Quercetin and Health: What Human Studies Show

This article summarizes what human studies show about quercetin, including where the evidence is weak and what is known about safety.

Quercetin is a phytochemical that belongs to the flavonoid group of polyphenols. It is found in fruits, vegetables, tea, wine, and many other plant-based foods.¹ In laboratory studies it has shown antioxidant, anti-inflammatory, and other biological activities.^1,2,3 Whether these effects translate into health benefits in people is less clear. This article 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 effects of quercetin supplementation in humans, though the results have been conflicting. A 2016 meta-analysis of 7 randomized controlled trials (RCTs; 587 patients) found small reductions in blood pressure, with pooled reductions of 3.04 mmHg in systolic blood pressure and 2.63 mmHg in diastolic blood pressure compared with placebo; the effect was seen at doses of 500 mg/day or more. The authors said further studies are needed to establish the clinical relevance of these results and whether quercetin could be used as an add-on to blood-pressure medicines.⁴ A later umbrella review of meta-analyses found a smaller reduction in systolic blood pressure (1.9 mmHg) and no effect on diastolic blood pressure, with the certainty of evidence rated very low to moderate.⁵ A 2017 meta-analysis of 5 RCTs found no clinically relevant effect of quercetin on LDL or HDL cholesterol; triglycerides were lower at doses of 500 mg/day or more taken for at least 4 weeks (by about 24.5 mg/dL), and total cholesterol was slightly higher.⁶

Antioxidant Effects

Quercetin is described as one of the most prominent dietary antioxidants. In laboratory tests it can scavenge free radicals.¹ Human studies on the antioxidant effects of quercetin supplementation are limited and inconsistent. In a small study of 10 men, 2 weeks of quercetin (30 mg/day) lengthened the time before LDL oxidized in a laboratory test (from 44 to 51 minutes), without changing plasma antioxidant vitamins; this is a laboratory marker, not a health outcome.⁷ In a placebo-controlled trial of 1,002 adults, 12 weeks of quercetin (500 or 1,000 mg/day, taken with vitamin C) did not change blood measures of oxidative stress or antioxidant capacity.⁸ Larger RCTs are needed to clarify whether quercetin has meaningful antioxidant effects in people.

Anticancer Effects

In cell and animal studies, quercetin has inhibited the growth of cancer cells and induced apoptosis (programmed cell death).³ These are laboratory findings, not results in people. Population studies of dietary flavonoid intake are limited; in one cohort of 66,940 women, total intake of five flavonoids including quercetin was not clearly associated with ovarian cancer (rate ratio 0.75 for the highest versus lowest intake, 95% confidence interval 0.51 to 1.09).⁹ Evidence from human interventional trials is currently insufficient to demonstrate anticancer effects of quercetin supplementation. People having cancer treatment should not combine quercetin supplements with it without checking with their oncology team, because quercetin can affect how some drugs are processed in the body.¹⁰

Anti-inflammatory Effects

In cell studies, quercetin reduced the production of the inflammatory molecule tumor necrosis factor alpha by human blood cells, via effects on the nuclear factor kappa B (NF-kB) pathway.² Human trials are small and results are mixed. In 51 women with rheumatoid arthritis, quercetin 500 mg/day for 8 weeks did not change C-reactive protein, oxidative markers, or blood pressure compared with placebo.¹¹ In 18 people with untreated sarcoidosis (12 given quercetin and 6 placebo), four 500 mg doses given within 24 hours were followed by lower blood markers of oxidative stress and inflammation.¹² A meta-analysis of 7 RCTs found C-reactive protein about 0.33 mg/L lower with quercetin,¹³ but an umbrella review of five meta-analyses found no effect on inflammation overall.⁵ Larger and longer-term RCTs are required to establish the efficacy of quercetin’s anti-inflammatory effects in humans.

Safety

Quercetin from food has a long history of consumption, and a critical review concluded that the weight of the available evidence supports the safety of quercetin for addition to food.¹⁴ For supplements, a safety review found that adverse effects reported in human intervention studies were rare and mild, but that adequate data on long-term use (more than 12 weeks) of high doses (1,000 mg or more per day) are not available.¹⁵ Animal studies suggest that high-dose quercetin might worsen damage in kidneys that are already injured and might promote the growth of estrogen-dependent tumors; these findings have not been shown in people.¹⁵ People with kidney disease or hormone-sensitive cancers should talk to a healthcare professional before taking quercetin supplements. Safety of quercetin supplements in pregnancy, breastfeeding, and children has not been established. Further research is needed to determine the safe upper limit for chronic quercetin intake.

Medicines. Quercetin can change how the body handles some medicines by affecting liver enzymes (cytochrome P450) and drug transporters such as P-glycoprotein.¹⁰ A 2026 systematic review found clinically significant interactions in people for only a limited number of drugs and concluded that, for most medicines, the clinical effect is not well characterized.¹⁰ In small studies of healthy volunteers, quercetin taken for 7 days (500 mg three times daily) raised blood levels of fexofenadine, a P-glycoprotein substrate, by 55%,¹⁶ and 500 mg/day for 13 days lowered exposure to midazolam, a CYP3A substrate, in people with certain CYP3A5 genotypes.¹⁷ Because effects differ by drug, people who take prescription medicines, including blood thinners, antibiotics, immunosuppressants, or cancer treatment, should check with their prescriber or pharmacist before taking quercetin supplements.

Kasivit's Product containing Quercetin

Daily Greens Plus: This greens powder formula combines green nutrition sources with adaptogens, an antioxidant blend, and a mushroom blend.

PolyResveratrol-SR: It contains trans-resveratrol, along with plant extracts and a resveratrol metabolite.

Conclusion

In summary, quercetin is a dietary flavonoid with diverse biological activities in laboratory studies. In human trials, the most consistent finding is a small reduction in blood pressure, while effects on blood lipids, antioxidant status, and inflammation markers are small or inconsistent, and no human trial has shown that quercetin reduces 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, and quercetin can interact with some medicines. 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) Boots AW, et al. Eur J Pharmacol. 2008;585(2-3):325-337. PubMed · DOI (2) Nair MP, et al. Clin Vaccine Immunol. 2006;13(3):319-328. PubMed · DOI (3) Gibellini L, et al. Evid Based Complement Alternat Med. 2011;2011:591356. PubMed · DOI (4) Serban MC, et al. J Am Heart Assoc. 2016;5(7):e002713. PubMed · DOI (5) Arabi SM, et al. Phytother Res. 2023;37(11):5080-5091. PubMed · DOI (6) Sahebkar A. Crit Rev Food Sci Nutr. 2017;57(4):666-676. PubMed · DOI (7) Chopra M, et al. Clin Chem. 2000;46(8 Pt 1):1162-1170. PubMed (8) Shanely RA, et al. Free Radic Res. 2010;44(2):224-231. PubMed · DOI (9) Gates MA, et al. Int J Cancer. 2007;121(10):2225-2232. PubMed · DOI (10) Sulaiman SH, et al. Eur J Clin Pharmacol. 2026;82(11):263. PubMed · DOI (11) Javadi F, et al. Int J Prev Med. 2014;5(3):293-301. PubMed (12) Boots AW, et al. Clin Nutr. 2011;30(4):506-512. PubMed · DOI (13) Mohammadi-Sartang M, et al. Eur J Clin Nutr. 2017;71(9):1033-1039. PubMed · DOI (14) Harwood M, et al. Food Chem Toxicol. 2007;45(11):2179-2205. PubMed · DOI (15) Andres S, et al. Mol Nutr Food Res. 2018;62(1). PubMed · DOI (16) Kim KA, et al. Eur J Clin Pharmacol. 2009;65(6):609-614. PubMed · DOI (17) Duan KM, et al. J Clin Pharmacol. 2012;52(6):940-946. PubMed · DOI

This article is for general information only and is not medical advice. Dietary supplements are not intended to diagnose, treat, cure or prevent any disease. Speak with a doctor, pharmacist or other healthcare professional before starting a supplement, especially if you take medicines, are pregnant or breastfeeding, have kidney disease or a hormone-sensitive cancer, or have another medical condition.