The jury is still out on that question because many zinc studies, both those that find it beneficial and those that don't, are flawed. However, the highest quality randomized trials generally show no benefit. In studies with positive results, zinc seemed most effective taken within 24 hours of the start of cold symptoms. Taking zinc lozenges with food may reduce side effects, such as a bad taste and nausea. Intranasal zinc isn't a good option because it may damage the sense of smell.
Jan. 15, 2013