Although previous research indicates that there exists a correlation between autoimmune disorders and psychosis, conflicting findings have made it difficult for researchers to reach definitive conclusions about the relationship between the two. Prompted by this, researchers from King’s College London conducted a meta-analysis of 30 studies, containing data of 25 million people total.

Their findings were published in the peer-reviewed journal Biological Psychiatry. Titled, “Associations Between Non-Neurological Autoimmune Disorders and Psychosis,” the meta-analysis was authored by Alexis E. Cullen, Scarlett Holmes, Dan W. Joyce, Matthew J. Kempton, Thomas A. Pollak, Graham Blackman, Robin M. Murray, Philip McGuire, and Valeria Mondelli.

King’s College London researchers focused on autoimmune disorders that affect the peripheral system. In particular, the focus was on disorders that target the body, as opposed to the brain, in order to see whether autoimmune disorders that target the body could still affect the mind.

For the main analysis, the researchers combined data from all non-neurological autoimmune disorders, bar one: rheumatoid arthritis. Rheumatoid arthritis was exempt from the analysis, since the negative association between the disorder and psychosis has been established by previous studies, the researchers noted. The primary analysis found that individuals with any autoimmune disorder were 40 percent more likely to have a psychotic disorder.

For the secondary analysis, King’s College London researchers examined individual autoimmune disorders, concluding that the likelihood of having psychosis was higher among individuals suffering from pemphigoid, psoriasis, coeliac disease, Grave’s disease, and pernicious anaemia. The likelihood was, however, lower for individuals suffering from ankylosing spondylitis and rheumatoid arthritis.

It remains unclear what exactly causes this, but the researchers noted that inflammation is the most likely candidate, considering individuals suffering from psychosis have been found to show higher levels of inflammatory markers in the blood and considering the fact that inflammation is inherent to autoimmune disorders.

Inflammation, however, cannot be the only underlying mechanism, the researchers noted, since autoimmune diseases such as ankylosing spondylitis and rheumatoid arthritis are also characterized by higher levels of inflammation. Genetics, however, could also play a part.

The researchers concluded the following.

“Regardless of the mechanism, these findings suggest that careful monitoring of individuals with specific autoimmune diseases (particularly anaemia, Graves’ disease, and pemphigoid, as these were the most consistent effects) for early signs of psychosis is warranted.”

“Our study shows that overall, people with any autoimmune disorder are around 40 percent more likely to develop psychotic disorders such as schizophrenia. The finding that psychosis is associated with non-neurological autoimmune disorders, which are not known to directly target the brain, is particularly important,” lead researcher Dr. Alexis Cullen said in a press release published on the KCL‘s official website.