Taking zinc may cut the time adults suffer with a common cold, but consuming it will likely come with unpleasant side effects such as nausea, according to a review of past studies.
The researchers, whose findings appeared in the Canadian Medical Association Journal, found that the benefits of zinc also appear to be modest and don't extend to children. But they could add up given that there are about 62 million cases of the common cold in the United States every year.
Michelle Science, from the Hospital for Sick Children in Toronto, and her colleagues compiled data from 17 clinical trials covering 2,121 people, comparing those who took zinc orally to another group that either took a placebo or received no treatment.
"The results of our meta-analysis showed that oral zinc formulations may shorten the duration of symptoms of the common cold," Science and her colleagues wrote.
"However, large high-quality trials are needed before definitive recommendations for clinical practice can be made."
Overall, the researchers noted that in the trials, which included people from one to 65-years-old, those taking zinc had colds that were shortened by a little more than two and a half days compared to those taking the placebo.
Little difference was seen in cold duration in children, though - perhaps, said the authors, because adults tended to use a different form of zinc than children.
Peoples' cold symptoms also seemed to clear up faster if they took a higher dosage of zinc compared to those who took the least. The various studies used different dosages, said Science.
While adults who didn't take zinc tended to have colds lasting a week or more, there was no difference in the severity of cold symptoms on day three in any of the groups.
But side effects were more common in people taking zinc. They were 64 percent more likely to experience nausea and 65 percent more likely to detect an unpleasant taste in their mouths.