Zinc administered within 24 hours of onset of symptoms reduces the duration and severity of the common cold in healthy people, according to an updated review published in the Cochrane Library.

Trials conducted since 1984 investigating the role of zinc for the common cold symptoms have had mixed results. Inadequate treatment masking and reduced bioavailability of zinc from some formulations have been cited as influencing results.

For this review, researchers evaluated randomized, double-blind, placebo-controlled trials using zinc for at least five consecutive days to treat, or for at least five months to prevent the common cold.

The assessment included 13 therapeutic trials (966 participants) and two preventive trials (394 participants). Intake of zinc is associated with a significant reduction in the duration and severity of common cold symptoms. There was a significant difference between the zinc and control group for the proportion of participants symptomatic after seven days of treatment.

When supplemented for at least five months, zinc reduces cold incidence, school absenteeism and prescription of antibiotics in children, researchers concluded. However, there is potential for zinc lozenges to produce side effects. In view of this and the differences in study populations, dosages, formulations and duration of treatment, it is difficult to make firm recommendations about the dose, formulation and duration that should be used, they said.