Zinc supplements can reduce the severity of the common cold and help people recover faster, say the authors of a new review.
A review on the ability of zinc to prevent and treat colds published in 1999 was inconclusive. This new paper, published in The Cochrane Library — a key resource for evidence-based medicine — includes an additional eight studies, bringing the total number of analyzed trials to 15 and number of participants to 1360.
Dr. Meenu Singh and Dr. Rashmi Das from the Post Graduate Institute of Medical Education and Research, Chandigarh, India, found patients who received zinc supplements within 24 hours of cold symptoms appearing and who continued to take them for a minimum of five days were more likely to recover within a week than those given placebos.
They also found, zinc given to healthy children as a preventative measure, reduced the number of colds and days absent from school. There was also a reduction in antibiotic use.
Associate Professor Luis Vitetta, director of the centre for integrative clinical and molecular medicine at the Princess Alexandra Hospital in Queensland, Australia, says the data chosen for the review was well considered and the authors had enough data to ensure the findings are statistically significant.
"They've chosen the right studies with appropriate controls and which are randomized in order to be able to come to these conclusions," says Vitetta.
There's no proven treatment for the common cold. Symptoms may include a sore throat, a blocked or runny nose, and a cough, and last up to two weeks.
"In Australia, healthy adults have four to five colds per year, susceptible people may have one to two a month and children two to three a year," he says. "And then you have secondary illnesses, such as bacterial infections, which require antibiotics."
More to be done
The studies included in the review used different formulations of zinc and were given as lozenges, syrup or, in one trial, as a tablet.
"It would be interesting to know if there any differences between these formulations in terms of bioavailability," says Vitetta.
"Zinc is an essential mineral in the body and it is used in hundred of reactions. While zinc has a plausible biological mechanism in terms of influencing the progression or establishment of a cold by way of eliciting an immune response, I'd now be asking what dose is required."
Professor Emeritus Bob Douglas, of the National Centre for Epidemiology and Population Health at The Australian National University, an author of one of the trials included in the meta-analyses and a former Cochrane review editor, says preventing and treating colds has been a very contentious question for a long time.
"This is a very interesting finding. I don't think the effect is huge, but it's substantial," says Douglas. "I'd be doing a lot more trials, particularly in different population groups."
Singh acknowledges not much is known about the optimum dose, formulation or length of zinc treatment and that the review only looked at supplementation in healthy people in high-income countries. "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," he says.
Singh and Das also say that more work needs to be carried out in low-income countries, where zinc deficiency may be prevalent.