Zinc is a popular ingredient in cold remedies. It is an essential element for the function of the immune system and has been shown, in some forms, to stimulate the immune system in its fight against viruses. Though zinc is present in many supplements for the treatment of many conditions, there are just two forms of zinc that have been developed to fight the common cold.
Lozenges and Tablets
The justification for the use of zinc to treat colds formally began with a placebo-controlled study of zinc gluconate lozenges in the January 1984 issue of "Agents Microbial Chemotherapy." A total of 23 mg of zinc was taken by the treatment group every two waking hours for seven days. At that point, 86 percent of the treatment group (as opposed to 46 percent of the placebo group) had kicked their colds. Since that time, however, the research has been relatively split. Bolser's summary of the evidence in the journal "Chest" in 2006 reported six studies showing some benefit and four studies showing no benefit.
The author of the original zinc lozenge paper has hypothesized that not all zinc lozenges are created equal. In a March 2010 analysis of all previous zinc lozenge and tablet research, Eby demonstrated that studies using a zinc lozenge with a high availability of "ionic zinc"---zinc that is not bound up to anything---have a dramatic effect on the duration of a cold. His analysis showed that lozenges with a low availability of ionic zinc were the same lozenges that performed poorly in clinical trials.
The most common side effects of zinc lozenges are mouth irritation and poor taste in the mouth. Eby argues that the use of flavor enhancers and taste maskers reduces the amount of available ionic zinc, rendering the lozenge essentially useless. From this point of view, the dose of the zinc that is in a lozenge is less important than the nature of the other ingredients that may be used to bind up the zinc to create a better-tasting product.
Nasal spray
Zinc has been shown in the laboratory to inhibit the growth of the common cold-causing rhinovirus. It does so on contact. Therefore, manufacturers have created delivery systems that maximize the time the zinc can spend on the surface of the infected body part. Lozenges and tablets do this in the throat. Nasal sprays were developed to better treat the nose and sinuses. However, these products are no longer on the market after they were recalled in 2009.
Serious side effects
In June of 2009, the FDA reported that it had received over 130 complaints of severe, and sometimes total, loss of smell (a condition known as "anosmia") after the use of a nasal spray containing zinc acetate. The FDA recommended consumers throw away any such nasal sprays and avoid buying them in the future. Five years earlier, in the May 2004 issue of the "American Journal of Rhinology," Jafek and two co-authors published a case series of 21 patients who had severely damaged their sense of smell through the use of a zinc nasal spray. They reported that this adverse effect had been known to be toxic to the sense of smell since the late 1930s. At that time thousands of kids were treated with an intranasal zinc spray in an experimental attempt to protect them from the polio virus. Unfortunately, the rate of polio infection in these children was not improved, and an estimated 10 to 13 percent of them lost their sense of smell. As the authors of this report pointed out, more recent controversies over the effects of zinc nasal sprays are yet another case of history repeating itself.
References
- "Antimicrobial Agents Chemotherapy"; "Reduction In Duration Of Common Colds By Zinc Gluconate Lozenges In A Double-Blind Study"; Eby GA; January 1984
- "Chest"; "Cough Suppressant And Pharmacologic Protussive Therapy: ACCP Evidence-Based Clinical Guidelines"; Bolser DC; January 2006
- "Medical Hypotheses"; "Zinc Lozenges As Cure For The Common Cold--A Review And Hypothesis"; Eby GA; March 2010
- 2009 FDA Public Health Advisory
- "American Journal of Rhinology"; "Anosmia After Intranasal Zinc Gluconate Use"; Jafek BW, Linschoten MR, Murrow BW; May 2004
