Depression and Anxiety in Type 2 Diabetes: Associations with Diabetes Onset, Clinical Management, and Long-Term Mortality

Abstract

Type 2 diabetes is a highly prevalent disease which could affect roughly 552 million people globally by the year 2030. In addition to a range of medical complications, individuals with diabetes experience higher rates of mental illness (e.g., depression and anxiety) than the general population. A growing body of evidence suggests that depression may exert important influences at key stages of the diabetes experience, including: diabetes onset, diabetes management, and mortality. A smaller body of research has explored the influence of anxiety on diabetes outcomes, and anxiety is demonstrated to elicit similar effects on the dysregulation of endocrinological or behavioural process as depression. This is of concern given that depression and anxiety co-occur in the majority of primary care cases, and individuals experiencing both disorders tend to have poorer prognoses than either alone. This thesis sought to study the independent and concurrent contributions of depression and anxiety to key diabetes outcomes in a population-based sample of Norwegian adults, through a series of four studies. The first study uses meta-analysis to demonstrate that both depression and anxiety are associated with a moderate increased risk of diabetes onset, and that these effects may only be significant in men. The second study illustrates that the fraction of incident diabetes cases attributable to metabolic and behavioural factors at the population level increases in the presence of depression and anxiety, especially in men. The third study demonstrates that depression and anxiety are differentially associated with some diabetes management outcomes (i.e., glycemic control, c-reactive protein levels, and diet adherence), with variations by patient sex. And the final study provides evidence that long-term mortality risk is lowest in diabetic individuals experiencing anxiety, higher in those with concurrent depression-anxiety, and highest for depression, with variation by sex. Overall, this body of work suggests that both depression and anxiety may result in poorer diabetes outcomes in men across all key stages, while symptoms of anxiety may provide protection against diabetes onset and risk of mortality in women with Type 2 diabetes. Future research should aim to differentiate and control for co-occurring depression and anxiety when examining diabetes outcomes, and report sex-specific estimates as a standard approach.