Quercetin: Health Benefits, Food Sources, Dosages, and Contraindications

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Quercetin has quickly become one of the hottest-selling nutritional supplements in recent history. And rightfully so. It’s a potent immune-supporting compound.

However, quercetin offers more health benefits than immune-support alone. Find out why this flavonoid is so fabulous.

What is quercetin?

Quercetin is one of more than 4000 types of flavonoids found in plants. Flavonoids include many subcategories you’ve probably heard of but given little thought to:

• flavones
• isoflavones
• flavanones
• chalcones 

Plants produce polyphenols as a defense against radiation and pathogens. When we eat or consume them, they play protective roles in our bodies too.

The average person consumes about 14 mg of quercetin per day through their diet. It’s found in a variety of plant foods, as shown in the table below.

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

Quercetin Health Benefits

Though quercetin offers numerous health benefits, once consumed, we don’t absorb it very well. To derive the benefits I discuss here, you either need to eat loads of quercetin-containing foods or supplement with quercetin liposomes or phytosome, specific types of supplements designed to maximize absorption.

Liposomes and phytosome surround quercetin in a lipid shell. Lipids pass from the digestive system into your circulation easily, so quercetin liposome and phytosome have much greater bioavailability than plain quercetin.

Research shows quercetin phytosome increases blood levels by 20 times compared to plain non-phytosome versions of the supplement.

Antioxidant support

Free radicals are 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 to be one of the most potent antioxidants.

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

Dong YS, et al.

Research shows quercetin protects cells from some of the damage of cigarette smoking, though that doesn’t negate the problems smoking causes. It might be helpful if you spend a lot of time in front of bonfires or campfires, too.

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

Body composition improvement

Animal research shows quercetin may prevent body fat gain when eating a higher-calorie, weight-gaining diet. In the study, animals ate a high-fat, high-calorie diet and took the supplement and showed an increase in their metabolic rates. The elevated metabolic rate may have offset the effects of the high-fat diet as they did not gain body fat.

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.

Cardiovascular health

People with hypertension and with the ApoE3 gene took 150 mg per day of quercetin for six weeks. Their blood pressure decreased by 3.4 mmHg. That might not seem like a lot, but each 1 mmHg decrease is equal to a 2-3% reduction in cardiovascular disease risk on a population level.

Endothelial cells line your blood vessels. When they become dysfunctional, the vessels don’t relax and contract like they’re supposed to. The rigid blood vessels become fragile, which leads to injury and inflammation. Quercetin helps relax blood vessels and enhances their function.

Supplementation with quercetin supports normal blood pressure at doses as low as 150 mg per day.

Combats cancer development

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

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

Exercise & sports performance

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

It may also directly affect 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 body’s antioxidant system’s function. 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.

Protects skin

Research shows quercetin can improve signs of inflammation in damaged skin. 

It may also maintain skin health through its antioxidants effects, which can slow the skin’s aging. It might not erase your wrinkles, but it could help slow their progression.

Reduces infection risk

Quercetin supplementation may reduce the risk of infection by various viruses. For example, animal studies show that it reduces infection risk when exposed to meningoencephalitis virus.

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

Ganesan S, et al.

Also, quercetin supplementation reduced the occurrence of upper respiratory tract infections. Interestingly, it did not reduce markers of inflammation or muscle damage in athletes.

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.

Quercetin may be especially useful in supporting the immune system against viruses when combined with supplemental zinc.

In addition to viruses, it also supports the immune system in combating bacterial infection. It also fights pathogenic bacteria on the skin and in the digestive, respiratory, and urinary systems.

Read also: 5 Nonnegotiable Habits for a Strong Immune System.

Reduces seasonal allergy symptoms

Quercetin inhibits histamine release, which makes it a powerful supplement to support symptoms of asthma and bronchitis.

In one study, quercetin phytosome supplementation reduced daytime symptoms of seasonal allergies by 50% and nighttime symptoms by 70%.

In another study, supplementation reduced skin-related allergy symptoms.

Relieves symptoms of arthritis

In a small study, 50 women with arthritis took 500 mg per day.

After eight weeks, they experienced less early morning stiffness and pain, as well as less pain after activity.

Being that arthritis is an inflammatory condition, and quercetin supports healthy inflammatory levels, it makes sense that it could help relieve arthritis symptoms.

Supports normal inflammation levels

Inflammation plays a role in developing heart disease, cancer, degenerative disease, and numerous other ailments. Quercetin supports healthy inflammation levels.

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

Overviews of Biological Importance of Quercetin: A Bioactive Flavonoid, David AVA, et al.

Quercetin Dosages

The average person consumes 14 mg of quercetin each day. Most research studies use 500 mg daily doses. Even better if it’s delivered as a liposome or phytosome.

In my opinion, most people would benefit from half that amount to support health and wellbeing and increase it during certain seasons of the year.

Contraindications

Quercetin is exceptionally safe and well-tolerated. However, I’ve worked with people who felt head and neck tension or developed headaches when using higher doses.

If you use a medication such as alprazolam (Xanax) or colchicine, talk to a doctor first. It may inhibit one of the pathways the drugs work through.

References

Photo by andrew welch on Unsplash