Do Probiotics Help Depression?
A recent study reviews gut microbiota in depressed individuals.
Posted Jun 23, 2020
Gut microbiota and probiotics
According to a review article by Sanada and colleagues, published in the April 2020 issue of Journal of Affective Disorders, people with depression appear to have reduced numbers of several populations of gut microbiota. The researchers also found that interventions using probiotics seem to improve symptoms of depression.1
Before looking at these findings, let me answer two basic questions: What are probiotics? And what is gut microbiota?
Probiotics are “microorganisms that confer health benefits to hosts when administered in adequate amounts” (p. S49).2 Much has been said about the health benefits of probiotics for depression. For instance, some health experts have encouraged the consumption of products containing probiotics (e.g., yogurt, kefir, sauerkraut, kimchi).
How are probiotics assumed to accomplish their beneficial actions? By modulating gut microbiota.
Gut microbiota refers to microorganisms (e.g., bacteria) residing in the gut. Gut microbiota is implicated in many processes, including ones involving the immune response and the brain. These processes and communication pathways (termed the microbiota-gut-brain axis) have important effects on how the body responds to stress. For instance, resilience (successful adaptation to stress) may require healthy gut microbiota.3
Research has shown that the composition of microorganisms in the intestines of people with certain mental health issues, such as depression, is different from those in the intestines of healthy individuals. Different in what way? And might probiotics help restore a healthy balance to the gut microbiota? To answer these questions, we turn to the review article by Sanada and colleagues.
Gut microbiota in depressed people and the use of probiotics for depression
Through a literature search and other sources, the authors identified 181 studies and articles on gut microbiota composition in patients with depression. Upon review, 22 of these papers were chosen for further assessment. The final list of studies included in the systematic review and meta-analysis consisted of 16 clinical trials: Ten (701 individuals) were observational, and six (302 individuals) were interventional.1
Analysis of data showed a number of differences in gut microbiota between patients with depression and healthy participants. Specifically, in patients with depression, some microbes, like the family Prevotellaceae, were less common. The same was true of the genus Coprococcus and genus Faecalibacterium.
But how do such differences in populations of microorganisms in the gut increase the likelihood of depression? The exact mechanisms are not clear. In the case of the family Prevotellaceae, for instance, the mechanisms may involve short-chain fatty acids (produced by several genera in the Prevotellaceae family), which might protect against depression.
The study also reviewed the potential benefits of probiotics for depression. The interventions reviewed had a large effect (SMD = -1.62, 95% CI = -2.73 to -0.51, p < 0.01) on the symptoms of depression. So probiotics appear to have a positive effect on depressive symptoms. Nevertheless, there were methodological limitations that reduce the strength of this finding (e.g., high risk of bias, and a small number of trials and sample sizes).
Hippocrates is reported to have said, “All disease begins in the gut.” Perhaps there is some truth to this claim, particularly when applied to major depression.
Though there is no consensus regarding the ideal gut microbiota composition, the research reviewed today suggests the populations of microorganisms in the guts of depressed people are significantly different from those in the guts of non-depressed individuals. This is important because stress may cause gut microbial imbalance, and this imbalance potentially increases vulnerability to depression.
The authors also concluded that probiotics seem to help reduce depressive symptoms. But this does not mean these microorganisms are a substitute for antidepressant medications or psychotherapy. Perhaps a day will come when probiotics are more strongly recommended, and when a specific strain and dose of bacteria are prescribed for the treatment of depression. But for now, as Athos Bousvaros of Harvard Medical School notes (not commenting on this paper), probiotics probably belong in the “doesn’t hurt, and might help” category.
1. Sanada, K., Nakajima, S., Kurokawa, S., Barceló-Soler, A., Ikuse, D., Hirata, A., ... & Kishimoto, T. (2020). Gut microbiota and major depressive disorder: a systematic review and meta-analysis. Journal of Affective Disorders, 266, 1-13.
2. Plaza-Diaz, J., Ruiz-Ojeda, F. J., Gil-Campos, M., & Gil, A. (2019). Mechanisms of action of probiotics. Advances in Nutrition, 10(suppl_1), S49-S66.
3. Cathomas, F., Murrough, J. W., Nestler, E. J., Han, M. H., & Russo, S. J. (2019). Neurobiology of resilience: Interface between mind and body. Biological Psychiatry, 86(6), 410-420.