Using probiotics to treat depression

By Neha MathurReviewed by Benedette Cuffari, M.Sc.Mar 15 2023

In a recent study published in the journal Nutrients, researchers in Malaysia discuss whether Lactobacillus and Bifidobacterium probiotics, which are the most widely studied and commercialized bacterial strains, could be used as supplementary or primary therapy to manage major depressive disorder (MDD). Herein, an evolutionary approach was used to find a conceptual framework of probiotics that could successfully fit into the precision psychiatry model, which has the ultimate goal of achieving personalized care.

Study: Microbial-Based Approach to Mental Health: The Potential of Probiotics in the Treatment of Depression. Image Credit: SciePro / Shutterstock.com

Background

Mental health is a critical healthcare domain; however, treatment options for mental health conditions remain limited.

Clinical depression, which is the most common neuropsychiatric disorder, affects nearly 322 million people worldwide. During the coronavirus disease 2019 (COVID-19) pandemic, clinical depression surged as a global health concern.

Studies have shown that different strains of probiotics use varied mechanisms to exert anti-depression effects. Given the vast potential of probiotics, including their anti-depressive potential to improve human health, researchers should explore whether probiotics could be used as a new and customizable treatment for this potentially fatal disorder.

Several studies have advocated using personalized probiotics to manage psychiatric disorders. Psychiatric disorders cannot be diagnosed through conventional imaging modalities; therefore, their diagnosis still largely depends on clinical expertise.

As a result, researchers have postulated that the precision psychiatry model, which considers all possible underlying neurobiological mechanisms, as well as environmental and lifestyle influences through the development of a psychiatric disorder, could help optimize its treatment.

Role of gut microbiota in depression

The human microbiota refers to all symbiotic microbes residing in and on the human body, including archaea, fungi, bacteria, protists, and viruses. As the colon houses over 1,000 bacterial species and over 7,000 strains, it is the largest reservoir of microbiota in the human body.

Although microbes are abundant in number, they comprise about 0.3% of the human body mass due to their insignificant volume. Nevertheless, the human microbiota has an indisputable role in human physio- and pathophysiology, with some scientists considering the gut microbiota a human organ.

Firmicutes, Actinobacteria, Bacteroidetes, Proteobacteria, Firmicutes, Bacteroidetes, Fusobacteria, and Verrucomicrobia, account for over 90% of bacterial species found in the gut microbiota. Lactobacillus and Bifidobacterium, which belong to Firmicutes and Actinobacteria phyla, respectively, are among the dominant natural residents within the human gastrointestinal (GI) tract and may directly or indirectly interact with hosts through their byproducts.

In a population-based European cohort study exploring the association of the gut microbiome with depression at the genome level, the researchers observed that the gut microbiome played a crucial role in depression. While 12 genera and one bacterial family correlated with depressive symptoms, Eggerthella showed a causal relationship with MDD. Indeed, the gut microbiota is the primary embodiment of communication within the gut-brain loop.

Although previous studies have not identified a standardized pattern of gut microbial dysbiosis in MDD patients, individuals with MDD frequently have significantly lower counts of Lactobacillus and Bifidobacterium as compared to healthy controls. Thus, probiotic supplementation could positively impact human health by endorsing the biotherapeutic activity of symbionts and suppressing the activity of pathobionts.

Lactobacillus and Bifidobacterium are gram-positive and anaerobic bacterial species that produce lactic acid as their primary metabolite and are among the first colonizers of the human gut. Accordingly, these species are naturally well-equipped to survive the various physiological stressors throughout the GI tract.

Clinical management of depression through probiotics

Microbial-based biomarkers, which can be assessed through a simple blood test, could provide a new dimension in the diagnosis of MDD. Some common examples of these biomarkers include pro-inflammatory cytokines, brain-derived neurotrophic factor (BDNF), kynurenine, and cortisol.

Previous studies have shown that neuroimaging tools like magnetic resonance imaging (MRI) can capture structural and functional changes within the human brain and correlate these findings with gut microbiota profiling and neuropsychological scorings.

Functional and structural assessments of the hippocampus and amygdala, both of which are limbic regions of the brain, and their neuronal circuitry through MRI could also help diagnose MDD. Thereafter, these patients could receive personalized probiotic complementing therapy.

The researchers also advocated metabiotics, which is a microbial-based application for clinical depression treatment. Metabiotics involve using metabolites of probiotic bacteria found within the human gut microbiota to achieve targeted psychiatric health outcomes.

Conclusions

Probiotics have immense potential as therapeutics for MDD and other psychiatric disorders. However, validating probiotics usage for mental health disorders like clinical depression remains challenging due to the scarcity of research in this area. Nevertheless, with the increased acceptance of precision psychiatry, the personalization of probiotics for clinical depression is expected to increase.

Probiotics could also serve as an adjunct and stand-alone treatment in mild MDD patients who do not require pharmacological treatment. Furthermore, probiotics could serve as a preventive intervention for individuals at a higher risk of developing MDD.