Beneficial effects of Lactobacillus paragasseri OLL2716 on sleep homeostasis during psychological stress and poststress recovery in healthy adults: A randomized, double-blind, placebo-controlled study

We investigated the effects of Lactobacillus paragasseri OLL2716 on sleep under psychological stress. In this randomized, double-blind, placebo-controlled trial, 78 healthy Japanese students in the fourth year of medical school were exposed to 2 consecutive academic exam stressors. They were randomly assigned to the OLL2716 or placebo group, and each group consumed 85 g of yogurt containing L. paragasseri OLL2716 or placebo yogurt daily for 8 wk. Two examinations were performed after 4 and 7 wk of intake. The State-Trait Anxiety Inventory (STAI) was used to assess anxiety level. As the primary endpoint, subjective sleep was evaluated using the Ogri-Shirakawa-Azumi sleep inventory MA version (OSA-MA) and the Pittsburgh Sleep Quality Index. Objective sleep was assessed using Fitbit, a sleep-monitoring device. Saliva was collected for 2 min between 1600 and 1800 h. Salivary cortisol and chromogranin A levels were measured to assess physiological stress response. These data were obtained at baseline (0 wk) and during the intake periods (2, 4, 5, 7, and 8 wk after intake). The STAI data showed that anxiety levels were similar in both groups. The OSA-MA data showed that the changes in "sleepiness on rising" score at 2 and 4 wk and "dreaming" score at 8 wk were significantly improved, and the changes in objective sleep length at 2, 4, and 7 wk were significantly increased in the OLL2716 group compared with those in the placebo group. Additionally, the salivary chromogranin A secretion rate at 4 wk and salivary cortisol level and secretion rate at 5 wk were significantly decreased in the OLL2716 group compared with those in the placebo group. These results suggest that the intake of L. paragasseri OLL2716 improves stress-induced sleep deprivation, maintains sleep homeostasis, and moderates the stress response. Therefore, L. paragasseri OLL2716 is a potential strategy for reduced daytime performance associated with sleep dissatisfaction among individuals living in the modern stressful society.