People suffering from schizophrenia are at greater risk of developing autoimmune diseases such as psoriasis and multiple sclerosis. This is the conclusion of new research from Aarhus University. It appears that infections play a determining role.

Researchers have long known that people with autoimmune diseases, such as hepatitis, type 1 diabetes, multiple sclerosis and psoriasis, are at greater risk of developing schizophrenia.

But new research based on data sets covering the majority of the Danish population shows that the development goes both ways: People suffering from schizophrenia also have an increased risk of contracting autoimmune diseases, especially if they have suffered from a severe infection.

Head of the new study is Michael Eriksen Benrós, MD and PhD, who is senior researcher at the National Centre for Register-Based Research at Aarhus University and the Psychiatric Centre Copenhagen. He has done the study in collaboration with researchers from Aarhus University and the University of Copenhagen as well as Johns Hopkins University in the USA.

This month the results will be published in an article in the internationally renowned American journal The American Journal of Psychiatry.

Three times higher risk

Drawing on data from the Danish Civil Registration, Danish hospitals and the nation-wide Danish Psychiatric Central Research Register, the researchers behind the project have had the unique opportunity to examine an extraordinarily large group of people consisting of 3.83 million Danes. The registry data showed that from 1987 to 2010 39,364 people were diagnosed with schizophrenia, while 142,328 people were diagnosed with an autoimmune disease.

By linking the data sets, the researchers found that a person suffering from schizophrenia has a 53 per cent higher risk of contracting an autoimmune disease compared to people who are not suffering from schizophrenia. Moreover, if you have schizophrenia and have been hospitalised or received treatment for a severe infection, you have a 2.7 times higher risk of getting an autoimmune disease.

According to Michael E. Benrós, this is very useful knowledge for psychiatrists working with schizophrenics:

“Six per cent of the schizophrenic patients have an autoimmune disease that requires treatment in a hospital. But the actual occurrence is significantly higher, seeing as our study does not incorporate all the people who are being treated by general physicians or have not been diagnosed yet. This means that psychiatrists should be on the lookout for signs of physical illness among their patients with schizophrenia, including autoimmune diseases,” explains Michael E. Benrós.