Impaired glucose metabolism moderates the course of illness in bipolar disorder.

Background: The longitudinal course of bipolar disorder (BD) is highly heterogeneous, and is moderated by the presence of general medical comorbidities. This study aimed to investigate the moderating effects of impaired glucose metabolism (IGM) on variables of illness course and severity in a BD population.

Methods: Fifty-five patients with BD were evaluated. All subjects were evaluated with respect to current and past psychiatric and medical disorders, as well as lifetime use of any medication. Body mass index (BMI) and metabolic parameters were obtained. IGM was operationalized as pre-diabetes or type 2 diabetes mellitus.

Results: Thirty (54.5%) individuals had IGM. After adjustment for age, gender, ethnicity, alcohol use, smoking, BMI and past and current exposure to psychotropic medications, individuals with IGM, when compared to euglycemic participants, had an earlier age of onset (RR: 0.835, p=0.024), longer illness duration (RR: 1.754, p=0.007), a higher number of previous manic/hypomanic episodes (RR: 1.483, p=0.002) and a higher ratio of manic/hypomanic to depressive episodes (RR: 1.753, p=0.028). Moreover, we observed a moderating effect of IGM on the association between number of mood episodes and other variables of illness course, with the correlation between lifetime mood episodes and frequency of episodes being significantly greater in the IGM subgroup (RR: 1.027, p=0.029). All associations observed herein remained significant after adjusting for relevant confounding factors (e.g. age, alcohol and tobacco use, exposure to psychotropic agents, BMI).

Limitations: Cross-sectional design, small sample size.

Conclusions: Comorbid IGM may be a key moderator of illness progression in BD.