Quercetin: Scientific studies + genetic connections

Quercetin is a natural flavonoid that acts both as an antioxidant and anti-inflammatory. This potent flavonoid is found in low levels in many fruits and vegetables, including elderberry, apples, and onions.

As a supplement, quercetin has many positive health benefits. This article focuses on the results of clinical trials involving quercetin as well as linking to specific genetic topics. By using your genetic data, you can make a more informed decision on whether quercetin is worth trying.

Quercetin Research:

Quercetin has been shown in cell studies to be a fabulous, wonder-supplement for lots of different conditions. But… the studies in humans don’t always match up with the cell studies and animal studies. I’m going to focus mainly on the human trials of quercetin and go into the cell studies just a bit in reference to genetics.

Food sources of quercetin:

Quercetin is a flavonol found in low levels in a lot of different fruits and vegetables.  Here is a list of foods with a higher quercetin content (from Phenol-explorer and the USDA)

  • Capers: 234mg/100g
  • Black elderberry: 42 mg/100g
  • Dark chocolate: 25 mg/100g
  • Shallots and onions: 10 – 31mg/100g
  • Apples, with skin: 2 -4 mg/100g
  • Billberry: 1.27/100g
  • Red Wine: 0.83 mg/100 ml
  • Apple juice: 0.48 mg/ 100ml

Blood pressure reduction studies that use quercetin

In a double-blind randomized placebo-controlled study, quercetin reduced blood pressure in men with hypertension. The study used 730 mg/day of quercetin and found that it reduced systolic blood pressure by 7 mm Hg and diastolic blood pressure by 5 mg Hg. [ref Trusted Source: Peer Reviewed Journal]

Another study using a smaller dosage of quercetin had a smaller decrease in blood pressure.  The study results showed a decrease in systolic blood pressure of 3.6 mm HG in overweight patients with high blood pressure using only 162 mg/day of quercetin.[ref Trusted Source: Peer Reviewed Journal]

A meta-analysis that combined the data from 7 clinical trials found that there was a significant reduction in blood pressure in randomized controlled trials that uses dosages of more than 500mg/day. [ref Trusted Source: Peer Reviewed Journal]

Quercetin for oxidative stress and oxidized LDL

When a cell has an imbalance of reactive oxygen species (ROS) to antioxidants, it is referred to as oxidative stress. These reactive oxygen species contain an unstable balance of electrons and can cause reactions that are damaging to the cell.  Too much oxidative stress can cause DNA damage, the production of inflammatory signals, and eventually cell death.

Quercetin is a free radical scavenger that has been shown in studies to help prevent oxidized cholesterol [ref Trusted Source: Peer Reviewed Journal] This is important because oxidized cholesterol may accelerate atherosclerosis or plaque build-up in the arteries.[ref Trusted Source: Peer Reviewed Journal]

A double-blinded, placebo-controlled cross-over trial in overweight adults with metabolic syndrome found that 150mg/day of quercetin decreased the concentration of oxidized LDL cholesterol.  There wasn’t much of an effect on any other health markers else at this dosage, but just decreasing the oxidized LDL should decrease the risk of cardiovascular disease. [ref Trusted Source: Peer Reviewed Journal]

Researchers theorize that oxidative stress contributes to Alzheimer’s disease pathology. Animal and cell studies show that quercetin can protect against oxidative stress in the brain and partially prevent the associated neuronal toxicity.[ref Trusted Source: Peer Reviewed Journal]

Most of the time, preventing oxidative stress is something that you want to do – but not always.  One of the benefits of exercise is to create stress, which causes cells to respond by adapting and producing more mitochondria. Quercetin’s effect on exercise performance has been researched. The results of the studies have varied, but most show that quercetin doesn’t increase exercise performance.[ref Trusted Source: Peer Reviewed Journal] If you are supplementing with quercetin, consider whether you should take it at a time that it won’t interfere with the benefits of exercise-induced stress.

Related article: Athletic Performance Genes

Quercetin as a senolytic (longevity benefits)

Cellular senescence occurs when a cell can no longer divide or do its normal function. Basically, the cell just sits there giving off proinflammatory signals. Those inflammatory factors can then impact the surrounding cells.  Kind of like a meth dealer moving into the neighborhood…  not good for the neighbors.

The body can get rid of senescent cells pretty well  — up to a point.  But when too many senescent cells accumulate, things start going downhill.  Recent research points to senescent cells actually causing a lot of the diseases of aging, rather than just being a symptom of aging.

Clearing out senescent cells could either delay or possibly reverse aging. That would be pretty cool…

Quercetin has been studied recently as a senolytic –  a way of clearing out senescent cells. Animal and cell studies are promising.[ref Trusted Source: Peer Reviewed Journal][ref Trusted Source: Peer Reviewed Journal]

But what about human trials?  When quercetin is combined with Dasatinib (a leukemia drug), it clearly reduces senescent cells. [ref Trusted Source: Peer Reviewed Journal][ref Trusted Source: Peer Reviewed Journal] This is an exciting field of study that shows a lot of promise for the future.

One more way that quercetin may improve atherosclerosis and oxidized LDL is by reducing senescent cells in the endothelium (lining of the arteries).  A new study out looked at quercetin’s effect on a cell model of atherosclerosis. The study found that quercetin inhibited the foam cells created by oxidized LDL in atherosclerosis and it also decreased senescent cells. While just a cell study, this points to quercetin possibly having multiple beneficial effects in cardiovascular disease. [ref Trusted Source: Peer Reviewed Journal]

Related article: NAD+

Advanced glycation end products:

The production of advanced glycation end products (AGEs) in the body (and through foods we eat) increases the diseases of aging.  For AGEs that are produced in the body, methylglyoxal levels are important.

A randomized, double-blind, placebo-controlled crossover trial found that 160 mg/d of quercetin reduced methylglyoxal, a precursor for AGEs by an average of 11% after 4 weeks. [ref Trusted Source: Peer Reviewed Journal]

Related article: Advanced Glycation End Products

Uric acid:

High uric acid levels are a risk factor for gout.  A double-blind, placebo-controlled cross-over trial in healthy men with higher uric acid found that quercetin lowered uric acid levels.  The trial used 500mg/day of quercetin for four weeks and decreased uric acid by 26·5 µmol/l  on average.[ref Trusted Source: Peer Reviewed Journal]

Rheumatoid Arthritis:

Since quercetin can reduce both pain and inflammation, it makes sense that it could help with rheumatoid arthritis.  Indeed, a two-month placebo-controlled trial found that quercetin reduced morning pain, stiffness, and post-activity pain. Quercetin also reduced TNF-alpha (inflammatory cytokine) levels.   The trial included 50 women with RA who took either 500mg/day of quercetin or a placebo.[ref Trusted Source: Peer Reviewed Journal]

Related article: TNF-alpha and rheumatoid arthritis

Immune boosting

A randomized placebo-controlled trial found that 12 weeks of quercetin at 1000mg/day reduced upper respiratory tract infections.[ref Trusted Source: Peer Reviewed Journal]

Excessive exercise can make you more susceptible to getting sick.  In a mouse trial where the mice exercised to fatigue (treadmill) for days, researchers found that quercetin offset the increased propensity to get sick after exercising to fatigue.[ref Trusted Source: Peer Reviewed Journal]  This may be something to try if you are training for an upcoming exercise-intensive event.

A human study showed that quercetin was safe (>5g/day) and effective for some people in reducing the viral load in hepatitis C patients.[ref Trusted Source: Peer Reviewed Journal]

Mast Cell Blocker

Mast cells are an important part of the immune system that can degranulate and signal for an inflammatory response. Overactive mast cells can be a problem, leading to allergic responses or to mast cell activation syndrome. One compound that mast cells can release is histamine.

Quercetin has been shown to stabilize mast cells and inhibit the release of histamine.[ref Trusted Source: Peer Reviewed Journal]

Related article: Histamine and Mast Cells

Caffeine and quercetin (CYP1A2 gene):

Quercetin inhibits CYP1A2, which is the enzyme the body uses to metabolize caffeine.[ref] If you are a slow metabolizer of caffeine, quercetin along with caffeine may mean that you feel the effects of caffeine for a longer period of time.

Relevant articles: CYP1A2 Variants

Absorption, transport, and metabolism

For any substance to have an effect in the body, it needs to be absorbed (usually in the intestines), transported throughout the body, and the broken down and eliminated (usually through the liver.  One big difference between cell studies and in vitro human studies is the absorption and metabolism of substances.

Absorption of quercetin:

A study found that the bioavailability of quercetin in humans is about 45%. The half-life is quercetin is between 11-28 hours, so taking it daily will build up more than just what was consumed that day.[ref Trusted Source: Peer Reviewed Journal]

Researchers have looked at the interaction between different types of foods and the absorption of quercetin. They found that eating a meal that contains fat along with the quercetin supplement can increase bioavailability.[ref Trusted Source: Peer Reviewed Journal]  Alternatively, if you normally take a fish oil supplement, you may want to take it at the same time as your quercetin.

Transdermal absorption of quercetin is an interesting idea, especially with the antioxidant properties and the possibility of enhancing the skin. Since it is hydrophobic, quercetin won’t dissolve well in water.  One study found that olive oil and soybean oils were better for transdermal absorption, compared to avocado, raspberry seed, and coconut oils.[ref Trusted Source: Peer Reviewed Journal] Another study used solid lipid nanoparticles with quercetin to enhance skin absorption.[ref Trusted Source: Peer Reviewed Journal]  (Personal note…   quercetin is a yellow-ish powder that stains everything it touches. When mixed with olive oil, it lends a jaundiced-hue to skin.)

Metabolism  and interactions:

Quercetin is an inhibitor of the CYP2C8 enzyme. If you have genetic variants that slow down the CYP2C8 variant and stack quercetin with a medication that uses that enzyme, you could majorly impair the metabolism of the medication.

Related article: CYP2C8 Genetic Variants

Quercetin has a catechol structure and is partly metabolized through the COMT enzyme.  If you carry the slower version of COMT, you may want to be careful and not go overboard with quercetin.

Related article: COMT variants

Transport of quercetin:

The MATE1 (multidrug and toxic compound extrusion transporter-1) protein is the quercetin transporter. It is coded for by the SLC47A1 gene. [ref Trusted Source: Peer Reviewed Journal]

What quercetin doesn’t do…

I don’t want to leave you with the impression that quercetin is a miracle cure for everything. Far from it! Instead, it may be another tool to use for a specific purpose at the right dosage.

For example, a trial of 162 mg/d of quercetin for six weeks showed little effect on C-reactive protein, leptin levels, or blood glucose levels in overweight adults with metabolic syndrome. The study did show that the 162 mg dose was safe. [ref Trusted Source: Peer Reviewed Journal]

Another study in healthy adult women found no significant effect from either 500 mg/day or 1000 mg/day on inflammatory markers and immune function. [ref Trusted Source: Peer Reviewed Journal]

The studies that show more of an effect seem to be using higher dosages (500-1,000 mg/day). Plus, it may be more effective in people who have a problem (e.g. high blood pressure or cholesterol) rather than having a large effect on people who are healthy.

Where to get quercetin:

You can get quercetin as a supplement in capsules or as a powder.  The advantage of getting it as a powder and either putting it in a smoothie or into capsules yourself is that you can eliminate the excipients in most capsule formulas. The drawback to the powdered form is that it is yellow and will stain everything that it touches a bright yellow. The stains do eventually come out of kitchen towels…  lessons learned.


Author Information:   Debbie Moon
Debbie Moon is the founder of Genetic Lifehacks. She holds a Master of Science in Biological Sciences from Clemson University and an undergraduate degree in engineering. Debbie is a science communicator who is passionate about explaining evidence-based health information. Her goal with Genetic Lifehacks is to bridge the gap between the research hidden in scientific journals and everyone's ability to use that information. To contact Debbie, visit the contact page.