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Quercetin: Health Benefits, Side Effects and Precautions


Quercetin: Health Benefits, Side Effects and Precautions

Quercetin is an antioxidant flavonoid which is found in many plant-based foods from apples to nuts to capers. What are the best sources of Quercetin, how does it work, and are there any side effects to its use? Read on to find out so many more great things about the many benefits of Quercetin.

What is Quercetin?

Most people have heard of flavonoids, plant-based antioxidant pigments that are being recognized for many of their health benefits. Flavonoids also give plants their color and belong to the class of polyphenols. Polyphenols have gained so much popularity recently when studies have suggested their benefits in preventing heart disease, cancer, and other chronic diseases. 1 2

Many vegetables, fruits, nuts, honey and medicinal herbs are rich in Quercetin. Raw capers and onions have the highest amount of Quercetin, while apples are the most common food source. Quercetin makes about 75% of all flavonoids consumed through our diet [3]. The only issue is we need to eat pound and pounds of onions to get a 500mg daily dose which makes getting an adequate daily dose difficult. 





Quercetin is also relatively better researched than most other flavonoids and has gained the nickname as the  “master flavonoid ". 3    




The health benefits of Quercetin

Quercetin’s health benefits are many and it is well known for an amazing ability to fight inflammation and its antioxidant properties, meaning it can neutralize damaging free radicals. These are by-products of chemical reactions in the human body which can be harmful. In fact, these are a common precursor to several chronic diseases.So eliminating these can be extremely beneficial to our health.



Research has suggested Quercetin has both brain-protective and antidepressant effects and may reduce inflammation and oxidative stress, a condition in which free radicals cause damage to cells.Inflammation as we also know is the root cause of many illnesses and diseases. 


Heart disease

Some studies show that Quercetin may protect against the buildup of plaque in the arteries, decreasing “bad” LDL levels, thus reducing risk of heart disease and high blood pressure. 


Quercetin has also shown some promise in relieving allergies as it stabilizes mast cells, which release histamine, says Robin Foroutan, RDN, an integrative medicine dietitian and spokesperson for the Academy of Nutrition and Dietetics. “Histamines are to blame for symptoms like seasonal allergies, so high doses of Quercetin can be really helpful to reduce seasonal allergy and hay fever symptoms.”


Cancer risk

Some in vitro data (meaning the research was done outside of a living organism, like a culture dish) has even indicated that Quercetin may help to decrease the formation of liver cancer cells and quantities of rectal tumors. Unfortunately, though, there are few large-scale clinical studies in people at present and this is a space to watch.


How to take Quercetin for the best results

Your body has some challenges absorbing Quercetin properly, so naturally a supplement helps. It also helps taking in a Quercetin Dihydrate form which helps it being more available to your body and for faster absorption. 

With medical supervision, Quercetin has been safely used in amounts up to 1,000 mg twice daily for 12 weeks.4 The most popular dosage remains as 500mg or 1000mg daily. 

The appropriate dose for you may depend on factors including your age, gender, and medical history. Speak to your healthcare provider to get personalized advice if you choose to take this supplement and you feel you need to exceed the recommended dose.


Side effects of taking Quercetin

Quercetin is generally well-tolerated when used following the recommended amounts. Some have reported tingling in the arms and legs, as well as upset stomach and headaches when taking Quercetin supplements at higher doses. So speaking with your professional if wanting to go outside the recommended dosage is essential. 

Very high doses—greater than 1000mg per day—may cause kidney damage. Avoid taking Quercetin if you're pregnant, nursing, or have a kidney condition. It may also interfere with some antibiotics or blood thinners.

Side effects of Quercetin supplementation may include:

  • Headache (oral use)
  • Numbness and tingling (oral use)
  • Kidney damage (intravenous use greater than 945 mg/m2)

Precautions when taking Quercetin supplements

Pregnant women, breastfeeding women, and people with kidney disease should avoid Quercetin.


Final thoughts on the benefits of Quercetin

In summary, Quercetin has a number of great health-promoting benefits for anybody looking to add a great dietary supplement towards a healthy diet, longevity and lifestyle. Some of the top Quercetin benefits include the ability to help your body reduce inflammation and to improve your immune system’s health. 

The recommended dosage for a Quercetin supplement is around 12.5 – 25mg per kilogram body weight. This equates to around 900 – 1800mg per day for a 75kg person, taken in two to three separate servings throughout the day. Generally people take either 500mg per day or 1000mg per day. 

Quercetin is a safe dietary supplement when used at the recommended dosage. It goes well with other bioflavonoids and plant-derived supplements. 



    4. Jin F, Nieman DC, Shanely RA, Knab AM, Austin MD, Sha W. The variable plasma quercetin response to 12-week quercetin supplementation in humans. Eur J Clin Nutr. 2010;64(7):692-7. doi:10.1038/ejcn.2010.91


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