Unlike Vitamin C, which studies have found likely does nothing to prevent or treat the common cold, zinc may actually be worth it. The mineral seems to interfere with the replication of rhinoviruses, the bugs that cause the common cold.
In a 2011 review of studies of people who'd recently gotten sick, researchers looked at those who'd started taking zinc and compared them with those who just took a placebo. The ones on the zinc had shorter colds and less severe symptoms.