The effect of overweight/obesity on cognitive function in euthymic individuals with bipolar disorder

Persistent impairment in cognitive function has been described in euthymic individuals with bipolar disorder. Collective work indicates that obesity is associated with reduced cognitive function in otherwise healthy individuals. This sub-group post-hoc analysis preliminarily explores and examines the association between overweight/obesity and cognitive function in euthymic individuals with bipolar disorder.

Euthymic adults with DSM-IV-TR-defined bipolar I or II disorder were enrolled. Subjects included in this post-hoc analysis (n=67) were divided into two groups (normal weight, body mass index [BMI] of 18.5-24.9 kg/m2; overweight/obese, BMI ≥ 25.0 kg/m2). Demographic and clinical information were obtained at screening. At baseline, study participants completed a comprehensive cognitive battery to assess premorbid IQ, verbal learning and memory, attention and psychomotor processing speed, executive function, general intellectual abilities, recollection and habit memory, as well as self-perceptions of cognitive failures.

BMI was negatively correlated with attention and psychomotor processing speed as measured by the Digit Symbol Substitution Test (P<0.01). Overweight and obese bipolar individuals had a significantly lower score on the verbal fluency test when compared to normal weight subjects (P<0.05). For all other measures of cognitive function, non-significant trends suggesting a negative association with BMI were observed, with the exception of measures of executive function (i.e., trail making test B) and recollection memory (i.e., process-dissociation task).

Notwithstanding the post-hoc methodology and relatively small sample size, the results of this study suggest a possible negative effect of overweight/obesity on cognitive function in euthymic individuals with bipolar disorder. Taken together, these data provide the impetus for more rigorous evaluation of the mediational role of overweight/obesity (and other medical co-morbidity) on cognitive function in psychiatric populations.