The new research was published the European Journal of Clinical Research. It was the work of a team from Hokkaido University in Sapporo, Japan and employees of the Yotsuba Milk Products Co.
The researchers were testing the theory that a probiotic strain labeled as Lactococcus lactis subsp. cremoris YRC3780 could ameliorate stress in young men taking a validated test known as the Trier Social Stress Test (TSST), which has been used in many other studies to introduce a psychological stimulus.
The TSST consists of:
- Stress response to socially evaluative situations
- Participant taken to a room with panel of three judges
- Five-minute anticipatory stress (prepare presentation), 5 minute presentation, 5 minute mental arithmetic test (count backwards from 1,022 in steps of 13, if a mistake is made, start from the beginning).
Probiotic cut cortisol levels but didn’t improve sleep
The researchers recruited 27 healthy young and relatively lean Japanese men for the study, who were divided into active (14) and placebo (13) groups. The young men took capsules of Lactococcus lactis subsp. cremoris YRC3780, which is isolated from kefir or a placebo. The researchers did not specify the dosage of the probiotic. The supplementation protocol lasted for eight weeks prior to administration of the TSST.
The primary measure was salivary cortisol levels to assess the HPA axis response. Sleep quality and general psychological health were assessed through a variety of questionnaires completed at intervals throughout the study. Periodic fecal samples were also taken and analyzed.
The researchers found that the probiotic decreased morning salivary cortisol levels at the weeks six and eight measures, and decreased salivary cortisol levels in response to the test. But only about half of the participants reacted to the test by secreting more cortisol. The probiotic group showed some very minor improvements in sleep quality, but there was no difference in the microbiome makeup between the groups.
Incremental addition to research
Ralf Jäger, PhD, a principal in the scientific consulting firm Increnovo said the study in an interesting addition to the body of research on probiotics and stress, but may be of limited value in product formulation.
“By measuring salivary cortisol levels, one can perform subgroup analysis of people that show a significant stress cortisol response, and the people that do not. Having to separate responders from non-responders allows you to check if you can reduce cortisol/stress responses in people that show a significant stress response, however, this has limited value for you and me, because neither you nor I know if we are or are responding to stress with an increase in cortisol levels, so we wouldn't know if the product would do anything good for us, and the general population wouldn't know,” Jäger told NutraIngredients-USA.
“Did we learn anything new from a mechanistic angle? No, probiotics have already been shown to reduce cortisol levels. Overall, there was no difference in fecal microbiota changes, no differences in sleep, however a mild effect on stress hormones in highly stressed individuals. Overall, a great addition to the body of science that probiotics can manage stress responses in humans, however, the link to functional benefits, e.g., sleep quality, was not there,” he added.
Source: European Journal of Clinical Nutrition
DOI: 10.1038/s41430-021-00978-3
Effects of Lactococcus lactis subsp. cremoris YRC3780 daily intake on the HPA axis response to acute psychological stress in healthy Japanese men
Authors: Matsuura N, et al.