What Fruits Have Quercetin


What Fruits Have Quercetin, Many fruits are great for your health and provide health benefits. Quercetin is an antioxidant found in red apples, grapefruit, green tea, berries, onions and dark chocolate. Quercetin helps preserve the elasticity of your blood vessels. Quercetin is a flavonoid found in fruits and vegetables. It’s part of the same family as anthocyanins, ellagitannins, and isoflavones.


Quercetin is a plant flavonol which is one of six subclasses of flavonoid compounds. Flavonoids are compounds that are found in plants. These plant compounds have many health benefits when consumed. They have antioxidant, anti-inflammatory, and anti-carcinogenic activity. Flavonoids can help in the prevention of various chronic diseases including cardiovascular disease, Alzheimer’s, and atherosclerosis (buildup of plaque in arteries).

Quercetin is part of one of the subclasses of flavonoids, flavonols. Flavonols are found in many fruits and vegetables as well as tea and red wine. Flavonols have strong antioxidant activity and can reduce the risk of vascular disease (relating to blood vessels).

Quercetin is a powerful antioxidant and anti-inflammatory agent. Quercetin helps neutralize reactive oxygen species (also called ROS). ROS cause damage in cells. In addition, studies have shown that it has other health benefits and can protect against diseases like osteoporosis, certain forms of cancer, lung and heart diseases, and can even help with aging.


One of the biggest things to consider when looking at plant compounds is whether or not they are bioavailable. What does this mean? Well, just because quercetin is found in lots of fruits and vegetables, it doesn’t mean that our bodies can absorb it. Bioavailability refers to the portion of a substance (in our case, quercetin) that enters into circulation and is able to have an effect on our bodies when consumed. This is a really important concept because if we are consuming a lot of something, but aren’t actually absorbing the bioactive compounds, then we would have to eat a lot of it to see or feel any benefits. 

The bioavailability of quercetin is somewhat dependent on the source. Foods that are higher in quercetin have better bioavailability and are better absorbed by our bodies. In general, quercetin is actually not very bioavailable meaning we do not absorb and use a lot of what we consume.

But, once we eat foods with quercetin, the quercetin is absorbed through our small intestine. From there it makes its way to various organs including our colon, liver and kidneys. Once the quercetin has reached some of our other organs, it is further metabolized (broken down) so that our body can begin to use it.

Now that we know how quercetin works, and its benefits, let’s talk about some of the foods that are high in quercetin.



 Capers are best known as small, little flower buds that are often pickled when consumed. They are native to various Mediterranean countries. Believe it or not, capers have the highest levels of naturally occurring quercetin of all foods. For every 100 grams of capers, you will be consuming 234 milligrams of quercetin. Even in its pickled form, as they are often consumed, capers still contain a considerable amount of quercetin.


Fan of spicy foods? If you are then you might be glad to hear that hot peppers make the list. Both yellow and green hot peppers are high in quercetin with about 51 milligrams and 15 milligrams of quercetin per 100 grams of peppers respectively.


Dill and cilantro are some of the best sources of quercetin. They contain 55 milligrams and 53 milligrams per 100 grams of the herbs respectively. While these herbs are great sources of quercetin, 100 grams is a lot of dill and cilantro. However, adding herbs to recipes is a great way to add flavour and sneak in a little quercetin!


Onions have been used in traditional and folk medicine for centuries due to their wide range of health benefits. So, it comes as no surprise that onions, and red onions in particular, contain high levels of quercetin. Quercetin levels in various colours of onions have been studied. Red onions have the highest levels of quercetin followed by yellow onions and chartreuse onions. Additionally, the outer peel of red onions contains more quercetin than the inner peel!   


Asparagus is a spring vegetable that is abundant in quercetin. If you are Canadian (like us!), then you’ll be glad to hear that asparagus are available all year round. These vegetables are a great staple to add to your diet to increase your quercetin intake.


Cranberries are a great source of quercetin. Seen in their bright red colour, cranberries contain 15 milligrams of quercetin per 100 grams of cranberries. Other berries including blueberries, lingonberries and elderberries also contain high levels of quercetin!


Broccoli is a cruciferous vegetable. It is related to other vegetables like cabbage, kale and cauliflower. Broccoli is another source of quercetin, but did you know that the cooking method used can affect quercetin levels in this vegetable? The best way to ensure that your broccoli maintains its quercetin levels is by eating it raw, or by steaming it!


Looking for a way to spice up your salads? Try swapping lettuce for kale! While some lettuce contains low levels of quercetin, kale contains considerably more. In addition, kale is super rich in other nutrients such as vitamin A and vitamin K making it an incredible addition to your diet.


Apples are another great source of quercetin. Red and yellow apples such as red delicious, gala and golden delicious contain higher amounts of quercetin than green apples. Did you know almost all of the quercetin is found in the peel? That’s right! So make sure if you reach for an apple the skin stays on!


Tomatoes also contain quercetin, but again it is mainly in the skin! Approximately 98% of the quercetin found in tomatoes is found in the skin with the rest in the seeds and flesh. Tomatoes not only contain quercetin but are also high in another flavonol, kaempferol.

Foods High in Quercetin (+ 5 Benefits)

We have all heard the health pitch, “an apple a day keeps the doctor away,” but do we know why? In addition to being a great source of fiber and vitamins, apples are a great source of health-promoting polyphenols like quercetin.

If you haven’t heard of quercetin, you’re certainly not alone; zinc and vitamins C and D tend to get all the credit when it comes to immune health support. Strange name notwithstanding, however, quercetin might be the most underrated nutrient in your diet. And its benefits go well beyond shoring up your body’s natural defenses.

So what is quercetin—and aside from apples, what other foods can you find it in?

What is quercetin?

Quercetin belongs to a group of plant compounds known as dietary flavonoids, which are a type of polyphenol that makes up the basis for pigments of many different plants. That’s why you always hear advice to “eat the rainbow”—those brightly colored fruits and vegetables get their bold hues from health-promoting flavonoids. Quercetin is a true stand-out among other flavonoids, though, because it has many unique—and beneficial—biological properties.

Like vitamin C, quercetin is an antioxidant, which means it helps fight off free radicals which can cause oxidative stress…and if there’s one thing we all need less of to maintain our health, it’s free radicals!

5 quercetin benefits

Healthy couple preparing broccoli which is high in quercetin

How, specifically, does quercetin benefit your health? Here are five important ways this flavonoid supports you from head to toe:

  1. Immune system health – Quercetin is an antioxidant which certainly belongs on our list of immune supporting supplements. In a large randomized-controlled trial, 12 weeks of quercetin intake (1000 mg daily) compared to placebo, produced beneficial effects including a smaller number of days of experiencing immune challenges related to the upper respiratory tract.
  2. Promotes a healthy inflammatory response – Inflammation is a normal part of the human experience; what matters is whether your body responds in a healthy way…and quercetin appears to promote exactly that. In a meta-analysis of clinical trials, quercetin supplementation in a subgroup was associated with maintaining already-healthy levels of cytokines such as C-reactive protein.
  3. Healthy cells – Senescent cells are the old cells that accumulate with aging. Quercetin is increasingly achieving recognition as a senolytic, meaning it helps remove these undesired cells—leaving the healthy, youthful, properly functioning cells to do their jobs.
  4. Supports already-healthy blood pressure – A meta-analysis of clinical trials found that supplementing with 500 mg or more of quercetin helped maintain blood pressure in healthy ranges.
  5. Already-healthy blood sugar support – A separate study found that this same dosage of quercetin also supported already-healthy blood sugar levels.

Healthy Foods High in Quercetin

Quercetin is a pigment that adds color to many fruits and vegetables. It’s found mainly in the skins and leaves of plants. Light stimulates the production of quercetin, so an apple at the top of a tree may have more quercetin than one that doesn’t get direct sunlight.

Quercetin may be referred to as a phytochemical, polyphenol, or flavonoid. Phytochemicals are substances produced by plants that may have health benefits for humans. Polyphenols and flavonoids are types of phytochemicals.

Quercetin is a powerful antioxidant. Antioxidants help fight free radicals, which are molecules that contain unpaired electrons. Because electrons naturally want to pair up, free radicals roam around the body, pulling electrons away from other molecules. This process can damage cells and DNA. Quercetin “cleans up” free radicals by pairing with their single electrons so they can no longer cause damage.

Dietary intakes of quercetin in the U.S. have been reported to be around 6-18 milligrams (mg) per day. However, if you’re eating several servings of fruits and vegetables on a daily basis, you’re likely consuming much more quercetin.

Why You Need Quercetin

Research shows that quercetin has many health benefits, including:

Heart Health

Quercetin has been shown to support the cardiovascular system by lowering blood pressure and cholesterol and relaxing blood vessels. Because reduced blood flow can cause erectile dysfunction, flavonoids like quercetin can also improve men’s sexual health.

Brain Health

Improved circulation improves brain health as well. But quercetin can protect the brain in other ways, too. It may reduce inflammation and protect brain cells from toxins. Its antioxidant powers could lower the risk of Alzheimer’s disease and other degenerative diseases of the brain.

Anti- C ancer Effects

When free radicals damage cells in the body, those cells sometimes develop into cancer. Quercetin and other antioxidants reduce the risk of cancer by combating free radicals. A few studies have targeted quercetin particularly. In one, it slowed tumor growth. In another, it lowered the risk of lung cancer. The third was a lab study, which found that quercetin had the ability to attack leukemia cells.


Quercetin is a flavonoid found in many plants, including citrus, berries, leafy vegetables, herbs, spices, legumes, tea, and cocoa (NTP, 1992).


Quercetin, a bioflavonoid available in many over-the-counter products, may have the anti-inflammatory effects of other members of this class of compounds found in fruits, vegetables, and some spices.Katske et al. (2001) administered 500 mg twice daily to 22 IC/BPS patients for 4 weeks. All but one patient had some improvement in the O’Leary-Sant symptom and problem scores and in a global assessment score. Further larger studies with placebo controls are necessary to determine efficacy.



Quercetin is a natural flavonoid found abundantly in vegetables and fruits. There is growing evidence suggesting that quercetin has therapeutic potential for the prevention and treatment of different diseases, including cardiovascular disease, cancer, and neurodegenerative disease. Mechanistically, quercetin has been shown to exert antioxidant, anti-inflammatory, and anticancer activities in a number of cellular and animal models, as well as in humans through modulating the signaling pathways and gene expression involved in these processes. This chapter focuses on experimental studies supporting the anticancer, cardioprotective, and neuroprotective effects of quercetin.


Quercetin is a dietary polyphenolic compound with potentially beneficial effects on health. Most research has focused on the antioxidant properties of quercetin, its effects on several enzyme systems, and effects on biological pathways involved in carcinogenesis, inflammation and cardiovascular diseases. Upon absorption in the small intestine, quercetin is metabolized immediately by enzymes in the epithelial cells and further metabolized by the liver. Even if the bioavailability of quercetin is now relatively well documented, data is still lacking on the association of this flavonoid in the diet with respective to absorption and metabolism. As there is increasing evidence that there is little to no free quercetin in the plasma, the effects of the glucoconjugates and not free quercetin must be further investigated. Most of the studies presented focus on the aglycone form of quercetin, so the effects of the conjugates are still unkown, although, free quercetin may be readily absorbed and not detectable. Therefore, especially in the intestinal epithelial cells where there is evidence of deglycosylation, studying the effect of free quercetin may be of greater value. Understanding the mechanism of action of quercetin and the determination of its free, and conjugated forms of quercetin in plasma and urine prior to or after supplementation seems to be an important aspect as its various biological actions seem to be dose-dependant in many of these studies we have cited in this chapter. The effects of quercetin concentration are varied with low doses (0–10 μM) resulting in chemoprevention, mid ranges (10–200 μM) resulting in mixed effects, and higher concentration (>200 μM) in pro-oxidant or potential direct therapeutic properties. From the studies presented, these lower concentrations appear to be achievable by diet, while the therapeutic concentrations might require supplementation or intravenous administration and result in little or no side effects.

The Allergic Patient


Quercetin is a bioflavonoid obtained from diverse sources, including apples, buckwheat, onions, and citrus fruits. Most data supporting the role of quercetin in attenuating allergic reactivity have been obtained from in vitro studies, as well as from animal models of allergic disease. In vitro studies have shown that quercetin stabilizes the membranes of mast cells and reduces the release of preformed histamine. In animal models, quercetin is able to suppress anaphylactic responses in sensitized rats, and it inhibits asthmatic inflammation in guinea pigs and rats.

Quercetin must be used as a preventative—taken before allergen exposure. Thus the activity of quercetin is similar to that of cromolyn, a drug that is often prescribed for allergy and asthma prophylaxis (see later). Quercetin also inhibits the production of enzymes responsible for manufacturing the potent leukotrienes. Practitioners usually recommend that quercetin be used regularly during an individual’s entire allergy season, or year-round for those with perennial allergies.

Quercetin is similar to cromolyn in its mechanism of action. Both are basophil and mast cell stabilizers.


The dose of quercetin is usually 400–600 mg of a coated tablet one to three times daily between meals (adjust dose for clinical response). Quercetin is not soluble in water, however, so it is a poorly absorbed nutrient. Bromelain, a protein-digesting enzyme extracted from pineapples, increases the absorption of quercetin, as does vitamin C. Therefore quercetin is typically sold blended with one or both additives.

Mechanism of the Anticancer Effect of Phytochemicals

2.1 Source

Quercetin is contained in abundance in apples, honey, raspberries, onions, red grapes, cherries, citrus fruits, and green leafy vegetables . Among vegetables and fruits, quercetin content is highest in onions. The bulb color and type seems to be a determining factor for quercetin concentration in onions.

Preparation and storage of food can affect quercetin content in it. Fried or boiled foods contain lower quercetin content with boiling being the main causative for reduction in quercetin level due to thermal degradation and leaching action of boiling water . Long-term storage of foods was found to change their quercetin content. While onions lose their quercetin content by up to 33% in the first 12 days of storage, quercetin level in strawberries has been shown to increase by approximately 32% when stored at − 20 °C for 9 months. Apart from storage and preparation, the conditions of the growth of plants were found to be a factor that influence quercetin levels in them. This is clear from studies that indicate a higher quercetin content in plants exposed to greater amount of UV-radiation is the cause of which is hypothesized to be a defence mechanism against UV-exposure.

Effects of Quercetin and Its Combinations on Health


Quercetin is a polyphenol substance abundant in plants and used for medical and nonmedical purposes from ancient times. Nowadays medical usage of quercetin is justified by its antioxidant, antiinflammatory, antiplatelet, antiapoptotic, nepho-, gastro-, angio-, cardio- and chondroprotective properties.This chapter provides brief characteristics of these qualities of quercetin, based on the data of scientific literature, and then continues with a concise summary of preclinical and clinical trials, performed by the authors, of the quercetin/diclofenac and quercetin/glucosamine combinations. The study of these pharmaceutical compositions showed that combining quercetin with the mentioned substances not only allows enhancing pharmacokinetic properties of quercetin but also boosts particular effects of its multidirectional pharmacodynamics and, as a result, broadens the possibilities for medical application of this substance in treatment of heart, kidney, and joint diseases. The obtained data determine expediency of implementation of the new, highly effective combinations of quercetin into medical practice.

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