Zinc supplements can reduce the severity and duration of common cold symptoms, a study has found.

Previous trials looking at whether zinc can combat a cold have produced conflicting results. The findings are published in the Cochrane Library, which reviews the latest evidence on medicines.

Researchers analysed data from 15 trials involving 1,360 participants. They concluded that taking zinc syrup, lozenges or tablets within a day of the onset of cold symptoms had a remedial effect.

Both the severity and length of the illness were reduced. After seven days, more patients who took zinc had fought off their colds than those who took dummy "placebos".

Giving zinc also reduced the use of antibiotics in children. Antibiotics are not effective against viruses such as those responsible for colds and flu, and overuse can lead to the development of resistant bacteria.

Dr Meenu Singh, from the Post-Graduate Institute of Medical Education and Research in Chandigarh, India, who led the study, said: "This review strengthens the evidence for zinc as a treatment for the common cold. However, at the moment, it is still difficult to make a general recommendation, because we do not know very much about the optimum dose, formulation or length of treatment."

Zinc is known to be important for the immune system, and deficiency may increase susceptibility to infections.

The idea that the mineral can fight colds was supported by a 1984 study which suggested zinc lozenges could reduce the length of time symptoms lasted. Since then other studies had failed to provide consistent results.

The Cochrane researchers said further work should focus on specific populations. "Our review only looked at zinc supplementation in healthy people," Singh said. "But it would be interesting to find out whether zinc supplementation could help asthmatics, whose asthma symptoms tend to get worse when they catch a cold."

More research should be conducted in low-income countries, where zinc deficiency may be common, said the scientists.