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Quercetin is a bioflavinoid found in a number of different common whole foods, including apples, cherries, dark berries, peppers, cruciferous veggies, leafy greens, green tea, citrus, tomatoes, cocoa, whole grains, asparagus, red wine, capers, and especially in onions. It’s also found in the herbs ginkgo, St John’s Wort, and elderberry. 

It has gained a lot of attention lately as an adjunctive immune support supplement, and for good reason. But it has a lot more health benefits than just immune support. 

Antiviral and Zinc Ionophore

Zinc is a very important cofactor for numerous enzymatic reactions in the body, many of which are critical for immune function. Therefore, zinc ionophores can also aid in immune support, as they will assist the zinc ion in its quest to get inside the cells, where it can be effectively utilized. Quercetin is one such ionophore. (ECGC, found in green tea, is another—and since quercetin is also found in green tea, that’s another good reason to incorporate more green tea into your diet.)

Quercetin acts like an all around cellular gatekeeper: in addition to helping zinc to get inside the cells, quercetin also blocks viruses from entering the cells, where they would otherwise hijack the cell’s genetic machinery for their own replication. It has been shown to have direct antiviral properties against influenza A, hepatitis B and C, Ebola, Dengue, Japanese Encephalitis Virus, and Zika virus. It stands to reason that it may perform similar actions against other viruses as well. 

Inflammation and Oxidation

All bioflavonoids share antioxidant and anti-inflammatory properties, and quercetin is no exception. It has been shown to specifically decrease secretion of inflammatory cytokines. Since many Western diseases are associated with chronic inflammation, this makes quercetin helpful for insulin resistance, cardiovascular disease, liver fibrosis and alcohol-induced liver injury. It also has promise as an adjunctive cancer support.

Because pain can often be inflammatory in nature (hence the ubiquitous use of NSAIDs for inflammatory pain), quercetin was also studied for its ability to arrest inflammatory pain. It was shown to be effective for this as well.


I have probably used quercetin the most in my practice over the years for its mast cell stabilizing properties. Mast cells carry histamine and release it in the presence of an allergic trigger. Prescription cromolyn is often prescribed to stabilize mast cells; however, its effectiveness declines quickly and it is less effective as a prophylactic for this. Quercetin can both be used prophylactically to stabilize mast cells, and also has been shown to be more effective than cromolyn. 

Additionally, quercetin helps to balance the Th1/Th2 immune cells, a teeter-totter that helps to mitigate allergic predisposition, It also has been shown to decrease IgE release, the immunoglobulin responsible for allergies. 

The Upshot

A whole foods based diet is definitely the place to begin with supplementing quercetin, as you will get not just quercetin but all of the supporting micronutrients necessary for optimal health. 

But if you’re interesting in adding additional quercetin to your supplement regime, typical doses range from 250-1000 mg, 1-2 times daily.