Quercetin: Benefits, side-effects, research

Antioxidants play critical roles in promoting longevity and healthspan. They act as the body’s scavengers of free radicals, compounds that can destroy cells and tissues and lead to early aging and various diseases. 

Although many individuals want to live longer, most suffer from long-term conditions, which result in poor health even when they have added years to their lives. Helping people achieve longevity while enjoying a healthy lifespan is now an important goal for healthcare practitioners and individuals. 

One way of achieving longevity is to increase the intake of antioxidant supplements. However, do you know that there are natural antioxidants in the body? One of these includes glutathione, which helps promote longevity through its antiaging and anti-inflammatory effects. While this is a natural antioxidant, its production decreases with aging, suggesting the need for people to take effective supplementation to promote longevity. 

One of the promising antioxidant supplements is quercetin. 

What is quercetin? 

Quercetin is a compound or pigment found in many vegetables, fruits and plants. Thai pigment is a powerful antioxidant and can help protect individuals from specific diseases such as heart disease. 

Quercetin is identified as a flavanol, which is one of the subcategories of the antioxidant flavonoid. Unlike natural antioxidants that can be produced in the body, quercetin is not produced in the body. 

Here are some excellent sources of quercetin: 

  • Apples
  • Berries
  • Grapes
  • Tea
  • Nuts and seeds
  • Wine
  • Onions 
  • Broccoli
  • Peppers

Research studies have extensively studied the health benefits of quercetin and how it can prevent specific diseases. 

Benefits of quercetin

It is a powerful antioxidant 

Nutritional flavonoids, such as quercetin, are more potent than vitamins E and C [1] as antioxidants. Due to the structure of quercetin and its chemical formula, it is ten times stronger and more potent than other synthetic antioxidants. Further, it scavenges reactive species such as hydroxyl radicals and peroxynitrite [2]. 

Not all quercetin, however, is made equal. For example, quercetin derived from onions has higher bioavailability, meaning more quercetin is absorbed in the body than in apples. 

Quercetin is involved in cell cycle progression

Cellular health is essential since this ensures that tissues are functioning well and balance or homeostasis within the human body is maintained. 

Quercetin plays a vital role in cell replication and division and in optimising the overall health of the cells. It is also involved in regulating the signalling pathway between cells. Communication between cells is vital in maintaining cellular health. 

Quercetin has anti-inflammatory effects 

Free radicals are typically produced during cellular metabolism and are removed by antioxidants in the body. However, too much production of free radicals or an imbalance between antioxidants and free radicals results in oxidative stress of the cells and eventual damage. 

Recent studies show that when free radicals are too high and overwhelm the natural antioxidants in the body, this can lead to the activation of genes involved in inflammation. Notably, inflammation is essential since this signals more cells of the immune system to ward off infections in the body. However, when inflammation becomes chronic, this can lead to the development of several conditions [2]. 

Quercetin research 

Several studies have shown the effects of quercetin on several illnesses and conditions. Here are some examples of quercetin’s effects: 

Diabetes complications 

Studies [3,4] have shown that quercetin is a promising drug in treating diabetes. It improves plasma insulin levels while reducing blood glucose levels. In addition, also maintains the function and number of beta-cells in the pancreas responsible for producing insulin. It also decreases oxidative stress, which delays the progression of diabetes and its complications. Further, the studies revealed that glucose uptake of cells in the body is increased when quercetin is taken. Through several mechanisms, quercetin can modulate free radicals and their effects on cells while increasing the insulin sensitivity of these cells. 

Cardiovascular diseases 

Due to its anti-inflammatory effects, quercetin is also suggested to reduce the risk of cardiovascular diseases. 

A 10-week study published in the International Journal of Preventive Medicine [5] examined the effects of 500 mg of daily intake of quercetin on inflammatory biomarkers and cardiovascular risks of female patients with type 2 diabetes. Results of this study suggested that daily intake of quercetin for ten months decreased systolic blood pressure. The results were significant, meaning the difference in the experimental group’s average systolic pressure was significantly lower compared with the group that only received placebo medicine. Further, high-density lipoprotein cholesterol and triglycerides were significantly lower in the experimental group than in the control group. High-density lipoprotein cholesterol and triglycerides have been implicated in developing cardiovascular diseases in patients with type 2 diabetes. 

The same study also reported that the experimental group significantly reduced inflammatory cells such as interleukin-6 and tumour necrosis factor-alpha. These inflammatory cells are known to increase the risk of cardiovascular diseases and complications in patients with type 2 diabetes. Lowering of these inflammatory cells suggests that quercetin has an anti-inflammatory effect and can be used as a supplement to prevent cardiovascular diseases. 

Alzheimer’s disease 

Brain fog is often described as a cloudy-headed feeling. One of the common complaints among older adults is forgetfulness.

Alzheimer’s disease is characterised by progressive cognitive impairment, memory loss and difficulties performing daily functions such as eating. Many patients with moderate to severe forms also have wandering behaviour, further complicating their care. 

A study [6] revealed that quercetin is used as part of formulations for drugs for Alzheimer’s disease. Quercetin is used due to its ability to regulate apoptosis or cell death mechanisms and its neuroprotective effect against oxidative stress. 

Neuron longevity is crucial in delaying the progression or the onset of Alzheimer’s disease. Quercetin has been shown to promote the longevity of neurons while increasing the production of neurons. 


Arthritis is a common condition associated with swelling, redness, stiffness and joint pain. As a result, individuals who have arthritis have difficulties moving around. This condition is related to several environmental, genetic and hormonal factors. 

Treatment of arthritis includes surgery use of nonsteroidal anti-inflammatory drugs and steroids. However, when steroids are used for a long time to manage arthritis, this can result in fractures and osteoporosis. The use of NSAIDS can also result in renal damage and gastric ulcers. Chronic inflammation of the joints would require surgery called arthroplasty, where destroyed joints are replaced. 

Quercetin has been reported to reduce inflammation and pain associated with arthritis [7]. Hence, supplementation of quercetin can help reduce inflammation and pain in arthritis. Since quercetin can help promote longevity, supplementation with this antioxidant could also improve health span as individuals suffer from fewer or no chronic conditions. 

Known side-effects 

Quercetin supplements are available as capsules or pills. The dosage will vary according to the condition treated. However, at 500 mg daily, quercetin supplementation has been shown to be generally safe. 

Currently, quercetin supplements are safe and effective in treating various diseases. Although this supplement is generally safe, there are some reports of upset stomach and headaches following this supplement. However, these reports are few, suggesting that it is safe to take this supplement. 

High doses, such as 1000 mg of the daily supplement, have been associated with kidney damage. Hence, it is always best to consult your doctor when taking quercetin supplements as a treatment for arthritis, cardiovascular disease and other conditions. 

Achieving longevity and a healthy life span is reachable with antioxidants such as quercetin. This supplement is safe and tolerable in many patients. However, pregnant women and older patients should seek medical advice when taking the supplement since there is still no sufficient evidence suggesting its long-term safety in these groups. 

[1] https://www.sciencedirect.com/science/article/abs/pii/S030881460600759X 
[2] https://pubmed.ncbi.nlm.nih.gov/18417116/
[3] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2992896/
[4] https://pubmed.ncbi.nlm.nih.gov/12927910/ 
[5] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3775217/ 
[6] https://pubmed.ncbi.nlm.nih.gov/18602817/ 
[7] https://pubmed.ncbi.nlm.nih.gov/29197723/ 

Photograph: Danijela Maksimovic/Shutterstock
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