Association of obesity with cognitive function and brain structure in patients with major depressive disorder

Background: Obesity has been implicated in the pathophysiology of major depressive disorder (MDD), which prompted us to examine the possible association of obesity with cognitive function and brain structure in patients with MDD. Methods: Three hundred and seven patients with MDD and 294 healthy participants, matched for age, sex, ethnicity (Japanese), and handedness (right) were recruited for the study. Cognitive function was assessed using the Brief Assessment of Cognition in Schizophrenia (BACS). Gray and white matter structures were analyzed using voxel-based morphometry and diffusion tensor imaging in a subsample of patients (n = 114) whose magnetic resonance imaging (MRI) data were obtained using a 1.5 T MRI system. Results: Verbal memory, working memory, motor speed, attention, executive function, and BACS composite scores were lower for the MDD patients than for the healthy participants (p < 0.05). Among the patient group, working memory, motor speed, executive function, and BACS composite scores were lower in obese patients (body mass index = 30, n = 17) than in non-obese patients (n = 290, p < 0.05, corrected). MRI determined frontal, temporal, thalamic, and hippocampal volumes, and white matter fractional anisotropy values in the internal capsule and left optic radiation were reduced in obese patients (n = 7) compared with non-obese patients (n = 107, p < 0.05, corrected). Limitations: Sample size for obese population was not very large. Conclusions: Obesity is associated with decreased cognitive function, reduced gray matter volume, and impaired white matter integrity in cognition-related brain areas in patients with MDD.