Zinc — Does It Actually Shorten a Cold? | Supplement of the Month

My bias, stated first

I lean towards zinc over elderberry. My reasoning is that whether zinc works depends on things most trials and most shoppers ignore: how much is in your diet already, how well you absorb it, the dose, the form, and what it's bound to in the lozenge. Those are exactly the things this piece has to check rather than assume.

Does it prevent colds?

Low certainty — probably little or no effect

The 2024 Cochrane review pooled 34 trials with 8,526 people. Taking zinc to prevent colds made little or no difference to the chance of catching one (risk ratio 0.93, 95% CI 0.85 to 1.01) (Nault et al., 2024). If you're taking zinc all winter to avoid colds, the evidence doesn't support it.

Does it shorten a cold?

Low certainty — may shorten it by about two days, with very inconsistent trials

Used once a cold has started, zinc may shorten it by an average of 2.4 days (95% CI 0.5 to 4.2 days), but the trials disagree with each other enormously (I² = 97%) (Nault et al., 2024). It also probably causes more minor side effects, mainly a bad taste and nausea (risk ratio 1.34, moderate certainty).

A narrower analysis of trials using more than 75 mg of zinc a day found colds were 33% shorter on average. Zinc acetate lozenges shortened colds by 40% and zinc gluconate by 28%, a difference that wasn't statistically significant. Doses above 100 mg a day did no better than 80–92 mg (Hemilä, 2017). Who paid for the positive trials? PubMed lists the two best-known ones as privately funded but doesn’t name the sponsor, and I haven’t been able to read their funding statements. Treat that as unknown rather than as independent. That analysis is by one author, a long-standing researcher of zinc and vitamin C for colds. His work is careful, but a single-author meta-analysis is worth reading alongside the Cochrane one, not instead of it.

Is zinc better than elderberry? On the quantity and consistency of trials, yes: more trials, more people, and an effect that appears across several of them. On certainty, the Cochrane grading is still low. So my bias is partly right. Zinc has the stronger case, but not a strong one.

Why the trials disagree: what the lozenge is made of

Mechanistic, with correlational support

Lozenges only work, if they work, by releasing free zinc ions in the mouth and throat. If a lozenge also contains ingredients that bind zinc tightly (citric acid is the one usually named), less free zinc is released. Re-analyses of the early trials found that lozenges releasing more free zinc shortened colds, and some that released almost none did nothing (Eby, 1997; Eby, 2004).

Two cautions. These are re-analyses of other people's trials, not new trials. And the author ran his own zinc lozenge research company (George Eby Research). The idea is plausible and fits the mixed results, but it hasn't been tested head to head.

What that means at the shop: your chelation point stands up as a hypothesis. It's the best available explanation for why some trials worked and some didn't.

What to look for on the label

Form: zinc acetate or zinc gluconate, as a lozenge that dissolves slowly in the mouth. Tablets you swallow aren't what the lozenge trials tested.
Dose: the positive trials used about 80–92 mg of elemental zinc a day, spread through the day. Check the label for elemental zinc per lozenge, and work out how many that means. The two best-known trials used one lozenge of about 13 mg every two to three hours while awake (Mossad et al., 1996; Prasad et al., 2000). Lozenges on sale in the UK commonly carry 15–19 mg, so five or six a day reaches the range the positive trials used.
Ingredients: as a precaution, avoid lozenges listing citric acid, which is thought to bind zinc.
Duration: a short course while the cold lasts, not all winter.

Who shouldn't — and the copper problem

Moderate (consistent case reports); the harms are uncommon but real

Nasal zinc: don't. Intranasal zinc gels sold for colds have been linked to loss of smell. In one clinic series of 17 people, all had measurably impaired smell after using a nasal zinc gel, typically after sniffing deeply and feeling burning (Alexander & Davidson, 2006).
High doses for weeks or months deplete copper. Zinc competes with copper for absorption. A 2026 systematic review found 37 cases of blood disorders caused this way: anaemia in nearly all, often low white cells too. Doses ranged from about 50 mg to more than 1,500 mg of zinc a day, for weeks to years, from supplements, denture adhesive creams and swallowed coins. The blood changes were often misdiagnosed at first as a bone-marrow disorder. Most people recovered after stopping zinc and taking copper, but nerve damage improved more slowly and sometimes not completely (Dutta et al., 2026).
Take it with food if it makes you sick, but know that food, and especially phytate in grains and pulses, reduces how much you absorb.
Medicines: zinc can reduce absorption of some antibiotics (tetracyclines, quinolones). Space them apart and check with your pharmacist. (General pharmacology; not re-checked for this piece.)

So: a week of lozenges during a cold is one thing. A 50 mg tablet every day "for immunity" for months is a different, and riskier, thing.

Can a test tell you if you need zinc?

This is the honest limit of Test, Don't Guess

Measuring zinc in one person is hard. An international expert panel recommends three measures: dietary zinc intake (allowing for phytate), plasma zinc, and in children, growth. Plasma zinc responds to severe deficiency and to supplements, but it also changes with your last meal, the time of day, inflammation and some medicines. And it drops during infections, including a cold. The panel found insufficient data to recommend hair, urine, nail or blood-cell zinc for assessing status (King et al., 2015).

Declared interest: I use hair mineral analysis (HTMA) in practice, for other reasons. By that panel's standard, it isn't a valid measure of zinc status, and I won't present it as one.

So the most useful "test" for zinc is often a good diet history: how much meat, shellfish, dairy, pulses and whole grains you eat, and how they're prepared. Blood work is useful mainly for the copper side, if someone has been taking high-dose zinc for a long time.

This month's recipe is built around the same mineral: Recipe of the Month 05: Scotch Broth, Built for Zinc.

The bottom line

Prevention: probably doesn't work. Don't take it all winter for that.
Treatment: may shorten a cold by a couple of days, if the lozenge actually releases zinc and you take enough, often enough. Low-certainty evidence, with a real side-effect cost.
Safety: never up the nose; no long-term high doses without a reason and a copper check.
Compared with elderberry: a better evidence base, not a strong one.

Your next step

Free: If You Can't Check It, It Isn't Evidence: how to tell a claim you can check from one you can't.

Test / talk: Blood testing options, if you have taken high-dose zinc for months and want your copper checked; or a free 20-minute call to work out whether testing is worth it for you.

I sell the testing above. The article’s grades apply to it too.

Sources

PubMed records resolved and abstracts read 30 September 2026.

Alexander TH, Davidson TM. Intranasal zinc and anosmia: the zinc-induced anosmia syndrome. Laryngoscope 2006;116(2):217–220. PMID 16467707. doi:10.1097/01.mlg.0000191549.17796.13

Dutta A, et al. Zinc-induced hematologic toxicities: a systematic review of descriptive studies. Biol Trace Elem Res 2026;204(9):6628–6642. PMID 42087025. doi:10.1007/s12011-026-05136-z

Eby GA. Zinc ion availability — the determinant of efficacy in zinc lozenge treatment of common colds. J Antimicrob Chemother 1997;40(4):483–493. PMID 9372416. doi:10.1093/oxfordjournals.jac.a020864

Eby GA. Zinc lozenges: cold cure or candy? Solution chemistry determinations. Biosci Rep 2004;24(1):23–39. PMID 15499830. doi:10.1023/b:bire.0000037754.71063.41

Hemilä H. Zinc lozenges and the common cold: a meta-analysis comparing zinc acetate and zinc gluconate, and the role of zinc dosage. JRSM Open 2017;8(5). PMID 28515951. doi:10.1177/2054270417694291

King JC, et al. Biomarkers of Nutrition for Development (BOND) — zinc review. J Nutr 2016;146(4):858S–885S. PMID 26962190. doi:10.3945/jn.115.220079

Mossad SB, et al. Zinc gluconate lozenges for treating the common cold: a randomized, double-blind, placebo-controlled study. Ann Intern Med 1996;125(2):81–88. PMID 8678384. doi:10.7326/0003-4819-125-2-199607150-00001

Prasad AS, et al. Duration of symptoms and plasma cytokine levels in patients with the common cold treated with zinc acetate. Ann Intern Med 2000;133(4):245–252. PMID 10929163. doi:10.7326/0003-4819-133-4-200008150-00006

Nault D, et al. Zinc for prevention and treatment of the common cold. Cochrane Database Syst Rev 2024;5:CD014914. PMID 38719213. doi:10.1002/14651858.CD014914.pub2 ---