According to researchers at Aarhus University in Denmark, infections may play a determining role in the connection.
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 this new research 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, according to scientists.
For the study, researchers examined data on more than 3.8 million people from the Danish Civil Registration, Danish hospitals, and the nationwide Danish Psychiatric Central Research Register. 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.
Upon further examination, the researchers found that a person suffering from schizophrenia has a 53 percent higher risk of contracting an autoimmune disease compared to people who are not suffering from schizophrenia. Moreover, those who have schizophrenia and have been hospitalized or received treatment for a severe infection have a 2.7 times higher risk of getting an autoimmune disease.
According to Michael Eriksen Benrós, M.D., Ph.D., a senior researcher at the National Centre for Register-Based Research at Aarhus University and the Psychiatric Centre Copenhagen, “this information will be very useful for psychiatrists working with schizophrenics. That’s because six percent of schizophrenic patients have an autoimmune disease that requires treatment in a hospital,” he said.
“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,” he said. “This means that psychiatrists should be on the lookout for signs of physical illness among their patients with schizophrenia, including autoimmune diseases.”
While the researchers were able to show a correlation between schizophrenia and autoimmune disease, they note that the study does not provide a definitive explanation for why schizophrenics have such an increased risk of contracting these diseases.
According to Benrós, a lot of the data points to infections as a determining factor.
“It could be that people with schizophrenia are genetically vulnerable to infections, which increases the risk of getting schizophrenia but also autoimmune diseases,” he said.
He explained that the immune system reacts to an infection by producing antibodies that do not just react to the infection — they also start breaking down the body’s own tissue. This is how autoimmune diseases develop.
“Another possible explanation could be that symptoms diagnosed as schizophrenia are the first signs that an autoimmune disease has developed, but has not yet been detected,” he said.
Other explanations are related to lifestyle and genetics. In the study, the researchers also examined whether family members of people with schizophrenia also have an increased risk of getting an autoimmune disease.
“If you have a family member with schizophrenia, there is a six percent higher chance that you yourself will develop an autoimmune disease. The genetic factor does not look to be so significant, even though genetic studies have shown a correlation between genes and schizophrenia,” said Benrós.
The next step is for the researchers to try and combine the registry data with biological data, such as blood samples, to further examine possible interactions between genes and environment.
The study was published in The American Journal of Psychiatry.
Source: Aarhus University