What is Quercetin?

Quercetin is abundant in many types of fruit and vegetables, it is also available as a dietary supplement in powder and capsule form. Quercetin, as an anti-inflammatory, antioxidant and a pain killer, has been described as a potential treatment for the main complications arising in people with COVID-19 (1). NF-κB activation is central to the acute virus-induced cytokine storm. During viral infection, quercetin balances inflammatory pathways such as NF-kB; this helps to regulate innate immunity.

What is quercetin found in?

Quercetin is a flavonoid that is naturally found in a variety of foods. It can be found in foods such as apples, berries (such as blueberries and cranberries), citrus fruits, onions, garlic, leafy greens (such as kale and spinach), tomatoes, and tea (particularly green tea).

Food sources of quercetin

apples

onions

grapes

berries

broccoli

citrus fruits

cherries

green tea

capers

What are the benefits of quercetin?

Quercetin and vitamin C

The antiviral properties of quercetin have been proven in numerous studies[i] [ii]. Use of vitamin C and quercetin together exerts a double action anti-viral effect and both substances demonstrate immune system modulating properties. Infact, vitamin C has the capacity to recycle quercetin in the body, further increasing its efficacy [iii].

Other benefits

Quercetin is one of the most abundant dietary antioxidants in the diet. It helps the body to combat free radical damage, which is linked to the development and exacerbation of chronic diseases. Quercetin has also been linked to several other health benefits, including reduced risk of heart disease, cancer, and degenerative brain disorders [iv] [v]. Antioxidants are compounds that can bind to and neutralise free radicals. The beneficial effects of quercetin come from the ability to function as antioxidants inside the body [vi] [vii].

Specific Uses for Quercetin

Allergy relief, hayfever and eczema

Test-tube and animal studies found that quercetin may block enzymes involved in inflammation and suppress inflammation-promoting chemicals, such as histamine [viii] [ix] [x]. This mechanism has been shown to improve seasonal allergies and atopic conditions such as asthma and eczema [xi].

One study showed that taking quercetin supplements suppressed peanut-related anaphylactic reactions in mice [xii].

Digestion and organ function

Quercetin supports tight junctions in the gut [xiii]. Proper functioning of gut tight junctions means avoidance of ‘leaky gut syndrome’, whereby particles that should not enter the body via the gut lining slip through and contribute to various aliments including brain fog, allergies, thyroid disorders and fatigue, to name a few.

Quercetin has also been shown to have liver protective qualities against some medications including paracetamol[xiv].

Cancer protection

Flavonoids such as quercetin were also shown to increase tumour cell death in conjunction with radiotherapy. The group in the study provided with both quercetin and radiotherapy saw greater benefits than those who received radiotherapy alone [xv].

In a review of test-tube and animal studies, quercetin was found to suppress cell growth and induce cell death in prostate cancer cells [xvi]. Similar studies observed that the protective effects in liver, lung, breast, bladder, blood, colon, ovarian, lymphoid, and adrenal cancer cells [xvii] [xviii] [xix].

Neuro-protective effects

Research suggests that quercetin’s antioxidant properties may help protect against degenerative brain disorders, such as Alzheimer’s disease and dementia [xx].

Another study supports this claim. A quercetin-rich diet reduced markers of Alzheimer’s disease and improved brain function in mice at the early middle stage of the condition. However, the diet had little to no effect on animals with middle-late stage Alzheimer’s [xxi].

Reduction in blood pressure

When mice with high blood pressure were given quercetin daily for 5 weeks, their blood pressure readings decreased by an average of 18% (systolic) and 23% (diastolic) [xxii].

Similarly, a review of 9 human studies in 580 people found that taking more than 500 mg of quercetin in supplement form daily significantly reduced blood pressure readings (systolic and diastolic) [xxiii].

Safety

In some instances, taking more than 1,000 mg of quercetin per day may cause mild symptoms like headaches, stomach aches, or tingling sensations [xxiv].

When consumed in food, quercetin is safe for pregnant and breastfeeding women. However, studies on the safety of quercetin supplements for pregnant and breastfeeding women are inconclusive. Therefore, it be may be pertinent to avoid taking quercetin if you’re pregnant or breastfeeding.

It is recommended to consult your healthcare provider before taking quercetin, as it can interact with some medications, including antibiotics and blood pressure medications.