Quercetin
Quercetin is the most well researched of all bioflavonoids. It is not actually that good of a supplement on its own, but is an interesting research topic. Tons of interactions, and synergistic with other bioflavonoids and increases absorption of Resveratrol and Green Tea Catechins.
Last Updated:October 13, 2024
Quercetin is a bioflavonoid found in fruits and vegetables, but highest levels are found in apples and onions.
Like many other bioflavonoids, Quercetin has anti-oxidant, anti-artherogenic, and anti-carcinogenic properties. Quercetin is also neuroactive, with some of the same abilities as caffeine but less potent.
There is a divide between the effects seen in quercetin in in vitro (cell cultured) studies and in vivo (in living) studies, with cell studies showing great results that are not that amazing in humans or animals. This is mostly due to quercetin having low oral bioavailability (low percentage of the compound is absorbed and put to use), but could also be due to in vitro studies using a form of quercetin called 'quercetin aglycone' whereas this particular form is never found in the blood, even after ingested, as it it gets changed in the liver.
Many studies also note a high range of differences between people who ingest the same amount of quercetin, suggesting a large degree of variability is possible with supplementation.
Quercetin has GRAS (Generally Recognized As Safe) status, and no side-effects have yet been noted in doses of a few grams a day in either humans or animals.
- Apple extract
- 3 4 5 7-pentahydroxylflavone
Dosages of quercetin used are in the range of 12.5 to 25mg per kg body weight, which translates to a range of 1,136-2,272mg daily consumption of quercetin when in isolation.
It is suggested to supplement with other bioflavonoids such as resveratrol, genistein, or green tea catechins to increase the potency synergistically and theoretically get the benefits at a reduced level of intake.
When looking for quercetin, the form of dihydrate has the apparent best bioavailability followed by glycosides, aglycone, and finally rutinoside.
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In this 6-week before-and-after study in 8 participants with gastrointestinal reflux disease (GERD), supplementation with quercetin did not result in any clear improvements to GERD signs or symptoms.
Quick Summary
In this 6-week before-and-after study in 8 participants with gastrointestinal reflux disease (GERD), supplementation with quercetin did not result in any clear improvements to GERD signs or symptoms.
The study
During the study the participants took a lozenge containing 200 mg of quercetin and 0.25 mg of riboflavin 3 times per day.
Supplementation did not result in any apparent changes in the severity of the participants’ disease symptoms — namely, heartburn, regurgitation, and indigestion.
Supplementation also did not appear to alter either esophageal sensitivity or the function of the esophageal mucosal barrier, 2 potential markers of disease severity in GERD.
The results
These results are consistent with those from a randomized controlled trial from 2023, which found that thrice daily supplementation with quercetin via a lozenge did not affect GERD symptoms.[1] Although more research is needed to be sure, current evidence does not support a benefit of quercetin in GERD.
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What was studied?
The effects of combined supplementation with quercetin (500 mg) and citrulline (3,000 mg) on measures of cycling performance, including average power, oxygen uptake, respiratory exchange ratio, 20-kilometer time trial performance, and rating of perceived exertion in trained cyclists.
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What was studied?
The effects of quercetin supplementation in people with type 2 diabetes (T2D).
The outcomes assessed included cardiometabolic biomarkers such as systolic and diastolic blood pressure and HbA1C. Additionally, lung function was assessed based on the forced expiratory volume (FEV) in the first second of exhalation (FEV1) and in the 6th second of exhalation (FEV6).
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What was studied?
The effect of quercetin on anxiety and quality of life.
Anxiety and quality of life were assessed with validated self-reported questionnaires (the Short Anxiety Screening Test and 36-item Short Form Health Survey, respectively).
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What was studied?
The effects of supplementing with a combination of mangiferin (a polyphenol concentrated in mango) and quercetin in basketball players.
The outcomes assessed were the average time to complete a circuit, average sprint time, average heart rate, rating of perceived exertion (RPE), subjective muscle soreness, and blood lactate.
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