Quercetin is a natural flavonoid present in various foods such as colored fruits and vegetables and have many health benefits due to its strong antioxidant, anti-cancer, anti-inflammatory, antiviral and antibacterial properties. Different experimental and animal studies have shown possible therapeutic benefits of quercetin (obtained through foods/supplements) in specific cancer types such as pancreatic, breast, ovarian, liver, glioblastoma, prostate and lung cancers, and also for improving the efficacy of specific chemotherapies and other cancer treatments. Large clinical trials need to be done to validate these benefits in humans. Also, excess use of quercetin may lead to side-effects like thyroid dysfunction.
What is Quercetin?
Quercetin is a naturally occurring flavonoid found abundantly in a number of nutrient packed foods including:
- Coloured Fruits such as apples, grapes and berries
- Red Onions
- Red wine
- Leafy greens
It has strong antioxidant, anti-inflammatory, antiviral and antibacterial properties.
Health Benefits of Quercetin
Being a strong antioxidant, quercetin and quercetin rich foods are considered to have many health benefits. Some of the health benefits of quercetin include:
- May reduce heart diseases
- May reduce inflammation
- May reduce the signs of aging
- May reduce the risk of respiratory and gastrointestinal infections
- May reduce blood pressure
- May reduce allergy
Side-Effects of Quercetin
Following are some of the common side-effects of quercetin when consumed orally:
- Numbness in arms and legs
Intravenous administration of very high dose of quercetin may have certain side-effects in some people such as :
- Flushing and sweating
- Nausea and vomiting
- Breathing difficulty
- Kidney damage
Another possible side-effect associated with excess intake of quercetin is that it may interfere with thyroid function. Apart from side-effects like thyroid dysfunction, taking quercetin may also worsen conditions in those with kidney problems.
Anti-Cancer Properties of Quercetin
The flavonoid quercetin appears to be a promising anti-cancer agent based on the findings from several laboratory and preclinical animal models and a few small clinical and observational studies. Below are the examples of some of these studies highlighting the potential anti-cancer benefits of quercetin.
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Impact of Using Quercetin along with Other Supplements or Cancer Treatments
Quercetin along with Curcumin may Reduce Adenomas in Patients with Familial Adenomatous Polyposis – Clinical Study
A small clinical study done by the researchers from the Cleveland Clinic in Florida, United States evaluated the efficacy of the combination of dietary supplements curcumin and quercetin to reduce adenomas in 5 patients with Familial adenomatous polyposis, a hereditary condition where a number of precancerous polyps develop in the colon or rectum, thereby increasing the chances for colorectal cancer. The study found that the number and size of the polyps decreased in all patients with a mean percentage decrease of 60.4% and 50.9%, respectively, after 6 months of treatment with curcumin and quercetin. (Marcia Cruz-Correa et al, Clin Gastroenterol Hepatol., 2006)
Quercetin may Improve the Efficacy of Temozolomide in Inhibiting Human Glioblastoma Cells- Experimental Study
A laboratory study done by the researchers form the Changshu Traditional Chinese Medical Hospital and Second Affiliated Hospital of Soochow University in China found that the use of quercetin along with temozolomide, a standard of care chemotherapy treatment for brain tumors, significantly improved Temozolomide’s inhibitory effect on the human glioblastoma/brain cancer cells and suppressed the glioblastoma cell survival. (Dong-Ping Sang et al, Acta Pharmacol Sin., 2014)
Quercetin may Improve the Anti-cancer effects of Doxorubicin in Liver Cancer Cells – Experimental Study
Another laboratory study done by the researchers from the Zhejiang University in China highlighted that the use of quercetin may enhance the anti-cancer effects of doxorubicin chemotherapy on liver cancer cells while protecting the normal liver cells. (Guanyu Wang et al, PLoS One., 2012)
Quercetin along with Cisplatin Chemotherapy may Enhance Apoptosis/Cell Death of Oral Cancer Cells – Experimental Study
In a study done by the researchers from the Guangdong Provincial Center for Disease Control and Prevention, Sun Yat-sen University and South China Institute of Environmental Sciences – Guangzhou in China, they evaluated the impact of using quercetin along with Cisplatin chemotherapy in human Oral Squamous Cell Carcinoma Cell lines (OSCCs) as well as in mice induced with oral cancer. The study found that the combination of quercetin and cisplatin enhanced cell death/apoptosis in the human oral cancer cells as well as inhibited the cancer growth in mice, suggesting the therapeutic potential of quercetin and cisplatin combination in Oral Cancer. (Xin Li et al, J Cancer., 2019)
Using Quercetin in Ovarian Cancer Refractory to Cisplatin Chemotherapy may be beneficial – Clinical Study
In a small phase 1 clinical trial done by the researchers of the University of Birmingham, UK, a patient with ovarian cancer who was not responding to the cisplatin treatment was given two courses of quercetin, post which the amount of the protein CA 125 (cancer antigen 125 – used as a marker for ovarian cancer) in the blood significantly reduced from 295 to 55 units/ml. (D R Ferry et al, Clin Cancer Res. 1996)
Quercetin Supplement along with Resveratrol may benefit in managing Prostate Cancer and Colon Cancer – Preclinical Study
A study done by the researchers from the University of Wisconsin and William S. Middleton VA Medical Center in Wisconsin in the United States in a mouse (transgenic adenocarcinoma of the mouse prostate -TRAMP) model which closely mirrors the pathogenesis of human prostate cancer, found that the combination of quercetin and resveratrol supplements, two antioxidants found abundantly in grapes, had anti-cancer benefits in this prostate cancer mouse model. (Chandra K Singh et al, Cancers (Basel)., 2020)
Another study done by the researchers from the Texas A&M University, in the United States found that the combination of Resveratrol and quercetin may have anticancer activity in colon cancer cells. (Armando Del Follo-Martinez et al, Nutr Cancer., 2013)
Quercetin may Improve the therapeutic efficacy of Fluorouracil treatment in Liver Cancer – Experimental study
A laboratory study done by Kurume University, in Japan found that the combination treatment with quercetin and fluorouracil (5-FU) may lead to an additional or synergistic inhibitory effect on liver cancer cell proliferation. (Toru Hisaka et al, Anticancer Res. 2020)
Quercetin Use and the Risk of Cancers
Quercetin Intake may Reduce the Risk of Non-Cardia Gastric Cancer
Researchers from the Karolinska Institutet in Sweden analyzed data from a large Swedish population-based study involving 505 gastric cancer cases and 1116 controls to evaluate the association between quercetin and the risk different types of gastric cancers such as cardia and non-cardia subtypes of gastric cancer. The study found that a high dietary quercetin intake significantly reduced the risk of noncardia gastric adenocarcinoma, especially in female smokers. (A M Ekström et al, Ann Oncol., 2011)
Taking quercetin rich foods may hence be beneficial in reducing the risk of cancers such as gastric cancer.
Experimental Studies on the Anti-Cancer Potential of Quercetin
Numerous laboratory studies have been carried out by researchers from different parts of the world to find out whether quercetin rich foods/supplements have anti-cancer effects on different types of cancers. Below are some examples of the recent laboratory studies or preclinical studies which evaluated the anti-cancer potential of Quercetin.
Liver Cancer : A study done by the researchers from the Kurume University in Japan highlighted that quercetin may inhibit the proliferation of liver cancer cells by triggering apoptosis/cell death as well as cell cycle arrest. (Toru Hisaka et al, Anticancer Res., 2020)
Lung Cancer : A study done by Hubei University of Medicine, China highlighted that quercetin may inhibit the proliferation and cancer spread of human Non-Small Cell Lung Cancer cell lines. (Yan Dong et al, Med Sci Monit,. 2020)
Prostate Cancer : A study done by the researchers from the University of Madras in India and the Pukyong National University in South Korea found that quercetin may reduce prostate cancer cell survival in preclinical animal models, and may also inhibit the proliferative and anti-apoptotic proteins, indicating possible benefits of quercetin supplements in preventing the risk of prostate cancer. (G Sharmila et al, Clin Nutr., 2014)
Ovarian Cancer : A study done by the researchers from the University of Madras, India highlighted that Quercetin has the potential to inhibit human metastatic ovarian cancer cell growth. (Dhanaraj Teekaraman et al, Chem Biol Interact., 2019)
Breast Cancer : In a lab study conducted by the researchers from the University of Madras in India, they highlighted that using Quercetin may help in inducing Apoptosis or Cell death in Breast Cancer Cells. (Santhalakshmi Ranganathan et al, PLoS One., 2015)
Pancreatic Cancer : Researchers from the David Geffen School of Medicine at UCLA, US evaluated the efficacy of oral administration of quercetin in a pancreatic cancer mouse model and found that quercetin was capable of inhibiting growth of pancreatic tumors in the mouse model. (Eliane Angst et al, Pancreas., 2013)
Different preclinical and laboratory studies have shown the potential/possible benefits of quercetin-rich foods and supplements in the treatment of specific cancer types such as pancreatic, breast, ovarian, liver, glioblastoma, prostate and lung cancers, as well as improving the therapeutic efficacy of specific chemotherapies and other cancer treatments. Large clinical trials are to be done to validate these anti-cancer benefits of quercetin in humans.
Quercetin has strong antioxidant, anti-cancer, anti-inflammatory, antiviral and antibacterial properties. The wide range of health benefits of quercetin can be obtained by including a variety of foods such as colored and nutrient packed fruits and vegetables as part of the diet. Quercetin supplements are often combined with other bioactive compounds such as Vitamin C or Bromelain to improve its absorption and potency. However, excess intake of quercetin may lead to many side effects including interference with proper thyroid functioning. Avoid consuming quercetin supplements without the guidance of your healthcare practitioners to stay away from side-effects like thyroid dysfunction and interactions with ongoing treatments.
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