Gut Microbiomes and Mental Health

One exciting and emerging field of mental health research which is gaining in popularity is the relationship between microbiomes in our gut, and our mental health. Our gut microbiome contains up to 1 trillion bacteria, as well as viruses and fungi, which form a kind of ‘eco-system’. Our microbiome begins forming after birth, and can be influenced by factors such a environment, diet, travel, hormones and illness (D’Argenio & Salvatore, 2015). It is crucial in digestion and our immune system, and recent research suggests that having a healthy microbiome is important for a healthy brain and nervous system (Foster & Neufeld, 2013).

Research into the link between the gut and brain (known as the microbiota-gut-brain axis – see image below) has found links between dysfunction in the microbiome and mental illness such as depression and anxiety (Foster & Neufeld, 2013).


For example, one study carried out at Stellenbosch University compared the gut microbiomes of people with and without Posttraumatic Stress Disorder (PTSD) after experiencing a traumatic event. They found that three bacteria were different in people who did and did not have PTSD, with those with PTSD showing lower levels (Hemmings et al, 2017).

Lots of research in this area has also been carried out using mice, which has shown that the microbiome can directly affect behaviour. For example, one study transplanted bacteria from mice who had high anxiety to mice who had low anxiety. The mice who had received the transplant then started to show symptoms of anxiety (Bercik et al., 2011a).

The interaction between the gut and brain can also work the other way, as stress and emotions can influence the microbiome via the hypothalamus–pituitary–adrenal (HPA) axis (Montiel-Castro et al., 2013). The HPA axis is involved in cortisol production and controls our immune system. Stress results in increased inflammation, which impacts the equilibrium of the microbiome which can lead to diseases, allergic reactions or risk of infection (Glaser & Kiecolt-Glaser, 2005).

This field of research could influence therapies for mental illness, with anxiety and depression treated by interventions targeted to alter the microbiome, as well as traditional drug or talking therapies. What are your thoughts about this new branch of medicine? Let me know in the comments below!



Bercik, P., Park, A. J., Sinclair D. Khoshdel, A., Lu J. Huang, X., Deng, Y., Belnnerhassett, P. A., et al. (2011a). The anxiolytic effect of Bifidobacterium longum NCC3001 involves vagal pathways for gut–brain communication. Neurogastroenterol. Motil. 23, 1132–1139.

D’Argenio, V. and Salvatore, F., 2015. The role of the gut microbiome in the healthy adult status. Clinica Chimica Acta451, pp.97-102.

Foster, J.A. and Neufeld, K.A.M., 2013. Gut–brain axis: how the microbiome influences anxiety and depression. Trends in neurosciences36(5), pp.305-312.

Glaser, R., and Kiecolt-Glaser, J. K. (2005). Stress-induced immune dysfunction: implications for health. Nat. Rev. Immunol. 5, 243–251. doi: 10.1038/nri1571

Hemmings, S.M., Malan-Müller, S., van den Heuvel, L.L., Demmitt, B.A., Stanislawski, M.A., Smith, D.G., Bohr, A.D., Stamper, C.E., Hyde, E.R., Morton, J.T. and Marotz, C.A., 2017. The microbiome in posttraumatic stress disorder and trauma-exposed controls: an exploratory study. Psychosomatic medicine79(8), pp.936-946.

Montiel-Castro, A.J., González-Cervantes, R.M., Bravo-Ruiseco, G. and Pacheco-López, G., 2013. The microbiota-gut-brain axis: neurobehavioral correlates, health and sociality. Frontiers in integrative neuroscience7, p.70.

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