Science 101

What Is Quercetin?

This plant-derived molecule may one day be used to reverse aging. But there is still much to learn about this potential senolytic.

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In January 2019, the first human study of senolytic therapies, a novel anti-aging strategy, was published in the journal Nature Medicine. Although it was just a pilot trial in 14 volunteers, it piqued interest because developing senolytic drugs that can eliminate senescent cells is a strategy biogerontologists have long been itching to test. The idea — heretofore only tested in laboratory studies — is that drugs can be developed to clear out these wayward cells, which have stopped dividing. An overwhelming increase in senescent cells is known to be a hallmark of aging, so eliminating them may turn back the clock on aging and fight off aging-related diseases. 

The results of the study were positive. After administering nine doses of two substances shown to combat senescent cells in lab studies to a group of patients with a rare and critical lung disease known to involve cellular senescence, the patients’ ability to walk and other measures of well-being were significantly improved. This was a small step for these patients to be sure, but a huge step forward in the fight to prove the promise of senolytics. 

One of the substances tested, quercetin (pronounced qu-air-SIT-in), is a plant-derived flavonol that’s already available in supplement form online and in the supplement aisle at your local natural food store. Does that mean you should head to the store now and start taking it? Not so fast. As exciting as these results are, there is still much work to be done before anyone can recommend quercetin as an anti-aging tool.

What Is Quercetin, And Why Are Aging Researchers Interested In It?

Quercetin is a polyphenol, a type of molecule made by plants. More specifically, quercetin is a flavanol, which is a class of polyphenols. These potent antioxidant molecules are found in the skin of certain plants, and we know that they are partly responsible for the health benefits of a diet rich in fruits and vegetables. High ingestion of flavanols has been linked to a reduced risk of cardiovascular disease, metabolic disorders, and certain types of cancer. And we know that these health benefits are the result of what flavanols are doing inside our bodies: they reduce oxidative stress in various tissues, inhibit the process that leads to clogged arteries, and keep our blood vessels flexible.

Quercetin, specifically, is found in deeply colored, nutrient-dense fruits and vegetables. Many healthy foods you are likely already eating are high in the nutrient — think onions, green tea, leafy green and cruciferous veggies, tomatoes, citrus, legumes, apples, berries, and even red wine. Capers are one of the best sources. Herbs, such as Ginkgo biloba, St. John's wort, and American elder, also contain high amounts of the flavanol.

Polyphenols and flavonoids, including quercetin, have fascinated aging researchers for many years. There are hundreds of polyphenols, each with slightly different functions and chemical makeup and properties, which may prove key for developing drugs or supplements. Their most-hyped quality is that they are antioxidants, meaning they help keep cell-damage-causing free radicals in check. In studying them, aging researchers have found that some of these compounds are more than just free radical fighters. 

For example, you’ve probably heard of resveratrol, the “it” polypehenol of years past that despite much hype as an anti-aging miracle ingredient (found in wine, no less) turned out to be somewhat of a dud due to its low bioavailability, meaning it’s not easily taken up by our cells. And perhaps you’ve heard of pterostilbene (pronounced tear-oh-STILL-bean), resveratrol’s much more promising cousin (and an ingredient in Elysium Health’s Basis

Resveratrol, pterostilbene, and quercetin have been found to act as “sirtuin activators.” Sirtuins are proteins in your cells important for managing the variety of basic cellular functions, everything from DNA maintenance to mitochondrial function. As you age, sirtuin activity declines, which is partly why cellular function begins to decline. One effect of this is the accumulation of senescent cells — as sirtuin activity declines, cellular senescence becomes more likely

That’s where quercetin comes in. Senolytic compounds like quercetin are interesting to aging researchers because of their alleged powers to eliminate senescent cells in aging tissues. Cellular senescence was first discovered in the 1950s, and since then scientists have learned much about it; just like division (when new cells are created), differentiation (when cells take on a specialized function), or cell death (either necrosis or apoptosis), senescence is a natural event. As you age, more and more of your cells become senescent, meaning they simply stop dividing. For a long time, scientists thought they were harmless, until it was discovered that they encourage further cellular breakdown because it turns out they emit a potent mix of chemicals that, when there are too many of them, provides a steady stream of inflammatory chemicals that facilitates aging and disease.

The idea is that by removing senescent cells, basically forcing them into necrosis for good, can help slow the aging process. In multiple preclinical studies, administering senolytic compounds has been shown to improve cardiac function and physical health in old mice, improve blood vessel health in mice with atherosclerosis, and even reverse signs of aging in mice. This is also why the 2019 study was so important: It was the first time similar beneficial effects were documented in humans. 

Quercetin isn’t the only compound that seems to work as a senolytic, but it is one of the most promising — especially when tested in combination with others, such as dasatinib, a leukemia drug that has exhibited senolytic activity in preclinical studies. Dasatinib was the other compound tested in the 2019 Nature Communications study.  Others being investigated include an industry-developed compound called UBX0101, which is already in phase 1 clinical trials for the treatment of osteoarthritis.

Does Quercetin Have Other Uses?

A quick Google search suggests that quercetin supplementation can help with just about anything that ails you. Proponents say it can lower inflammation, support heart health, combat pain, boost athletic performance and endurance, and even fight cancer. While there are varying amounts of scientific support for each of these claims, most experts agree they are largely inconclusive

The good news is, because quercetin is so plentiful in fruits and veggies, you’re probably getting a healthy daily dose of quercetin already, and the even better news is that when you get your quercetin in the form of foods you’re also getting a dose of all the other potent polyphenols contained in them as well. 

Meanwhile, the science marches on. With ongoing preclinical work and the publication of the first human study, there is more reason than ever to be enthusiastic about the promise of quercetin as a senolytic. That future is still a ways off, this underscores the bigger picture: One day, senolytics — whether it’s quercetin in combination with dastinib or another cocktail yet to be discovered — could revolutionize the treatment of all sorts of diseases.

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