Whether training for a marathon or trying to score for your community football team, the common cold can slow down even the most tenacious athlete. Luckily, a study found that a supplement made with a heat-killed preparation of a probiotic bacteria known as Lactococcus lactis JCM 5805 may reduce the symptoms of colds and fatigue related to high-intensity exercise by activating dendritic cells. Dendritic cells are a type of immune cell that help initiate the response to infection. Published in the Journal of the International Society of Sports Nutrition, the double-blind trial included 51 men belonging to a university sports club. Every day for 13 days, half the men took capsules containing 100 billion heat-killed L. lactis bacteria and the other half took a placebo containing cornstarch. During that time, the men performed high-intensity exercises with their sports club and recorded their physical conditions, including any cold symptoms, in a diary. Researchers took blood and saliva samples on days 1 and 14 to measure markers of muscle damage and stress. At the end of the study, they found that:

• The group taking L. lactis JCM 5805 had increased dendritic cell activity compared with the placebo group.
• The group taking L. lactis JCM 5805 had fewer cumulative days of reports of cold symptoms and fewer days of reports of fatigue than the placebo group.
• The group taking L. lactis JCM 5805 also reported fewer specific cold symptoms, like sneezing and runny nose, than the placebo group.
• There were no significant differences in markers of muscle damage and stress between the two groups, indicating that the intensities of their exercise regimes were similar.

These results indicate that this heat-killed probiotic strain may stimulate an immune response and help athletes stay healthy. The findings add to evidence from a few previous trials showing that probiotic supplements with viable bacteria may help athletes avoid respiratory and gastrointestinal illnesses, and further show a possible positive effect on energy level. It’s important to note, however, that the researchers conducting this trial were affiliated with the supplier of the study capsules, so research by unaffiliated parties to verify their findings is needed. While we await future findings, remember that staying hydrated, eating balanced meals, and getting enough sleep can help keep your physical and immune function in top shape.