Daily administration of paraprobiotic Lactobacillus gasseri CP2305 ameliorates chronic stress-associated symptoms in Japanese medical students

Administration of Lactobacillus gasseri CP2305 for 4 weeks improved stress-associated behaviours in healthy young adults and clinical symptoms in patients with irritable bowel syndrome. The present study was designed to confirm the stress-relieving effects of heat-inactivated, washed CP2305 (paraprobiotic CP2305) on 69 sixth-year medical students (40 males and 29 females) preparing to take the national examination for medical practitioners. Administration of the paraprobiotic CP2305 for 12 weeks significantly improved sleep quality assessed by both the Pittsburgh Sleep Quality Index and a one-channel sleep electroencephalogram during the pre-examination period compared with that of the placebo administration. The paraprobiotic CP2305 administration also prevented increases in basal salivary cortisol release and expression of stress-responsive microRNAs (miR-144 and miR-144 ∗ ). In addition to the improvement in parasympathetic nerve activity, the paraprobiotic CP2305 normalized the bowel habits under the stressful conditions. Based on these results, we propose that paraprobiotic CP2305 may be used as a para-psychobiotic.