Higher body mass index associated with smaller frontal cortical volumes in older adult patients with bipolar disorder

Background and objectives: Patients with bipolar disorder (BD) tend to have accelerated decline in executive function during the aging. Thus far, only few studies have examined the effect of obesity on frontal cortical volumes in young patients with BD. Herein we aimed to ascertain the association between body mass index (BMI) and frontal cortical volumes in older adult patients with BD. Methods: We recruited outpatients who were diagnosed as bipolar I disorder (BD-I) and aged over 50 years to undergo volumetric magnetic resonance imaging and anthropometric measurement. Clinical data were obtained through interview and chart review. Results: A total of 42 patients (mean age, 59.5 ± 7.9 years) with BD-I were recruited in this study. Compared with normal BMI group, overweight/obese patients (59.5%, n = 25) had significantly smaller volumes of the bilateral prefrontal cortex and right orbitofrontal cortex. After adjusting cardiometabolic variables, higher BMI and age were significantly associated with smaller volumes of the left prefrontal cortex and bilateral orbitofrontal cortex, accounting for 29.8% (left prefrontal cortex), 33.1% (left orbitofrontal cortex), and 42.0% (right orbitofrontal cortex) of the variance. BMI alone was negatively associated with the volumes of the right prefrontal and right medial frontal cortexes, accounting for 25.7% and 14.7% of the variance, respectively. Conclusions: Higher BMI was associated with smaller cortical volumes across individual frontal regions in older patients with BD independent of cardiometabolic morbidity. Future research is necessary to elucidate the mechanisms underlying the association between BMI and frontal cortical volumes in older patients with BD.