

Quercetin is one of the plant world’s most potent polyphenols. Polyphenols are nutrients known to protect the body from stress and help to manage inflammation. Quercetin, specifically, can offer health benefits including protection for the brain, improved body composition, enhanced exercise recovery, and more.

Below is what we feel is helpful to understand about quercetin and more about the health advantages it can provide.

What Is Quercetin?

Quercetin is a flavonoid, which is a sub-group of polyphenols. More than 6,000 flavonoids exist in plants to protect them from stressors, radiation, infection, temperature changes, and drought. Quercetin is one of the polyphenols that can have the most significant impact on human health.

Unlike vitamins and minerals, there are no recommended dietary intake levels for polyphenols. You don’t develop deficiency symptoms or diseases by not consuming them, but you do derive certain health benefits if you choose to.

Quercetin is the compound that gives some plants a deep, vibrant color. Though you won’t consume therapeutic levels from food alone, you will find quercetin in many plant-based foods.

Food Sources of Quercetin
Apples	Black and green tea
Blueberries	Broccoli
Buckwheat	Capers
Curly kale	Cherries
Chokeberries	Cilantro
Citrus fruits	Cranberries
Dill	Grapes
Leeks	Lingonberries
Lovage	Onions
Red wine	Strawberries
Tomatoes

Though each of the foods above contain quercetin, the way the plants are grown affects their concentration when harvested. Once the plants are harvested or picked, their levels of quercetin change as well.

For example, onions lose one-third of their quercetin concentration within 12 days of storage. On the other hand, strawberries increase their concentration if stored below -20 degrees C (-4 degrees F) for nine months. This point merely demonstrates that relying on food alone makes it difficult to consume a high dose of quercetin consistently.

Health Benefits of Quercetin

The effects of quercetin are impressive. However, we do always like to remind that before delving into more targeted supplements like quercetin, it’s important to start with foundational healthy habits — such consuming a higher-protein diet, sleeping at least seven hours every night, and strength training at least four days per week — as well as with foundational supplementation.

1. Reduction in Allergies and Asthma

Quercetin inhibits the release of histamine, which makes it a powerful supplement to support symptoms of asthma and bronchitis. It is also often recommended to lessen symptoms of seasonal allergies.

2. Antioxidant Support

Free radical production is a natural part of life. Intense exercise, environmental toxins, smoking, stress, and poor nutrition accelerate free radical production.

Antioxidants squelch free radicals before they can cause widespread damage to your cells. Quercetin seems be one of the most potent diet- or supplement-based sources of antioxidants.

“Quercetin is a more potent antioxidant than other antioxidant nutrients, such as vitamin C, vitamin E, and beta-carotene, and it can chelate transition metal ions, including iron.”

Dong YS, et al.

Research shows it protects cells from some of the damage of cigarette smoking, though that doesn’t negate other problems related to it.

3. Supports Normal Inflammation Levels

Quercetin modulates inflammation.

Quercetin inhibits inflammatory enzymes cyclooxygenase (COX) and lipooxygenase, thereby decreasing inflammatory mediators such as prostaglandins and leukotrienes.

David AVA, et al.

Chronic inflammation increases the risk of cardiovascular disease, neurodegenerative disease, and autoimmune disease. It also interferes with recovery from exercise.

Inflammation may also make your cells more vulnerable to infection, so minimizing systemic inflammation can impact the strength of your immune system.

4. Supports Healthy Blood Pressure

High blood pressure is a known risk factor for cardiovascular disease. It’s also a risk factor for severe virus infections, such as COVID.

Research has shown that supplementation with quercetin at doses as low as 150 mg per day may reduce blood pressure. If blood pressure is kept in check, it reduces potential damage to vessel walls that contribute to heart disease.

5. Protects Cognitive Function

Animal research shows the combination of quercetin and fish oil can protect the brain from oxidative stress. Oxidative stress is a known contributor to neurodegenerative diseases such as Alzheimer’s or Parkinson’s disease.

Though this is far from a cure for these diseases, it may help to slow their progression.

6. Protects Skin

Like the impact on inflammation inside your body, quercetin may support normal inflammation outside as well. Research shows it can improve signs of inflammation in damaged skin.

It may also maintain skin health through its antioxidant effects, which can slow the aging of the skin.

7. Supports Immune Function

Animals taking quercetin and exposed to a rhinovirus were shown to have a lower viral load than those who did not take it. The research shows that the use of quercetin before viral exposure could lessen infection, and during infection, could lessen symptoms.

One mechanism through which quercetin combats viruses is with zinc. It may transport zinc to infected cells, which allows zinc to disrupt the virus’ ability to transcribe RNA, preventing it from duplicating.

Quercetin inhibits viral infection at multiple stages, including endocytosis, transcription of the viral genome and viral protein synthesis.

Ganesan S, et al.

Cell studies also show quercetin slowed the replication of the hepatitis B virus. It may also have a positive effect on respiratory viruses and Japanese encephalitis. It may also enhance resistance to MERS-coronavirus, and there’s now evidence that quercetin supplementation significantly improves illness severity and viral clearance in SARS-CoV-2 patients.

In addition to viruses, it also supports the immune system in fighting bacterial infections. Quercetin also combats pathogenic bacteria on the skin and in the digestive, respiratory, and urinary systems.

Human studies show that quercetin in addition to a healthy diet my reduce total sick days and upper respiratory tract infection severity. Interestingly, quercetin’s immune support is most consistent in people who exercise regularly.

8. Weight Loss and Improved Body Composition

Animal research shows quercetin may prevent body fat gain when eating a higher calorie, weight-gaining diet. In the research, animals were fed a high-fat diet — quercetin raised their metabolic rate, which may have offset the effects of the high-fat diet.

In overweight and obese humans, supplementation with 100 mg per day of quercetin over 12 weeks reduced body fat percentage and body mass index. In another study using 150 mg per day, people experienced a reduction in waist circumference and triglyceride levels.

9. May Combat Cancer Development

Being that quercetin is a food or supplement and not a pharmaceutical, it doesn’t treat cancer. It can, however, help slow the progression of certain cancers.

As an antioxidant, it combats free radicals, which can trigger cancer progression. In addition, quercetin helps induce apoptosis, the programmed death of faulty (i.e., cancerous) cells and affects cell signaling in other ways. 

10. Enhances Exercise Performance

Based on its effect on immune function, quercetin could support athletic performance by reducing the chance of an athlete getting sick and missing training days. Even mild symptoms of this nature could compromise training for a while.

It may also directly enhance training results through its effects on inflammation and antioxidant function.

Research shows direct antioxidants, such as vitamins C and E, can reduce exercise performance by limiting the function of the body’s own antioxidant system. Quercetin and other polyphenols are more indirect antioxidants, boosting the body’s internal antioxidant function.

Reduced oxidative stress can improve recovery between training sessions, leading to faster improvements in performance. 

Bioavailability, Supplements, and Dosages

Standard quercetin, whether from food or supplements, is not absorbed well by the body. That’s not to say eating fruits and vegetables won’t help, but to get efficacious amounts of quercetin into the bloodstream, we recommend using a supplement form designed to enhance absorption.

Though some studies show benefits at doses as low as 100 mg per day, most recommend a standard dose of quercetin of 1,000 mg, or 1 gram per day. That’s a pretty high dose.

Fortunately, a delivery technology called a phytosome enhances absorption of quercetin by up to fivefold. To create the quercetin phytosome, quercetin is wrapped in a fatty acid shell. Fatty acids freely pass from the digestive system into your circulation. As a result, a dose of 250 mg of quercetin wrapped in a phytosome is the equivalent of 1,000 to 1,250 mg of standard quercetin.

As with all supplementation, consult with your healthcare provider before adding anything new to your routine. If you’re considering supplementing with quercetin, the one we recommend and sell at Life Time is Thorne Quercetin Phytosome.