Can Zinc lozenges prevent colds?

5 min read – fact checked ✔

Brief critical evaluation of the efficacy of Zinc lozenges in preventing and reducing the duration of colds

The common cold is caused predominantly by rhinoviruses, and to a lesser extent certain Coronaviruses, representing a significant burden to public health and individual productivity worldwide. As a readily available over-the-counter remedy, zinc lozenges have garnered attention for their potential to alleviate cold symptoms and shorten their duration. However, the evidence surrounding their efficacy remains nuanced and occasionally contradictory. This blog critically evaluates the scientific evidence regarding zinc lozenges and their role in managing the common cold.

Mechanism of Action

Zinc is thought to interfere with viral replication by inhibiting viral binding and replication within the nasal mucosa. Additionally, zinc may modulate the immune response by enhancing the activity of T-cells and stabilising cell membranes, potentially reducing inflammation. Zinc lozenge ensures targeted and localised delivery of zinc in the upper respiratory tract, where the rhinovirus primarily replicates (1).

Evidence Supporting Efficacy

Several randomized controlled trials (RCTs) and meta-analyses suggest that zinc lozenges can reduce the duration of cold symptoms if administered within 24 hours of onset. A prominent meta-analysis by Hemilä and Chalker (2015) examined the effects of zinc acetate and zinc gluconate lozenges, concluding that doses exceeding 75 mg/day were associated with a significant reduction (figure 1) in cold duration by approximately 33% (2). Another study highlighted that zinc lozenges not only shortened symptom duration but also reduced severity, particularly for symptoms like nasal congestion and sore throat (3). These findings support the hypothesis that adequate zinc ion concentrations in the oropharyngeal region may help inhibit viral activity and ameliorate cold symptoms.

Limitations and Conflicting Evidence

Despite promising results, the efficacy of zinc lozenges remains inconsistent across studies. Variability in the outcomes often stems from differences in zinc formulations, dosages, and study methodologies. Some trials using lower subtherapeutic zinc doses (<75 mg/day) or suboptimal formulations, reported negligible effects (4). Adverse effects, such as nausea and an unpleasant metallic taste, also limit widespread acceptance and adherence. Moreover, prolonged excessive zinc intake can lead to copper deficiency and other health risks, raising concerns about safety (5).

Practical Considerations

For individuals considering zinc lozenges, several factors must be considered:

• Timing: Lozenges appear to be most effective when taken within the first 24 hours of symptom onset.
• Dosage: Effective doses typically exceed 75 mg/day but should not surpass recommended limits to avoid toxicity.
• Formulation: Zinc acetate and zinc gluconate appear to be the most effective forms, as they provide optimal zinc ion availability (6).

Conclusions

While evidence supports the potential of zinc lozenges to reduce the duration and severity of the common cold, their efficacy appears to be influenced by factors such as dosage, formulation, and timing of administration. Other variables that perhaps were not considered in the studies discussed was the effects of physical and perceived stress on participant immune response via the HPA-axis. The side effects and risks associated with excessive zinc intake must also be carefully weighed. Further high-quality RCTs are needed to establish standardised guidelines for zinc lozenge use in cold management.

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