In a review of trials using zinc for the common cold, researchers analysed 13 therapeutic trials (966 participants) and two preventive trials (394 participants). They found that zinc administered within 24 hours of onset of symptoms reduced the duration and severity of the common cold in healthy people. When supplemented for at least five months, it reduced cold incidence, school absenteeism and prescription of antibiotics in children.
Singh M, Das RR. Zinc for the common cold. Cochrane Database Syst Rev. 2011;2:CD001364.