Probiotics reduced negative mood in a new clinical trial, adding to mounting evidence that the gut-brain connection plays a crucial role in mental health.
In the randomised, double-blind, placebo-controlled study, researchers observed that participants began feeling mood improvements within about two weeks of taking probiotics. Because the study involved healthy adults, not just people with diagnosed depression, the findings suggest probiotics could benefit mental health across the general population.
The results were published on April 9 in the journal npj Mental Health ResearchTrusted Source.
The researchers noted that their use of daily mood tracking may have helped detect subtle improvements that other mental health assessments could miss. “This is the first study to implement daily mood monitoring to assess the effects of probiotics, and in fact, by the end of the month-long study, their negative mood still appears to be improving,” Katerina Johnson, PhD, first author of the study and a research associate at the University of Oxford in the United Kingdom, told Healthline.
The study adds to growing interest in the gut-brain connection, a complex communication system that is thought to influence mood and emotions between the gut and the brain.
The gut produces a large amount of serotonin (about 95%), a neurotransmitter involved in everything from mood to appetite. This suggests that improving gut health could positively impact mental health.
Researchers conducted a comprehensive study involving 88 healthy volunteers with an average age of 22. Participants in the study were not overweight, which was based on their body mass index (BMI). They also did not engage in excessive drinking, nor drug use.
Once enrolled, participants were randomly assigned to receive either a multispecies probiotic mixture or a placebo for 28 days.
The probiotic mixture contained nine bacterial strains, including various Bifidobacterium, Lactobacillus, and Lactococcus species. Participants consumed one 2-gram sachet daily dissolved in lukewarm water.
The researchers administered a comprehensive battery of validated psychological questionnaires before and after the four-week intervention, including measures of anxiety (STAI), worry (PSWQ), depression (CES-D), and negative affect (PANAS).
Despite this thorough approach, these standard psychological assessments detected minimal differences between the probiotic and placebo groups.
However, daily mood reporting told a different story.
This daily monitoring revealed the study’s most significant finding: participants who received probiotics showed a reduction in negative mood starting around the two-week mark, while those on placebo showed no such improvement.
“By monitoring people daily, rather than just assessing them before and after, it gives us a much better resolution of changes over time when taking probiotics,” Johnson said.
“One disadvantage with psychological questionnaires is that they attempt to dissect how people are feeling into discrete categories, e.g., stress, anger, anxiety, or depressive tendencies. In contrast, asking how positive or negative someone is feeling can holistically capture a change in any emotional state,” she explained.
These findings suggest that probiotics can benefit mental health even in generally healthy populations and that common research methods may miss these effects. Interestingly, the improvements in negative mood didn’t affect positive mood, which remained unchanged in both groups.
