A Look at Microbes in Schizophrenia

Guest BloggerClinical Corner, Microbiome Environment


Marked by delusions and hallucinations, schizophrenia is not uncommon. More than 50 million people or 1% of humans suffer with this devastating psychiatric disorder.

What causes schizophrenia?

Researchers believe that a combination of genetics, brain chemistry and environment contributes to development of the disorder. The gut-brain axis may be one pathway.

Risk factors for schizophrenia

  • Family history of schizophrenia
  • Older age of the father
  • Some pregnancy and birth complications, including malnutrition or exposure to toxins or viruses that may impact brain development
  • Taking psychoactive or psychotropic drugs during teen years and young adulthood
  • Increased immune system activation, such as from inflammation or autoimmune diseases

Immune system troubles are where the microbiome emerges as a player in the disorder. And in another clue, antipsychotics, routinely given as treatment in schizophrenia patients, produce anti-inflammatory effects.

In the past, an autoimmune process along with excess immune activation has been found in subgroups of schizophrenia patients.

A role for microbiota

The role of microbiota in the pathogenesis of schizophrenia and major depressive disorder and the possibility of targeting microbiota as a treatment option which appeared in Oncotarget in 2017 nicely reviews the data.

In one study cited, schizophrenic patients had more Lactobacillus in oral samples than normal controls. Numbers correlated with severity of symptoms in another study.

The pathogenesis of schizophrenia is not fully understood; however, a decrease in brain-derived neurotrophic factor (BDNF) expression and the resultant hypoactivity in N-methyl-D-aspartate (NMDA) receptor have been implicated in the pathology of schizophrenia.

  • As we know, dysregulation of microbiota, or dysbiosis, can play a key role in the pathogenesis of inflammatory diseases in the host. Microbiota can impact the structure of the brain. Brain volume can be affected. Furthermore, bacteria-derived metabolites could affect the expression of BDNF and other proteins that are important in cognition, which in turn affects host behavior.
  • In addition, changes in the composition of microbiota as a feature of schizophrenia might induce an immune response and contribute to symptoms of the disorder.
  • Dysregulation in the metabolic pathway of tryptophan has been implicated in the pathogenesis of schizophrenia.  An increased level of a tryptophan metabolite called kynurenic acid in the central nervous system has been found in schizophrenia patients. And gut microbiota influence the level of plasma tryptophan, thereby presenting an interesting link.
  • Early exposures or lack thereof such as during vaginal vs C-section delivery have been looked at. However, further analyses did not find that birth by cesarean section was correlated with schizophrenia. Nevertheless, further examination of early-life events, including mode of delivery, type of feeding, and use of antibiotics by the mother is needed.

A trial with probiotics in schizophrenia patients

One study investigated the effects of supplemental probiotics on the symptoms of schizophrenia and gastrointestinal function. Recruited schizophrenia patients were given strains of Lactobacillus rhamnosus and Bifidobacterium animalis or placebos for 14 weeks. While no improvement in schizophrenia symptoms was seen, the probiotic group showed improved gut function.


Gut microbiota can affect the brain by releasing essential amino acids and participating in the immune and inflammatory responses AND the brain can change specific bacterial species.

The microbiota is a valid target in the search for effective treatments for schizophrenia.