Psychiatric disorders are common conditions. According to a systematic review from 2014, almost 1 in 5 adults worldwide meet the criteria for a psychiatric disorder during a 12-month period . The life-time prevalence of psychiatric disorders was 29% (26–33%) . Different psychiatric disorders do not only seriously impact the quality of life of those affected and their family members, the disorders may also have a negative impact on other health outcomes. For example, a systematic review of longitudinal studies showed that mortality rates were significantly higher in people with psychiatric disorders than in those without such disorders (pooled relative risk = 2.22; 95% CI, 2.12–2.33; n = 133 studies) . Furthermore, the median years of potential life lost was 10 years (n = 24 studies) .
It is important to better understand how different psychiatric disorders can impact long-term health outcomes. One adverse outcome is diabetes, which is a chronic metabolic condition that affected approximately 463 million people worldwide in 2019 . Ninety percent of all people with diabetes are diagnosed with type 2 diabetes . Many studies have shown a link between psychiatric disorders and type 2 diabetes [5,6,7]. In the last decades, complex associations between psychiatric disorders and type 2 diabetes have been theorized and investigated. For example, in 2014, de Jonge et al. determined the association in a large cross-national study that used diagnostic psychiatric interviews and data on self-reported diabetes. In this study, after adjusting for co-morbid psychiatric disorders, particularly depression, intermittent explosive disorder, binge eating disorder, and bulimia nervosa were associated with diabetes . For several psychiatric disorders, it has been postulated that they have a bidirectional association with type 2 diabetes [6, 7]. Already 10 years ago, De Hert et al. described diabetes and cardiovascular diseases as significant issues in patients with severe mental illness . However, the care for diabetes in people with psychiatric disorders remains far from optimal . A recent Danish study indicated lower quality of diabetes care in people with diabetes and schizophrenia, compared to people with diabetes, but without schizophrenia (relative risk [RR] = 0.91, 95% confidence interval [CI] = 0.88–0.95) . For example, people with schizophrenia were less likely to receive foot and eye examinations (RR = 0.96, CI = 0.93–0.99; RR = 0.97, CI = 0.94–0.99), blood pressure monitoring (RR = 0.98, CI = 0.96–0.99), and treatment with antihypertensive drugs (RR = 0.83, CI = 0.70–0.97) . If a relatively large number of people with psychiatric disorders also have type 2 diabetes, this may put already vulnerable populations at increased risk for future health problems such as macro- and microvascular diseases.
Several systematic reviews have explored the prevalence of type 2 diabetes in people with different psychiatric disorders such as schizophrenia, major depression, bipolar disorder, and post-traumatic stress disorder (PTSD), indicating that the prevalence of type 2 diabetes is higher in people with psychiatric disorders, compared to people without psychiatric disorder [11,12,13,14]. To date, in a meta-analysis of 25 studies, Stubb et al. found that 9.5% of people with schizophrenia had type 2 diabetes and pooled relative risk compared to healthy control was 1.82 (95% CI 1.56–2.13, n = 4,489,125) . Similarly, Vancampfort et al. estimated the prevalence of type 2 diabetes in people with major depression disorder, bipolar disorder, or PTSD to be 8.7–10% [12,13,14].
However, a comprehensive and systematic umbrella review with a critical appraisal of the existing literature into the prevalence of type 2 diabetes in people with different psychiatric disorders is lacking. Such an umbrella review of existing systematic reviews will not only help clarifying whether there are differences in the prevalence of type 2 diabetes in people with different psychiatric disorders, but will also contribute to evaluating the quality of the existing evidence.
The umbrella review that we have planned to conduct aims to systematically summarize existing literature systematic reviews describing the prevalence of type 2 diabetes in people with a psychiatric disorder such as major depression, schizophrenia, PTSD, bipolar disorder, sleep disorder, or an anxiety disorder. Furthermore, when information is available in the identified systematic reviews, comparisons with control groups (from the general population or control groups without a psychiatric disorder) will be made. Finally, an assessment of the quality of the included systematic reviews will be conducted and discussed, providing directions for future research.