Quercetin
Enzymatically modified isoquercitrin (EMIQ) or a quercetin phytosome — plain quercetin aglycone is poorly absorbed. Trials used 500-1000 mg/day of quercetin dihydrate, usually with vitamin C and niacin to aid absorption.
Early
First results, or a theory about how it works
The headline '33% fewer URTIs' figure is for flavonoids as a class across 14 trials with only 531 participants, not quercetin alone, and the same meta-analysis found sick days non-significant (ratio 0.60, 95% CI 0.24-1.47). The one adequately powered quercetin trial was null on its primary endpoint. As an ergogenic, the pooled effect size is 0.15 (~2%), which the meta-analysts themselves classed as trivial.
The biggest study found no effect on colds for most people. Only fit adults over 40 had milder symptoms and fewer sick days, and that was spotted after the fact, so it is a weak result.
The largest trial (n=1002, 12 weeks) found no effect on URTI in the population overall; only a post-hoc subgroup of fit adults aged 40+ showed 36% lower symptom severity (p=0.020) and 31% fewer sick days (p=0.048) at 1000 mg/day.
Flavonol with antioxidant, mast-cell-stabilising and in-vitro antiviral (antireplicative) activity against RSV and parainfluenza type 3; it does not correct the post-exercise immune perturbations it was hypothesised to fix.
Fit adults over 40 during heavy training blocks — the only subgroup where anything showed. Untrained people showed a slightly larger (but still small) VO2max response in individual trials.
We compare each effect with how much that number normally swings from one night to the next. An effect smaller than the swing is real, but you will not see it in a week of data.
- Endurance capacity (VO2max + performance pooled)Too small to seeeffect: 0.15 SMD (~+2%, classed as trivial)normal swing: ±1.2 SMD (~+2%, classed as trivial)
What to buy
- ✓Enzymatically modified isoquercitrin (EMIQ) or a quercetin phytosome — plain quercetin aglycone is poorly absorbed. Trials used 500-1000 mg/day of quercetin dihydrate, usually with vitamin C and niacin to aid absorption.
- ✓1000 mg/day (500 mg twice daily). The 500 mg/day arm was negative on every outcome.
- ✓Third-party tested (USP, NSF, Informed Sport)
- ✕Proprietary blends that hide the dose per ingredient
- ✕Unstandardised extracts with no active-compound percentage
- · Long-term safety above 1 g/day is not established; nephrotoxicity has been reported with intravenous quercetin.
- · Headache and peripheral tingling were reported in supplementation trials.
- · GI upset; avoid in pregnancy and breastfeeding for lack of data.
As an Amazon Associate, Umbral earns from qualifying purchases. Product data is provided by Amazon and may change; ratings and prices shown are Amazon’s, not Umbral’s. Recommendations are based on the evidence grade and the form used in trials, never on commission.
Bromelain is there to help absorption, which plain quercetin badly needs. Twenty-one thousand ratings makes this both the best-selling and the best-reviewed option.
Buy on Amazon
1000 mg/day is the dose that worked; the 500 mg arm of the same trial was negative on every outcome. This one reaches it without doubling capsules.
Buy on Amazon
Single ingredient, 500 mg per capsule, twice a day. Pick it if you want nothing else in the bottle while you test.
Buy on AmazonPrefer to compare yourself? This opens Amazon’s full selection for this supplement, filtered to the form we recommend.
See all on AmazonEvery result, next to the line that means no effect
Each diamond is a study's best estimate. The thin line shows how sure the study was: the shorter the line, the more certain the result.
- URTI incidence (flavonoids as a class, not quercetin alone)% relative reduction · Somerville 2016, Advances in Nutrition−33.0−36 … −31
- Sick days (non-significant)ratio vs control · Somerville 2016, Advances in Nutrition+0.60+0.24 … +1.47
- Endurance capacity (VO2max + performance pooled)SMD (~+2%, classed as trivial) · Kressler 2011, Med Sci Sports Exerc (11 studies)+0.15[not given]
- URTI severity, fit adults 40+ (post-hoc)% vs placebo (p=0.020) · Heinz 2010, Pharmacological Research−36.0[not given]
Each unit gets its own scale, so numbers are never mixed on one line. When a study gave no range, we leave it blank instead of inventing one.
4 studies over 9 years
The studies
- 1.Quercetin supplementation and upper respiratory tract infection: A randomized community clinical trialPharmacological Research · 2010 · rct · 1 experiments · n = 1,002
12 weeks of 500 or 1000 mg/day produced no significant group differences in URTI rates, sick days or severity overall; only in fit adults 40+ (n=325) did 1000 mg/day cut severity 36% (p=0.020) and sick days 31% (p=0.048).
- 2.Effect of Flavonoids on Upper Respiratory Tract Infections and Immune Function: A Systematic Review and Meta-AnalysisAdvances in Nutrition · 2016 · meta-analysis · 14 experiments · n = 531
Flavonoid supplementation cut URTI incidence 33% (95% CI 31%, 36%); the sick-day ratio was non-significant (0.60, 95% CI 0.24-1.47). Only three of the trials used quercetin (1 g/day, 14-38 days).
- 3.Quercetin and endurance exercise capacity: a systematic review and meta-analysisMedicine & Science in Sports & Exercise · 2011 · meta-analysis · 11 experiments
Statistically significant but very small benefit to endurance capacity (effect size 0.15, ~2% over placebo); the authors judged the effect trivial and concluded quercetin is unlikely to be a meaningful ergogenic aid.
- 4.Quercetin reduces illness but not immune perturbations after intensive exerciseMedicine & Science in Sports & Exercise · 2007 · rct · 1 experiments
Quercetin reduced post-exercise illness rates in cyclists without correcting the underlying immune perturbations; we could not retrieve the exact incidence figures (paywalled), so treat the effect size as unverified.
Umbral is a wellness product, not a medical device. It does not diagnose, treat, cure or prevent any disease. Supplement information is educational; talk to a clinician before starting anything, especially if you are pregnant, under 18, managing a condition or taking medication.
These statements have not been evaluated by the Food and Drug Administration.