Research review
Does zinc help with infection? What the research does and doesn't show
Zinc's best-tested respiratory-illness evidence is for the common cold, covered separately. For influenza specifically, no randomized trial isolating lab-confirmed flu was found. For COVID-19, a 214-patient outpatient trial found high-dose zinc gluconate, with or without high-dose vitamin C, didn't significantly shorten symptom duration compared with usual care.
The evidence doesn't support zinc as a treatment for confirmed influenza specifically — no trial isolating lab-confirmed flu was found for this page. For COVID-19, the one dedicated outpatient trial (214 people) found high-dose zinc, with or without high-dose vitamin C, made no significant difference to how fast symptoms resolved compared with usual care.
What the evidence doesn't support
It doesn't support zinc as a treatment for COVID-19: a 214-person randomized trial found no significant benefit for symptom duration. It doesn't support zinc as a treatment for confirmed influenza either, because no randomized trial testing zinc specifically against lab-confirmed flu was found — most of zinc's respiratory-illness trial data is about "the common cold," a mix of viruses studied separately (see zinc benefits), not influenza on its own. And it doesn't support taking zinc to prevent catching a respiratory illness in the first place — the trials below tested zinc as a treatment after symptoms started, not as prevention.
What the trials found
A 2021 randomized, open-label trial (the COVID A to Z study) enrolled 214 ambulatory adults with a PCR-confirmed SARS-CoV-2 diagnosis in Ohio and Florida. Patients were randomized to 10 days of high-dose zinc gluconate (50 mg/day), high-dose ascorbic acid (8,000 mg/day), both together, or usual care with neither. The time to a 50% reduction in symptoms was similar across all four groups — 6.7 days with usual care, versus 5.5-5.9 days in the supplemented groups — and the difference wasn't statistically significant (p=0.45). Secondary outcomes, including hospitalization and time to full symptom resolution, also showed no significant difference. The trial was stopped early because an interim analysis found it had too little statistical power left to detect a benefit even if it continued to full enrollment — a sign the researchers themselves didn't see a promising trend worth chasing further.
Separately, the Cochrane review behind zinc's best-documented respiratory result — a roughly one-day shorter cold at lozenge doses of 75 mg/day or more, detailed on zinc benefits — studied naturally acquired colds broadly, which include several virus families. That review didn't isolate laboratory-confirmed influenza cases, so it doesn't answer the flu question on its own, and no other randomized trial doing that was found for this page.
| Illness | Trial evidence | Result |
|---|---|---|
| COVID-19 | 2021 RCT, 214 outpatients, 50 mg/day zinc gluconate ± vitamin C | No significant difference in symptom duration vs. usual care |
| Lab-confirmed influenza | No trial found isolating this specifically | Not established |
| Common cold (mixed viruses) | Cochrane review, 16 trials, ≥75 mg/day lozenges | About 1 day shorter (see zinc benefits) |
Questions people ask
Will zinc help the flu?
No trial testing zinc specifically against lab-confirmed influenza was found for this page. The related evidence that exists — a Cochrane review of zinc lozenges — studied the common cold broadly, which is caused by several different viruses and isn't the same diagnosis as influenza.
Does zinc help with COVID-19?
A 2021 randomized trial in 214 outpatients with confirmed COVID-19 found no significant difference in symptom duration between high-dose zinc, high-dose vitamin C, both, or usual care, and the trial was stopped early for low likelihood of finding a benefit.
Does zinc prevent colds or the flu?
The trials reviewed here and on zinc benefits tested zinc as a treatment started after symptoms began, not as something taken beforehand to prevent getting sick. No prevention trial was reviewed for this page.
Should I take zinc for cold and flu symptoms?
For cold symptoms specifically, zinc lozenges at 75 mg/day or more, started within 24 hours of symptoms, shortened a cold by about a day in a 2013 Cochrane review — with more reported nausea and bad taste, detailed on zinc benefits. That evidence doesn't extend to confirmed influenza or COVID-19, which are different diagnoses tested separately above.
When to talk to a doctor
Flu symptoms, a positive COVID-19 test, or any respiratory illness with fever, breathing difficulty, or symptoms that worsen should be evaluated by a doctor, who can discuss antiviral treatment, testing, and monitoring directly. Zinc is not a treatment for influenza or COVID-19, and nothing in the evidence above supports using it as a substitute for medical care or an established antiviral treatment. If you take prescription medication or are pregnant or nursing, talk to a doctor before adding any supplement.
Related reading: zinc benefits: what the research does and doesn't show, how much zinc should you take a day, and zinc side effects.
Sources
- Effect of High-Dose Zinc and Ascorbic Acid Supplementation vs Usual Care on Symptom Length and Reduction Among Ambulatory Patients With SARS-CoV-2 Infection: The COVID A to Z Randomized Clinical Trial A 2021 randomized trial in 214 outpatients with confirmed COVID-19 found high-dose zinc gluconate (50 mg/day), alone or with high-dose vitamin C, didn't significantly shorten symptom duration compared with usual care, and was stopped early because it was unlikely to show a benefit even if continued.
- Zinc for the common cold Zinc lozenges taken within a day of a cold starting shortened its length by about a day in a 2013 review of 16 trials, but only at doses of 75 mg/day or more, with more nausea and bad taste than placebo.
*These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease.