Probiotic supplements have been shown to reduce the number and length of infections suffered by long-distance runners. Strenuous training can affect the immune system and make athletes vulnerable to coughs and colds, but a study has shown that taking probiotics more than halves the days that runners show symptoms.
The study focused on 20 top-level endurance runners during their intensive winter training program. All 20 received two month-long courses of pills -- one containing the bacterium Lactobacillus fermentum, and the other containing no active ingredients.
There were a total of 72 days in which people taking the "dummy" pills complained of cough or cold symptoms, compared to only 30 days on the course of probiotics.
* BBC News February 14, 2008