Increased prevalence of type 2 diabetes mellitus among psychiatric inpatients with bipolar I affective and schizoaffective disorders independent of psychotropic drug use.

Background: There are numerous reports of abnormal glucose metabolism, including increased rates of type 2 diabetes mellitus, in psychiatric patients. It remains unclear, however, whether there is an intrinsic relationship between abnormal glucose metabolism and particular psychiatric disorders, because the relationship is complicated by treatment with psychotropic medications that promote weight gain and hyperglycemia. This study aimed to clarify this relationship.
Methods: The medical records of 243 inpatients, aged 50-74 years, with diagnoses of major depression, bipolar I disorder, schizoaffective disorder, schizophrenia, and dementia were reviewed. Psychiatric and type 2 diabetes mellitus diagnoses, medications, body mass index (BMI), age, gender, and race were recorded. Diabetes rates were compared to age, race, and gender-matched rates in the US general population.
Results: Rates of type 2 diabetes mellitus were: schizoaffective (50%) > bipolar I (26%) > major depression (18%) = dementia (18%) > schizophrenia (13%) (p < 0.006). Diabetic patients had a higher mean BMI (p = 0.01), but not a significantly higher use of psychotropic medications previously reported to be associated with new-onset type 2 diabetes (e.g., phenothiazines, clozapine, olanzapine). Logistic regression revealed that psychiatric diagnosis and BMI were the only significant and independent predictors of diabetes diagnosis. Compared to national norms, diabetes rates were significantly elevated only in bipolar I affective and schizoaffective patients.
Limitations: This study was a retrospective chart review of older, hospitalized patients.
Conclusions: This is the first published study to show an increased prevalence of type 2 diabetes mellitus among psychiatric patients with particular psychiatric illnesses independent of the effects of age, race, gender, medication, and body mass. This finding, which requires replication in a larger scale, prospective study, suggests an intrinsic relationship between abnormal glucose metabolism and bipolar I affective and schizoaffective disorders.