The association between schizophrenia and diabetes has been recognized for more than a century. The prevalence of diabetes is increased 2- to 3-fold in patients with schizophrenia. This relationship is specific to type 2 diabetes mellitus (T2DM); type 1 diabetes mellitus, an autoimmune disease, is less common in patients with schizophrenia. Factors that contribute to comorbidity between schizophrenia and T2DM include:
- illness susceptibility: the mechanisms remain unclear but include the thrifty phenotype hypothesis, autonomic hyperactivity, and potential cellular and genetic links
- lifestyle: diet, physical inactivity, and cigarette smoking
- antipsychotic use
- social health determinants, such as income, housing, and food insecurity.
The relative contribution of factors underlying this association is unknown; it is likely that they all contribute. Nevertheless, based on information from our facility’s metabolic monitoring database, depending on demographic variables, such as ethnicity and cigarette smoking, 20% to 30% of patients with schizophrenia will develop diabetes or prediabetes during the course of psychiatric treatment.
When evaluating a patient’s risk for a cardiac event, we consider having a diabetes diagnosis equivalent to having had a myocardial infarction. Likely, the high prevalence of T2DM among schizophrenia patients and challenges in managing diabetes and prediabetes underlies these patients’ reduced life expectancy. Self-care, a cornerstone of diabetes management, is challenging for patients with schizophrenia because of deficits in executive functioning, working memory, and motivation, coupled with negative symptoms and social and economic disadvantages that often accompany schizophrenia.
by Tony Cohn, MB, ChB, MSc, FRCPC