Writing in the journal Scientific Reports, researchers at Yotsuba Milk Products reported that Japanese adults who had an initial positive stress test result improved their scores after consuming YRC3780 for eight weeks.
However, they found no difference in salivary cortisol levels and fatigue scores.
Rising stress levels
The study noted that over 80% of Japanese workers feel that their work life causes them strong anxiety or stress, exposing them to a greater risk of mental health issues and chronic diseases.
Probiotics have gained increasing attention for their potential to modulate the stress response. The gut-brain interaction involves signaling molecules, including short-chain fatty acids, serotonin produced by intestinal cells and immune cells.
Previous studies have suggested that YRC3780 increases natural killer cell activity in mice and alleviates allergic reactions in humans.
“Therefore, YRC3780 may act on immune cells in the intestinal tract to enhance cytokine production, and these cytokines in turn may improve the stress response,” the researchers wrote.
YRC3780 has shown potential to support stress and sleep response, as well as reduce cortisol levels, in single-sex cohorts in their twenties. The current study expanded the age range and gender of subjects using a stress test adapted to a wide range of age groups.
Study details
The double-blind, placebo-controlled, parallel-group trial involved 107 Japanese adults who initially showed a positive Uchida-Kraepelin (U-K) test stress response. The U-K test is a psychological assessment tool designed to measure mental performance, work efficiency and personality traits.
Participants were randomly assigned to consume a capsule containing 59 billion CFUs of YRC3780 or placebo daily for eight weeks.
The researchers employed appropriate questionnaires and scales to assess mental status, stress and fatigue, in addition to measuring salivary cortisol levels.
The Profile of Mood States 2nd Edition (POMS2) Total Mood Disturbance (TMD) scores after the U-K test at eight weeks, and the change in score from baseline, were significantly lower in the YRC3780 compared to placebo. This was also the case for other subscores such as tension–anxiety, depression–dejection, anger–hostility, confusion–bewilderment and fatigue–inertia.
There were no significant differences between the supplement and placebo for salivary cortisol and other scores, such as the visual analog scale for fatigue.
The researchers recommend further studies to explore the anti-stress and anti-fatigue effects of YRC3780.
Source: Scientific Reports, 2025, 15, 23393. doi: 10.1038/s41598-025-07783-z. “Lactococcus cremoris YRC3780 improves subjective stress response in the Uchida-Kraepelin test: a randomized, double-blind, placebo-controlled study”. Authors: I. Fujioka et al.
