Quercetin is a Powerful Antioxidant – But it Won’t Extend Your Life
I’ll admit coming into this research with an assumption – that antioxidants, including Quercetin, were close to a ‘no brainer’ as supplements.
As with everything in longevity, the truth is far more nuanced.
It is true that having too many free radicals (oxidative stress) is a major health risk. What is less clear is whether topping up over and above sufficient quantities of antioxidants has any benefits. In fact, disrupting the natural balance of antioxidants may be dangerous.
On this page, I dive into Quercetin, covering its role in longevity, where you can get it naturally, and whether taking Quercetin supplements is beneficial.
Quercetin: How it Reduces Oxidation
Oxidation is happening billions of times a day in our cells.
It is a by-product of the ATP energy cycle.
As food it turned into energy by our mitochondria, compounds missing an electron are created. They are ‘free radicals’, which damage cell components including DNA, lysosomes, and cell membranes.
Here is where antioxidants, including Quercetin, come in. They provide the missing electrons, nullifying free radicals before they do any damage. This works in parallel with cell repair processes, which are fixing damage throughout your body.
Quercetin is a specific type of antioxidant, a flavonoid. It belongs to a family of plant-based compounds known as polyphenols. Other antioxidants in this group are Fisetin and Myricetin.
It is not easily absorbed. Trials show that between 3% and 17% becomes bioavailable from natural sources, with only 2% making it into our cells from supplements. Taking those supplements alongside healthy oils may boost intake.
Once in the bloodstream, Quercetin is rapidly metabolised in the small intestine, liver, and kidneys. It’s half-life averages 3.5 hours. With excretion via urine, bile, and faeces.
Low absorption may explain the differences between clinical trials in cell cultures (in vitro) and in people (in vivo). Quercetin has shown promise for treating certain cancers, and as a senolytic in cell cultures.
Where Quercetin Comes from: Natural Sources
Quercetin is abundant. You get it from foods which have other longevity benefits. They include fruit, vegetables, and green tea.
Here are some delicious sources:
- Red Onions: Super-high flavonoid content, best eaten raw.
- Apples: Keep the doctor away (though be careful not to overdo that fructose) with these Quercetin-rich fruits.
- Cranberries / Blueberries: Low sugar fruit options which are high in flavonoids.
- Broccoli: Add some raw broccoli to your salads for sulforaphane and Quercetin.
- Green Tea: Packed with polyphenols and antioxidants.
- Capers: Depending on your taste, eating too many capers can be a challenge.
The list goes on: Dill, buckwheat, fennel, plums, and dark grapes are all great natural Quercetin sources.
Oxidative Foods: Sugars, Oils and Processed Carbohydrates
It is easy to see at individual eating habits have a major effect on the oxidation / antioxidant balance.
The people that choose to eat multiple foods from the Quercetin-rich list above are not the same people that enjoy excess sugar, simple carbs (especially hyper-processed forms) and excess fats / processed seed oils.
Put the other way around, those with excess oxidative stress from their food are often doing little or nothing to reduce this.
Could it be that the people likely to take Quercetin supplements are those that stand to benefit the least? While people that could genuinely benefit (due to bad food, lack of sleep or stress) are the least likely to seek this out?
Let’s look at Quercetin alongside the many other antioxidant compounds, before returning to this question.
Quercetin and Longevity: Interaction with Other Antioxidants
Quercetin is a specific type of antioxidant – a part of a group known as flavonoids, specifically a flavonol.
Other compounds which have antioxidant properties include Vitamin C, Beta-Carotin, Vitamin E, Selenium, Manganese and many more. There are chemical variations of each – for example eight distinct types of Vitamin E.
A recent review of antioxidants by the Harvard school of public health said that:
This raises a question:
How does supplementing (especially at high doses) affect the natural balance of antioxidant chemicals?
Let’s dig into the evidence for from high-dose clinical trials involving Vitamins C and E, and Beta-Carotin.
Clinical Evidence: High-Doses of Specific Antioxidants Have Limited Benefits (and Some Big Negatives)
Large scale clinical trials investigated the link between antioxidants and chronic diseases.
Placebo controlled, double blind trials involving antioxidants found no major benefits to all-cause mortality. This meta-analysis also covered specific causes including cancer and respiratory diseases.
Worryingly, a link to increased risk of haemorrhaging stroke was found in with high-dose vitamin E supplementation. Note that other studies (with dietary antioxidants) have found reduced stroke risk.
A different study linked Beta-Carotin with an increased chance of developing lung cancer for smokers (whose lungs experience massive oxidative stress daily).
There are some caveats with these studies.
- Supplements are single chemical versions of the antioxidants (for example Vitamin E uses only one of the eight naturally occurring variations).
- High-dose of a single antioxidant compound may have upset the balance of antioxidant substances in ways we don’t yet understand.
- While the headlines are strong, replication of these results and the specific pathways affected are still under investigation. The classic ‘more research required’ phrase is prevalent.
Quercetin: Clinical Evidence of Longevity / Health Benefits from Supplements
Clinical work with Quercetin and longevity continues. Below are some papers I found interesting, covering cell senescence, autophagy, and the immune system.
- Autophagy: A trial investigating lower back pain found that Quercetin induced autophagy via the SIRT1 pathway. Note that this was in vitro.
- Cell Senescence: Selective removal of senescent cells would be a big win for any natural substance. This study found significant results.
- Immune Health: Multiple studies link Quercetin to immune health via anti-inflammatory pathways, here is an example covering allergies.
Wrapping Up: Quercetin and Longevity via a Healthy, Balanced Diet
The ‘all antioxidants = good’ line of thinking is pervasive, but wrong.
It has been amplified by generations of businesses selling supplements.
After completing this deep-dive, I’m aiming to boost my natural intake of antioxidants including Quercetin.
I won’t be buying any Quercetin supplements.
I’d like to see trials which boost Quercetin intake at times of significant oxidative stress. Times of sunburn, viral infection or mental stress will increase the number of free radicals in cells. Exercise also boosts oxidative stress.
Could targeted antioxidants at specific times assist the body in mopping up those excess free radicals and boosting cell repair?
Until then, getting the right balance between foods which boost Quercetin and other healthy antioxidants – and those that cause added oxidative stress on our cells (sugars and simple carbs) is key.
Come back soon for a wider deep dive into the complex and often misleading world of antioxidants.
More Longevity and Nutrition Articles:
- Omega 6 Seed Oils and Healthy Ageing
- Linking Zinc to Longevity
- Drinking Alcohol and Healthspan
- Supplement Buying Behaviour (from surveys)