Inflammation from Infections and Autoimmune Diseases Increases Risk of Mood Disorders

A study published online in JAMA Psychiatry found that hospitalization for an infection or an autoimmune disease increased the risk of a subsequent mood disorder diagnosis.

Inflammation that can result from a severe infection or autoimmune disease may contribute to the development of mental illness later in life, a study published online June 12, 2013, in JAMA Psychiatry indicated.

Prior studies have linked the development of mood disorders with inflammation and demonstrated that pro-inflammatory cytokines and brain-reactive antibodies produced as a result of an immune response can induce neurotransmitter changes related to certain psychiatric disorders. In addition, animal studies have suggested that inflammation causes the same blood-central nervous system (CNS) barrier dysfunction that is the hallmark of severe depression.

There has also been a reported connection between infection and autoimmunity; infection has been said to cause “autoantibody-mediated central nervous system (CNS) disorders,” according to the authors of the current study.

From January 1, 1977, through December 31, 2010, the researchers followed 91,637 patients included in the Danish Psychiatric Central Research Register who had a history of hospitalization for a mood disorder. Before receiving their mood disorder diagnosis, 29,194 participants had been diagnosed with 1 or more infections, 4195 had been diagnosed with 1 or more autoimmune diseases, and 2113 had been diagnosed with both an infection and an autoimmune disease.

The results of the study indicated that any history of hospitalization for infection increased the risk of mood disorders by 62%. Autoimmune disease hospitalizations increased the risk of mood disorders by 45% after accounting for the effect of infections. Patients with a history of hospitalization for both autoimmune disease and infection were 2.35 times more likely to develop a mood disorder, which the researchers wrote may be due to the “synergistic effect” of the biological interactions that can occur between autoimmune disease and infections.

The authors of the study noted that the link between autoimmune disease or infections and mood disturbances may be explained in part by a common factor: inflammation. “The increased inflammation that occurs in autoimmune diseases and infections may influence the brain through increased blood-CNS barrier permeability, making the brain vulnerable to infectious agents and immune components, such as cytokines and brain-reactive antibodies,” they wrote. In other words, long-term inflammatory activity has the capability to induce a “sickness behavior,” which could further activate an immunologic response and create an imbalance in the levels of neurotransmitters known to affect mood, such as serotonin and cortisol.

The authors also pointed out that the inflammation involved in infections and autoimmune diseases and its association with mental problems could, in fact, be “bidirectional because psychological stress associated with mood disorders might also be a trigger for autoimmune disease activity and infections.”