Author – Phoebe Chan – BSc (Hons) Nutrition and Human Health
Quercetin is a naturally occurring plant compound found in many fruits and vegetables, known for its antioxidant and anti-inflammatory properties. It belongs to a group of plant nutrients called flavonoids, which are compounds that help protect the body from oxidative stress and support overall health (1).
Over the past few decades, quercetin has attracted growing scientific interest, particularly in areas such as immune health, inflammation, and sports performance (2).
What is Quercetin?
Quercetin is an antioxidant that may have health benefits, including reducing inflammation and lowering the risk of developing certain diseases. It is a pigment that belongs to a group of plant flavonoids that are present in many vegetables, fruits, beverages and grains. It is one of the most abundant antioxidants in the diet and plays an important role in helping the body combat free radical damage, which is linked to chronic diseases (3).
Key Health Benefits of Quercetin
Antioxidant Effects
Free radicals are highly reactive molecules produced naturally during metabolic processes or by external factors such as UV radiation, pollution and certain chemicals. In excess, they can cause oxidative stress to proteins and lipids, leading to various chronic health conditions.
Quercetin exerts its antioxidative effects through multiple mechanisms. It can directly scavenge free radicals, by donating electrons to stabilise them, preventing damage to cells. In addition, it may bind metal ions that promote free radical formation and support the body’s natural antioxidant defences (4).
Anti-Inflammatory Properties
High levels of free radicals may activate signalling pathways that promote inflammation, leading to an increased inflammatory response. Quercetin may help counter this by exerting anti-inflammatory effects at the molecular level. Studies suggest that quercetin can inhibit the production of pro-inflammatory cytokines, such as tumour necrosis factor alpha (TNFα) and interleukin-6 (IL-6) (5), which play key roles in the inflammatory response.
Furthermore, some human studies indicate potential benefits. For example, women with rheumatoid arthritis who took 500 mg of quercetin reported reduced morning stiffness, morning pain and after-activity pain (6).
Immune System Support
Quercetin has been shown to have antiviral, antimicrobial, anti-oxidant and anti-allergic effects. One of the most common reasons people use quercetin is to help manage symptoms of seasonal allergic rhinitis (hay fever) (7). Test tube and animal studies suggest that quercetin may inhibit enzymes involved in inflammation and suppress inflammation-promoting compounds, such as histamine (8).
Moreover, one of quercetin’s unique benefits is its ability to stabilise mast cells – immune cells that release histamine in response to allergens (9). This makes quercetin particularly helpful for managing seasonal allergies and improving respiratory health (10).
Heart Health Benefits
As a potent antioxidant, quercetin reduces oxidative stress, which is a key contributing to cardiovascular disease. The antioxidant nature of quercetin helps counteract the damaging effects of free radicals in the body, therefore aiding in the prevention of heart diseases. Quercetin’s ability to reduce systemic inflammation and enhance endothelial function also plays a crucial role in maintaining cardiovascular health.
Research indicates it may lower blood pressure and reduce the risk of atherosclerosis, a condition characterised by plaque buildup in the arteries. One trial revealed a significant reduction in systolic and diastolic blood pressure with quercetin supplementation. Another showed that quercetin could inhibit the formation of plaque in arteries (11).
Brain and Cognitive Health
Some research suggests that quercetin may support brain health and cognitive function, potentially reducing the risk of age-related cognitive decline and neurodegenerative diseases such as Alzheimer’s disease. Its antioxidant properties help protect neurons from oxidative stress, which can damage brain cells over time, while its anti-inflammatory effects may reduce neuroinflammation that contributes to cognitive decline. Together, these actions may help preserve neuronal function and support overall brain health.
Quercetin’s antioxidant and anti-inflammatory actions may help protect neurons from damage and promote overall brain health.
How to Get Quercetin
Quercetin is one of the most common flavonoids and is present in many foods for example onions, kale, cherry tomatoes, broccoli, blueberries and apples. It is also present in red wine, black tea and green tea. When you get quercetin from fruits and vegetables, you also benefit from the increased fibre intake.
Quercetin is also available as a supplement, with a recommended dose of 500-1,00 mg per day. It is considered safe to us, but may interact with several medications, including antibiotics and blood thinners (13).
Strategic nutrient pairing significantly enhances quercetin absorption. Vitamin C acts as a natural absorption enhancer, while bromelain, an enzyme from pineapple, may improve quercetin’s role in supporting a healthy inflammatory response (14).
Safety, Side Effects and Considerations
Quercetin is generally considered safe when consumed through foods. As a supplement, it appears to be safe for most adults when taken at recommended doses for a short amount of time, for example 500 mg twice a day for 12 weeks. Higher doses may cause side effects including headaches or tingling in arms and legs if the dosage is exceeded.
Individuals who are pregnant or breastfeeding should consult a healthcare professional before taking quercetin supplements, as there is limited research on supplemental safety in these groups. Caution is also advised when taking quercetin alongside certain medications such as antibiotics, cyclosporine, warfarin or any drugs that are changed by the liver. Quercetin may change how these drugs work and raise the risk of side effects (15).
Conclusion
Quercetin is a naturally occurring plant compound found in many fruits and vegetables. It is well known for its antioxidant and anti-inflammatory properties and may also support immune, heart and brain health.
Good food sources of quercetin include onions, kale, broccoli, cherry tomatoes, blueberries and apples. Whenever possible, it is best to obtain quercetin through a balanced diet, as whole foods provide additional nutritional benefits such as fibre, vitamins and minerals. However, supplementation may be an option for some individuals after consulting a healthcare professional.
FAQ’s (Frequently Asked Questions)
What is quercetin?
Quercetin is a naturally occurring plant compound known as a flavonoid. It is found in many fruits, vegetables, and plant-based foods and is valued for its antioxidant and anti-inflammatory properties.
What foods are high in quercetin?
Foods rich in quercetin include onions, apples, kale, broccoli, blueberries, cherry tomatoes, grapes, and capers. Red onions are considered one of the richest dietary sources.
What are the potential health benefits of quercetin?
Quercetin may help support immune function, heart health, brain health, and overall wellbeing due to its antioxidant and anti-inflammatory effects. Research also suggests it may help protect cells from oxidative stress.
References
- https://oxfordvitality.co.uk/blogs/news/quercetin-are-we-getting-enough
- https://www.health-mall.in/files_hl/Quercetin_%20Scientific_Journey_Discovery.pdf
- https://www.healthline.com/nutrition/quercetin
- https://www.intechopen.com/chapters/1180684
- https://pubmed.ncbi.nlm.nih.gov/27294919/
- https://www.healthline.com/nutrition/quercetin#benefits
- https://www.metagenics.co.uk/news/supporting-immune-health-with-quercetin/
- https://www.mdpi.com/1420-3049/21/5/623
- 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://foryouth.co/blogs/magazine/quercetin-in-cardiovascular-health?srsltid=AfmBOor7iOUOo-AqVkTK4Z3D7JtZxO8vXKFGgHujOtbfgICk2JFMD9Uk
- https://help.decodeage.com/decode-age-support/supplement-information/quercetin-supplement/what-are-the-benefits-of-quercetin
- https://www.webmd.com/diet/foods-high-in-quercetin
- https://supplementsstudio.com/blogs/blog/immune-support-supplements-with-quercetin?srsltid=AfmBOoo6nzOMNi6a3G6ekZPz_5p4A46cNb-5vbHlfUjX5dWRe4aWzPVP
- https://www.webmd.com/vitamins-and-supplements/quercetin-uses-and-risks
