Clinical Microbiology: Open Access

Microbiome and Mental Health: The Gut-Brain Axis

Chong Wen^* Department of Obstetrics and Gynecology, China Medical University, Shenyang, China
^*Correspondence: Chong Wen, Department of Obstetrics and Gynecology, China Medical University, Shenyang, China, Email:

Received: 27-Feb-2025, Manuscript No. CMO-25-28509; Editor assigned: 01-Mar-2025, Pre QC No. CMO-25-28509 (PQ); Reviewed: 07-Mar-2025, QC No. CMO-25-28509; Revised: 14-Mar-2025, Manuscript No. CMO-25-28509 (R); Published: 28-Mar-2025, DOI: 10.35248/ 2327-5073.25.14.428

Description

The human body is home to trillions of microorganisms, collectively known as the microbiome, which play necessary roles in health and disease. Among the various microbiomes in the body, the gut microbiome has achieved significant attention for its influence on both physical and mental health. Research has increasingly shown that the gut microbiota communicates with the brain through a bidirectional pathway known as the gutbrain axis. This communication system links the digestive system to the central nervous system, affecting mood, cognition and even psychiatric disorders. Understanding the connection between the microbiome and mental health may lead to new strategies for preventing and treating neurological and psychiatric conditions.

Understanding the gut-brain axis

The gut-brain axis is a complex network of interactions involving the gut microbiota, the nervous system, the immune system and metabolic pathways. This connection allows the gut to influence brain function and vice versa. The key components of this communication system include:

The vagus nerve: The vagus nerve is a major pathway that connects the gut to the brain. It transmits signals from the gastrointestinal tract to the central nervous system, allowing the gut microbiota to influence brain activity. Studies have shown that stimulating the vagus nerve can have antidepressant effects, highlighting its role in mood regulation [1].

Neurotransmitters and metabolites: Gut bacteria plays an important role in producing neurotransmitters such as serotonin, dopamine and Gamma-Aminobutyric Acid (GABA), which are necessary for mood regulation. For example, about 90% of the body's serotonin, a key neurotransmitter in mood stabilization, is produced in the gut. Additionally, bacterial metabolites such as Short-Chain Fatty Acids (SCFAs) influence brain function and behavior.

The immune system: The gut microbiome plays a significant role in modulating the immune system, which, in turn, affects brain health. Chronic inflammation, often linked to gut dysbiosis (microbial imbalance), has been associated with mental health disorders such as depression and anxiety. Beneficial bacteria help regulate immune responses, reducing inflammation and promoting mental well-being [2,3].

The endocrine system and stress response: The gut microbiota influences the Hypothalamic-Pituitary-Adrenal (HPA) axis, which controls the body's response to stress. An imbalance in gut bacteria can lead to an overactive HPA axis, resulting in elevated levels of cortisol (the stress hormone). High cortisol levels have been linked to anxiety, depression and cognitive impairment.

The Microbiome’s role in mental health disorders

Disruptions in the gut microbiome have been implicated in various mental health conditions, including depression, anxiety and schizophrenia and autism spectrum disorder.

Depression and anxiety: Several studies have found that individuals with depression and anxiety often have an altered gut microbiome, with reduced levels of beneficial bacteria such as Lactobacillus and Bifidobacterium. These bacteria are known to produce mood-enhancing neurotransmitters and regulate inflammation.

A landmark study on germ-free mice (mice raised without gut bacteria) showed that they exhibited higher levels of stress and anxiety-like behaviors compared to normal mice. When their microbiome was restored, their behavior improved, suggesting a direct link between gut bacteria and mood regulation [4,5].

Schizophrenia and psychosis: Emerging research suggests that gut microbiome alterations may contribute to schizophrenia and psychotic disorders. Individuals with schizophrenia often have increased gut inflammation and reduced microbial diversity. Some studies have proposed that microbial metabolites influence dopamine pathways, which are heavily implicated in schizophrenia.

Autism Spectrum Disorder (ASD): The gut-brain connection is particularly evident in Autism Spectrum Disorder (ASD). Many individuals with ASD experience gastrointestinal issues, such as Irritable Bowel Syndrome (IBS) and chronic constipation, which suggests a link between gut health and neurological function [6].

Fecal Microbiota Transplantation (FMT), a procedure that restores the gut microbiome by transferring fecal bacteria from a healthy donor, has shown potential results in reducing ASD symptoms.

Cognitive function and neurodegenerative diseases: The gut microbiome also influences cognitive function and the risk of neurodegenerative diseases such as Alzheimer’s and Parkinson’s disease.

In Alzheimer’s disease, gut dysbiosis has been linked to increased inflammation and the accumulation of amyloid plaques in the brain.

In Parkinson’s disease, specific gut bacteria have been associated with disease progression, with some studies suggesting that guttargeted therapies could slow neurodegeneration [7,8].

Modulating the gut microbiome for mental health

Given the strong connection between the microbiome and mental health, researchers are exploring ways to modulate gut bacteria as a therapeutic strategy.

Probiotics and prebiotics: Probiotics are live beneficial bacteria that can improve gut health. Strains such as Lactobacillus and Bifidobacterium have been shown to reduce symptoms of anxiety and depression.

Prebiotics are dietary fibers that feed beneficial gut bacteria, promoting their growth and activity. Foods rich in prebiotics include garlic, onions, bananas and whole grains.

Diet and nutrition: A diet rich in fiber, fermented foods and polyphenols supports a healthy gut microbiome. The Mediterranean diet, which includes fruits, vegetables, whole grains and healthy fats, has been associated with a reduced risk of depression and improved cognitive function.

Fecal Microbiota Transplantation (FMT): FMT involves transferring gut bacteria from a healthy donor to a recipient with a disrupted microbiome. While primarily used to treat severe gut infections, FMT is being investigated for its potential in treating psychiatric and neurological disorders [9,10].

Conclusion

The gut-brain axis is a critical pathway linking the microbiome to mental health. The gut microbiota influences brain function through neurotransmitter production, immune modulation and stress regulation. Imbalances in the microbiome have been associated with various mental health disorders, including depression, anxiety, schizophrenia and autism. Emerging research suggests that targeting the gut microbiome through probiotics, diet and lifestyle interventions may offer new approaches for mental health treatment.

References

1. Singh S, Sharma P, Pal N, Kumawat M, Shubham S, Sarma DK, et al. Impact of environmental pollutants on gut microbiome and mental health via the gut–brain axis. Microorganisms. 2022;10(7):1457.

   [Crossref] [Google Scholar] [PubMed]

2. Dinan TG, Cryan JF. The microbiome-gut-brain axis in health and disease. Gastroenterol Clin North Am. 2017;46(1):77-89.

   [Crossref] [Google Scholar] [PubMed]

3. Skonieczna-Å»ydecka K, Marlicz W, Misera A, Koulaouzidis A, Łoniewski I. Microbiome—the missing link in the gut-brain axis: Focus on its role in gastrointestinal and mental health. J Clin Med. 2018;7(12):521.

   [Crossref] [Google Scholar] [PubMed]

4. Verma A, Inslicht SS, Bhargava A. Gut-brain axis: Role of microbiome, metabolomics, hormones and stress in mental health disorders. Cells. 2024;13(17):1436.

   [Crossref] [Google Scholar] [PubMed]

5. Góralczyk-BiÅ?kowska A, Szmajda-Krygier D, KozÅ?owska E. The microbiota–gut–brain Axis in psychiatric disorders. Int J Mol Sci. 2022;23(19):11245.

   [Crossref] [Google Scholar] [PubMed]

6. Foster JA, Rinaman L, Cryan JF. Stress & the gut-brain axis: Regulation by the microbiome. Neurobiol Stress. 2017;7:124-136.

   [Crossref] [Google Scholar] [PubMed]

7. Appleton J. The gut-brain axis: Influence of microbiota on mood and mental health. Integr Med (Encinitas). 2018;17(4):28.

   [Crossref] [Google Scholar] [PubMed]

8. Bhatia NY, Jalgaonkar MP, Hargude AB, Sherje AP, Oza MJ, Doshi GM. Gut-brain axis and neurological disorders-how microbiomes affect our mental health. CNS Neurol Disord Drug Targets. 2023;22(7):1008-1030.

   [Crossref] [Google Scholar] [PubMed]

9. Foster JA, Neufeld KA. Gut–brain axis: How the microbiome influences anxiety and depression. Trends Neurosci. 2013;36(5):305-312.

   [Crossref] [Google Scholar] [PubMed]

10. Berding K, Vlckova K, Marx W, Schellekens H, Stanton C, Clarke G, et al. Diet and the microbiota–gut–brain axis: Sowing the seeds of good mental health. Adv Nutr. 2021;12(4):1239-1285.

    [Crossref] [Google Scholar] [PubMed]