A new study conducted by researchers Katerina Johnson and Laura Steenbergen at the University of Leiden in the Netherlands found that daily supplementation with a probiotic marketed as Ecologic Barrier by Winclove Probiotics was associated with significant improvements in various measures of self-reported mood. The findings were published in NPJ Mental Health Research.

The probiotic formula contained nine bacterial strains: Bifidobacterium bifidum W23, B. lactis W51 and W52, Lactobacillus acidophilus W37, Levilactobacillus brevis W63, Lacticaseibacillus casei W56, Ligilactobacillus salivarius W24, and Lactococcus lactis W19 and W58.

Human studies on the relationship between probiotic supplementation and mood have been inconsistent thus far. Johnson and Steenbergen used a combination of methods outside of standard evaluations to capture how probiotics might influence one’s ability to regulate emotions and mood. These included psychological questionnaires, daily mood reports, and computer tasks testing how people process emotions.

“The gut-brain connection provides various routes through which bacteria in the gut can influence how we feel and behave, including via the vagus nerve, immune system, and hormones,” said Johnson.

In the study, a population of 88 young adults took either a probiotic or placebo for one month.

According to the authors, this is the first study of its kind to rely on daily mood reports, as opposed to less consistent assessments, to assess the probiotic supplement’s effects. Significant reductions in self-reported negative feelings were clear, the authors noted.

“It is striking that by simply asking participants how they were feeling each day, we could detect the beneficial effects of probiotics on mood,” said Steenbergen. “In contrast, the standard psychological questionnaires that are common in this field were not sensitive enough to pick up these changes.”

The researchers found that it took about two weeks for probiotics to achieve significant reductions in negative feelings. Typically, antidepressants take about the same amount of time to work, however, in addition to reducing negative feelings, antidepressants also improve indices of positive mood, which wasn’t seen in the treatment group.

In a subgroup analysis, the researchers found that participants were most likely to benefit from probiotic supplementation if they had a “propensity for risk avoidance,” said Johnson.

Probiotic supplementation was also linked to an improved ability to recognize facial expressions, signaling an impact on how participants processed emotional cues.

The research highlights a potential preventive role of probiotic supplementation, potentially reducing the chances of negative feelings progressing to mental health issues, the authors noted. However, more research is needed.

Additionally, the authors called for other mental health researchers to include simple daily measures of mood in their studies. “In an attempt to delineate the complexity of the human brain and emotion, we cannot lose sight of asking the obvious,” they concluded in their paper. “Sometimes, the most simple questions reveal the most meaningful answers.”