Autoimmune diseases and infections appear to be risk factors for a subsequent mood disorder diagnosis, according to a new study from Denmark.
A total of 91,637 people born in Denmark between 1945 and 1996 were found to have visited a hospital for a mood disorder. Dr Michael Benros of Aarhus University and his research colleagues found a prior hospital contact because of autoimmune disease increased the risk of a subsequent mood disorder diagnosis by 45 per cent. Any history of hospitalisation for infection increased the risk of later mood disorders by 62 per cent.
Approximately one-third (32 per cent) of the participants diagnosed as having a mood disorder had a previous hospital contact because of an infection, whereas 5 per cent had a previous hospital contact because of an autoimmune disease, the study found.
The team found that the risk of mood disorders increased with the temporal proximity of the last infection, especially in persons with autoimmune diseases for whom an infection within the past year increased the risk of mood disorders more than four times, suggesting that the results might be due to a contemporary inflammatory process.
Hospital contacts for infections increased the risk of mood disorders in a dose-response relationship, with individuals with five or more hospital contacts with different types of infections having an increased risk of subsequent mood disorders of almost five times.
It remains unclear, however, whether the results can be generalised to the more frequently-occurring, less severe infections and mood disorders treated by the GP or to those going untreated because only hospital contacts are included in the Danish national registers.
“Autoimmune disease and the number of severe infections are independent and synergistic risk factors for mood disorders, with hospital-treated infections being the most common risk factor… these associations are compatible with the hypothesis of a general immunologic response affecting the brain in subgroups of patients with mood disorders,” the study concluded.
Although the hypothesis of an immunologic contribution was interesting, the researchers added that it remained unclear precisely how the immunologic process affected the brain and whether it was a causal relationship or an epiphenomenon of underlying genetic, psychological or non-immune-related mechanisms.
JAMA Psychiatry. Published online June 12, 2013. doi:10.1001/jamapsychiatry.2013.1111.
