A team of scientists, including an Indian-origin researcher, believes that zinc supplements can reduce the severity and duration of illness caused by the common cold.
The findings, based on a review of data from 15 trials, could help reduce the amount of time lost from work and school due to colds.
The idea that zinc might be effective against the common cold came from a study carried out in 1984, which showed that zinc lozenges could reduce how long symptoms lasted.
Since then, trials have produced conflicting results and although several biological explanations for the effect have been proposed, none have been confirmed.
The review updates a previous Cochrane Systematic Review, carried out in 1999, with data from several new trials. In total, data from 15 trials, involving 1,360 people, were included.
According to the results, zinc syrup, lozenges or tablets taken within a day of the onset of cold symptoms reduce the severity and length of illness. At seven days, more of the patients who took zinc had cleared their symptoms compared to those who took placebos.
Children who took zinc syrup or lozenges for five months or longer caught fewer colds and took less time off school.
Zinc also reduced antibiotic use in children, which is important because overuse has implications for antibiotic resistance.
"This review strengthens the evidence for zinc as a treatment for the common cold," said lead researcher Meenu Singh of the Post Graduate Institute of Medical Education and Research in Chandigarh, India.
"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."
Further research should focus on the benefits of zinc in defined populations, the review suggests.
"Our review only looked at zinc supplementation in healthy people," said Singh. "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."
The researchers also say that more work needs to be carried out in low-income countries, where zinc deficiency may be prevalent.
The findings have been published in The Cochrane Library .