Inflammatory markers in persons with clinically-significant depression, anxiety or PTSD: A systematic review and meta-analysis

BACKGROUND: Depression, anxiety and PTSD appear to be risk factors for dementia, but it is unclear whether they are causal or prodromal. The inflammatory-mediated neurodegeneration hypothesis suggests a causal link, proposing that mental illness is associated with an inflammatory response which, in turn, triggers neurodegenerative changes that lead to dementia. Existing meta-analyses have yet to examine inflammatory markers in depression, anxiety or PTSD with the view to exploring the inflammatory-mediated neurodegeneration hypothesis. The current meta-analysis therefore examined whether: a) depression, anxiety and PTSD are individually associated with inflammation, independently of comorbid mental illnesses and physical health problems with known inflammatory responses, and b) there are any similarities in the inflammatory profiles of these disorders in order to provide a basis for exploring inflammation in people with dementia who have a history of clinically-significant anxiety, depression or PTSD. METHODS: PubMed, EMBASE, PsycINFO and CINAHL searches identified 64 eligible studies. RESULTS: Depression is associated with an inflammatory response, with tentative evidence to suggest anxiety and PTSD are also associated with inflammation. However, the specific response may differ across these disorders. LIMITATIONS: The data for anxiety, PTSD and multiple inflammatory markers were limited. CONCLUSIONS: Depression, anxiety, and PTSD each appear to be associated with an inflammatory response in persons who do not have comorbid mental or physical health problems that are known to be associated with inflammation. Whether this inflammatory response underlies the increased risk of dementia in persons with a history of depression and anxiety, and possibly PTSD, remains to be determined.