A February 2011 study showed that zinc supplementation reduced the duration and severity of the common cold in otherwise healthy people. Unfortunately, what is not known is exactly how much or how often you should take it. As with any any nutritional supplement, it is best to use zinc in moderation, and always on a full stomach, since it can cause nausea if you haven't eaten first. Popular and safe choices for zinc supplementation are the over-the-counter products such as Airborne or Zicam. Since there are no studies indicating the efficacy or safety of high doses, it's best to stay away from taking anything above the package recommendations on these products.