Quercetin Benefits Foods Dosage & Side Effects

Quercetin is a plant compound found in various foods that has a wide range of beneficial effects on the body. It also seems to be very promising in the prevention and treatment of colds. This is because quercetin can reduce symptom severity and the number of days of illness, as well as susceptibility to upper respiratory tract infections.

Table of Contents

Quercetin, a plant substance against colds

Quercetin is a natural yellow pigment, belongs to the flavonoid group and is found in many foods (see list at the bottom of the text). The plant substance has a variety of effects on health and, according to various studies, can also be used preventively as well as therapeutically for colds.

 

The Effects of Quercetin

Researchers found that quercetin has positive effects on the body at various levels. On the one hand, it has an antioxidant effect and can thus interrupt the chain reaction of free radicals that attack cells and can lead to oxidative stress, thus preventing cell damage (for more antioxidant substances, see our article Antioxidants protect our cells).

 

Other beneficial effects of quercetin are the following :

Quercetin in upper respiratory tract infections

The most common upper respiratory infections are the so-called colds, which usually bring symptoms such as a runny or stuffy nose, as well as pain when swallowing, fatigue or cough . The studies presented below were able to show a positive effect of quercetin preparations in upper respiratory tract infections.

Reduction in days of illness and symptom severity.

A placebo-controlled, double-blind, randomized trial demonstrated that taking quercetin twice daily (in the morning after awakening and between 2 pm and the last meal of the day) for 12 weeks resulted in a reduction in symptom severity and days of illness. Individuals aged 18-85 years with varying fitness levels were studied, but the beneficial effect of quercetin supplements was seen only in those who considered themselves physically fit and were 40 years or older .

Fewer infections after intense exercise

Further studies focused on the effect of quercetin after intense exercise, as it is associated with an increased risk of upper respiratory tract infections . This showed a reduction in new cases when quercetin was taken 3 weeks before and 2 weeks after exercise  .

Quercetin was also observed to offset increased susceptibility to infection after intense exercise in mice administered an influenza virus .

Antiviral activity of quercetin

In vitro studies (are conducted outside a living organism) have demonstrated potent antiviral properties of quercetin in both adenoviruses ⑺ and coronaviruses , both of which can be the cause of upper respiratory tract infections.

For other agents you can use to protect yourself from coronaviruses, see the article Over-the-counter Agents to Prevent Covid-19, where we present a concept that includes quercetin.

Taking Quercetin for colds

Quercetin can therefore have an extremely positive effect on infections of the upper respiratory tract. Moreover, due to the low risk of side effects when taken in the correct dosage (see below), quercetin preparations can be integrated into the prevention and treatment of colds without hesitation. Quercetin can also serve as a good supplement for the prevention of upper respiratory tract infections that can occur after strenuous exercise.

The positive effects of the above studies were due to a dose of 500 mg of quercetin taken twice daily for up to 12 weeks. This showed an increase in quercetin plasma levels without side effects ⑷. We therefore recommend that this duration and dose not be exceeded, as it is not known whether longer-term use is safe.

Combination of quercetin with other vital substances

Additional intake of other phytochemicals (e.g., resveratrol, catechins) and curcumin may enhance the effects of quercetin, so that the beneficial effects may occur even at lower doses . Furthermore, the effects of quercetin can be enhanced by the additional intake of vitamin C or by bromelain .

Quercetin is also a zinc ionophore and makes the cell membrane permeable to zinc ions so that the cell can be better supplied with them. Since zinc plays an important role in strengthening the immune system, these two substances can also be combined well.

To learn how you can additionally support your body against colds, see our article What really helps against colds.

What to look for when buying quercetin

Be sure to select high-quality quercetin preparations that do not contain allergens (e.g., gluten or lactose) or unnecessary additives. There are pure quercetin preparations or combination preparations (e.g. quercetin with vitamin C from effective nature) in which the dosages are coordinated (*quercetin with 500 mg per capsule).

Possible side effects

The intake of quercetin through foods such as fruits and vegetables is very healthy and cannot cause any damage to the body. In supplement form, quercetin is considered safe if a dose of 1000 mg/day is not exceeded for 12 weeks. However, it is not known whether larger amounts and longer-term use are safe, as there are no specific studies on this.

Quercetin in high doses (more than 1000 mg/day) may cause headache or tingling in the arms and legs. Intravenous use may also cause kidney damage in case of overdose. If you experience side effects while taking quercetin preparations, contact your doctor.

Possible drug interactions

If you are taking any medications, talk to your doctor before taking quercetin preparations, as quercetin may alter the way the medications work and increase the risk of side effects .

In children and during pregnancy

Since there are no studies on quercetin and its effectiveness or possible side effects for pregnant women and children under 12 years of age, quercetin preparations should not be taken here as a precaution. In the form of food, quercetin can of course be consumed by these groups of people without concern.

Quercetin in foods

Quercetin is found in a wide variety of fruits and vegetables as well as in cereals and pseudocereals. These include, for example, capers, apples, berries, onions, tomatoes and buckwheat. Particularly good sources of quercetin are the following, whereby the quercetin value always refers – unless otherwise stated – to 100 g of the raw food :

More Quercetin in old apple varieties.

 

However, be sure to use apples of older varieties, as new varieties (e.g., Fuji) seem to contain significantly less quercetin. Old apple varieties are generally richer in phytochemicals – and they’re also less allergenic, as we explain in our article on the five benefits of apples.

It is possible that the anti-allergenic effect of old apple varieties is also due to their higher quercetin content. This is because quercetin protects against allergies and allergic reactions. It stabilizes the cell membranes of the mast cells and thus prevents them from releasing histamines and other pro-inflammatory messenger substances too quickly. Histamines are the substances that cause allergic reactions in the body: swelling of mucous membranes, redness and itching.

Quercetin is heat stable

Quercetin passes into the cooking water during cooking, but is not destroyed. Therefore, if you cook vegetables, use the cooking water for sauces or soups, for example. It is easier to steam the vegetables or prepare them in a pan. According to a study, the quercetin content is not reduced either when frying in a pan or when preparing in the microwave ⒀.

FAQ

Can you take Quercetin daily?

In the form of dietary supplements, quercetin is considered safe if a dose of 1000 mg/day is not exceeded for 12 weeks. However, it is not known whether larger amounts and longer-term intake are safe, as there are no concrete studies on this.

What is the best source of Quercetin?

Particularly good sources of quercetin are the following, whereby the quercetin value always refers - unless otherwise stated - to 100 g of the raw food: Capers (in jar) 180 mg. Lovage 170 mg. Dill 55 mg.

Is Quercetin an inflammatory?

Quercetin calms pro-inflammatory and histamine-releasing immune cells. These include immune cells. Quercetin can have a balancing effect on the activity of certain immune cells and thereby reduce the amount of pro-inflammatory messenger substances (cytokines such as IL-6, CRP, IL-4 and TNF-α). In addition, via the regulatory effects on so-called mast cells, the release of histamine should be reduced. In the same way, quercetin can bring the formation of certain antibodies (IgE antibodies), which initiate the release of histamine in the course of an allergic reaction, to a normal level.

Does Quercetin affect sleep?

According to a study published in 2011 6 weeks of dietary quercetin supplementation did not affect transient moods of energy and fatigue and sleep quality in young moderately trained military individuals.

Does Quercetin cause anxiety?

Quercetin may exert antidepressant effects by inhibiting HPA axis hyperactivity, which has been confirmed by several studies.

How long does it take for Quercetin to start working?

The effect of quercetin in strengthening the cell membrane of mast cells takes time. It may be necessary to take it for 3 to 6 weeks to notice an antihistamine effect, and it is more effective to take it preventively before the allergy season begins and to maintain it throughout.

Can Quercetin raise heart rate?

According to some Studies and User Reviews on Drugs.com Quercetin can have a negative effect on your heart rate and even cause heart palpitations. "It took a while for me to put it together but this supplement caused pretty significant heart palpitations and racing heart." A user wrote on Drugs.com after taking a Quercetin supplement for 10 days.

Is Quercetin good for lung health?

Quercetin does have many benefits for your lung health because of it's anti-inflammatory properties. One Study in 2020 concluded that it even Attenuates Acute Lung Injury Caused by Cigarette Smoke.

Does Quercetin lower blood pressure?

A research team analyzed 17 studies on the effect of quercetin. 13 of the studies examined were able to demonstrate a significant reduction in blood pressure through the regular intake of quercetin. The analysis was recently presented in the journal Nutrition Reviews.

Can Quercetin make you depressed?

Overall, the anti-depressant effects of quercetin has been proven in numerous studies, and the relevant mechanisms have been continuously explored. Quercetin has many anti-depressant benefits.

Who should not take Quercetin?

Quercetin supplements should be avoided during pregnancy. Quercetin is strongly suspected of causing leukemia because it attacks the baby's genetic material during pregnancy. In combination with drugs/medication, further undesirable effects are to be expected: polyphenols paralyze important detoxification enzymes (cytochrome P450 enzymes).

  • (1) Nieman, D. C., Henson, D. A., Gross, S. J., Jenkins, D. P., Davis, J. M., Murphy, E. A., … & Mayer, E. P. (2007). Quercetin reduces illness but not immune perturbations after intensive exercise. Medicine & Science in Sports & Exercise, 39(9), 1561-1569.
  • (2) Nair, M. P., Kandaswami, C., Mahajan, S., Chadha, K. C., Chawda, R., Nair, H., … & Schwartz, S. A. (2002). The flavonoid, quercetin, differentially regulates Th-1 (IFNγ) and Th-2 (IL4) cytokine gene expression by normal peripheral blood mononuclear cells. Biochimica et Biophysica Acta (BBA)-Molecular Cell Research, 1593(1), 29-36.
  • (3) Ott, Sebastian: Infektionen der oberen Atemwege – DGIM Innere Medizin. (German Article)
  • (4) Heinz, S. A., Henson, D. A., Austin, M. D., Jin, F., & Nieman, D. C. (2010). Quercetin supplementation and upper respiratory tract infection: A randomized community clinical trial. Pharmacological research, 62(3), 237-242.
  • (5) Davis, J. M., Murphy, E. A., McClellan, J. L., Carmichael, M. D., & Gangemi, J. D. (2008). Quercetin reduces susceptibility to influenza infection following stressful exercise. American Journal of Physiology-Regulatory, Integrative and Comparative Physiology.
  • (6) Nieman, D. C., Henson, D. A., Maxwell, K. R., Williams, A. S., McAnulty, S. R., Jin, F., … & Lines, T. C. (2009). Effects of quercetin and EGCG on mitochondrial biogenesis and immunity. Medicine & Science in Sports & Exercise, 41(7), 1467-1475.
  • (7) Chiang, L. C., Chiang, W., Liu, M. C., & Lin, C. C. (2003). In vitro antiviral activities of Caesalpinia pulcherrima and its related flavonoids. Journal of Antimicrobial Chemotherapy, 52(2), 194-198.
  • (8) Chen, L., Li, J., Luo, C., Liu, H., Xu, W., Chen, G., … & Jiang, H. (2006). Binding interaction of quercetin-3-β-galactoside and its synthetic derivatives with SARS-CoV 3CLpro: Structure–activity relationship studies reveal salient pharmacophore features. Bioorganic & medicinal chemistry, 14(24), 8295-8306.
  • (9) Nishtha S. , Rai Ajit K. Curcumin and quercetin synergistically inhibit cancer cell proliferation in multiple cancer cells and modulate Wnt/β-catenin signaling and apoptotic pathways in A375 cells. Volume 52, January 2019, Pages 117-128.
  • (10) Colunga Biancatelli, R. M. L., Berrill, M., Catravas, J. D., & Marik, P. E. (2020). Quercetin and vitamin C: an experimental, synergistic therapy for the prevention and treatment of SARS-CoV-2 related disease (COVID-19). Frontiers in immunology, 11, 1451.
  • (11) Lakhanpal, P., & Rai, D. K. (2007). Quercetin: a versatile flavonoid. Internet Journal of Medical Update, 2(2), 22-37.
  • (12) Stuart, Annie (2021, 20.Mai): Quercetin: Anwendungen und Risiken. (German Article) URL: https://www.webmd.com/vitamins-and-supplements/quercetin-uses-and-risks [02.01.2022].
  • (13) Nishimuro H, Ohnishi H, Sato M, et al. Estimated daily intake and seasonal food sources of quercetin in Japan. Nutrients. 2015;7(4):2345-2358. Published 2015 Apr 2.

Leave a Comment