There is evidence that inflammation may play a role in the association between physical illness and depression. Our aim was to compare the impact of chronic medical conditions on incidence of depression and to examine if risk of depression varies in terms of the presence and degree of inflammation.

This is a secondary analysis conducted within the Spanish sample of the predictD-study. Participants: 5437. Primary outcome: Incident major depression measured with the Composite International Diagnostic Interview. Exposure: Presence of chronic medical conditions recorded by GPs using the International Classification of Primary Care, ICPC-2. All analyses were conducted using multivariable logistic regression to allow adjustment for confounders.

The odds of depression are higher in almost all inflammatory than in non-inflammatory illnesses. There is an increasing risk of depression as a consequence of an increasing inflammatory load, with higher odds of depression in the autoimmune group than in the cardio-metabolic group, while both had higher odds of depression than the non-inflammatory groups.

Inflammation may be part of the pathway by which chronic physical illness leads to depression. Future studies should examine the role of inflammation in the prevention and management of depression.