Was reading up on the Vitamin C cold remedy wives tail a year or so ago (basically it has zero effect on duration of cold symptoms) and found where Zinc had a very minor effect on reducing symptom longevity in clinical studies ...reduced a 14 day cold to 13 days or something along those lines. I stopped buying $18/bottle Zicam after that.
My daily vitamin has 100 percent of the recommended daily allowance of zinc. Not sure on whether there is some kind of synergy with the others.