Objective: Disturbance in glucose homeostasis in psychiatric populations has been suggested since the early part of this century. Increased comorbidity of diabetes mellitus in persons with major mood disorders has also been suggested. The goal of this study was to determine whether subjects diagnosed with bipolar disorder have an elevated rate of comorbid diabetes mellitus.
Method: Three hundred forty-five hospitalized patients, aged 20-74 years, who met the DSM-III-R criteria for bipolar disorder, manic or mixed subtype, were evaluated for a comorbid diagnosis of diabetes mellitus. The frequency of diabetes mellitus in the study group was determined and compared with the expected frequency, calculated as a weighted average based on sex and age from national norms. Variables characterizing the course and severity of the affective disorder in the group of diabetic bipolar subjects and a group of nondiabetic age-matched bipolar subjects were compared.
Results: The prevalence of diabetes mellitus among these bipolar patients was 9.9%, significantly greater than expected from national norms (3.4%). The patients with comorbid diabetes mellitus had significantly more lifetime psychiatric hospitalizations than the nondiabetic subjects, but age at first hospitalization and duration of psychiatric disorder were similar in the two groups.
Conclusions: The frequency of diabetes mellitus in hospitalized patients diagnosed with bipolar disorder is higher than in the general population. Manic-depressive patients with diabetes mellitus have a more severe course of illness, as indicated by a greater number of psychiatric hospitalizations. Possible reasons for this increased comorbidity include a genetic relationship between the disorders, a causal relationship in which hypercortisolemia induces diabetes or diabetic vascular lesions contribute to mania, an overlapping functional disturbance affecting similar regions of the brain, or the effect of psychotropic medications.