Everything You Ever Wanted to Know About Quercetin

Published November 29th, 2021 by Chris Riley
Fact Checked by
Camille Freking

What is quercetin | Benefits | Daily Intake | Risks or Side Effects? | Food Sources | Where can I buy?

Quercetin is a powerful antioxidant and quercetin supplements are often taken as a way to support good health. Quercetin can also be found in many fruits and vegetables but it's not always easy to get the quercetin we need from food sources alone. This article will answer all your quercetin-related questions such as what quercetin is, how much quercetin you should take daily, what are the beneficial effects, and more.

What is quercetin?

Quercetin is a naturally occurring compound that can be found in plants and fruits and it is a flavonoid, which is a group of plant chemicals. Flavonoids are polyphenols themself, which are antioxidants like vitamin C and vitamin E and they help your body's tissues against oxidative stress and are known to help prevent certain illnesses. Oxidative stress has been known to increase your chances of heart disease, cancer, and other diseases. Flavonoids are found in many fruits, vegetables, and spices with quercetin being one of the most abundant flavonoids. There are three different types of flavonoids, flavonoids or bioflavonoids, isoflavonoids, and neoflavonoids. The main function of flavonoids is to help protect plants from harmful UV rays and quercetin is also found in many other plant-based foods like onions, kale, apples, broccoli, and green tea. Quercetin is an antioxidant and works synergistically with other flavonoids. Antioxidants work to prevent cellular damage that may lead to chronic diseases such as cancer, cancer prevention, atherosclerosis, diabetes mellitus type II, autoimmune disease, Alzheimer's disease, or Parkinson's disease. Foods rich in quercetin also contain bioactive quercetin aglycone and quercetin glycosides, which can be easily absorbed by the body because of their solubility in water. It was first isolated from Oak trees in 1933 by Drs Haworth and Hunter at the University of Western Ontario. Quercetin has been found to have many health benefits such as quercetin's ability to lower LDL cholesterol levels, quercetin's ability to lower blood pressure, quercetin's anti-inflammatory properties.

What are the benefits of quercetin?

Quercetin is known to be a powerful antioxidant that can help prevent or delay the onset of many chronic degenerative diseases and its anti-inflammatory properties are also very beneficial. There have been studies done on quercetin and its effects on some major health concerns which include cardiovascular disease, diabetes mellitus type II, atherosclerosis, chronic fatigue syndrome (CFS), and quercetin's ability to reduce oxidative stress. Quercetin has been found to be effective in treating many conditions that are related to cardiovascular disease which includes coronary heart disease (CHD) or atherosclerosis. Studies have shown quercetin can help lower LDL cholesterol levels, increase HDL cholesterol levels, and lower blood pressure by increasing the production of nitric oxide in endothelial cells which relaxes smooth muscles and increases vasodilation. Here is a list of potential benefits from taking quercetin:

Anti-inflammatory properties

Free radicals are molecules that contain oxygen and an uneven amount of electrons. This uneven amount of electrons makes it much easier for free radicals to interact with other molecules in your body. These reactions can damage cells and be harmful to your body. Antioxidants are molecules that can interact with free radicals without becoming unstable, hence why they are good for you. When the balance is off between free radicals and antioxidants this can lead to oxidative stress which can damage cells and harm your body. It has been shown that an overabundance of free radicals can help promote inflammation and it has been shown in studies that quercetin may help reduce this inflammation. Some of the beneficial properties of quercetin are:

Allergy relief

Due to its ability to help with inflammation, quercetin may also be very beneficial for allergy relief. Some studies have shown that it may help block inflammation and lessen the symptoms of allergies although more studies are needed.

Anticancer effect

Quercetin is an antioxidant, and due to its ability to help stabilize free radicals, it has been shown in studies to have anticancer properties.

Helps your brain

As noted above, it may help with certain brain disorders like Parkinson's disease. The way it does this is by using its antioxidant properties to help fight it. Some studies have shown that it helps prevent it and other brain disorders.

Reduces blood pressure

In some studies, quercetin has been shown to reduce cholesterol too. Quercetin is thought to be a vasodilator, which means it widens the blood vessels and lowers your blood pressure. Many people are at risk of heart disease as it is the 

Please read this caution

All of the studies above were done in labs in test tubes or on mice. There have been some human studies of quercetin but not enough to become scientific fact. More clinical studies on human subjects will need to be carried out to ensure that these benefits occurin quercetin in humans.

How much quercetin do I need daily?

Most people get about 5mg to 40 mg daily of quercetin through eating certain foods. Most doses of quercetin recommend 500mg while some go as high as 1000mg as the recommended concentrations of quercetin. The quercetin dosage may also depend on your age, weight, health condition, and how quercetin interacts with other medications you may be taking.

Are there any risks or side effects of quercetin?

There are not many adverse effects associated with quercetin, although the most common effects of quercetin supplemenation being that some people may experience an upset stomach or headaches. There is a possibility that quercetin can interact with certain medications so it is best to consult your physician before taking quercetin supplements.

What are good food sources for quercetin?

Foods with quercetin can be found in a wide range of fruits, vegetables, leaves, teas, and even wine. Quercetin is the most abundant of all flavonoids in many foods like onions, capers (the flower bud), tomatoes, apples, peppermint tea, and shallots. The quercetin content in foods can vary depending on where they are grown when they are harvested/picked, and how fresh the fruit or vegetable is. Food sources of quercetin include:

  • red apples
  • red grapes
  • broccoli
  • kale
  • red leaf lettuce
  • berries, all berries
  • tea, both the green and black varieties
  • capers
  • green and yellow bell peppers
  • red and white onions
  • shallots
  • asparagus
  • cherries
  • tomatoes
  • dill
  • cilantro
  • radicchio
  • watercress
  • kale
  • broccoli
  • nuts and seeds
  • olive oil

These are just some of the most common foods available that contain quercetin. You can check out the USDA's site here to view a more extensive list and to see how much quercetin is contained by each food.

Are there other options besides food sources for quercetin?

There are quercetin supplements available, but it is very important to know that quercetin may interact with certain medications so it is important to talk to your doctor or healthcare provider before you start taking it. Some people have also found quercetin in fresh juices and teas.

Where can I buy quercetin?

Many health food stores and pharmacies will sell quercetin supplements since it is a dietary antioxidant. You can also check online to see if anyone is selling quercetin capsules or tablets forms of quercetin at a cheaper price than what you would find in your local health store. Please check the labels and talk to your doctor to determine the correct amounts of quercetin for your quercetin supplementation. 

Summary

Quercetin is a flavonoid antioxidant that is found in many foods and vegetables. It can have many beneficial antioxidant effects from preventing brain disorders like Parkinson's disease to lowering cholesterol but more studies are needed in humans to conclusively state it as fact. Typically, most people eat between 5mg - 40mg in a day although most doses of the dietary supplement are for 500mg to 1000mg. There are slight risks of taking too much quercetin as it can cause an upset stomach and headaches. There are many food sources for quercetin ranging from tomatoes to olive oil and we recommend checking out the USDA's website to get a complete list. Quercetin is also available as a supplement in most health stores and online. If you think quercetin may help you or you have more questions, please discuss taking quercetin with your doctor, pharmacist, or healthcare provider.

References and Sources:

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