Discuss the varying results from studies that have investigated the effects of zinc supplementation ...

The role of zinc in the health of our immune system is well known. Zinc has been shown to inhibit the replication of rhinovirus and other viruses that cause the common cold, thus leading to speculation that taking zinc supplements may reduce the length and severity of colds. Consequently, zinc lozenges were formulated as a means of providing potential relief from cold symptoms.

Does taking zinc in lozenge form actually reduce the length and severity of a cold? Over the past 20 years, numerous research studies have been conducted to try to answer this question. Unfortunately, the results of these studies are inconclusive because about half have found that zinc lozenges do reduce the length and severity of a cold, while about half find that zinc lozenges have no effect on cold symptoms or duration.

Some reasons that various studies report different effects of zinc on a cold include:

Inability to truly "blind" participants to the treatment – because zinc lozenges have a unique taste, it may be difficult to keep the research participants uninformed as to whether they are getting zinc lozenges or a placebo. Knowing which lozenge they are taking could lead participants to report biased results.

Self-reported symptoms are subject to inaccuracy – many studies had the research participants self-report changes in symptoms, which may be inaccurate and be influenced by mood and other emotional factors.

Wide variety of viruses that cause a cold – because more than 200 viruses cause a cold, it is highly unlikely that zinc can combat them all. It is possible that people who do not respond favourably to zinc lozenges are suffering from a cold virus that cannot be treated with zinc.

Differences in zinc formulations and dosages – the type of zinc formulation and the dosages of zinc consumed by study participants differed across studies. These differences most likely contributed to various responses across studies. It is estimated that for zinc to be effective, at least 80 mg of zinc should be consumed each day, and that people should begin using zinc lozenges within 48 hours of onset of cold symptoms. Also, sweeteners and flavourings found in many zinc lozenges, such as citric acid, sorbitol, and mannitol, may bind the zinc and inhibit its ability to be absorbed into the body, limiting its effectiveness.