Lactococcus lactis JCM 5805 (LC-Plasma), a unique lactic acid bacteria (LAB), activates plasmacytoid dendritic cells (pDC). The present study evaluated the effect of LC-Plasma on dendritic cell (DC) activity and subjective indices of upper respiratory tract infections (URTI) and fatigue in athletes under high-intensity exercise.

It included fifty-one male subjects belonging to a university sports club and randomized them into placebo (n = 25) and LC-Plasma (n = 26) groups. Individuals received placebo capsules containing cornstarch or LC-Plasma capsules containing 100 billion cells of heat-killed LC-Plasma per day for 13 days. 

During the intervention period, the study subjected the participants to perform high-intensity exercises according to their sports club training regime. It obtained blood and saliva sampling on days 1 and 14 and recorded physical conditions in a diary. 

The study investigated the expression of maturation markers on DCs, muscle damage, and stress markers and compared them between groups. It also investigated cumulative days of symptoms regarding infections and fatigue and compared between groups. 

The study found:

• Significant increase in CD86 as a maturation marker on pDC in the LC-Plasma group on day 14.
• significantly lower cumulative days of URTI in the LC-Plasma group and significantly lower symptoms like a sneeze or running nose in the LC-Plasma group.
• Significantly fewer cumulative days of fatigue in the LC-Plasma group.
• No significant difference in the markers of muscle damage and stress markers between groups.

This study shows that heat-killed LC-Plasma supplementation can relieve morbidity and symptoms of URTI by activating pDC and decreasing fatigue accumulation during consecutive high-intensity exercise in athletes. However, LC-Plasma ingestion does not affect markers of muscle damage and stress.

Komano Y, Shimada K, Naito H, et al., Efficacy of heat-killed Lactococcus lactis JCM 5805 on immunity and fatigue during consecutive high-intensity exercise in male athletes: a randomized, placebo-controlled, double-blinded trial. Journal of the International Society of Sports Nutrition. 2018; 15:1. DOI: 10.1186/s12970-018-0244-9