Course of bipolar illness worsens after onset of insulin resistance

Cross-sectional studies indicate that comorbid insulin resistance (IR) and type 2 diabetes are associated with a more severe course of bipolar disorder (BD); however, this relationship has not previously been assessed longitudinally. To address this, we reviewed health records of a case series of six patients with BD and comorbid IR. Severity and length of affective episodes (both mania and depression) over the lifetime were recorded using the Affective Morbidity Index; these data were obtained from ongoing prospective follow-up and from detailed retrospective chart reviews. All six patients with a previously episodic, relapsing-remitting course of illness experienced a worsening of morbidity after the onset of laboratory-demonstrated IR. These results suggest that IR may be a potential testable, modifiable factor in the progression of BD from a treatment responsive (episodic) to a non-responsive (chronic) course of illness.