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Total Quercetin

Also known as: Quercetin, Quercetin aglycone, Total Quercetin

Overview

Quercetin is a naturally occurring flavonoid found in various fruits, vegetables, and grains, including onions, apples, berries, and tea. It is commonly used as a dietary supplement due to its antioxidant, anti-inflammatory, cardiovascular, and immune-supportive properties. As a flavonoid polyphenol, quercetin exhibits antioxidant activity, modulates inflammatory pathways, and influences lipid metabolism and vascular function. Extensive research, including numerous randomized controlled trials (RCTs), systematic reviews, and meta-analyses, supports its health benefits. Quercetin's effects vary depending on the population and dosage, but high-quality evidence generally supports its use for exercise recovery, cardiovascular health, and potentially as an adjunct therapy for COVID-19. It is available in various forms, including capsules and powders, often as quercetin aglycone or glycosides to enhance bioavailability.

Benefits

Quercetin supplementation has several evidence-based benefits. It significantly promotes recovery after exercise-induced muscle damage, improving muscle function and reducing markers of muscle damage, as shown in a systematic review and meta-analysis of RCTs. For cardiovascular health, meta-analyses indicate that quercetin can significantly reduce both systolic and diastolic blood pressure, especially at doses of 500 mg/day or higher. Additionally, it has been shown to lower total cholesterol, LDL cholesterol, and C-reactive protein (CRP), all markers associated with cardiovascular risk. In the context of COVID-19, quercetin supplementation has demonstrated a significant reduction in lactate dehydrogenase (LDH) activity, hospital admission risk, ICU admission, and mortality, based on a meta-analysis of multiple RCTs. These benefits are observed in healthy adults, athletes, individuals at cardiovascular risk, and COVID-19 patients.

How it works

Quercetin primarily functions as an antioxidant by scavenging free radicals and inhibiting pro-inflammatory enzymes such as cyclooxygenase and lipoxygenase. It modulates signaling pathways, including NF-κB, which plays a crucial role in inflammation. Additionally, quercetin improves endothelial function, contributing to cardiovascular benefits. Its interaction with body systems involves influencing the cardiovascular system by enhancing vascular endothelial function and reducing blood pressure, as well as modulating the immune response and inflammation. Molecular targets include enzymes involved in inflammation and oxidative stress, such as NADPH oxidase, inducible nitric oxide synthase (iNOS), and inflammatory cytokines. Quercetin has moderate bioavailability, which can be enhanced when consumed with fats or in glycoside forms. It undergoes metabolism in the liver and intestines.

Side effects

Quercetin is generally safe and well-tolerated at typical supplemental doses of up to 1,000 mg/day. The most common side effect is mild gastrointestinal discomfort, which occurs in some individuals. Uncommon side effects, affecting 1-5% of users, include headache and tingling sensations. Rare side effects, occurring in less than 1% of users, may include allergic reactions. Quercetin has potential interactions with anticoagulants (e.g., warfarin), antiplatelet drugs, and certain chemotherapeutics, so caution is advised when taken with these medications. It is contraindicated in individuals with a known allergy to quercetin or related flavonoids. Due to limited data, pregnant or breastfeeding women should use quercetin with caution. It is important to adhere to recommended dosages and consult with a healthcare provider, especially when taking other medications or having pre-existing health conditions.

Dosage

The minimum effective dose of quercetin is approximately 500 mg/day for cardiovascular and exercise recovery benefits. Optimal dosage ranges commonly used in RCTs showing efficacy are between 500 and 1,000 mg/day. The maximum safe dose is considered to be up to 1,000 mg/day; higher doses should only be taken under medical supervision. It is recommended to take quercetin in divided doses with meals to enhance absorption and reduce potential gastrointestinal side effects. Quercetin glycosides or formulations with enhanced bioavailability are preferred. Co-administration with fats or vitamin C may improve absorption. Vitamin C may also synergistically enhance the antioxidant effects of quercetin. Adhering to these guidelines helps maximize the benefits and minimize potential risks associated with quercetin supplementation.

FAQs

Is quercetin safe for long-term use?

Current evidence supports the safety of quercetin for use up to several months. However, long-term safety data are limited, and it is advisable to consult with a healthcare provider for extended use.

When should quercetin be taken for best results?

Quercetin should be taken with meals to improve absorption. Consuming it with fats can further enhance its bioavailability and effectiveness.

How soon can benefits be expected from quercetin?

Benefits such as improved exercise recovery may be noticeable within days. Cardiovascular improvements typically require several weeks of consistent supplementation.

Does quercetin interact with medications?

Yes, quercetin can interact with certain medications, especially blood thinners. It is crucial to consult with a healthcare provider before starting quercetin if you are taking any medications.

Is quercetin effective for COVID-19?

Evidence from RCTs suggests that quercetin may help reduce the severity and mortality of COVID-19. However, it should not replace standard medical care and should be used as an adjunct therapy under medical supervision.

Research Sources

https://pubmed.ncbi.nlm.nih.gov/37398956/ – A systematic review and meta-analysis of RCTs demonstrated that quercetin supplementation significantly improved recovery after exercise-induced muscle damage. The study found reductions in muscle soreness and biomarkers of muscle damage, indicating its potential as an exercise recovery aid. The limitations included heterogeneity in exercise protocols, but the overall evidence quality was high.
https://pubmed.ncbi.nlm.nih.gov/31017459/ – Meta-analyses of RCTs showed that quercetin significantly lowers total cholesterol, LDL cholesterol, and CRP levels, suggesting cardiovascular benefits. The sample sizes were adequate, and the effect sizes were moderate, although some heterogeneity was noted. These findings support quercetin's role in improving lipid profiles and reducing cardiovascular risk.
https://www.ahajournals.org/doi/10.1161/jaha.115.002713 – A systematic review and meta-analysis of RCTs found that quercetin supplementation significantly reduced systolic and diastolic blood pressure, particularly at doses of 500 mg/day or higher. The included studies were well-controlled with appropriate statistical analyses, although there was some variability in the populations studied. This research highlights quercetin's potential in managing blood pressure levels.
https://onlinelibrary.wiley.com/doi/abs/10.1002/fsn3.3715 – A meta-analysis of five RCTs involving 544 COVID-19 patients showed that quercetin significantly reduced hospital admission, ICU admission, mortality, and LDH levels. The studies were randomized and controlled, but the sample sizes per study were moderate, suggesting that further large-scale trials are warranted. These results indicate that quercetin may be a beneficial adjunct in the treatment of COVID-19.
https://www.tandfonline.com/doi/abs/10.1080/10408398.2014.948609 – This meta-analysis of RCTs demonstrated quercetin significantly lowers total cholesterol, LDL cholesterol, and C-reactive protein (CRP) levels, indicating cardiovascular benefit. Sample sizes were adequate; effect sizes moderate; some heterogeneity noted. This supports the use of quercetin for improving cardiovascular health markers.