Table 1.

Preventive effects of probiotics in stress-exposed young adults.

Intervention	Participants	Results
8 week RCT; probiotic as a stand-alone agent for preventing stress-induced changes.	49 healthy medical students (<30 years) preparing to take nationwide examination for academic advancement.	•In both studies, salivary cortisol levels increased significantly 1 day before the examination in the placebo group compared with the baseline levels. •Conversely, no significant elevation of salivary cortisol was observed in the L. casei strain Shirota group.
100-ml bottle of either L. casei strain Shirota-fermented milk (L. casei strain Shirota at more than 1.0 × 1011 CFU per 100-ml bottle) or placebo milk taken daily prior to standardized examination.	Placebo group: 22.8 ± 0.3 yo
Kato-Kataoka et al. (2016a)	Probiotic group: 22.8 ± 0.4 yo
8 week RCT; probiotic as a stand-alone agent for preventing stress-induced changes.	51 healthy medical students (<30 years) preparing to take nationwide examination for academic advancement.	•Participants in L. casei strain Shirot (LcS) group had significantly higher gut microbiota alpha-diversity, with a significantly lower percentage of Bacteroidaceae compared to the placebo group. •Participants in LcS group had significantly lower rates of physical symptoms at 5–6 weeks and 7–8 weeks compared to the placebo group.
100-ml bottle of either L. casei strain Shirota-fermented milk (L. casei strain Shirota at more than 1.0 × 109 CFU/ml) or placebo milk taken daily prior to standardized examination.	Placebo group: 22.7 ± 0.4 yo
Kato-Kataoka et al. (2016b)	Probiotic group: 23.0 ± 0.4 yo
8 week RCT; probiotic as a stand-alone agent for preventing stress-induced changes.	149 healthy medical students (<30 years) preparing to take nationwide examination for academic advancement.	•Salivary cortisol increase from baseline to pre-exam was significantly greater in the placebo group (compared to the LcS group). •Physical symptom rate increased in placebo group, and decreased in LcS group, from baseline to pre-exam. At weeks 7–8, significantly greater number of physical symptoms in placebo group compared to LcS group. •In rats exposed to WAS, increases in plasma corticosterone were significantly greater in those given feed w/o LcS (compared to those pretreated with LcS).
100-ml bottle of either L. casei strain Shirota-fermented milk (L. casei strain Shirota at more than 1.0 × 109 CFU/ml) or placebo milk taken daily prior to standardized examination.	Placebo group: 22.8 ± 0.2 yo
Rats given feed w/or w/o LcS for 2 weeks, prior to Water avoidance stress (WAS).	Probiotic group: 23.0 ± 0.2 yo
Takada et al. (2016)	Rats aged 8–9 weeks old
12 week RCT; probiotic as a stand-alone agent for preventing stress-induced changes.	69 healthy medical students (aged 22–35) preparing to take nationwide examination for academic advancement.	•Salivary cortisol increase from baseline was significantly greater in the placebo group (compared to CP2305 group) at both 6 weeks and 12 weeks. •In female students: significant difference in STAI-state and GHQ-28 scores between placebo group and CP2305 group after 12 weeks.
200 mL beverage containing containing Lactobacillus gasseri strain CP2305 (CP2305) or placebo beverage daily prior to standardized examination.	Placebo group: 25.1 ± 0.4 (22–35) yo
Nishida et al. (2017)	Probiotic group: 24.9 ± 0.3 (23–32) yo
11 week placebo-controlled, crossover-designed trial (3 week washout). Probiotic as a stand-alone agent for preventing stress-induced changes.		Participants in CP2305 group had: •significantly reduced salivary cortisol levels compared to pre-intervention (a reduction which was significantly greater than that seen in placebo group); •significantly reduced fecal microbiota growth of Enterobacteriaceae after intervention (compared to the increase seen in placebo group); •significantly reduced HADS-depressive mood score after intervention compared to placebo group; •significantly reduced STAI-state anxiety score after intervention compared to placebo group.
Daily consumption of Lactobacillus gasseri CP2305 (CP2305) at 1.0 × 1010 CFU dissolved in water, compared to placebo dissolved in water.
Sawada et al. (2017)	24 healthy medical students taking cadaver dissection course.