Zinc and the common cold

Zinc gluconate 50 mg tablets (GNC brand)

Zinc supplements (frequently zinc acetate or zinc gluconate lozenges) are a group of dietary supplements that are commonly used for the treatment of the common cold.[1] The use of zinc supplements at doses in excess of 75 mg/day within 24 hours of the onset of symptoms has been shown to reduce the duration of cold symptoms by about 1 day.[1][2] Due to a lack of data, there is insufficient evidence to determine whether the preventative use of zinc supplements reduces the likelihood of contracting a cold.[2] Adverse effects with zinc supplements by mouth include bad taste and nausea.[1][2] The intranasal use of zinc-containing nasal sprays has been associated with the loss of the sense of smell;[1] consequently, in June 2009, the United States Food and Drug Administration (USFDA) warned consumers to stop using intranasal zinc products.[1]

The human rhinovirus – the most common viral pathogen in humans – is the predominant cause of the common cold.[3] The hypothesized mechanism of action by which zinc reduces the severity and/or duration of cold symptoms is the suppression of nasal inflammation and the direct inhibition of rhinoviral receptor binding and rhinoviral replication in the nasal mucosa.[1]

Effectiveness

A 2016 meta-analysis on zinc acetate-lozenges and the common cold found that colds were 2.7 days shorter by zinc lozenge usage. This estimate is to be compared with the 7 day average duration of colds in the three trials.[4]

The Cochrane review from 2013 found that zinc supplementation at doses in excess of 75 mg/day within 24 hours of the onset of cold symptoms reduced the average duration of symptoms by 1 day.[1][2] It also found that the likelihood of experiencing cold symptoms 1 week after the onset of symptoms was lower in individuals who used supplemental zinc relative to those who did not.[2]

A 2015 meta-analysis on zinc lozenges and the common cold found no difference in the effects of zinc acetate lozenges on diverse respiratory symptoms. Although zinc lozenges most probably lead to highest concentration of zinc in the pharyngeal region, a subsequent meta-analysis showed that the effects of high-dose zinc acetate lozenges did not significantly differ in their effects on pharyngeal and nasal symptoms. The duration of nasal discharge was shortened by 34%, nasal congestion by 37%, sneezing by 22%, scratchy throat by 33%, sore throat by 18%, hoarseness by 43%, and cough by 46%. Zinc lozenges shortened the duration of muscle ache by 54%, but there was no significant effect on the duration of headache and fever.[5]

A 2012 systematic review suggested that "zinc formulations may shorten the duration of symptoms of the common cold", but that further research was needed and that possible adverse effects needed to be studied.[6]

The effects of zinc supplementation on the duration and severity of cold symptoms in individuals with AIDS/HIV or chronic illness is not known due to a lack of studies involving these populations.[2]

Safety

In some studies zinc lozenges caused acute adverse effects, such as bad taste, but none of the studies reported long term harm. Furthermore, many of the adverse effects, in particular regarding taste, may be caused by the specific lozenge composition and probably do not reflect the effects of zinc ions themselves. For example, zinc gluconate with dextrose or sugar becomes extremely vile in taste several weeks after manufacture, while zinc acetate dihydrate in a 1:100 mixture with dextrose by weight is permanently pleasant tasting.[7] The most recent trial on zinc acetate found no significant differences between the zinc and placebo groups in the recorded adverse effects with a 92 mg daily dose of zinc.[8]

There have been several cases of people using zinc nasal sprays and suffering a loss of sense of smell.[1][9] In 2009 the US Food and Drug Administration issued a warning that people should not use nasal sprays containing zinc.[1]

Mechanism of action

The human rhinovirus – the most common viral pathogen in humans – is the predominant cause of the common cold.[3] The hypothesized mechanism of action by which zinc reduces the severity and/or duration of cold symptoms is the suppression of nasal inflammation and the direct inhibition of rhinoviral receptor binding and rhinoviral replication in the nasal mucosa.[1]

History

Zinc has been known for many years to have an effect on cold viruses in the laboratory.[10]

Research into the effect of zinc lozenges on colds between 1984 and 2009 produced a wide range of differing results. It has been hypothesized that these differences were due in part to differences in the lozenges' constituents, mainly the amount of the active ingredient, ionic zinc (iZn). For example, the amount of ionic zinc ranged from 0 to 100%, depending upon the lozenge ingredients in the trials.[7] More recently, the evidence from trials has been reviewed to try to assess the evidence of zinc's effectiveness as a cold cure but the results, while suggestive of a positive effect, have not been conclusive, since no consideration was given to the amount of the active ingredient (iZn) in the lozenges.[10]

References

  1. 1 2 3 4 5 6 7 8 9 10 "Zinc – Fact Sheet for Health Professionals". Office of Dietary Supplements, US National Institutes of Health. February 11, 2016. Retrieved January 7, 2018.
  2. 1 2 3 4 5 6 Singh M, Das RR (June 2013). "Zinc for the common cold". The Cochrane Database of Systematic Reviews (6): CD001364. doi:10.1002/14651858.CD001364.pub4. PMID 23775705.
  3. 1 2 "Common Cold and Runny Nose". United States Centers for Disease Control and Prevention. September 26, 2017. Retrieved January 7, 2018.
  4. ↑ Hemila, H.; Petrus, E.; Fitzgerald, J.; Prasad, A. (2016). "Zinc acetate lozenges for treating the common cold: an individual patient data meta-analysis". British Journal of Clinical Pharmacology. 82: 1393–1398. doi:10.1111/bcp.13057. PMC 5061795. PMID 27378206.
  5. ↑ Hemila, H.; Chalker, L. (2015). "The effectiveness of high dose zinc acetate lozenges on various common cold symptoms: a meta-analysis". BMC Family Practice. 16: 24. doi:10.1186/s12875-015-0237-6. PMC 4359576. PMID 25888289.
  6. ↑ Science, M.; Johnstone, J.; Roth, D. E.; Guyatt, G.; Loeb, M. (2012). "Zinc for the treatment of the common cold: A systematic review and meta-analysis of randomized controlled trials". Canadian Medical Association Journal. 184 (10): E551–61. doi:10.1503/cmaj.111990. PMC 3394849. PMID 22566526.
  7. 1 2 Eby, George A. (2010). "Zinc lozenges as cure for the common cold – A review and hypothesis". Medical Hypotheses. 74 (3): 482–92. doi:10.1016/j.mehy.2009.10.017. PMID 19906491.
  8. ↑ Prasad, Ananda S.; Beck, Frances W. J.; Bao, Bin; Snell, Diane; Fitzgerald, James T. (2008). "Duration and Severity of Symptoms and Levels of Plasma Interleukin-1 Receptor Antagonist, Soluble Tumor Necrosis Factor Receptor, and Adhesion Molecules in Patients with Common Cold Treated with Zinc Acetate". The Journal of Infectious Diseases. 197 (6): 795–802. doi:10.1086/528803. PMID 18279051.
  9. ↑ "Zinc for Colds: Lozenges & Nasal Sprays". WebMD. Retrieved October 25, 2013.
  10. 1 2 "Zinc 'can cut length of common cold'". NHS Choices. May 8, 2012.
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