Quercetin is a polyphenolic flavonoid – one of the most abundant of the flavonoids and widely found in vegetables and fruits.

Quercetin has been much studied for its affects on our biology and today I’m going to share with you how important it is not only for breast cancer patients, but also for those of us looking to protect themselves from the big C-virus sweeping around the world yet again.

Quercetin has been shown to be very beneficial for us as breast cancer survivors, and here are the top 12 reasons why. Please read all the way to the bottom of the article if you wish to know about its anti-viral properties.

1. Anti-mutagenic – Quercetin prevents and protects against DNA damage. DNA damage is well recognized as an important factor in cancer development and progression. [1]-[5]

2. Inhibits Proliferation, Promotes Tumor Suppressor Genes, Induces Cell Cycle Arrest – Quercetin not only blocks the continuous multiplication of the cellular replication cycle known as proliferation, it also upregulates (promotes) a gene known as P53, which is a tumor suppressor gene. P53 is responsible for regulating cell division by keeping cells from proliferating (growing and dividing too fast). When P53 is faulty, there has been found to be an associated increase in cancer risk. P53 is considered to be one of the most frequently mutated genes leading to cancer development. [6]-[10]

One study [11] found that quercetin also inhibited the proliferation of multi-drug resistant estrogen receptor negative breast cancer cells. Researchers stated that quercetin inhibited cell proliferation better than the anti-estrogen drug Tamoxifen.

3. Anti-inflammatory – Quercetin has been shown in many studies to reduce inflammation. Since cancer is an inflammatory process, this contributes to its anti-cancer properties. [12]-[14]

4. Anti-Aromatase Activity – Quercetin inhibits excess estrogen production by blocking the activity of an enzyme known as aromatase, which is required for the synthesis of estrogen. [15], [16]

5. Promotes Apoptosis – Quercetin has been found to promote apoptosis in both estrogen receptor-positive and -negative breast cancer cells. Apoptosis is programmed cell death, which normal cells exhibit. This is the ability for cells to self-destruct if they receive signals that the replication process is occurring too rapidly. Tumor cells lose this ability, and this contributes to their rapid growth rate. [17]-[20]

6. Blocks Angiogenesis – Quercetin blocks the ability of tumors to feed themselves by creating new blood vessels, a process that is known as angiogenesis. This inhibits their ability to grow and spread into other tissues. [21], [22]

7. Down-regulates Survivin – Quercetin down-regulates a protein known as survivin, known to be highly expressed in most cancers and is associated with chemotherapy resistance, increased tumor recurrence, and shorter patient survival times. [23]

8. Suppresses Breast Cancer Stem Cells – Quercetin has been shown to suppress breast cancer stem cells. This is important because chemotherapy and radiation are known to promote the generation of breast cancer stem cells, the cells which give rise to more breast cancer. [24]

9. Protects Bones – Quercetin has bone-protective qualities and exerts this influence by increasing alkaline phosphatase (ALP) activity in bone-building cells known as osteoblasts. I include this because the bones are a common metastasis site for breast cancer. [25]

10. Works Synergistically with Hyperthermia – A preliminary study (in vitro and with animals with prostate tumors) had interesting findings. Researchers investigated the effects of quercetin combined with hyperthermia, a natural form of cancer treatment using infra-red technology to heat the core temperature of the body, which is believed to be effective in killing cancer cells. They found that quercetin worked synergistically with the hyperthermia to suppress tumor growth. [26]

11. May Combine Well with Doxorubicin Chemotherapy – For those undergoing chemotherapy with doxorubicin (aka Adriamycin) a Chinese research team discovered that quercetin amplified the anti-tumor effects of the chemotherapy drug. It increased intracellular accumulation of doxorubicin so that a lower dose could be given (thus less toxicity) and it eased the toxicity of the drug. [27]

12 Protects Nerves – Quercetin has been shown to protect nerve cells from the damaging effects of chemotherapy and radiation. Peripheral neuropathy is a common complaint from patients receiving these treatments. 2013 research found that quercetin and rutin (also a flavonoid) work synergistically to protect neurons in the spinal cord that play a role in sensory information and pain perception. [28]

All of this make quercetin look like the anti-cancer superstar. However, let’s just temper this with the knowledge that most of the studies being done have been only preliminary – cell studies and animal studies. Very few clinical studies have assessed the anti-cancer effects of quercetin in actual human bodies, nor proper dosages. Considering that it is non-toxic to healthy cells and widely present in our food chain, however, it certainly would not hurt to work with a naturopath or integrative physician in establishing the right dose of quercetin for you.

Along those lines, in his book “Natural Strategies for Cancer Patients” Dr Russell Blaylock has a protocol to minimize the nerve damaging effects of chemotherapy using a combination of quercetin and curcumin. Here’s what he recommends:

(1) 500 mg capsule of curcumin
(1) 500-1000 mg capsule of quercetin
Dissolve the contents of both capsules in one tablespoon of extra virgin olive oil (Marnie’s note: the phytosomal quercetin mentioned below was probably not available at the time of Dr Blaylock’s book, so I think you could substitute that in lieu of taking these with 1 tbsp olive oil).  Take this combination orally three times daily with meals.

Now then, as to my mention of the use of quercetin to help with coronavirus, Dr Mercola has shared with us this week in his article “Quercetin — An Alternative to Hydroxychloroquine, and More” (which has now been taken down from his website but I saved a copy which includes all the relevant references) that quercetin works very much like hydroxychloroquine, a drug found to be effective against SARS-CoV-2, when used early enough.

The way in which quercetin works should be available to everyone, so I am sharing it here.

Quercetin:

(a) inhibits the spike protein from binding to the ACE2 receptor docking, which inhibits viral attachment and entry into the cell and infecting that cell. It also inhibits replication of already-infected cells, AND reduces the infected cells’ resistance to treatment with anti-viral medication;

(b) modulates the NLRP3 inflammasome, a part of the immune system involved in the uncontrolled release of pro-inflammatory cytokines known as the “cytokine storm” you’ve been hearing about;

(c) is anti-inflammatory which is important for the inflammation seen in the respiratory tract in those with the virus;

(d) has antioxidative benefits, acts as a free radical scavenger – important in any disease process;

(e) has immunomodulatory activity – meaning that if the immune system is under-reacting, it helps to boost it; and if the immune system is over-reacting, it helps to dampen down its activity;

(f) inhibits platelet aggregation – important because a higher incidence of platelet aggregation has been noted in COVID patients;

(g) not only has direct anti-viral activity, including against SARS-CoV-2, but also helps shuttle zinc into cells – and zinc has potent anti-viral and immune-promoting activity;

(h) boosts interferon response to viral activity. A cell secretes interferon when a foreign substance, like a virus, is detected.

In Mercola’s article, he mentions that one COVID-19-specific clinical trial [29] (which I’d encourage everyone to read!) investigated zinc and zinc transporters; vitamins C, D3 and E; and l-lysine. The people who took zinc and two zinc transporters – quinine drops and quercetin – had a lower incidence of COVID-19 than the control group. Over the 20- week course of the study, only two of the 53 test subjects became symptomatic, compared to 12 of the 60 controls.

Dr Mercola also mentions another trial [30], in which 152 patients who tested positive for COVID-19 and had only mild symptoms were split into two groups. 76 were given 1,000 mg of Quercetin Phytosome® (quercetin in sunflower phospholipids that significantly increase its absorption) per day for 30 days, in addition to standard care (analgesics, oral steroids and antibiotics). The other 76 patients only received standard of care. In the quercetin group, just 9.2 percent of patients went on to require hospitalization, compared with 28.9 percent of patients who received just standard of care. Researchers stated “The results revealed a reduction in frequency and length of hospitalization, in need of non-invasive oxygen therapy, in progression to intensive care units and in number of deaths.”

Dr Mercola obtained some of his information from the Front Line Critical COVID-19 Care Alliance. Their early treatment protocol includes:
*Quercetin 250 mg twice per day (best taken as a phytosome which combines quercetin with sunflower lecithin for better bioavailability)
*Elemental zinc 100 mg once per day
*Vitamin C 500-1,000 twice per day

Besides taking quercetin as a supplement, it is also available in all of these foods: adzuki beans, almonds, amla, Anasazi beans, apples with peels, apricots, artichoke, arugula (rocket), asparagus, avocados, bananas, barley, beets, bell peppers, bilberries, black beans, black-eyed peas, black raspberries, black rice, black tea, blackberries, blackcurrants, blueberries, bok choy, Brazil nuts, broccoli, brown rice, Brussel sprouts, buckwheat, buckwheat bran, cantaloupe, capers, cauliflower, celery, cherries, chickpeas, chia seeds, chilies and hot peppers, cocoa powder (unsweetened), collard greens, corn, cranberries, cucumbers, daikon, dandelion greens, dates, dill, dragon fruit, durian, eggplant, elderberries, figs, garlic, gingko biloba, goji, grapefruit, grapes, graviola, green beans, green pepper, green tea, guava, honey, honeydew melon, horseradish, kale, kiwi, kohlrabi, leeks, lemons, lentils, lettuce (esp romaine and red leaf varieties), lima beans, limes, lingonberries, lychee, mangoes, maqui, mulberries, nectarines, noni, onions, parsley, passionfruit, peaches, pears with peels, peas, peppers, persimmons, pigeon pea leaves & seeds, pineapple, plums, pomegranates, pumpkin seeds, quinoa, radishes, raspberries, red onions, rutabaga, sage, scallions, sesame seeds, shallots, spelt, spinach, spring onions, strawberries, sunflower seeds, tea (black and green), tomatoes, turnips, watercress, white button mushrooms, yellow snap beans

DISCLAIMER: Advice in this article should not be substituted for medical advice. Always seek the guidance of your doctor or other qualified health professional with any questions you may have regarding your health or a medical condition. Never disregard the advice of a medical professional, or delay in seeking it because of something you have read in this website.

References:

[1] DNA Damage/Repair Management in Cancers – https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7226105/

[2] Quercetin, a Natural Flavonoid Interacts with DNA, Arrests Cell Cycle and Causes Tumor Regression by Activating Mitochondrial Pathway of Apoptosis – https://www.nature.com/articles/srep24049

[3] Quercetin exerts synergetic anti-cancer activity with 10-hydroxy camptothecin – https://www.ncbi.nlm.nih.gov/pubmed/28822757

[4] Plant flavonoids in cancer chemoprevention: role in genome stability – https://www.ncbi.nlm.nih.gov/pubmed/27951449

[5] Cancer Chemoprotection Through Nutrient-mediated Histone Modifications – https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5012963/

[6] Quercetin, a Natural Flavonoid Interacts with DNA, Arrests Cell Cycle and Causes Tumor Regression by Activating Mitochondrial Pathway of Apoptosis – https://www.nature.com/articles/srep24049

[7] Growth inhibitory effects of quercetin on bladder cancer cell – https://www.ncbi.nlm.nih.gov/pubmed/16720314

[8] Effects of quercetin on the proliferation of breast cancer cells and expression of survivin in vitro – https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3820718/

[9] Quercetin induces apoptosis and necroptosis in MCF-7 breast cancer cells – https://www.ncbi.nlm.nih.gov/pubmed/28814095

[10] Effects of low dose quercetin: Cancer cell-specific inhibition of cell cycle progression – https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2736626/

[11] Quercetin inhibits the growth of a multidrug-resistant estrogen-receptor-negative MCF-7 human breast-cancer cell line expressing type II estrogen-binding sites – https://link.springer.com/article/10.1007/BF00685531

[12] Quercetin attenuates collagen-induced arthritis by restoration of Th17/Treg balance and activation of Heme Oxygenase 1-mediated anti-inflammatory effect -https://www.ncbi.nlm.nih.gov/pubmed/29149703

[13] Quercetin, Inflammation and Immunity – https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4808895/

[14] Quercetin Suppresses Cyclooxygenase-2 Expression and Angiogenesis through Inactivation of P300 Signaling – https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3152552/

[15] Inhibitory Aromatase Effects of Flavonoids from Ginkgo Biloba Extracts on Estrogen Biosynthesis – https://www.ncbi.nlm.nih.gov/pubmed/26434836

[16] Quercetin-induced apoptotic cascade in cancer cells: antioxidant versus estrogen receptor alpha-dependent mechanisms – https://www.ncbi.nlm.nih.gov/pubmed/19194971

[17] Quercetin, a Natural Flavonoid Interacts with DNA, Arrests Cell Cycle and Causes Tumor Regression by Activating Mitochondrial Pathway of Apoptosis – https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4828642/

[18] Quercetin induces apoptosis and necroptosis in MCF-7 breast cancer cells –
https://www.ncbi.nlm.nih.gov/pubmed/28814095

[19] Quercetin induces apoptosis and cell cycle arrest in triple-negative breast cancer cells through modulation of Foxo3a activity – https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5343054/

[20] Quercetin, a Natural Flavonoid Interacts with DNA, Arrests Cell Cycle and Causes Tumor Regression by Activating Mitochondrial Pathway of Apoptosis – https://www.nature.com/articles/srep24049

[21] Quercetin Suppresses Cyclooxygenase-2 Expression and Angiogenesis through Inactivation of P300 Signaling – https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3152552/

[22] Quercetin inhibits angiogenesis by targeting calcineurin in the xenograft model of human breast cancer – https://pubmed.ncbi.nlm.nih.gov/27041643/

[23] Effects of quercetin on the proliferation of breast cancer cells and expression of survivin in vitro – https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3820718/

[24] Quercetin suppresses breast cancer stem cells (CD44+/CD24-) by inhibiting the PI3K/Akt/mTOR-signaling pathway – https://www.ncbi.nlm.nih.gov/pubmed/29355544

[25] Stimulatory effect of naturally occurring flavonols quercetin and kaempferol on alkaline phosphatase activity in MG-63 human osteoblasts through ERK and estrogen receptor pathway – https://www.sciencedirect.com/science/article/abs/pii/S0006295203009006

[26] Effects of the flavonoid drug quercetin on the response of human prostate tumours to hyperthermia in vitro and in vivo – https://www.ncbi.nlm.nih.gov/pubmed/11471985

[27] Quercetin enhances chemotherapeutic effect of doxorubicin against human breast cancer cells while reducing toxic side effects of it – https://www.ncbi.nlm.nih.gov/pubmed/29475141

[28] The antioxidant effects of the flavonoids rutin and quercetin inhibit oxaliplatin-induced chronic painful peripheral neuropathy – https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3835704/

[29] 20-Week Study of Clinical Outcomes of Over-the-Counter COVID-19 Prophylaxis and Treatment – https://www.ncbi.nlm.nih.gov/labs/pmc/articles/PMC8264737/

[30] Possible Therapeutic Effects of Adjuvant Quercetin Supplementation Against Early-Stage COVID-19 Infection: A Prospective, Randomized, Controlled, and Open-Label Study – https://thrombosisjournal.biomedcentral.com/articles/10.1186/s12959-021-00311-9