Quercetin: Health benefits, dosage, and side effects

People can get quercetin through a balanced diet or by taking a supplement.

This article details the possible benefits of quercetin. It also looks at the potential side effects.

What is quercetin?

Quercetin is a flavonol, which is a sub-category of flavonoids.

Flavonoids are a particular chemical in plants, called phytonutrients, and have a wide range of health benefits.

Humans cannot make quercetin in their body, but many fruits, vegetables, and drinks contain it.

Foods and drinks that contain quercetin include:

  • grapes
  • berries
  • cherries
  • apples
  • citrus fruits
  • onions
  • buckwheat
  • broccoli
  • kale
  • tomatoes
  • red wine
  • black tea

Quercetin is also present in herbal remedies, such as ginkgo biloba and St John’s wort. People can also take quercetin as a supplement.

Quercetin is one of the most common and well-researched flavonoids.

Quercetin may contain anticancer properties that might help prevent the spread of cancerous cells and tumor growth.

Research has shown that a diet high in flavonoids, such as quercetin, can help prevent cancers. Fruits and vegetables are full of flavonoids, so increasing intake of these foods might reduce the risk of many types of cancer.

A 2015 report found that quercetin restricted the growth of prostate cancer cells in mice and rats.

A 2018 in vitro study indicated that quercetin showed promise in both the treatment and prevention of prostate cancer. In vitro means the researchers performed the experiment outside of a living thing, for example, in a test tube.

Researchers still need to find out more about the anticancer properties of quercetin in humans and to ensure the body can absorb high doses of quercetin effectively.

4. Preventing neurological diseases

Quercetin may help to prevent neurodegenerative diseases, such as Alzheimer’s or Parkinson’s disease.

Oxidative stress contributes to the development of neurodegenerative diseases. Oxidative stress occurs when there is an imbalance of free radicals in the body. The antioxidant properties of quercetin may help fight free radicals.

Research on rats showed that quercetin could protect against oxidative stress. It also showed quercetin could protect against the toxic effect of certain metals on the nervous system.

People can get quercetin through their diet by eating a range of fruit and vegetables each day.

Onions have the highest level of quercetin compared to other tested produce, containing approximately 300 mg per kilogram.

If people take quercetin as a supplement, the most common dose is 500 mg per day, but some people can take up to 1,000 mg per day.

Supplements may also include other substances, such as bromelain or vitamin C, which may help the body absorb quercetin more effectively.

Side effects and risks

The natural antioxidants found in fruits and vegetables can be very beneficial when consumed as part of a balanced and nutritious diet.

The United States Food and Drug Administration (FDA) class quercetin as a generally safe substance.

Some people reported minor side effects when taking high doses of quercetin, such as 1,000 mg per day, long-term.

Side effects may include:

  • headaches
  • nausea
  • tingling sensations

Quercetin may interact with some medications, so people should ask their doctor before taking a supplement.


Quercetin is a flavonoid found in fruit and vegetables. It has a wide range of benefits, which people can get by including a variety of fruit and vegetables in their diet.

Although many studies have found many potential benefits of quercetin, many of these studies have been animal or in vitro studies.

Further research on humans is necessary to understand the benefits and side effects fully.

If people want to supplement their diet with quercetin, they should seek advice from a healthcare professional first.

Quercetin is available from pharmacies, health food stores, and online.

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