Supplements
quercetin prevents upper respiratory tract infection
In plain terms: Does quercetin stop you catching colds?
Part of: 🧪 quercetin
Probably not. A small 2007 trial in 40 cyclists looked impressive, but the same research group's much larger trial (1,002 people) found nothing. Small trial positive, big trial null, one lab: that pattern usually resolves toward no effect.
📅 Last reviewed: 2026-07-26 ⓘ
Evidence ladder
How far up the ladder this claim has climbed. A high consensus on a low rung means "consistent so far," not "proven in people."
Top evidence so far: Human trials (RCT / n-of-1)
How the studies fall
What the evidence shows
The evidence is small-positive and large-null, from the same research group — the classic pattern of an early optimistic finding that does not survive scale. A 2007 double-blind RCT in 40 trained cyclists reported markedly fewer infections after intense exercise (1/20 vs 9/20, p=0.004), notably with no change in any immune marker measured.
The evidence (3)
| Source | Grade | Stance | Quality | Finding |
|---|---|---|---|---|
| Heinz SA et al 2010 · study_type: RCT | RCT | contradicts | high | RCT, N=1002 community adults (18-85y), 500 or 1000 mg/d quercetin vs placebo x12wk, WURSS symptom diary: no significant group difference in URTI incidence/symptomatology overall, or by sex/BMI/age (primary endpoint null). Post-hoc subgroup |
| Nieman DC et al 2007 · Medicine and science in sports and exercise | RCT | supports | low | Double-blind RCT, trained male cyclists (N=40), quercetin 1000 mg/d x3wk vs placebo around a 3-day intensive exercise bout; URTI incidence over the 2-wk post-exercise period was significantly lower with quercetin (1/20) vs placebo (9/20), p |
| Cho H et al 2024 · study_type: RCT | RCT | mixed | moderate | RCT, N=80 adults with prior URTI history + high perceived stress, 1000 mg/d onion peel extract (quercetin-rich, not isolated quercetin) vs placebo x8wk, WURSS-21 diary + NK-cell/cytokine assays. Primary immune outcomes (NK activity, IL-2/6/ |
Disagree, or know a study we missed?
We grade by evidence, not opinions. The way to weigh in is to point us to a study we haven't cited (check the evidence table above first), or to flag a problem with one we have. Every submission is reviewed; if it holds up, the grade updates and shows in Science Changes Its Mind.
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Educational only, not medical advice. Grades and scores reflect published evidence weighted by study design and quality; see the methodology.