Investigating inflammation in depression in the chronically ill: Theoretical model and perspectives.

BACKGROUND:Inflammation is a risk factor for chronic physical illnesses. Evidence is building that inflammation is also a risk factor for mental illnesses making inflammation a common mechanism which could explain the high comorbidity between mental and physical illnesses. METHODS:Based on a systematic search, a review on factors associated with inflammation in the depressed chronically ill has been conducted. Relevant articles have been selected according to the methodological considerations (scope, sample size, type of analysis and bias). RESULTS:Five categories of factors mediate the association between chronic physical and mental illnesses: (1) social-demographic factors, (2) social-economic background, (3) adverse health behaviours, (4) psychological stress and (5) genetics. Psychological therapies and medication also moderate this association. A theoretical model of the interplay between inflammation, depression and chronic physical illness is then presented. DISCUSSION:Inflammation contribute to both chronic physical and mental illnesses. These conclusions support future advances in clinical and research practice, as well as training and education.