According to a review of research published by the Cochrane Collaboration, an international organization that evaluates medical research, zinc supplements appear to shorten the length of colds by approximately one day as well as lessen the symptoms. Their findings are based on based on 13 trials with close to 1,000 participants who either took zinc or a dummy treatment at the beginning of their symptoms. Two other trials indicated zinc helped stave off colds, but the research quality of the studies were considered poor. Exact zinc dosage and formulation for optimal effectiveness is not known, nor is the mechanism of how zinc reduces the length and symptoms of colds. It should also be noted that taking zinc over a long period of time should be done carefully as it can interfere with other metals in the body resulting in unpredictable consequences.