Are non-communicable diseases communicable? The role of the microbiome in mental illness

Gut microbes influence brain function and behaviour through a variety of neural, endocrine and immune mechanisms — the microbiota–gut–brain axis. Professor Valerie Taylor of the University of Calgary highlighted results of research linking the gut microbiome to the pathophysiology of bipolar and mood disorders in a keynote presentation for ISBD 2020.

How do gut microbes affect the brain?

Microbial composition, immune activation, Vagus nerve signaling, tryptophan metabolism, and microbial metabolites are contributory factors to the effects of gut microbes on brain function and behaviour,1 explained Professor Taylor.

Gut microbes produce neurotransmitters and modulate neurotransmitter receptors2–4

Gut microbes produce neurotransmitters that modulate behavior including norepinephrine2 and serotonin,3 and modulate the expression of neurotransmitter receptors, including mu-opioid and cannabinoid receptors.4

Most research so far has been preclinical, said Professor Taylor, and it is not clear how to extrapolate the data to clinical care.

[For more on these mechanisms, click here]

Links between the gut microbiome and bipolar disorder

Gut microbiota of people with bipolar disorder differs from that of healthy controls7

Research results demonstrating preliminary signals linking the gut microbiome to bipolar disorder include the following:

  • patients recently discharged following hospitalization for mania whose treatment included probiotic supplementation had a lower rate of rehospitalization5
  • patients with bipolar disorder compared to healthy controls had:
    • a significantly decreased fractional representation (p<0.001) of Faecalibacterium6 
    • significantly more of the phylum Actinobateria and class Coriobacteria7
  • a negative correlation between microbial alpha‐diversity and illness duration7

Is depression communicable?

Depression is associated with decreased gut microbiota diversity

The role of the gut microbiome in a range of psychiatric disorders, including depression and anxiety, has become a major focus of scientific interest, for more click here.

Depression is associated with decreased gut microbiota richness and diversity, said Professor Taylor, and this may play a causal role in the development of depressive features:8

  • fecal microbiota transplantation (FMT) that increases microbiota diversity improves depressive and anxiety symptoms9
  • microbiota-depleted rats who receive FMT from people who have major depressive disorder (MDD) develop behavioral and physiologic features characteristic of depression, including anhedonia and anxiety-like behaviors, as well as alterations in tryptophan metabolism8

For more information on the microbiome and brain disorders, please click here

Our correspondent’s highlights from the symposium are meant as a fair representation of the scientific content presented. The views and opinions expressed on this page do not necessarily reflect those of Lundbeck.


  1. Cryan JF, Dinan TG. Nat Rev Neurosci 2012;13:701–12.
  2. Lyte M. PLoS Pathog 9(11): e1003726.
  3. Wikoff WR, et al. PNAS 2009;106:3698–703.
  4. Rousseaux C, et al. Nat Med 2007;13:35–7.
  5. Dickerson F, et al. Bipolar Disorders 2018;20:614–21.
  6. Evans SJ, et al. J Psychiatr Res 2017;87:23–29.
  7. Painold A, et al. Bipolar Disorders 2019;21:40–9.
  8. Kelly JR, et al. J Psychiatr Res 2016;82:109-18.
  9. Kurokawa S, et al. J Affect Disord 2018 Aug 1;235:506-512.