Type 2 diabetes in people with a psychiatric disorder – an exploration of the prevalence, incidence, and potential mediating mechanisms

Research output: ThesisPh.D. thesis

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Abstract

Psychiatric disorders are common in the general population with about one out of three to develop a psychiatric disorder during their lifetime. Psychiatric disorders can substantially impair quality of life and are associated with two to three times higher mortality rates. High comorbidity of somatic disorders in people with psychiatric disorders has been suggested as the main explanation for these elevated mortality rates. In the last three decades, many researchers have investigated the prevalence as well as the incidence of type 2 diabetes in people with a psychiatric disorder. However, a comprehensive overview of this literature is currently lacking. A systematic summary of the existing evidence can provide knowledge and insight which can form a starting point for future suggestions for optimizing new prevention and treatment initiatives of this vulnerable population. However, to be able to optimize our services to this population, more knowledge is needed regarding mediators explaining the associations between psychiatric disorders and type 2 diabetes.

The aim of this PhD thesis was to provide an overview of the prevalence and the incidence of type 2 diabetes in people with a psychiatric disorder and to explore mediating mechanisms explaining the associations. The thesis consists of four sub-studies containing six papers.

Sub-study 1: Umbrella review: prevalence of type 2 diabetes in people with a psychiatric disorder. Previous research has investigated the prevalence of type 2 diabetes in people with a psychiatric disorder, but an overview of the literature is currently lacking. In our umbrella review, we summarized findings from existing systematic reviews and additionally, we conducted metaanalyses to investigate the prevalence estimates of type 2 diabetes for each investigated psychiatric disorders. Based on 32 systematic reviews and 245 primary studies, we estimated type 2 diabetes prevalence estimates ranging from 8% to 40% for ten different psychiatric disorders. The findings suggest a generally increased prevalence of type 2 diabetes in people with a psychiatric disorder compared to people without. (Sub-study 1 consists of two papers: a protocol paper and an umbrella review).

Sub-study 2: Umbrella review: incidence of type 2 diabetes in people with a psychiatric disorder. To provide an overview of the existing literature, we conducted an umbrella review exploring the incidence of type 2 diabetes in people with a psychiatric disorder. A total of 25 systematic reviews were identified reporting the incidence of type 2 diabetes in six different categories of psychiatric disorders. Across all investigated psychiatric disorders, increased risk of type 2 diabetes was reported ranging from relative risk (RR) 1.18 (95% CI 1.12-1.24) to odds ratio (OR) 1.94 (95% CI 1.34-2.80). However, more knowledge of potential mediating mechanisms explaining these associations was needed. (Sub-study 2 consists of two papers: a protocol paper and an umbrella review).

Sub-study 3: Nationwide, register-based cohort study investigating the incidence of type 2 diabetes in people with a psychiatric disorder. We conducted a nationwide, register-based, dynamic cohort study to investigate the incidence rate ratios (IRR) and age-specific incidence rates in people with a psychiatric disorder, compared to people without a psychiatric disorder. Using data from 1995 to 2018, we followed more than 5,000,000 Danish adults. We investigated ten different categories of psychiatric disorders as well as a composite category (containing any psychiatric disorder) as exposures and defined our outcome as incident type 2 diabetes. Across all psychiatric disorders, we found that the incidence of type 2 diabetes was higher in people with a psychiatric disorder, compared to those without a psychiatric disorder ranging from IRR 1.52 (1.19-1.31) to 3.08 (2.14-4.44) pending on the specific psychiatric disorders. Further, the biggest difference in incidence rates was seen in the younger population. (Sub-study 3 consists of one paper).

Sub-study 4: A mediation analysis exploring potential mediating mechanisms explaining the associations between psychiatric disorders and incident type 2 diabetes. More knowledge onpotential mediating mechanisms explaining the increased incidence of type 2 diabetes in people with a psychiatric disorder is warranted. In a longitudinal cohort study, we followed more than 250,000 people for up to 8.9 years. We explored to what extent potential mediating mechanisms explained the associations between a broad spectrum of psychiatric disorders and incident type 2 diabetes. In most of the investigated psychiatric disorders (substance use disorders, schizophrenia, mood disorders, neurotic disorders, and personality disorder) a statistically significant increased risk of incident type 2 diabetes was detected. For these psychiatric disorders, we found that most of the investigated mediators (except from unhealthy diet and somatic comorbidity) partially explained the associations and that the use of antidepressant medication contributed the most (13%-32% pending on the specific psychiatric disorder). (Sub-study 4 consists of one paper).

In this PhD thesis, the results from the sub-studies will be discussed in relation to existing knowledge, methodological challenges, and limitations. Likewise, clinical implications and future research were also discussed.
Original languageEnglish
Awarding Institution
  • University of Southern Denmark
Supervisors/Advisors
  • Pouwer, Francois, Principal supervisor
  • Henriksen, Jan Erik, Co-supervisor
  • Lasgaard, Mathias, Co-supervisor
  • Rubin, Katrine Hass, Co-supervisor
Publisher
DOIs
Publication statusPublished - 13. Jan 2022

Note re. dissertation

Print copy of the full thesis is restricted to reference use in the Library.

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