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Quercetin: A Synergistic Antioxidant That Slows Ageing?

Posted on 18 January 2024

Quercetin is a dietary supplement that has been studied for its potential health benefits. There’s some suggestion that quercetin might be able to delay certain aspects of the ageing process. It may also improve the effectiveness of other dietary supplements. Let’s take a closer look at the research.

What is it?

Quercetin is a flavonoid, a group of plant compounds with antioxidant and anti-inflammatory effects. Apples, onions, and kale are among the best sources.

What does it do?

Quercetin is, first and foremost, a powerful antioxidant. It neutralises harmful by-products of our metabolism that would otherwise damage cellular structures. While this property of quercetin is not in doubt, we still don’t know how important antioxidants are in general health and disease prevention. There does seem to be an association between ageing, age related diseases, and reduced antioxidant defences within the body, so it is possible that introducing more antioxidants into the body would be beneficial.

Quercetin has been investigated for its ability to suppress cellular senescence, often in combination with a drug called dasatinib. Senescence is a state that cells may enter in various circumstances, such as when damaged or after having replicated a maximum number of times. Senescent cells are unable to divide and also release various harmful molecules into their surroundings. The presence of senescent cells is associated with most age-related diseases, so some scientists believe that preventing and suppressing senescence or destroying senescent cells might prevent such diseases. 

Quercetin also has some wide-ranging metabolic and immune system benefits. It suppresses inflammation and may lower blood sugar, improve lipid profile (reduce LDL levels and raise HDL levels) and protect against infectious diseases through its antibacterial and antiviral properties. 

Finally, quercetin inhibits the activity of sulfurotransferases. These are enzymes in the gut and liver that break down some other supplements such as resveratrol. This means that quercetin might improve the effectiveness of other supplements by preventing their destruction.

What’s the evidence?

There’s plenty of evidence from cell culture for the effects of quercetin mentioned above, but the evidence in humans is less clear. Unfortunately, quercetin is not very well absorbed – when you take a given dose of quercetin, most of that dose does not actually reach the bloodstream. There also seems to be quite a lot of variability between the effects of quercetin in different people taking the same dose.

Meta-analyses of randomised trials suggest that taking flavonoids in general is associated with reduced risk of respiratory tract infections, suggesting that they may protect against infectious disease. Quercetin has also been found to have some antidiabetic, antihypertensive, and cholesterol-lowering properties in randomised trials. However, not all studies agree and more research is needed.

Similarly, while quercetin appears to suppress senescence in cell culture, more research is needed when it comes to the ability of quercetin to suppress senescence in living humans. Though there is some evidence that it works in combination with dasatinib, we don’t currently know if it works alone. 

Is it safe?

There are no known complications associated with long-term quercetin supplementation as long as recommended doses aren’t exceeded. Quercetin can however interact with some medications and may also worsen kidney problems, so it’s important to check with your doctor whether it’s OK to take. 

The take home message

There’s a good amount of evidence that plant flavonoids like quercetin are healthy. Quercetin seems to be among the most promising flavonoids, but its specific effects on human health need more investigation.

It is always best to consult with a doctor before taking any new drug, supplement, or making significant changes to your diet.


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    References

    Title image by Laura Johnston, Upslash

    Inhibition of human liver and duodenum sulfotransferases by drugs and dietary chemicals: a review of the literature https://doi.org/10.5414/cpp42488

    Effect of Flavonoids on Upper Respiratory Tract Infections and Immune Function: A Systematic Review and Meta-Analysis1,2 https://doi.org/10.3945%2Fan.115.010538

    Antidiabetic effect of quercetin: A systematic review and meta-analysis of animal studies https://doi.org/10.1016/j.fct.2019.01.037

    Effect of quercetin supplementation on plasma lipid profiles, blood pressure, and glucose levels: a systematic review and meta-analysis https://doi.org/10.1093/nutrit/nuz071

    Quercetin Reduces Blood Pressure in Hypertensive Subjects1,2 https://doi.org/10.1093/jn/137.11.2405

    First evidence that senolytics are effective at decreasing senescent cells in humans https://doi.org/10.1016/j.ebiom.2019.09.053

    Examine.com: Quercetin https://examine.com/supplements/quercetin

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