Quercetin - A Secret Weapon for Immune Support?

What if you were plucked from obscurity and suddenly became a rock star? That’s probably how quercetin feels right now (let’s pretend this inanimate substance has feelings, ok?). What was once a little-known niche supplement used for healing the digestive tract and relieving allergies has become a hot commodity among alternative medicine practitioners as a way to boost the immune system and potentially decrease chances of severe COVID-19 infection (vaccination is currently the only proven method).

Over the last several years, research has been indicating quercetin’s usefulness in the body’s defense against viruses. In this model using influenza infection of MDCK cells, quercetin demonstrated reduced changes in host cells 48 hours after infection. This makes it harder for viruses to move in and get cozy. In a 2016 study, quercetin was shown to prevent death in mice infected with Ebola. A more recent study of Quercetin and vitamin C found strongly suggested the combination for preventing and early treatment of COVID-19.

Quercetin stabilizes the body's mast cells, which store and release histamine, which is why it is commonly used by individuals who suffer from allergies. Quercetin appears to have other beneficial effects on human health, including repair and defense of the gastrointestinal tract and protection of the cardiovascular system, where it scavenges free radicals and inhibits oxidation of LDL cholesterol (LDL oxidation can lead to heart attacks and strokes).

Quercetin is an antioxidant, which may be responsible for many of its benefits. By itself, and paired with vitamin C, quercetin can reduce oxidative damage to the skin and nerves caused by depletion of glutathione (something the body makes, yet can’t seem to get enough of). This may be one of the mechanisms that make it useful to Long Covid sufferers.

Where to Find Quercetin

Quercetin is a pigment found in many foods, which are listed in no particular order below. For example, white onions are lower in quercetin than yellow or red onions due to lower levels of pigment.

Colorful vegetables like red onions are a natural source of quercetin.

Colorful vegetables like red onions are a natural source of quercetin.

  • Capers

  • Red onions

  • Yellow onions

  • Shallots

  • Red apple skins

  • Grapes

  • Berries

  • Cherries

  • Scallions

  • Kale

  • Tomatoes

  • Broccoli

  • Red wine

  • Black tea

  • Lovage leaves

  • Okra

  • Plums

  • Red bell peppers

Supplemental Quercetin

Because it is somewhat poorly absorbed in the body, getting a lot of quercetin is key. Other compounds such as bromelain, phytosome technology and vitamin C help with absorption and recycling. Of all the foods listed above, Capers pack the most quercetin per gram with 131 milligrams quercetin per 100 grams (about 7 tablespoons). Supplementation is a no-brainer for people who may have challenges getting it all in through diet. Recommended dosages for supplementation are between 250 and 500 mg quercetin twice a day.

Many manufacturers use combinations and make unique formulations to boost quercetin’s efficacy. It should be noted that dietary supplements are not regulated by the FDA, so choosing high-quality supplements is very important. Let’s look at a supplement in our supplement dispensary by Thorne Research, which is one of my personal favorite pharmaceutical-grade supplement brands.

Quercenase combines quercetin phytosome (quercetin bound to sunflower-sourced phospholipids, which increases the body's ability to absorb the quercetin) and bromelain, a compound of protein-digesting enzymes derived from the pineapple plant. Bromelain also has immune-enhancing properties and can help modulate cytokines, which can be particularly useful if infected with COVID-19. Bromelain can also help reduce bruising and swelling after an injury or surgery.

The advantage of quercetin phytosome is the technology used to make it, which helps the body absorb and use quercetin better. Phytosome complexes are created by a patented process that binds a botanical extract to a phospholipid, which are key components of every cell membrane.

Getting it in

As a nutrition coach, my recommendation is to get nutrients from food first, and supplement what you can’t. Aim to incorporate vegetables and fruit in your diet, and pair with foods rich in vitamin C (think tart, like lemons).

For some, quercetin can inhibit thyroid function, so those with hypothyroidism should consult with a physician before taking quercetin, and consider alternatives.

These statements have not been evaluated by the Food and Drug Administration. This post and its contents are not intended to diagnose, treat, cure, or prevent any disease.

Gary Berglund