9 Health Benefits Of Quercetin, Food Sources, & Side Effects

The benefits of quercetin are attributed to its antioxidant properties. It is found in a variety of fruits and vegetables. This powerful pigment can help protect human health. Quercetin is a type of flavonoid antioxidant that can scavenge free radicals. As a result, it can protect the body against many harmful effects. Research shows that it may protect against various serious health issues, including inflammation and cancer (1).

This article examines the benefits of quercetin, including its sources and possible side effects. Take a look.

More On Quercetin

Quercetin is a flavonoid that has biological properties that may promote mental and physical performance. It exhibits anti-inflammatory, anti-carcinogenic, antiviral, antioxidant, and psychostimulant properties (1).

Quercetin happens to the most abundant flavonoid in the human diet (2). Its most important use is as an antioxidant, where it fights free radicals and helps prevent disease.

It has a role to play in the prevention of cardiovascular disease, neurodegenerative issues, cancer, ulcers and other gastric problems, allergies, and microbial ailments (3).

Most of these benefits are backed by extensive research studies conducted all over the world. In the upcoming section, we shall look at them.

What Are The Health Benefits Of Quercetin?

Quercetin can help fight cancer and inflammation. Its ability to fight free radicals also promotes heart health, manages diabetes, and improves vision. The antioxidant also boosts brain health and may delay the signs of aging.

1. May Help Fight Cancer

Quercetin induces apoptosis (cancer cell death) and prevents the proliferation of malignant cells. The compound also may have synergistic effects when combined with chemotherapy (4).

Quercetin inhibits cancers of the breast, lung, prostate, colon, and the cervix. The potent antioxidant properties of quercetin play a role here. They fight free radicals, which are among the major contributors to cancer (5).

A high intake of foods rich in quercetin, including most fruits and vegetables, has been associated with a reduced risk of intestinal cancer. Similar food groups have also been linked to lower incidences of renal cancer (6).

2. May Promote Heart Health

Quercetin was found to lower blood pressure levels (7). This effect was also observed in individuals with type 2 diabetes.

In certain animal studies, quercetin could also lower the levels of triglycerides and total cholesterol (7).

Flavonoids, in general, can reduce the risk of coronary heart disease. They achieve this by promoting the functioning of the blood vessels and reducing platelet activity (resulting in fewer blood clots, which may otherwise lead to stroke) (8).

LDL (the bad cholesterol), when oxidized, can lead to plaque formation in the blood vessels. Quercetin may fight this by preventing the oxidation of LDL (9).

The anti-hypertensive properties of quercetin can also prevent heart damage, as per reports. This effect was observed to be far greater in smokers and those with metabolic syndrome (10).

3. May Aid Diabetes Treatment

Treatment with quercetin and resveratrol can have beneficial effects on diabetes. The antioxidant helps lower plasma glucose levels and improves other parameters related to diabetes. It achieves this by restoring the glucose-regulating enzymes in the liver (11).

Other studies have also called quercetin as a promising component in managing the symptoms of type 2 diabetes. The antioxidant activates multiple therapeutic agents in the body, thereby aiding the treatment of type 2 diabetes (12).

Dietary quercetin was also found to improve the health of the pancreas and the liver. This may help ameliorate diabetes symptoms since those are the two important organs responsible for preventing the disease (13).

Quercetin was also found to treat liver inflammation. It has been identified as a novel compound in the treatment of fibrotic liver disease (14).

Quercetin may also protect the liver from injury. It achieves this by scavenging free radicals and combating oxidative stress (15).

4. May Fight Inflammation

Quercetin inhibits the secretion and production of pro-inflammatory cytokines, which are compounds that promote inflammation in the human body. It may also protect the body’s cells involved in allergic inflammation (16).

In studies conducted on healthy subjects, quercetin supplementation had improved various markers of inflammation (17).

Quercetin also has a role to play in the treatment of rheumatoid arthritis. It preserves the basement membranes of the cartilage and even prevents its damage (18).

5. May Cut Obesity Risk

There is limited evidence here. A supplement with quercetin as the primary ingredient caused reduced lipid accumulation in obese rats (19).

Quercetin also can increase energy expenditure, and this may help reduce the risk of obesity (20). However, further research is warranted.

6. May Enhance Vision Health

Quercetin was found to treat corneal inflammation, thus promoting long-term vision health. When human conjunctival and corneal cell lines were tested, the antioxidant and anti-inflammatory effects of the compound seemed to help with the treatment of a few ocular diseases (21). However, more studies are required to establish its efficacy.

In mice studies, quercetin could also help treat dry eyes (21).

Quercetin may also reduce the risk of cataracts. It achieves this by fighting oxidative stress (22).

7. May Promote Kidney Health

In a rat study, quercetin improved renal function and protected the kidneys from further harm. Its ability to fight oxidative stress and inflammation could be attributed to this benefit (23).

In another study, quercetin ameliorated renal damage and the corresponding oxidative stress (24).

8. May Boost Brain Health

 Quercetin fights oxidative stress and mitochondrial dysfunction, thereby helping prevent brain diseases like Alzheimer’s and Parkinson’s (25). More research is needed to arrive at a conclusion.

In a study, quercetin was found to prevent spatial memory impairment in mice. It achieves this by increasing brain antioxidant capacity (26). This way, the flavonoid may potentially slow down brain aging.

Reports also suggest that apples, which are rich in quercetin, can help prevent brain damage that may otherwise trigger Alzheimer’s and Parkinson’s (27).

Quercetin can also help treat stress and anxiety. Individuals dealing with chronic stress may experience improvements in memory following the intake of quercetin (28).

9. May Improve Exercise Endurance

Studies show that quercetin may improve endurance exercise capacity and exercise performance, though the improvements are trivial (29).

In another study involving male badminton players, quercetin was found to improve endurance exercise performance (30).

10. May Help Fight Infections And Pain

The antibacterial properties of quercetin may help fight infections. The compound was found to be especially effective against Staphylococcus aureus. In combination with other antibiotics, quercetin showed enhanced antibacterial activity (31).

Quercetin may also help treat allergies. It fights viruses by stimulating the immune system. It is also efficient in suppressing inflammatory mediators (32).

Quercetin may have a role to play in asthma treatment as well. It may help treat the condition by relaxing the airway smooth muscles. The anti-inflammatory properties of quercetin may also aid asthma treatment (33).

Quercetin also acts as a natural antihistamine (histamine is a compound released during inflammation or an allergic reaction). This way, it aids the treatment of other respiratory infections, like bronchitis (34).

The flavonoid may also have a role to play in relieving pain. It achieves this by inhibiting oxidative stress and the production of cytokines (compounds that contribute to inflammation) (35). Studies shed light on quercetin’s possible role in treating chronic pelvic pain syndrome (36).  

11. May Promote Sexual Function

Flavonoids, in general, could be associated with improved sexual function (37).

Quercetin may also help treat erectile dysfunction as it helps combat oxidative stress (a common cause of the issue) (38).

12. May Help Treat Leaky Gut

Leaky gut, also known as intestinal permeability, is a condition in which the lining of the small intestine becomes damaged. This causes the toxic wastes in the small intestine to leak into the bloodstream, causing issues.

Studies show that quercetin boosts the intestinal barrier function, which may help in treating leaky gut (39). However, more research is warranted in this regard.

Quercetin may also have other gastroprotective effects. The compound can increase gastric mucus production, thereby aiding the treatment of ulcers (40).

13. May Help Delay Aging

Quercetin has been found to extend cellular lifespan and survival, thereby possibly delaying the signs of aging. It was also found to rejuvenate fibroblasts (41).

Quercetin also happens to be one of the popular ingredients in most anti-aging skin care creams (42).

When we talk about antioxidants, quercetin tops the list, for sure. Most of the benefits we have discussed have been confirmed by research studies. Further research is ongoing.

Quercetin is among the common antioxidants available in the human diet. In the following section, we will look at the top food sources of the flavonoid.

What Are The Food Sources Of Quercetin?

The top food sources of quercetin include the following (43):

• Apples
• Grapes
• Licorice
• Oregano
• Capers
• Onions
• Peppers
• Tomatoes
• Cherries
• Asparagus
• Green tea

In addition to these, quercetin supplements are on the rise. They could be a way of supplementing your diet with adequate quercetin. But how effective can they be?

A Note On Quercetin Supplements

Though quercetin is commonly present in most everyday foods, its levels could be low. Isolated quercetin is used and marketed as a dietary supplement and may help promote health benefits. Adverse effects following the intake of quercetin supplements are rare, and any such effects were only mild (44).  

The safety of the use of high supplemental doses of quercetin (>1000 mg per day) is not available (44). Hence, we suggest you consult with your doctor on the usage.

The typical dosage of quercetin could be between 500 to 1000 mg per day (45).

Does Quercetin Pose Any Side Effects?

Though most often quercetin supplements may not cause any adverse effects, they may lead to certain mild issues. These can include stomach ache or headaches as per anecdotal evidence.

There is some research that states that excess intake of quercetin may have carcinogenic effects (8). There is limited information on the ideal dosage of quercetin. Hence, if you are to take quercetin supplements, please check with your health care provider.

Frequently Asked Questions

Does quercetin affect the thyroid gland?

Some research states that quercetin may restrict thyroid function (46). Hence, if you have thyroid issues, please check with your health care provider before taking quercetin supplements.

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Ravi Teja TadimallaSenior Editor

 

Ravi Teja Tadimalla is a senior editor and a published author. He has been in the digital media field for over eight years. He graduated from SRM University, Chennai, and has a Professional Certificate in Food, Nutrition & Research from Wageningen University. He has written over 300 articles about ingredients and their benefits for the skin, hair, and health. He...more