A prospective study of the association between depression and inflammation in type 2 diabetes

Abstract

There is a bidirectional association between type 2 diabetes mellitus and depression. People with type 2 diabetes mellitus and comorbid depression have an increased risk of premature mortality. Type 2 diabetes mellitus has an underlying inflammatory basis, and there may be related underlying inflammatory process in depression. However, there is little knowledge of how systemic inflammation is involved in this depression-diabetes link. This thesis examines whether there is a correlation between concentrations of 12 inflammatory markers and depressive symptoms in newly diagnosed type 2 diabetes mellitus. The primary hypothesis was that those with depression are more likely to have higher concentrations of inflammatory markers compared to those that are not depressed, adjusting for confounding (including obesity). The design was a prospective cohort derived from the South London Diabetes Cohort (n = 1790). Patients were recruited < 6 months post diagnosis of type 2 diabetes mellitus and followed-up at 12 months. Depressive symptoms were assessed using the Patient Health Questionnaire-9 and inflammation was measured using standard hospital assays and a biochip immunoassay. Multiple linear regression was used to adjust for covariates and factor analysis was used to identify underlying latent factors to explain the observed association between inflammatory markers and depressive symptoms. The findings were as follows; firstly, there was a cross-sectional association between depression and five inflammatory markers (C-reactive protein (CRP), interleukin-1 receptor antagonist, monocyte chemotactic protein-1, white blood cell count, and triglycerides). Secondly, a composite measure of inflammation including these five markers was more closely correlated with depression score than any individual marker. Thirdly, depression was associated with higher concentration of CRP at 12 months. Finally, baseline CRP was not significantly associated with increased risk for new cases of depression. These findings may help explain the poorer prognosis of those with type 2 diabetes mellitus and comorbid depression.

Date of Award	1 May 2015
Original language	English
Awarding Institution	King's College London
Supervisor	Khalida Ismail (Supervisor) & John Pickup (Supervisor)