Zinc

Zinc is an essential trace mineral that participates in over 300 enzymatic reactions in the human body, from DNA synthesis and cell division to immune signalling and wound repair. It cannot be stored long-term, which is why a steady daily intake matters.

The European Food Safety Authority (EFSA) lists zinc among the small group of nutrients with Article 13.1 approved health claims for immune-system function, normal cognitive function, and protection from oxidative stress. Clinical research on zinc lozenges for the common cold is one of the most studied integrative interventions of the last 30 years.

Zinc deficiency as a clinical syndrome was first identified in the early 1960s by Ananda Prasad, who described growth retardation and delayed puberty in adolescent Iranian and Egyptian boys whose diets were dominated by phytate-rich unleavened breads. Supplementation reversed the syndrome within months. That was the discovery that zinc is an essential human nutrient.

The therapeutic use of zinc compounds in topical wound healing and skin disease is much older. Zinc-oxide ointments appear in Greek medical texts and have been continuously produced since the 19th century for treating dermatitis, nappy rash, and minor wounds. Internally, zinc was not widely used until the 1980s, when the first lozenge trials for common-cold duration appeared.

At the cellular level, zinc is a structural cofactor for zinc-finger proteins, which are transcription factors that bind DNA and regulate gene expression. Approximately 10% of the human proteome contains a zinc-binding site. This explains why zinc deficiency affects so many systems at once: every dividing cell needs zinc to express the genes that drive division.

In the immune system specifically, zinc is required for thymulin (a thymic hormone that matures T-cells), for the cytotoxic activity of natural-killer cells, and for the oxidative burst that neutrophils use to kill phagocytosed bacteria. In the respiratory mucosa, zinc ions disrupt the binding of rhinovirus to ICAM-1 receptors. That is the molecular basis for the lozenge-format cold-duration effect.

For cold-duration outcomes, the most robust evidence comes from a 2013 Cochrane Review by Singh and Das and a 2017 meta-analysis by Hemilä, which together include over 20 randomised controlled trials. Pooled results show zinc lozenges started within 24 hours of symptom onset, delivering 75 to 100 mg of elemental zinc per day, can shorten common-cold duration by roughly one day on average compared with placebo.

Form matters: the effect is most consistent with zinc-acetate or zinc-gluconate lozenges. Capsules, syrups, and effervescent tablets bypass the throat, where rhinoviruses replicate, and have weaker and less consistent results. The mechanism is partly local antiviral action and partly modulation of ICAM-1 expression on respiratory epithelial cells.

For broader immune function, the EFSA Article 13.1 claim “Zinc contributes to the normal function of the immune system” rests on observational and interventional data showing zinc deficiency impairs neutrophil and natural-killer-cell activity, and that correction of deficiency restores function. This evidence is strong enough for an approved health claim but does not justify high-dose long-term supplementation in zinc-replete adults.

Zinc also has approved EFSA Article 13.1 claims for cognitive function, fertility and reproduction, macronutrient metabolism, and protection from oxidative stress. The NIH Office of Dietary Supplements rates the overall evidence for zinc supplementation as among the highest in the supplement category.

Forms and preparation

Zinc supplements come in several mineral salts that differ in bioavailability. For systemic supplementation, zinc-bisglycinate and zinc-picolinate show the best absorption in head-to-head trials. For cold-duration use, slow-dissolving lozenges of zinc acetate or zinc gluconate are the studied formats, taken to coat the throat. Effervescent or syrup forms bypass this local exposure and are not interchangeable for the cold-duration indication.

Dosage by outcome

Daily dietary zinc intake recommendations vary by country and sex: EFSA lists 9.4 to 16.3 mg per day for adult men and 7.5 to 12.7 mg per day for adult women, depending on phytate content of the diet. Multivitamin doses of 8 to 15 mg per day are appropriate for long-term immune maintenance. Therapeutic doses studied for cold-duration are much higher (75 to 100 mg per day) but only for the brief 5 to 7 day window described in trials. The EFSA tolerable upper intake level for chronic adult intake is 25 mg per day.

Interactions

Drug interactions

Zinc forms insoluble chelates with several drug classes, reducing absorption of both. The most important pairings are tetracycline and fluoroquinolone antibiotics, where zinc can reduce drug levels enough to impair antibacterial efficacy. Separate zinc and these antibiotics by at least 2 hours. Long-term high-dose zinc also reduces copper status and can interfere with the copper-dependent enzyme ceruloplasmin.

Contraindications

Avoid therapeutic-dose zinc supplementation if you have Wilson disease (copper retention disorder), are on tetracycline or fluoroquinolone antibiotics within ±2 hours, or are taking penicillamine for arthritis or copper chelation. Patients with chronic kidney disease should consult their nephrologist before adding zinc above multivitamin doses.

Side effects

The most common side effect, particularly with acetate and sulfate forms, is gastrointestinal upset (nausea, metallic taste, mild cramping) when taken on an empty stomach. Taking zinc with a light meal substantially reduces this. Zinc nasal sprays were associated with anosmia (loss of smell) and are no longer recommended; oral lozenges do not carry this risk.

1. Hemilä. Hemilä 2017. 2017. PMID:28515951
2. Singh & Das. Singh & Das 2013. 2013. PMID:23775705
3. Prasad. Prasad 2008. 2008. PMID:18385818
4. Lin et al.. Lin et al. 2017. 2017. PMID:29202751
5. Skrovanek et al.. Skrovanek et al. 2014. 2014. PMID:25349082