Clinical studies have shown that probiotics can decrease anxiety, improve mental outlook, and induce positive mood changes and outlook. In fact, some bacteria strains have been shown to reduce anxiety and depression in mice by directly modulating nerve firings associated with these cognitive maladies. A recent study conducted by Leiden University in The Netherlands explored further in human subjects to assess whether or not probiotics, composed of various strains of Bifidobacteria and Lactobacilli could specifically modulate cognitive reactivity to sad mood, a well-characterized indicator for vulnerability to depression.
In brief, cognitive reactivity is defined as a series of dysfunctional patterns of thinking prompted by subtle mood changes, such as rumination, aggression, and hopelessness. It is thought that cognitive reactivity is central in the development, maintenance, and recurrence of depression episodes. This behavioral reaction is considered to have significant predictive value in detecting vulnerability to developing clinical depression. Due to this implication, cognitive reactivity is considered a target for therapeutic intervention to prevent depression onset, and was thus analyzed in this study.
40 healthy, non-depressed adults were selected and split into two groups, each receiving a 4-week regiment of a probiotic or a placebo. The participants filled out questionnaires before and after the regiment to assess cognitive reactivity and depression symptoms. Of the several behavioral indicators of cognitive reactivity that were assessed, aggression and rumination were significantly modified according to the behavioral questionnaires. Specifically, post-regiment scores in the probiotic group were significantly lowered from pre-regiment scores, and this was not observed in the placebo group. All told, this suggests that a probiotic regiment eased cognitive reactivity to aggressive and ruminative thoughts.
This study is the first to show that probiotics can modulate an important cognitive process that determines vulnerability to clinically diagnosed depression. These findings are additionally enlightening with respect to the gut microbiome’s role in overall cognitive health. As is often the case however, there were some limitations. Specifically, it would have been interesting to investigate biological underpinnings of these interactions in complementary animal models, especially in light of previous findings that indicate probiotics can facilitate microbiota to synthesize and release serotonin. On Monday we highlighted work done by Professor Diane Hsiao’s group at Cal Tech that stressed the gut microbiome’s role in serotonin production. As we mentioned, serotonin is implicated in many bodily functions, including a vast range of cognitive mechanisms. Indeed, serotonin systems have been primary target for therapeutic treatment of depression. Zoloft, one of the most highly prescribed antidepressants in the world, blocks serotonin metabolism to facilitate its endogenous mode of action in the brain.
Not only do the current findings complement those from the Cal Tech lab, but they also highlight an exciting new potential toward therapeutic approach. Conventional therapies that directly target serotonin systems can be ineffective and have many undesired side-effects and limitations. Understanding the microbiome’s role in serotonin production can give us more insight and perhaps pave a way toward a more organic therapeutic approach aimed at preventing and/or treating depression.