Kato-Kataoka A et al. (2016), Beneficial Microbes 7(2): 153-156
Aim: This pilot study investigated the effects of the probiotic Lactobacillus casei strain Shirota (LcS) on psychological and physical stress responses in medical students undertaking an authorized Nationwide examination for promotion.
Method: In a double-blind, placebo-controlled trial, 24 and 23 healthy medical students consumed a fermented milk containing LcS and a placebo milk, respectively, once a day for 8 weeks until the day before the examination. Psychological state, salivary cortisol, faecal serotonin and plasma L-tryptophan were analysed on 5 different sampling days (8 weeks before examination, 2 weeks before examination, 1 day before examination, immediately after examination and 2 weeks after the examination). Physical symptoms were also recorded in a dairy by subjects during the intervention period for 8 weeks.
Results: In association with a significant elevation of anxiety at 1 day before the examination, salivary cortisol and plasma L-tryptophan levels were significantly increased in only the placebo group (P < 0.05). Two weeks after the examination, the LcS group had significantly higher faecal serotonin levels (P < 0.05) than the placebo group. Moreover, the rate of subjects experiencing common abdominal and cold symptoms and total number of days experiencing these physical symptoms per subject were significantly lower in the LcS group than in the placebo group during the pre-examination period at 5-6 weeks (each P < 0.05) and 7-8 weeks (each P < 0.01) during the intervention period.
Conclusions: The results suggest that daily consumption of fermented milk containing LcS may exert beneficial effect by preventing the onset of physical symptoms in healthy subjects exposed to stressful situations.