Quercetin Supplementation

How and why to take QuercetinQuercetin is a flavonoid – a type of antioxidant that modulates the body’s immune system and directly fights free radicals.

Supplementally, it has the potential to protect against infections, cardiovascular disease, gut conditions and even allergies.


Quercetin for Allergies

Got the seasonal sniffles? Quercetin could help.

This powerful antioxidant works as an antihistamine to reduce symptoms of hay-fever and other allergic reactions like contact dermatitis and asthma.

Mast cells release histamine to attack pathogens – but in cases of allergies, this histamine release is a knee-jerk reaction to the presence of otherwise harmless proteins. Quercetin helps to stabilize the membranes of mast cells, making them less likely to release histamine and inflammatory chemicals that lead to hay-fever symptoms like runny noses, itchy eyes, and sneezing; or asthma attacks, skin break outs, and upset tummies.

A study in 2012 found that quercetin was more effective than Cromolyn (a pharmaceutical option) at stabilizing mast cells [1]. Participants in the study took 2g of quercetin per day – this is quite a high dose, so speak to a qualified nutritionist for personalized advice.


Quercetin and Exercise

Quercetin may protect against upper respiratory infections in most populations, and it could have a similar impact on athletes… Maybe.

In a three week double-blind trial, participants were given a placebo or 1g of quercetin per day before, during and after an endurance cycling simulation. The participants cycled for three hours each day for three days, and had blood taken to monitor the impact of the quercetin on their immune function. While there was no significant difference in the biomarkers of immune health between the quercetin and placebo groups, the group that didn’t take quercetin had a much higher rate of post-exercise illness during the two weeks following the trial.

Quercetin may reduce the risk of post-exercise upper respiratory tract infections, particularly following strenuous exercise. [2]

However, another study – this one on marathon runners – also found that quercetin had no impact on the biomarkers of immune health after exercise. In this trial, the group that took quercetin had just as many cases of post-race upper respiratory infections as the group that took a placebo. [3]

The discrepancy may have to do with the pathogens responsible for the infections. may be that quercetin’s anti-infection actions has more to do with fighting off specific pathogens:


Quercetin for Infections

Quercetin vs Viruses

While boosting the immune system’s response to pathogens, in vitro research has shown that quercetin can also directly attack viruses and stop them from replicating. It acts as a broad spectrum antiviral against the viruses that cause upper respiratory tract infections such as rhinoviruses, adenoviruses, and coronaviruses [4], and animal studies suggest that quercetin may even protect against Zika-virus, Ebola virus and influenza-A infections [5] [6] [7].

Quercetin vs Bacteria

Quercetin has also shown strong antimicrobial actions against pathogenic bacteria in the gut, respiratory system, urinary system and skin including Staphylococcus and H. pylori [8][9]. It even inhibits the growth of oral bacteria like Streptococcus mutans and Porphyromonas gingivalis, and other strains that are responsible for gingivitis, plaque and cavities [10].


Quercetin in Gut Health

Quercetin’s anti-inflammatory, antioxidant, and immune-boosting actions all play a key role in protecting the gut.

Quercetin for Gastrointestinal Infections

Quercetin has been shown to directly attack gut pathogens such as H. pylori, a bacteria that causes reflux, poor digestion and serious stomach ulcers. By strengthening the immune system throughout the gut, quercetin may help to reduce the risk of infections in the stomach, intestines, and even the mouth!

Quercetin for Food Allergies & Intolerances

By strengthening the membranes of mast cells, quercetin can reduce the amount of inflammatory chemicals and histamine released throughout the body, including the gastrointestinal system. Too much histamine and inflammation in the gut results in food allergy and intolerance symptoms such as bloating, diarrhea, constipation, cramping, and indigestion. By stabilizing mast cells and reducing histamine, quercetin has an anti-inflammatory effect and can help to reduce these symptoms [11].

CAUTION: Quercetin supplements may interact with anti-heartburn and anti-reflux medications like Zantac. Speak to a healthcare professional for advice.


Quercetin and Cardiovascular Health

Quercetin is a versatile nutrient with multiple protective actions against cardiovascular disease. As an antioxidant, quercetin may protect against damage to arteries, excessive blood clotting, oxidation on LDL cholesterol, and atherosclerosis. Its anti-inflammatory actions may protect heart cells against oxidative damage, and could promote liver metabolism to prevent excessive cholesterol production. While there are only a few human trials supporting supplementation, a landmark study found that people who regularly consumed quercetin had biomarkers of healthier arteries [12].

Quercetin Reduces Cholesterol

Studies on quercetin and cholesterol are quite conflicted. A 2015 meta-analysis of randomized controlled trials concluded that quercetin supplementation didn’t have a significant effect on cholesterol levels [13]. This may be to do with the populations involved.

One significant study on male smokers found that participants who took a supplement containing a low dose of quercetin (100mg) and mixed flavonoids for 10 weeks had significantly lower LDL cholesterol levels [14].

Perhaps the effects of quercetin are most significant in populations that are at high risk of cardiovascular disease. More human trials are definitely needed before we can draw any conclusion.

Quercetin Normalizes Blood Pressure

Quercetin has been shown to relax blood vessels, reduce blood clotting, and support the production of nitric oxide – a chemical required by the lining of the arteries to control blood pressure.

In one study, women with type 2 diabetes took 500mg of quercetin, or a placebo, for 10 weeks. The participants who took quercetin experienced a significant reduction in systolic blood pressure compared to the placebo group. No other biomarkers of cardiovascular disease risk or inflammation were reduced – however, the dose used in this study is at least half of what is considered a therapeutic dose. Most studies on quercetin use 1g or more per day.


How to Take Quercetin

Quercetin supplements usually contain quercetin dihydrate, often extracted from . In truth, quercetin is a tricky antioxidant for the body to absorb. It is quickly excreted, and the intestines don’t . This is partially why such high doses are used in supplementation:

Quercetin Dosage

Quercetin is generally considered quite safe to supplement at high doses. Many studies use to 1g per day, taken in divided doses of 250mg four times per day. Speak to a qualified nutritionist for personal advice before taking high doses.

Side Effects of Quercetin Dihydrate

Quercetin supplements taken at any dose can cause side effects. Risks of adverse reactions increase with higher doses.

Side effects of quercetin include:

  • Stomach pain
  • Nausea
  • Headache
  • Numbness

Do NOT take quercetin if you are also taking:

  • Everolimus
  • Topotecan
  • Antibiotics
  • Cyclosporin
  • Effexor
  • Risperdal
  • Prozac
  • Zantac
  • Allegra 

There is no information regarding the safety of quercetin supplementation in pregnancy or breastfeeding.

Speak to your doctor before taking quercetin supplements if you are on ANY medication.


Top 5 Quercetin Supplements

#5 Revly Quercetin (500mg, 50 capsules)

Vegan Quercetin SupplementRevly has combined quercetin dihydrate with another antioxidant – bromelain. These two anti-inflammatory agents have been shown to work synergistically and have a more powerful effect when combined than when taken alone.

This product is vegan-friendly and gluten free, and comes with a money-back guarantee from Amazon.

Do not take if you are taking blood thinner or anticoagulant medications.


#4 Physician Nutrients Resveratrol & Quercetin (250mg, 60 capsules)

Resveratrol with QuercetinIf you’re looking for a powerful quercetin supplement to boost cardiovascular health, you’ve found it – this product contains therapeutic doses of quercetin dihydrate and trans-resveratrol, antioxidant bioflavonoids with powerful anti-inflammatory actions to protect your eyes, heart, arteries, and capillaries from oxidative stress.

Taken together, quercetin boosts the bioavailability of resveratrol and this combination of nutrients can boost cellular energy production and may help to protect against premature ageing.


#3 LiftMode Quercetin (50g)

Exercise quercetinLiftMode have produced a capsule-free, powdered quercetin of super high quality. This stuff is 95%+ pure, comes with a certificate of authenticity and manufacture, as well as a handy scoop to measure out your dosage. This is a great choice if you have a hard time swallowing capsules or are using high doses – just combine with water, hold your nose, and swallow it down. It can also be combined into food like smoothies and soups and doesn’t leave a strong taste.


#2 Airloom Conscious Seasonal Wellness (500mg, 120 capsules)

QuercetinAirloom have blended a high dose of quercetin with other nutrients and herbs to specifically target seasonal allergies, asthma, and upper respiratory infections. Along with 500mg of quercetin dihydrate, each capsule contains a therapeutic dose of grapeseed extract, bromelain, butterbur root extract, and turmeric.

All ingredients are sourced within the USA, and this product is completely vegan-friendly, dairy-free, soy-free and gluten-free. Airloom is made in small batches by an FDA registered manufacturer, and each batch is independently tested.

Do not take if you are taking blood thinner or anticoagulant medications.


#1 Thorne Quercetin Phytosome (250mg, 60 capsules)

Quercetin is difficult for the body to absorb. It’s a water soluble antioxidant that is quickly excreted, requires a very particular environment for its absorb in the small intestines, and is readily metabolized in the liver.

It takes a lot to get quercetin into the body, and it leaves really quickly. Thorne have engineered a solution – phytosomes.

Phytosomes are liposomes or “carriers” that transport phytonutrients (plant-nutrients), and have a similar structures to cells. They have a fatty membrane that keeps its contents or “package” safe from destruction in the gut, and deliver the “package” (in this case: quercetin) through the lymph system instead of its usual direct route to the liver. By spending more time in the lymph, quercetin can act directly on the immune system rather than being metabolized and excreted by the liver. In theory, this makes quercetin more bioavailable and active.

This is a great choice if you want a high quality, bioavailable quercetin supplement. As far as we know, it’s the only phytosome quercetin available on the market.

Get Thorne Quercetin on Amazon

About James Lyons

James Lyons (BHSc Nutritional Medicine) is a clinical nutritionist, medical writer, and educator. He specialises in plant-based nutrition and is passionate about improving public access to reliable and accurate health information.

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