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It’s cold season; your nose is running and your throat is sore. CYNTHIA WENSLEY looks at the evidence for zinc as a cold remedy.

CLINICAL BOTTOM LINE:

In otherwise healthy adults, high dose zinc acetate lozenges taken within 24 hours of the onset of a cold may shorten the duration of a cold and its various symptoms (such as nasal discharge, nasal congestion and muscle ache) by 33–54 per cent. The amount of zinc (around 80 mg/day of zinc ion) is far higher than the recommended daily dietary intake but appears to be well tolerated when taken for a period of two weeks or less.

CLINICAL SCENARIO:

You have the usual miserable symptoms of the common cold. Keen to get over it quickly, you wonder how effective over-the-counter remedies are for reducing the duration of cold symptoms. Your work colleague swears by zinc and so you decide to examine the evidence for its effectiveness.

QUESTION:

In normally healthy adults, how effective is zinc for reducing the duration of common cold symptoms?

SEARCH STRATEGY:

PubMed-Clinical queries (Therapy/Narrow): zinc AND common cold

CITATION:

Hemila, H., & Chalker, E. (2015). The effectiveness of high dose zinc acetate lozenges on various common cold symptoms: a meta-analysis. BMC Fam Pract, 16, 24. doi: 10.1186/s12875-015-0237-6

STUDY SUMMARY:

A systematic review assessing whether high dose zinc acetate lozenges have different effects on the duration of common cold symptoms. Inclusion criteria were:

• Type of study: placebo controlled trials involving people with the common cold who were otherwise untreated
• Types of intervention: zinc acetate lozenges in which the dose was >75 mg/day of zinc ion compared with placebo
• Outcomes: total duration of the cold, and duration of respiratory and systemic symptoms. Adverse events were also recorded. Symptom duration was to be converted from days to a percentage scale to enable meaningful comparison between different patient groups and different outcome definitions.

STUDY VALIDITY:

A simple but appropriate search strategy was used to search the PubMed database (in Jan 2015) to locate published trials additional to those included in the 2013 Cochrane Review on this topic. No language or date restrictions applied. No process for locating unpublished studies was described but authors are experts in this field and knowledge of all relevant studies is presumed. The review process involved both study authors checking the accuracy of data extraction, data entry and data calculations. The included studies were assessed for risk of bias by considering randomisation method, allocation concealment, blinding of participants and personnel, blinding of outcome assessment, loss to follow-up and selective outcome reporting. Publication bias was not discussed. Overall this was a high-quality review involving three small but high-quality studies.

STUDY RESULTS:

From 28 trials identified, three randomised, placebo-controlled, double-blind studies involving 199 participants were identified as being eligible for inclusion. Participants were students or staff from two universities in the United States. A cold was defined as presence of ≥2 of the typical respiratory (nasal discharge, nasal congestion, cough, hoarseness, scratchy throat, sore throat, sneezing) or systemic (muscle aches, fever, headache) symptoms. All three studies compared zinc acetate lozenges with placebo lozenges. The daily dose of zinc varied between 80–92 mg/day and was taken in divided doses throughout the day. In the majority of participants, the intervention began within 24 hours of onset of symptoms. Compared with placebo, zinc lozenges significantly reduced the duration of colds by 42 per cent, the duration of nasal discharge by 34 per cent, nasal congestion by 37 per cent, scratchy throat by 33 per cent, hoarseness by 43 per cent and cough by 46 per cent (Table). The reduction in duration of sneezing and sore throats seen in the zinc group was not significant. In comparison with the placebo, zinc lozenges halved the duration of muscle ache (Table) but made no difference to the duration of headache or fever. Heterogeneity between the included studies was generally low. There was no substantial difference in adverse events between zinc and placebo groups and low drop-out numbers suggest the intervention was well tolerated.

COMMENTS:

When converted back to days, these results mean that the duration of common cold symptoms may be reduced by 1–2 days (possibly more), which seems worthwhile.

The recommended daily dose of zinc is 11 mg/day for men and 8 mg/day for women.

Based on adverse events data from the included studies (and other studies involving high dose zinc for extended periods) the review authors concluded that high dose zinc taken for the duration of the cold (under two weeks) was unlikely to cause serious, irreversible adverse events.

The included studies excluded people with comorbidities and children, therefore safety and efficacy of high dose zinc in these populations cannot be presumed.

Zinc acetate lozenges are not readily available in New Zealand; pharmacists can advise regarding substituting lozenges for other forms of zinc supplementation.

Reviewer:

Cynthia Wensley RN, Honorary Professional Teaching Fellow, The University of Auckland, and PhD candidate, Deakin University, Melbourne
[email protected]