Does Quercetin Help With COVID? What the Science Says

Quercetin is a naturally occurring plant pigment, or flavonoid, found in a variety of foods. This article explores the scientific understanding and current evidence regarding quercetin’s potential role in managing or treating COVID-19.

Understanding Quercetin

Quercetin is a flavonoid, a plant compound known for its vibrant colors and biological activities. It is abundant in many common fruits and vegetables, including apples, onions, berries, capers, and green tea. It is consumed regularly through diet.

This compound is recognized for its general biological properties, which include antioxidant and anti-inflammatory effects. As an antioxidant, quercetin helps to neutralize unstable molecules in the body that can cause cellular damage. Its anti-inflammatory actions involve modulating pathways related to the body’s inflammatory responses.

How Quercetin Might Interact with COVID-19

Quercetin’s broad biological activities suggest potential mechanisms against COVID-19. It has been hypothesized to possess antiviral properties. For instance, studies suggest quercetin might inhibit the virus from entering human cells by interacting with the ACE2 receptor, which the virus uses for entry.

Quercetin may also disrupt viral replication once the virus is inside cells. Research indicates it could inhibit key viral enzymes necessary for multiplication, such as the main protease (Mpro) and RNA-dependent RNA polymerase (RdRp). Its anti-inflammatory effects are also thought to be relevant, potentially helping to mitigate the excessive inflammatory response, often called a “cytokine storm,” observed in severe COVID-19 cases.

Current Scientific Evidence

Scientific investigations into quercetin’s role in COVID-19 include laboratory (in vitro), animal studies, and human clinical trials. Initial in vitro and computational (in silico) studies have shown that quercetin can inhibit SARS-CoV-2 replication and block viral entry mechanisms in cell cultures.

Human clinical trials have explored quercetin as a supplemental therapy for COVID-19 patients. Some meta-analyses have reported that quercetin supplementation might decrease the risk of intensive care unit (ICU) admission and hospitalization. These analyses also suggest a potential reduction in mortality risk and improved certain clinical outcomes and inflammatory markers, such as lactate dehydrogenase (LDH).

However, the overall scientific evidence remains preliminary and sometimes mixed. While some studies point to benefits like faster viral clearance and quicker resolution of symptoms, larger-scale, robust randomized controlled trials are still needed to confirm these findings definitively.

Safety and Important Considerations

Quercetin, commonly found in diet, is generally considered safe when consumed through food sources. As a dietary supplement, it appears generally safe for short-term use, typically up to 12 weeks, at doses up to 1,000 mg per day.

Taking quercetin supplements can lead to mild side effects such as headaches, upset stomach, nausea, or tingling sensations. High doses have been associated with kidney damage. Therefore, individuals with pre-existing kidney disease should avoid quercetin supplements.

Quercetin can also interact with certain medications. It may increase the risk of bleeding when taken with blood thinners like warfarin. It could also interfere with blood pressure medications, certain antibiotics, and immunosuppressants like cyclosporine.

There is insufficient reliable information regarding the safety of quercetin supplements for pregnant or breastfeeding individuals. Due to the lack of human data, it is generally advised to avoid quercetin supplements during pregnancy and lactation unless specifically recommended and monitored by a healthcare professional.

Official Health Organization Guidance

Major health organizations worldwide, including the World Health Organization (WHO), Centers for Disease Control and Prevention (CDC), and National Institutes of Health (NIH), continuously review evidence for COVID-19 treatments. As of now, these organizations have not issued official recommendations for the use of quercetin in the prevention or treatment of COVID-19. Their guidance typically emphasizes established medical advice and approved treatments. This position reflects the need for more extensive and conclusive research before quercetin could be considered a standard intervention for COVID-19.