Inflammation seems to contribute to at least some cases of depression, anxiety disorders and bipolar disorder. People with inflammatory diseases (e.g. inflammatory bowel disease, multiple sclerosis and rheumatoid arthritis) are at increased risk of developing psychiatric co-morbidities.

Now a new Canadian study in Epidemiology and Psychiatric Sciences reports that psychiatric conditions may emerge five years before the diagnosis of inflammatory diseases.

The study matched 3,766 people with IBD, 2,190 with MS and 6,350 with RA with 65,424 controls. After adjusting for age and sex, the incidence of depression and anxiety disorders was 54 and 30 per cent higher five years before diagnosis of the inflammatory disease compared with controls. In the year of diagnosis, the incidence was double.

The incidence of bipolar disorder was 63 per cent higher three years before the diagnosis of the inflammatory disease and 88 per cent higher in the year of diagnosis.

The 71 per cent increase in the incidence of schizophrenia in the year the inflammatory disease was diagnosed was not statistically significant, although the number of patients was small.

The consistency of the link across IBD, MS and RA “suggests a common underlying biology”, the authors conclude.

Future studies should determine whether the link between psychiatric and inflammatory disease reflects shared risk factors, a shared final common pathway or actually arises from other causes.

(Epidemiology and Psychiatric Sciences 2019; 28:333-342)