Why should we study the affects of zinc on the common cold?

The common cold occurs very frequently and results in substantial morbidity and economic losses each year. Adults experience, on average, two to four colds per year, while children may suffer from as many as eight colds per year. The cost of the illness has been estimated to be over $2.5 billion, with an inestimable price in human suffering. Researchers continue to search for new therapies for the common cold because no effective therapy has been well documented. Researchers are examining the affects of zinc on the common cold, as a possible solution.

Researchers have suggested many possible mechanisms to zinc's benefits and have studied various formulations of zinc.

** Newer studies:

2007, Caruso et al- This was a structured systematic review of the literature. The review found 14 randomized, placebo controlled studies that studied oral zinc lozenges, zinc nasal gel, or zinc nasal spray on naturally acquired common colds. Only 4 studies met the 11 criteria that the review placed for validity. Three of the four studies showed no benefit for oral zinc lozenges or nasal spray. One study that met the criteria did show positive results from the nasal gel.
2007, Kurugol et al- This was a randomized, double blind study testing oral zinc sulfate vs. placebo in children presenting with cold symptoms within 24-48 hrs. from the start of symptoms. The study showed no change in the duration of symptoms but did show a decrease in the severity of symptoms in healthy children. The improvement in severity of symptoms was mostly due to decreased nasal symptoms.
2003, McElroy et al - This was a prospective, intent-to-treat, single center, phase IV clinical trial. The control was a putative control from a previous study. The conclusion showed zinc gluconate glycine lozenges given 1/day as prophylaxis and 4/day as treatment decreased # and duration of colds in children 12-18 years with no adverse side effects. However, as this was unblinded and not placebo controlled, the actual validity of this study is uncertain.
2003, Mossad - This was a randomized, placebo controlled, double-blind study. Results were that 33mmol/L zinc gluconicum nasal gel spray, 1 spray 4x daily after onset of symptoms significantly decreased severity and duration of cold symptoms in healthy adults when started within 48 hrs of onset of cold symptoms. These results are more promising, with a more reliable experimental design.
2002, Hung et al - This laboratory study elucidated that zinc ion inhibits human rhinovirus HRV-16 3D polymerase at an IC(50) of 0.6microM, at a site distinct from magnesium ion activation. This gives a basic science explanation as to why zinc purportedly decreases the number and duration of common colds.
2001, Turner - This double-blind, placebo controlled study showed that intranasal zinc gluconate did not decrease duration or symptom score in experimentally given rhinovirus colds. However, the experimental intranasal inoculation with 2 drops of saline containing the virus may have a different effect on a person that is exposed to fine droplets in the environment.