Decreased working memory capacity among individuals with a mood disorder who have increased metabolic burden

Abstract

Background: Individuals with mood disorders experience a higher rate of obesity than the general population, putting them at risk for poorer outcomes. The relationship between obesity and a core feature of the mood disorders, neurocognition, is less understood. We examined the interaction of obesity as indexed by body mass index (BMI) and working memory performance in a large sample of individuals with bipolar disorder (BD), major depressive disorder (MDD), and healthy controls (HC).

Methods: Participants with BD (n = 133), MDD (n = 78), and HC (n = 113) (age range 18-40) completed a spatial working memory (SWM) task that included three-graded increases in the number of target locations. Participants were subdivided by BMI classification into six diagnostic-BMI (BMI groups: Normal Weight, Overweight/Obese) subgroups. Performance on the task was indexed by number of errors within each difficulty level.

Results: The number of errors, across all groups, increased with task difficulty. There was an interaction between errors and diagnostic-BMI group. Post-hoc analyses indicated that while the Normal Weight-BD group did not differ in performance from the other groups, the Overweight/Obese-BD group performed significantly worse than HC groups.

Limitations: Metabolic effects of psychotropic medications due to the naturalistic nature of the study, younger age of the MDD sample, and utilizing self-reported indicators of obesity may limit generalizability.

Conclusions: Individuals with BD with increased metabolic burden exhibit increased working memory errors than non-psychiatric controls who also have increased metabolic burden. Future work could address prevention and amelioration of such difficulties to reduce associated functional morbidity.

Keywords: BMI; Bipolar; Cognition; Depression; Mood disorders; Obesity; Working memory.