Some of the studies reviewed also found that those who used zinc had less severe symptoms compared with those who took a placebo. two other studies, which included nearly 400 participants, found that those who took zinc lozenges daily for at least five months developed 36 percent fewer colds than those who took a placebo.

Children who took zinc prophylactically had fewer missed days of school and fewer prescriptions for antibiotics.

“I think the results are interesting and show significance for the use of zinc to shorten or prevent the common cold,” says Dr. Richard Zane, vice chair of emergency medicine at Brigham and Women’s Hospital. “Does it convince me to take zinc? Probably not.”

Zinc appears to have antiviral properties and may have some immune boosting effects. over the past 25 years, however, clinical trials of zinc supplements have had conflicting results: 11 have shown zinc to be useful for colds whereas seven have found no benefit. 

(The Cochrane Review only included trials in which people took zinc for at least five days during a cold or at least five months to prevent a cold.)

Part of the problem, experts say, is that it’s tough to design studies where participants don’t know that they’re taking zinc versus a sugar pill. That’s because zinc tastes chalky and bitter and often causes nausea.

Those are two downsides you’d have to consider if you decide to take zinc for cold prevention or to manage any cold you catch. the Cochrane researchers stopped short, though, of recommending this, given that none of the trials were large enough on their own to determine an exact dose or formulation that should be used.

Also, the review didn’t include studies involving zinc nasal swabs like Zicam, which don’t have the bad taste and nausea problem. But the US Food and Drug Administration has warned against using Zicam after receiving reports of users losing their sense of smell from the product.

Zane predicts the finding will spur a host of new cold products on the market containing zinc.”But it’s important to emphasize that the common cold is usually self-limiting” and, unlike the flu, doesn’t pose much risk of turning into something life-threatening.