antioxidant · for frequent colds
Quercetin
Shows antiviral activity in the lab and helps zinc get inside cells.
Say that in clinical terms
Exhibits antiviral properties against respiratory viruses, acts as zinc ionophore, modulates immune cell function.
How strong is the research?
No Benefit evidence
No benefit across 1,002 people. A smaller after-the-fact look at fit over-40s hinted at something, which is not the same as showing it.
Different group studied
1 paper read, 1 against.
Who was studied: The cited work is mice on a treadmill. The nearest human trial was 40 cyclists.
How much to take
daily
500–1000 mg
Prophylactic use may reduce incidence. Works synergistically with zinc.
Before you take it
- No NIH ODS Tolerable Upper Intake Level (UL) has been established for quercetin; doses above 1 g/day have been associated with adverse effects including headache and tingling in human studies
- Potential nephrotoxicity at very high doses documented in animal models; clinical significance in humans at typical supplemental doses (500–1000 mg/day) is not well established
- Quercetin inhibits CYP3A4, CYP2C8, CYP2C9, CYP1A2, and P-glycoprotein — clinically significant drug interaction risk with warfarin, cyclosporine, CYP3A4-metabolized statins (e.g., simvastatin, lovastatin), digoxin, and other drugs with narrow therapeutic windows
- Drug interaction with quinolone (fluoroquinolone) antibiotics: quercetin can impair antibiotic absorption — separate dosing by at least 2 h before or 4–6 h after the antibiotic
- Insufficient safety data in pregnancy and lactation; avoidance is generally recommended until more evidence is available
- Standard quercetin aglycone has approximately 1–2% oral bioavailability; more bioavailable forms exist (isoquercetin, quercetin-3-glucoside, quercetin phytosome) but most commercial products do not specify the form, making dose-to-effect extrapolation unreliable
- The protective effect is established only in the context of severe acute exercise stress (3-day exhaustive treadmill running in mice); recommending quercetin for 'Frequent Colds' in general users without this specific stressor extrapolates beyond what this study supports
What we make of it
Mice on a treadmill, then given flu.
The detail
The study ran mice to exhaustion on a treadmill, infected them with influenza and fed them quercetin by tube. It is not a human trial.