Quercetin

• −3.04 mmHgsystolic · p=0.028
• −2.63 mmHgdiastolic · p<0.001
• 7 trials / 587pooled patients

In a pooled meta-analysis of 7 RCTs (9 treatment arms, 587 patients), quercetin produced a small but statistically significant reduction in both systolic and diastolic blood pressure. The effect on systolic BP was driven by the higher-dose subgroup: significant only at >=500 mg/day (-4.45 mmHg) and not significant below that dose (-1.59 mmHg, p=0.273), supporting a dose threshold for any BP signal.

Reported effect: Systolic WMD -3.04 mmHg (95% CI -5.75, -0.33, P=0.028); diastolic WMD -2.63 mmHg (95% CI -3.26, -2.01, P<0.001); at >=500 mg/day systolic WMD -4.45 mmHg (P=0.007)

“Systolic BP: WMD: -3.04 mm Hg, 95% CI: -5.75, -0.33, P=0.028 ... Diastolic BP: WMD: -2.63 mm Hg, 95% CI: -3.26, -2.01, P<0.001 ... Subgroup (>=500 mg/day) Systolic BP: WMD: -4.45 mm Hg, 95% CI: -7.70, -1.21, P=0.007 ... Subgroup (<500 mg/day) Systolic BP: WMD: -1.59 mm Hg, 95% CI: -4.44, 1.25, P=0.273”

Source: PMID 27405810 · Serban 2016 · J Am Heart Assoc

• −0.33 mg/lCRP · p<0.001
• 7 RCTs10 treatment arms
• −0.34 mg/l>=500 mg/day subgroup

A meta-analysis of 7 RCTs (10 treatment arms) found quercetin significantly lowered circulating C-reactive protein, a systemic inflammation marker. The reduction was most evident in trials using >=500 mg/day and in participants with baseline CRP <3 mg/l, though meta-regression found no significant association between CRP change and either dose or baseline CRP.

Reported effect: Circulating CRP WMD -0.33 mg/l (95% CI -0.50 to -0.15; P<0.001); >=500 mg/day subgroup WMD -0.34 mg/l (95% CI -0.52, -0.16; P<=0.001)

“The meta-analysis of seven RCTs (10 treatment arms) showed a significant reduction of circulating CRP levels (WMD: -0.33 mg/l; 95% CI: -0.50 to -0.15; P<0.001) following quercetin supplementation. ... A significant reducing effect was observed in trials with >=500 mg/day dosage (WMD: -0.34 mg/l; 95% CI: -0.52, -0.16; P<=0.001)”

Source: PMID 28537580 · Mohammadi-Sartang 2017 · Eur J Clin Nutr

• 4% vs 18%post-op AF · quercetin vs placebo

In a randomized double-blind trial of 97 coronary-artery-bypass patients (500 mg twice daily peri-operatively), quercetin reversed overexpressed senescence and inflammaging pathways in male vascular cells and improved endothelium-dependent relaxation in men, with significantly lower post-operative atrial fibrillation (4% vs 18%). Notably, the effect was sex-specific: in female cells quercetin had minimal endothelial benefit and a pro-inflammatory effect, an important honest caveat against generalizing the benefit.

Reported effect: Post-operative atrial fibrillation 4% (quercetin) vs 18% (placebo); endothelial relaxation improved in men but not women; senescence/inflammaging pathways reversed in male but not female vascular cells

“Post-operative atrial fibrillation incidence was significantly lower with quercetin, representing 4% of the patients compared to 18% in the placebo group. ... Endothelial acetylcholine-induced relaxation improved significantly with quercetin ... with effects in men but not in women. ... In female cells, quercetin had minimal endothelial benefit and increased inflammaging in fibroblasts.”

Source: PMID 40375481 · Mury 2025 · Aging Cell

• 11.5%→9.6%liver fat · p=0.013

In a randomized, double-blind, placebo-controlled crossover trial (36 completers, 500 mg/day for 12 weeks), quercetin moderately reduced intrahepatic lipid content from 11.5% to 9.6% versus placebo, with a small body-weight reduction and no change in other secondary outcomes or liver enzymes. The hepatic-fat reduction was about twice as large in women as in men.

Reported effect: Intrahepatic lipid 11.5%+/-6.4% to 9.6%+/-5.8% with quercetin vs placebo (P=0.013, adjusted P=0.028); body weight -1.5+/-2.6 kg (P<0.05)

“quercetin intervention moderately decreased the intrahepatic lipid contents from 11.5% +/- 6.4% to 9.6% +/- 5.8%, compared with the placebo intervention ... P = 0.013, adjusted P = 0.028 ... Body weight and body mass index were mildly reduced by 1.5 +/- 2.6 kg and 0.5 +/- 0.9 kg/m2 after the quercetin intervention (P < 0.05)”

Source: PMID 39032786 · Li 2024 · Am J Clin Nutr

In a randomized, placebo-controlled, double-blind parallel study (66 subjects, 200 mg quercetin phytosome for 4 weeks), allergic symptom scores (eye itching, sneezing, nasal discharge, sleep disorder) and quality-of-life measures were reported as significantly improved versus placebo. The abstract describes direction only and reports no p-values or effect-size numbers, so the magnitude is not extractable; note this used an enhanced-bioavailability phytosome form, not standard powder.

Effect size: this study reports the direction of the finding but does not state a specific numeric effect size, so none is given here rather than estimated.

“several scores of JRQLQ, including allergic symptoms, such as eye itching, sneezing, nasal discharge, and sleep disorder, were significantly improved in the quercetin-containing supplement group compared with the placebo group.”

Source: PMID 35776034 · Yamada 2022 · Eur Rev Med Pharmacol Sci

• 1/20 vs 9/20URTI · p=0.004

In 40 trained male cyclists given 1000 mg/day, quercetin significantly reduced upper-respiratory-tract infection incidence in the 2 weeks after intensive exercise (1/20 vs 9/20). The honest mechanistic caveat: it did NOT change natural-killer-cell activity, lymphocyte proliferation, neutrophil oxidative burst or salivary IgA, so the clinical benefit occurred without measurable immune-marker shifts.

Reported effect: URTI incidence 1/20 (quercetin) vs 9/20 (placebo), Kaplan-Meier statistic=8.31, P=0.004; no significant change in NKCA, PHA-LP, POBA, or sIgA

“URTI incidence during the 2-wk postexercise period differed significantly between groups (quercetin=1/20 vs placebo=9/20, Kaplan-Meier analysis statistic=8.31, P=0.004). ... Pre- to postexercise changes in NKCA, PHA-LP, POBA, and sIgA did not differ significantly between quercetin and placebo groups.”

Source: PMID 17805089 · Nieman 2007 · Med Sci Sports Exerc

• OR 0.25hospitalisation · 95% CI 0.10–0.62
• OR 0.31ICU · 95% CI 0.10–0.99

A meta-analysis of 6 RCTs found quercetin (often as phytosome) was associated with reduced odds of hospitalization and ICU admission in COVID-19 patients, but did NOT reduce all-cause mortality or the rate of non-recovery. The authors stress that large-scale RCTs are still needed, so this is a preliminary, mixed signal rather than established benefit.

Reported effect: ICU admission OR=0.31 (95% CI 0.10-0.99); hospitalisation OR=0.25 (95% CI 0.10-0.62); no reduction in all-cause mortality or rate of no recovery

“decreased the risk of intensive care unit admission (OR = 0.31; 95% CI 0.10-0.99) ... decreased ... the incidence of hospitalisation (OR = 0.25; 95% CI 0.10-0.62) ... did not decrease the risk of all-cause mortality and the rate of no recovery”

Source: PMID 36779438 · Cheema 2023 · Rev Med Virol

• −26.5 µmol/luric acid · p=0.008

In a randomized, double-blind, placebo-controlled crossover trial of 22 healthy pre-hyperuricaemic males (500 mg/day for 4 weeks), quercetin significantly lowered plasma uric acid by 26.5 micromol/l. The reduction occurred without changing fasting glucose, urinary uric acid excretion or blood pressure, suggesting a specific effect on circulating urate.

Reported effect: Plasma uric acid lowered by -26.5 micromol/l (95% CI -7.6, -45.5; P=0.008); no effect on fasting glucose, urinary uric acid excretion or blood pressure

“plasma uric acid concentrations were significantly lowered by -26.5 micromol/l (95% CI, -7.6, -45.5; P=0.008) ... without affecting fasting glucose, urinary excretion of uric acid or blood pressure”

Source: PMID 26785820 · Shi 2016 · Br J Nutr