Author – Phoebe Chan – BSc (Hons) Nutrition and Human Health
Quercetin is an anti-oxidant that may have health benefits, including reducing inflammation and lowering the risk of developing certain diseases. It is consumed in foods like peppers, berries and kale. It is one of the most abundant antioxidants in the diet and plays an important role in helping your body combat free radical damage, which is linked to chronic stress. Its antioxidant properties may also help reduce inflammation, allergy symptoms and blood pressure. This blog will focus on the benefits of quercetin, its uses and how it works in the body (1).
What Is Quercetin?
Quercetin is a naturally occurring plant compound known as a flavonoid, found in a wide range of fruits, vegetables and wholegrains. Flavonoids are colourful plant pigments that help protect plants from environmental stress and are well researched for their health-promoting properties. They can also offer similar protective benefits when consumed as part of the human diet.
Some of the best sources of quercetin include: red or yellow onions, capers, apples, leafy vegetables, asparagus, broccoli and berries and much more. Including a rainbow of foods with red, green and purple pigments will give you a great source of quercetin (2).
How Quercetin Works in the Body
Antioxidant properties:
Antioxidants help protect cells against oxidative stress, which occurs when an excess of free radicals overwhelms the body’s natural defences. Free radicals are unstable molecules that can damage cells, increase the risk of disease and accelerate aging. They are produced naturally during processes such as energy production, as well as external factors like pollution, cigarette smoke, radiation, sun exposure, stress and alcohol consumption.
Quercetin acts as a powerful antioxidant by helping to neutralise these free radicals, reducing oxidative damage and supporting overall cellular health. Its antioxidant activity has been shown to be comparable to, or even stronger than nutrients such as vitamin C, vitamin E and beta-carotene (3).
Anti-inflammatory effects:
Inflammation is the body’s natural response to stress and injury and usually helps the body heal. However, chronic inflammation can harm the body and contribute to specific health conditions.
Quercetin has been shown to have anti-inflammatory effects by helping to regulate the body’s inflammatory response (3). In particular, it may reduce the production of pro-inflammatory molecules such as tumour necrosis factor alpha (TNF-α) and interleukin-6 (IL-6) (4). By lowering these markers, quercetin may help reduce excessive inflammation and support overall health.
Immune system support:
Quercetin supports immune health by helping to regulate the body’s inflammatory and antioxidant response (5). Inflammation is a natural defence mechanism, but when it becomes chronic, it can weaken the immune system and make you more susceptible to illness (6).
One of quercetin’s unique benefits is its ability to stabilise mast cells – immune cells that release histamine in response to allergens (7). By helping to limit the release of histamine, quercetin may support a more balanced immune response, making it particularly helpful for managing seasonal allergies and supporting respiratory health (8).
Potential antiviral properties:
Quercetin has antibacterial and antiviral properties. Lab tests show that quercetin can inhibit the growth of many bacteria, including such as Salmonella enteritidis and Staphylococcus aureus. Quercetin, along with other flavonoids may help inhibit the growth of many viruses (9).
Key Health Benefits of Quercetin
Supports Immune Health
Quercetin has multiple influences on your immune system, including cold and flu prevention. It is able to boost white blood cell activity and help to mobilise them towards the area of infection.
Reduces Inflammation
Quercetin provides anti-inflammatory benefits, which further protect the body from diseases that arise from inflammation, such as respiratory diseases, cancer, gastrointestinal diseases, skin infections and heart disease (10).
Allergy Relief
Quercetin is thought to have antiallergic properties, as it can influence several of the mechanisms involved in allergic reactions. For example, it can stabilise mast cells, reducing the release of histamine.
As well as acting as a natural antihistamine, quercetin can inhibit the release of inflammatory cytokines that are involved in allergic responses. Overall, it may support a more balanced immune response, helping to reduce the overactivation of the immune system seen in allergies (2).
Heart Health
Quercetin has been shown to have potential cardiovascular benefits in animal and test-tube studies (11). Research suggests it may help lower blood pressure, reduce cholesterol levels, improve glucose control and prevent the buildup of plaque in arteries, while also helping to protect the heart from oxidative damage.
Some clinical trials have also found that quercetin supplementation can contribute to improved cholesterol levels (12).
Exercise Performance and Recovery
Quercetin may enhance endurance performance by supporting mitochondrial function, improving oxygen utilisation, and reducing exercise-induced oxidative stress and inflammation. Together, this can help delay fatigue and support recovery (13).
Common Uses of Quercetin
Quercetin is available as a supplement in a capsule, powder or liquid form and is often combined with zinc. This is partly because quercetin may act as a zinc ionophore, helping transport zinc into cells, where zinc can interfere with viral replication.
Another nutrient which is commonly combined with quercetin is vitamin C as this results in better immune enhancement and anti-virus effects than when used alone (14).
Natural Food Sources of Quercetin
Onions: red and yellow onions contain the most quercetin. To keep the quercetin, peel off as little as possible of the outer layers.
Kale: besides quercetin, it’s also a rich source of vitamin A, vitamin C and fibre.
Cherry tomatoes: all tomatoes are good sources of quercetin, however cherry tomatoes have the highest ratio of skin to flesh, therefore contain more quercetin.
Broccoli: along with quercetin, broccoli is rich in vitamin K and vitamin C.
Blueberries: a great source of antioxidants and, on top of quercetin, they contain 17 different phytochemicals including resveratrol.
Apples: these contain four different phytochemicals along with the beneficial fibre know as pectin. To get the benefits of quercetin, eat your apples unpeeled (15).
Conclusion
Quercetin is a plant compound with antioxidant and anti-inflammatory properties. It may support immune function and help with inflammation and allergy symptoms, with emerging evidence for heart health and exercise performance.
It is generally best to obtain quercetin through a balanced diet rich in fruits and vegetables. However, if dietary intake is insufficient, consulting a healthcare professional can help determine whether supplementation is appropriate and what dosage may be suitable.
FAQ’s (Frequently Asked Questions)
What is quercetin?
Quercetin is a naturally occurring plant compound (a flavonoid) found in many fruits, vegetables, and grains. It is known for its antioxidant and anti-inflammatory properties.
What foods are high in quercetin?
Quercetin is commonly found in foods such as onions, apples, berries, grapes, citrus fruits, leafy greens, broccoli, and green tea.
What are the main benefits of quercetin?
Quercetin may support immune function, help reduce inflammation, and relieve allergy symptoms. There is also emerging evidence suggesting potential benefits for heart health and exercise performance, although more research is needed.
References
- https://www.healthline.com/nutrition/quercetin
- https://www.cytoplan.co.uk/ask-the-expert/what-is-quercetin-and-how-can-it-support-my-health?utm_medium=cpc&utm_source=google&utm_campaign=fallback_22329047750_x&gad_source=1&gad_campaignid=22322583303&gbraid=0AAAAAD7jWi3mW0kZ_jm5e-h9DS-JvPDri&gclid=Cj0KCQjwkrzPBhCqARIsAJN460niJ1YLhI0GQIQAMd6-7djNWTjEikOt006sszxKRdTiTPUSbBe_tQgaAuE-EALw_wcB
- https://www.medicalnewstoday.com/articles/324170#8-benefits
- https://pubmed.ncbi.nlm.nih.gov/27294919/
- https://pmc.ncbi.nlm.nih.gov/articles/PMC6273625/#:~:text=Quercetin%20is%20known%20for%20its,and%20cytosolic%20calcium%20level%20increase
- https://my.clevelandclinic.org/health/symptoms/21660-inflammation
- https://pmc.ncbi.nlm.nih.gov/articles/PMC3314669/
- https://www.lovelifesupplements.co.uk/blogs/love-life-health-blog/unlock-the-immune-boosting-potential-of-quercetin
- https://pmc.ncbi.nlm.nih.gov/articles/PMC8662201/
- https://nutritionhouse.com/blogs/immune-antioxidant-articles/why-should-you-consider-quercetin-for-immune-health?srsltid=AfmBOoqPi47TfVBsaryjsw76mU5BnK33bKKxTiqyVaczMUIHWaBl90Yi
- https://pmc.ncbi.nlm.nih.gov/articles/PMC9412669/
- https://foodrevolution.org/blog/benefits-of-quercetin-foods-supplements/
- https://pmc.ncbi.nlm.nih.gov/articles/PMC10824311/
- https://www.qyherb.com/info/what-is-the-synergy-of-quercetin-zinc-and-vc-63602716.html
- https://www.webmd.com/diet/foods-high-in-quercetin
