http://www.webmd.com/vitamins-and-supplements/quercetin-uses-and-risks

Quercetin

Quercetin is a plant pigment (flavonoid) that people sometimes take as a medicine.

It is found in many plants and foods.

Why do people take quercetin?

People take quercetin to try to manage a variety of issues, including:

Early quercetin research on heart and vessel disease is mixed. Some study results are positive but some are open to debate. For example, researchers link eating lots of foods high in quercetin to a lower risk of heart-related death in older men. But other studies are less convincing.

Some research suggests that oral doses of quercetin may decrease pain from prostate infections.

Some athletes try to increase endurance and improve athletic performance by using quercetin. Although animal studies are promising, the effects in humans, if any, are likely small.

Some studies link a diet high in quercetin with a lowered risk of cancer. But more research is needed.

In general, much of the research on quercetin has been in animals or in cell cultures. More study is needed to prove quercetin’s benefits and safety in humans, especially when taken as a supplement instead of in food.

Common oral dosages are 500 milligrams twice a day. People have also used lower dosages as well. However, optimal doses of quercetin have not been established for any condition. Quality and active ingredients in supplements may vary widely from maker to maker. This makes it hard to establish a standard dose.

Can you get quercetin naturally from foods?

Quercetin is abundant in nature and foods. People typically get between 5 and 40 milligrams a day from food. But if you eat lots of fruits and vegetables, you can get as much as 500 milligrams daily.

For example, think “quercetin” the next time you pour a glass of red wine, bite into a crunchy apple, treat yourself to some berries, flip a buckwheat pancake, slice an onion, or sip a cup of green tea. Other vegetables that have high amounts of quercetin include:

• Kale
• Tomatoes
• Broccoli
• Raw Asparagus
• Capers
• Raw red onion

Quercetin is also in herbs such as:

• American elder
• St. John’s wort
• Ginkgo biloba

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Study: Vitamin C plus quercetin a solid remedy for coronavirus

Eastern Virginia Medical School and University of Rome, July 28, 2020

New research published in the journal Frontiers in Immunology has revealed that vitamin C combined with quercetin represents a powerful natural remedy for the Wuhan coronavirus (COVID-19).

Entitled, “Quercetin and Vitamin C: An Experimental Synergistic Therapy for the Prevention and Treatment of SARS-CoV-2 Related Disease (COVID-19),” the paper takes a detailed look at the antiviral properties of these two nutrients, which together show incredible promise in helping Wuhan coronavirus (COVID-19) patients recover.

It explains that quercetin has the ability to interfere “at multiple steps of pathogen virulence,” including at “virus entry, virus replication, (and) protein assembly” to inhibit the viral infection and proliferation. And when combined with vitamin C, quercetin is effective “for both the prophylaxis and the early treatment” of the Wuhan coronavirus (COVID-19), as well as other respiratory tract infections.

In case you are unfamiliar with it, quercetin is a plant pigment in the flavonoid family that possesses antioxidant, anti-inflammatory, antiviral, and immune-protective properties. It has also been studied extensively for its ability to inhibit polymerases, proteases, and reverse transcriptase, as well as to suppress DNA gyrase and bind viral capsid proteins.

This might sound like complicated language to the average “Joe,” but suffice it to say that quercetin, especially when amplified by the presence of vitamin C, obstructs viral infection, as well as viral replication and proliferation.

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Quercetin helps to reduce the risk of pancreatic cancer

Univ. of Hawaii and Univ. of Southern California, November 1, 2021

Quercetin, which is found naturally in apples and onions, has been identified as one of the most beneficial flavonols in preventing and reducing the risk of pancreatic cancer. Although the overall risk was reduced among the study participants, smokers who consumed foods rich in flavonols had a significantly greater risk reduction.

This study, published in the American Journal of Epidemiology, is the first of its kind to evaluate the effect of flavonols – compounds found specifically in plants – on developing pancreatic cancer. According to the research paper, “only a few prospective studies have investigated flavonols as risk factors for cancer, none of which has included pancreatic cancer. “

Researchers from Germany, the Univ. of Hawaii and Univ. of Southern California tracked food intake and health outcomes of 183,518 participants in the Multiethnic Cohort Study for eight years. The study evaluated the participants’ food consumption and calculated the intake of the three flavonols quercetin, kaempferol, and myricetin. The analyses determined that flavonol intake does have an impact on the risk for developing pancreatic cancer.

The most significant finding was among smokers. Smokers with the lowest intake of flavonols presented with the most pancreatic cancer. Smoking is an established risk factor for the often fatal pancreatic cancer, notes the research.

Among the other findings were that women had the highest intake of total flavonols and seventy percent of the flavonol intake came from quercetin, linked to apple and onion consumption.

It is believed that these compounds may have anticancer effects due to their ability to reduce oxidative stress and alter other cellular functions related to cancer development.

“Unlike many of the dietary components, flavonols are concentrated in specific foods rather than in broader food groups, for example, in apples rather than in all fruit,” notes the research study. Previously, the most consistent inverse association was found between flavonols, especially quercetin in apples and lung cancer, as pointed out in this study. No other epidemiological flavonol studies have included evaluation of pancreatic cancer.

While found in many plants, flavonols are found in high concentrations in apples, onions, tea, berries, kale, and broccoli. Quercetin is most plentiful in apples and onions.