Quercetin - What Is It, Benefits, Side Effects & Dosage [Complete Guide]

Quercetin is a seemingly useful supplement that can reduce inflammation and is a potent antioxidant.


Quercetin is a plant flavonol from the flavonoid group of polyphenols.


Click to skip to the topics below or continue to scroll down.


What Is Quercetin

Quercetin is a compound called a plant flavonol (also known as a flavonoid or pigment), from the flavonoid group of polyphenols.


Quercetin is a type of plant flavonoid.

Flavonoids appear naturally in:

  • Fruit (commonly apples, berries & grapes)

  • Vegetables (commonly broccoli, onions and kale)

  • Grains

  • Tea

  • Wine


Capers are also very high in quercetin.


Quercetin has many benefits, very similar to curcumin, including reducing the risk of heart disease, cancer, brain diseases and other inflammatory diseases. (Source, Source)


Quercetin has benefits which mostly arise from its ability to work as a powerful antioxidant and anti-inflammatory within the body. (Source)


Antioxidants are compounds that can neutralize free radicals.


Free radicals are unstable molecules that roam around the body and seek other electrons to become a pair.


These free radicals can cause damage to cells, proteins and DNA if left unchecked.


The harm caused by these free radicals may result in various chronic inflammatory conditions, including cancer, heart disease, brain disease, diabetes, and more. (Source)


Food sources of quercetin:

  • Apples

  • Grapes

  • Berries

  • Citrus Fruits

  • Cherries

  • Capers

  • Broccoli

  • Onions

  • Green & Black Tea

  • Coffee

  • Red Wine


See more sources of quercetin here.


Quercetin is one of the most abundant flavonoids found in the diet.


The average person consumes an estimated 10-100mg of quercetin per day via various food and drinks. (Source)


Quercetin also comes as a supplement in powder and capsule form.


Reasons people take quercetin:

  • To Support General Health

  • To Reduce Allergies

  • To Boost Immunity

  • To Reduce Inflammation

  • To Improve Exercise Performance


Summary:

Quercetin is a type of flavonoid with potent anti-inflammatory and antioxidant properties. You can find quercetin in many typical food and drinks, and you can also consume as a supplement.


Quercetin can be found in many foods and also taken as a supplement.

How Does Quercetin Work

Quercetins primary mechanism is by functioning as an antioxidant.


An antioxidant neutralizes free radicals - these are the unstable chemical by-products that harm cells and damage DNA, which results in chronic health issues.


Quercetin also has other properties, most notably; antihistamine and anti-inflammatory qualities.


It also seems to have other functions:

Quercetins Benefits

Quercetin has many benefits associated with its supplementation.


Below is a list of the top 8 benefits of quercetin.


Click to skip to the benefits below or continue to scroll down.


Top 8 Quercetin Benefits:

  1. Reduces Risk Of Cancer

  2. Reduces Risk Of Brain Disease

  3. Reduces Risk Of Heart Disease

  4. Reduces Risk Of Diabetes

  5. Reduces Inflammation

  6. Reduces Symptoms Of Allergies

  7. Improves Exercise Performance

  8. Helps Slow Ageing

1) Reduces Risk Of Cancer

Due to quercetins primary role as a powerful antioxidant, it may have some anticancer properties. (Source)


Studies in the lab and on animals show that quercetin can suppress cellular growth and produce cell death in prostate cancer cells. (Source)


Other studies noted that quercetin had similar results on the following types of cancer cells: (Source, Source, Source, Source)

  • Liver & Lung Cancer Cells

  • Breast, Bladder & Blood Cancer Cells

  • Colon, Lymphoid, Ovarian & Adrenal Cancer Cells


Interestingly, quercetin might promote tumour development in estrogen-dependent cancer. (Source, Source)


Human studies are lacking; this is why quercetin is not used as an alternative cancer treatment and cannot be recommended as an alternative either.


Summary:

Preliminary research on quercetin as an anticancer agent has produced promising results, especially for reducing cancer risk. However, it cannot be recommended as an alternative cancer treatment due to a lack of human studies and conflicting data.


Quercetin has shown promise in reducing the risk of certain cancers.

2) Reduces Risk Of Brain Disease

Quercetins antioxidant and anti-inflammatory properties may also help protect against degenerative neurological brain diseases, such as Alzheimer's disease and dementia. (Source)


In one study, a diet high in quercetin had lessened Alzheimer's disease markers and improved brain function in mice at the early-middle stage of the disease.


Interestingly, this diet high in quercetin had a minimal effect on animals with the middle-late stage of Alzheimer's disease. (Source)


In another study, mice with Alzheimer's disease were given a quercetin injection every two days for three months.


After three months, the mice exhibited better cognition on the learning tests and even reversed various Alzheimer's disease markers. (Source)


A beverage linked to a reduced risk of Alzheimer's disease is coffee.


Research shows that quercetin is the primary compound in coffee responsible for its protective effects against brain disease. (Source)


Summary:

These studies provide promising results, especially for preventing brain and cognitive conditions such as Alzheimer's disease; however, there needs to be more research in humans to conclude any effect.


Quercetin may prevent brain diseases such as Alzheimer's and dementia.

3) Reduces Risk Of Heart Disease

About 1 in 3 adults experience high blood pressure worldwide.


High blood pressure increases the risk of heart disease. (Source)


Heart disease is the leading cause of death in adults worldwide.


Quercetin may be able to reduce blood pressure, thus reducing the risk of heart disease.


Research suggests that quercetin appears to possess a relaxing effect on blood vessels. (Source, Source)


In one study, quercetin was given to mice with high blood pressure each day for five weeks.


Their systolic blood pressure value decreased by around ~18%, and their diastolic blood pressure value decreased by around ~23%. (Source)


A review of 9 human studies discovered that taking above 500mg of quercetin each day decreased blood pressure.


Above 500mg, quercetin decreased systolic blood pressure by around ~2.6mm Hg, and it decreased diastolic blood pressure by around ~5.8mm Hg. (Source)


Summary:

This research is promising, but more human studies are needed to conclude if quercetin is a viable treatment or preventative measure for high blood pressure and heart disease.


Quercetin may reduce the risk of heart disease.

4) Reduces Risk Of Diabetes

Quercetin may reduce blood sugar levels.


High blood sugar levels can result in an increased risk of diabetes.


There are studies on the effects of quercetin in animals with type 2 diabetes. (Source)


Those who received quercetin showed lower blood sugar levels relative to the control group.


There was no observed difference in insulin sensitivity.


Human and animal studies suggest that quercetin can reduce fasting blood sugar levels, protecting against diabetes. (Source, Source, Source)


Summary:

Quercetin has shown promising results for protecting against diabetes. However, more human studies are needed to assume quercetin as a viable antidiabetic.


Quercetin may protect against diabetes.

5) Reduces Inflammation

A chronic state of inflammation can cause various diseases, including cancer, heart disease, diabetes, and more. (Source)


Free radicals don't just damage cells; they also activate genes responsible for promoting inflammation.


Therefore, high levels of free radicals within the body may lead to a heightened inflammatory response. (Source)


Research suggests that quercetin may reduce inflammation, likely due to its ability to reduce free radical levels.


Quercetin reduces inflammation markers in human cells (test-tube studies), including tumour necrosis factor-alpha (TNFα) and interleukin-6 (IL-6). (Source, Source)


In one small, eight-week study on rheumatoid arthritis, those who took 500mg of quercetin each day experienced significantly lessened morning pain, morning stiffness, and after-activity pain. (Source)


Those who were taking quercetin exhibited reduced inflammation markers, such as TNFα. (Source)


Summary:

Quercetin seems to reduce inflammation. However, there needs to be more research on its effects to conclude anything.


Quercetin seems to reduce inflammation.

6) Reduces Symptoms Of Allergies

Quercetin may have anti-allergy effects and reduce symptoms, likely due to its anti-inflammatory effects.


Research suggests that quercetin may block enzymes involved in inflammation and suppress the chemicals involved in allergy symptoms such as histamine. (Source, Source, Source)


One study in mice noted that quercetin supplementation suppressed anaphylactic reactions. (Source)


Summary:

It is unclear whether quercetin has anti-allergy effects in humans; more human studies need to assess whether quercetin is an effective anti-allergy supplement.


Quercetin may reduce the symptoms of allergies.

7) Improves Exercise Performance

Quercetin may improve exercise performance and endurance.


Studies show that VO2 max and endurance performance measures improved significantly in those taking quercetin, compared to the control group. (Source)


A review of 11 human studies discovered that supplementing with quercetin may slightly improve endurance exercise performance. (Source)


Summary:

Studies suggest that quercetin may improve endurance performance. However, there needs to be more research on humans to come to any conclusions.


Quercetin seems to be able to improve endurance exercise performance.

8) Helps Slow Ageing

Quercetin may be able to slow the ageing process.


It seems to be able to slow or reverse ageing in cells.


Research suggests that quercetin may help restore or eliminate ageing cells and can reduce ageing markers. (Source, Source, Source)


However, more human research is needed.


Summary:

Quercetin seems to reduce ageing in cells, thus may have potential as an anti-ageing supplement. However, there needs to be more research on this matter.


Quercetin may be able to slow the ageing process.

Quercetins Side Effects & Interactions

Many food sources contain quercetin.


Quercetin appears to be safe for consumption with minimal side effects.


Some people may experience mild side effects when taking more than 1,000mg of quercetin per day, such as listed below. (Source)


Quercetins Side Effects:

  • Headaches

  • Stomach Aches

  • Tingling Feeling

Quercetin might also make kidney issues worse, avoid taking quercetin if you have pre-existing kidney issues. (Source)


Interestingly, quercetin might also promote tumour development, especially in estrogen-dependent cancer. (Source, Source)


You should also avoid taking quercetin supplements if you're pregnant or nursing due to minimal studies on this matter. (Source)


However, quercetin is safe for pregnant and breastfeeding women when consumed in foods.


Quercetin Interactions: (Source, Source)

  • Antibiotics

  • Blood Pressure Medications

  • Drugs Affected By The Liver (P450 enzymes)

  • Drugs Affected By Pumps In Cells (P-Glycoprotein Substrates)


Summary:

Quercetin seems to be safe, with minimal side effects. It may interact with various medications. There are minimal human studies though, so pregnant and breastfeeding women should avoid it. Also, those with estrogen-dependant breast cancer should avoid it.

Sources Of Quercetin

Quercetin can be found in many common fruits, vegetables and other plant-based foods.


The outer layers or peel of these foods usually contains higher concentrations of quercetin. (Source)


Food Sources Of Quercetin: (Source)

  • Capers

  • Yellow & Green Peppers

  • Red & White Onions

  • Cooked Asparagus

  • Red Leaf Lettuce

  • Broccoli

  • Shallots

  • Kale

  • Tomatoes

  • Cherries

  • Red Apples

  • Red Grapes

  • All Berries (blueberries, raspberries, cranberries etc.)

  • Green & Black Tea

  • Coffee

  • Red Wine

Quercetin is found in many common foods.

In one study, tomatoes grown organically appear to contain up to ~79% more quercetin than tomatoes grown conventionally. (Source)


However, other studies point out differences between the quercetin content in various tomatoes species, regardless of the farming method.


There was no difference observed in quercetin concentration in organically grown bell peppers than conventionally grown bell peppers. (Source)


The amount of quercetin found in foods may depend on how it was grown and produced.


However, there appears to be a conflict of data here, meaning more research needs to conclude whether the growing and production method affects quercetin concentration.


Quercetin is also available in supplement form.


You can purchase quercetin in both capsule and powder form.

Quercetin Dosage

An appropriate dosage of quercetin depends on several factors, such as the person's age and health.


However, there is not enough research to define an appropriate dosage of quercetin, nor is there an official guide on its dosage.


Despite this fact, quercetin has safely been used for up to 12 weeks at 500mg each day.


Typical dosages range between 500mg and 1000mg per day.


If you consider taking quercetin, use it with caution, there is minimal research on quercetin's long-term or high dosage safety.


Natural supplements are not always safe, and different dosages can have significantly different effects.


Consult your pharmacist or physician or other healthcare professional before using.


Strictly avoid quercetin if you:

  • Have kidney issues.

  • Have estrogen-dependant breast cancer.

  • Are breastfeeding or pregnant.

  • Are taking antibiotics or blood pressure medication.

  • Are taking medicines that are affected by the liver.


Click here to read more about its side effects and interactions.

Summary Of Quercetin

Quercetin seems to have multiple benefits.


It is a potent antioxidant and anti-inflammatory compound.


Quercetin also appears to be generally safe with minimal side effects when consumed naturally in foods.


However, it can have some interactions with certain drugs and diseases.


Also, its long term and high dosage safety research are minimal.


Overall, quercetin seems to be a generally safe supplement, with powerful antioxidant and anti-inflammatory properties.


Quercetin seems to be a generally safe and useful supplement.

Synergistic Supplements

Quercetin has several synergies with supplements.


Quercetin has potent anti-inflammatory and antioxidant effects.


For this reason, it pairs well with the supplements below.


Top 4 Synergistic Supplements:

  1. Curcumin (Turmeric)

  2. Catechins (Green Tea)

  3. Resveratrol (Red Wine, Grapes etc.)

  4. Genistein (Soybeans)


Quercetin also has a low bioavailability, meaning the body does not well absorb it. (Source, Source)


Some quercetin supplements may also include other ingredients, such as vitamin C or bromelain; their purpose is to improve absorption. (Source, Source)

Frequently Asked Questions


Q: What are the health benefits of quercetin?

A: Quercetin is a powerful antioxidant and anti-inflammatory, it has various benefits such as reducing blood pressure and blood sugar levels. It may have anti-allergy and anticancer properties, and may reduce the risk of brain diseases.


Q: Who should not take quercetin?

A: You should avoid taking quercetin if you have kidney issues, or are a breastfeeding or pregnant woman. Also, those with estrogen-dependant cancer should strictly avoid quercetin.


Q: What are the side effects of quercetin?

A: Side effects from quercetin are mild and not very common, the reported side effects include; headache, stomach ache and tingling feelings. However, quercetin has interactions with some medications and diseases.


Q: Is quercetin the same as CoQ10?

A: No, CoQ10 and quercetin are not the same. CoQ10 is a type of enzyme and quercetin is a type of flavonoid. They have similar effects but are not the same.

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