Autoimmune disorders and infections may increase patients' risk for mood disorders, according to a new study.
Researchers performed a nationwide population-based prospective cohort study to evaluate the relationship between risk for mood disorders and autoimmune diseases and infections. Data encompassing 78 million person-years of follow-up were obtained from longitudinal registers in Denmark. Survival analysis techniques were used for analysis, and data were adjusted for calendar year, age and sex. The study's main outcome measure was the risk for first lifetime diagnosis of a mood disorder from a psychiatrist at a hospital, outpatient clinic or emergency department.
Mood disorders were classified as bipolar affective disorder, unipolar depression, psychotic depression, or a group of any of the remaining mood disorders. Results were published early online June 12 by JAMA Psychiatry.
Overall, 3.56 million people born between 1945 and 1996 were followed from Jan. 1, 1977, through Dec. 31, 2010. Of these, 91,637 (55,677 women and 35,960 men) were diagnosed with a mood disorder.
Previous hospital contact because of autoimmune disease appeared to increase the subsequent risk for mood disorder diagnosis (incidence rate ratio [IRR], 1.45; 95% CI, 1.39 to 1.52), as did history of hospitalization for infection (IRR, 1.62; 95% CI, 1.60 to 1.64). When both of these risk factors were present, the mood disorder risk appeared even higher (IRR, 2.35; 95% CI, 2.25 to 2.46), and a dose-response relationship was noted. Thirty-two percent and 5% of patients with mood disorders had previous hospital contact for infection and autoimmune disease, respectively.
The authors acknowledged that recording of the time of disease onset may have been biased and that their study did not include less severe cases of any of the disorders studied. However, they wrote, “The associations found in this study suggest that autoimmune diseases and infections are important etiologic factors in the development of mood disorders in subgroups of the patients possibly because of the effects of inflammatory activity.” It's still unclear, they said, how the brain is affected by the immunologic process and whether there is a causal relationship.