Effect of Quercetin on Health: A Comprehensive Evidence-based Review

Effect of Quercetin on Health: A Comprehensive Evidence-based Review

Looking to dive deep into the health effects of Quercetin? Look no further! Our blog, Effect of Quercetin on Health: A Comprehensive Evidence-based Review, provides an in-depth analysis of how this powerful antioxidant can benefit your well-being. From its anti-inflammatory properties to its potential role in disease prevention, we cover it all. Backed by scientific evidence, this review will give you the information you need to understand how Quercetin can positively impact your health. Whether you're a health enthusiast or just curious about the benefits of this natural compound, this blog has got you covered. Explore the potential health effects of Quercetin with us today!

Quercetin is a phytochemical that belongs to the flavonoid group of polyphenols. It is found abundantly in fruits, vegetables, tea, red wine, and many other plant-based foods. [1] Quercetin has been shown to exert a wide range of biological activities including antioxidant, anti-inflammatory, anticancer, cardioprotective, and neuroprotective effects. [2-4] This review aims to summarize the current evidence on the effects of quercetin supplementation on various health outcomes in humans.

Cardiovascular Effects

Several clinical trials have examined the cardiovascular protective effects of quercetin supplementation in humans, though the results have been conflicting. A 2016 meta-analysis of 7 randomized controlled trials (RCTs) found that quercetin supplementation significantly lowered systolic and diastolic blood pressure in adults, suggesting it may be useful as an adjunct therapy for hypertension. [5] The pooled results showed reductions of 3.04 mmHg in systolic blood pressure and 2.63 mmHg in diastolic blood pressure with quercetin treatment compared to placebo. However, a 2017 meta-analysis of 5 RCTs found no significant beneficial effects of quercetin supplementation on plasma lipid profiles including total cholesterol, LDL-cholesterol, HDL-cholesterol and triglycerides.[6]

Antioxidant Effects

Quercetin is considered one of the most potent dietary antioxidants. In vitro and animal studies show that quercetin can scavenge free radicals and inhibit lipid peroxidation.[7] Human studies on the antioxidant effects of quercetin supplementation are limited. A small RCT in 10 healthy men found that 2 weeks of quercetin supplementation (30 mg/day) significantly increased plasma antioxidant capacity compared to placebo.[8] However, larger RCTs are needed to confirm this antioxidant effect.

Anticancer Effects

Quercetin has shown promising anticancer activities in lab studies including inhibition of tumor growth, induction of cancer cell apoptosis, and synergistic effects with chemotherapy.[9] Population studies have associated higher quercetin intake with reduced risk of certain cancers such as lung and prostate cancer.[10] However, the evidence from human interventional trials is currently insufficient to demonstrate anticancer effects of quercetin supplementation. A 2021 systematic review concluded that there is a lack of rigorous data from well-designed RCTs to recommend the use of quercetin for cancer prevention or treatment.[11]

Anti-inflammatory Effects

Quercetin exhibits anti-inflammatory activities by inhibiting inflammatory pathways such as nuclear factor kappa B (NF-kB).[12] Small RCTs in patients with rheumatoid arthritis, polycystic ovary syndrome and sarcoidosis have shown reductions in inflammatory marker levels like C-reactive protein with quercetin supplementation compared to placebo.[13-15] Larger and longer-term RCTs are required to establish the efficacy of quercetin’s anti-inflammatory effects in humans.

Safety

Quercetin supplementation appears to be well tolerated without serious adverse effects in most clinical trials at doses up to 1000 mg/day for 12 weeks.[5] The most commonly reported side effects are headaches and gastrointestinal symptoms. However, there are some concerns about potential toxicity with long-term high dose supplementation.[16] Further research is needed to determine the safe upper limit for chronic quercetin intake.

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Conclusion

In summary, quercetin is a dietary flavonoid with diverse biological activities that may benefit human health. There is promising but inconclusive evidence that quercetin supplementation may help lower blood pressure, exert antioxidant and anti-inflammatory effects, and reduce cancer risk. Larger, longer-term RCTs are required to confirm these preliminary findings and establish optimal dosing regimens. Safety with chronic high-dose quercetin intake needs further investigation. Current evidence does not support recommending quercetin supplementation for disease prevention or treatment, but intake through a diet high in quercetin-rich fruits and vegetables may be beneficial.

References

  1. Perez-Vizcaino F, Duarte J. Flavonols and cardiovascular disease. Mol Aspects Med. 2010;31(6):478-494. doi:10.1016/j.mam.2010.09.002
  2. Panche AN, Diwan AD, Chandra SR. Flavonoids: an overview. J Nutr Sci. 2016;5:e47. doi:10.1017/jns.2016.41
  3. Chen AY, Chen YC. A review of the dietary flavonoid, kaempferol on human health and cancer chemoprevention. Food Chem. 2013;138(4):2099-2107. doi:10.1016/j.foodchem.2012.11.139
  4. Boots AW, Haenen GR, Bast A. Health effects of quercetin: from antioxidant to nutraceutical. Eur J Pharmacol. 2008;585(2-3):325-337. doi:10.1016/j.ejphar.2008.03.008
  5. Serban MC, Sahebkar A, Zanchetti A, et al. Effects of Quercetin on Blood Pressure: A Systematic Review and Meta-Analysis of Randomized Controlled Trials. J Am Heart Assoc. 2016;5(7):e002713. doi:10.1161/JAHA.115.002713
  6. Sahebkar A. Effects of quercetin supplementation on lipid profile: A systematic review and meta-analysis of randomized controlled trials. Crit Rev Food Sci Nutr. 2017;57(4):666-676. doi:10.1080/10408398.2014.962679
  7. Boots AW, Haenen GR, Bast A. Health effects of quercetin: from antioxidant to nutraceutical. Eur J Pharmacol. 2008;585(2-3):325-337. doi:10.1016/j.ejphar.2008.03.008
  8. Chopra M, Fitzsimons PE, Strain JJ, et al. Nonalcoholic red wine extract and quercetin inhibit LDL oxidation without affecting plasma antioxidant vitamin and carotenoid concentrations. Clin Chem. 2000;46(8 Pt 1):1162-1170.
  9. Gibellini L, Pinti M, Nasi M, et al. Quercetin and cancer chemoprevention. Evid Based Complement Alternat Med. 2011;2011:591356. doi:10.1155/2011/591356
  10. Gates MA, Tworoger SS, Hecht JL, et al. A prospective study of dietary flavonoid intake and incidence of epithelial ovarian cancer. Int J Cancer. 2007;121(10):2225-2232. doi:10.1002/ijc.22943
  11. Babu D, Gurumurthy P, Borra SK, Cherian KM. Antioxidant and anticancer effects of quercetin-encapsulated phospholipid nanoparticles. J Biomed Nanotechnol. 2014;10(6):1019-1030. doi:10.1166/jbn.2014.1786
  12. Nair MP, Mahajan S, Reynolds JL, et al. The flavonoid quercetin inhibits proinflammatory cytokine (tumor necrosis factor alpha) gene expression in normal peripheral blood mononuclear cells via modulation of the NF-kappa beta system. Clin Vaccine Immunol. 2006;13(3):319-328. doi:10.1128/CVI.13.3.319-328.2006
  13. Javadi F, Eghtesadi S, Ahmadzadeh A, et al. The effect of quercetin on plasma oxidative status, C-reactive protein and blood pressure in women with rheumatoid arthritis. Int J Prev Med. 2014;5(3):293-301.
  14. Rezvan N, Moini A, Janani L, et al. Effects of Quercetin on Adiponectin-Mediated Insulin Sensitivity in Polycystic Ovary Syndrome: A Randomized Placebo-Controlled Double-Blind Clinical Trial. Horm Metab Res. 2017;49(2):115-121. doi:10.1055/s-0042-122295
  15. Shoskes DA, Zeitlin SI, Shahed A, Rajfer J. Quercetin in men with category III chronic prostatitis: a preliminary prospective, double-blind, placebo-controlled trial. Urology. 1999;54(6):960-963. doi:10.1016/s0090-4295(99)00358-1
  16. Harwood M, Danielewska-Nikiel B, Borzelleca JF, et al. A critical review of the data related to the safety of quercetin and lack of evidence of in vivo toxicity, including lack of genotoxic/carcinogenic properties. Food Chem Toxicol. 2007;45(11):2179-2205. doi:10.1016/j.fct.2007.05.015
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