Probiotic bacteria reduced duration and severity but not the incidence of common cold episodes in a double blind, randomized, controlled trial

To investigate the effect of long-term consumption of probiotic bacteria on viral respiratory tract infections (common cold, influenza), a randomized, double blind, controlled intervention study was performed during two winter/spring periods (3 and 5 month). Four hundred and seventy-nine healthy adults were supplemented daily with vitamins plus minerals with or without probiotic lactobacilli and bifidobacteria. The intake of the probiotic had no effect on the incidence of common cold infections (verum = 158, control = 153 episodes, influenza was not observed), but significantly shortened duration of episodes by almost 2 days (7.0 ± 0.5 versus 8.9 ± 1.0 days, p = 0.045), reduced the severity of symptoms and led to larger increases in cytotoxic T plus T suppressor cell counts and in T helper cell counts.