The Impact of Obesity on Cognitive Functioning in Euthymic Bipolar Patients: A Cross-Sectional and Longitudinal Study.

Objective: To determine the influence of body mass index (BMI) on cognition in euthymic bipolar patients and healthy matched controls in a post hoc study of 2 cross-sectional and longitudinal exploratory studies.

Method: A total sample of 121 individuals was examined, which included 52 euthymic bipolar disorder I or II patients (DSM-IV-TR criteria) and 69 healthy controls matched by age and gender, categorized in 2 subgroups in terms of body mass index (BMI-factor): normal weight (BMI: 18.5-24.9 kg/m²) versus overweight-obesity (overweight, BMI: 25.0-29.9 kg/m²; and obese, BMI ≥ 30 kg/m²). Demographic, clinical, cognitive, and psychosocial functioning data were collected from 2003 until 2011. Cognitive domains studied were executive function, attention, processing speed, verbal memory, and visual memory. Fifty-four subjects (28 bipolar and 26 healthy controls) were reevaluated after 6 years of follow-up.

Results: Obesity and bipolar disorder showed a significant effect on cognition in cross-sectional and long-term MANOVA analyses (F₇,₁₁₁ = 2.54, P = .018 and F₁₉,₂₃ = 2.25, P = .033, respectively). In the cross-sectional linear regression model, global cognitive functioning was predicted by the interaction of BMI-factor by group (β = -0.44, SE = 0.14, P = .002), current age (β = -0.44, P < .0001), and premorbid IQ (β = 0.28, P = .0002), which explained 56% of variance (F₅,₁₁₅ = 29.6, P < .0001). Change in cognitive functioning over time was predicted by the interaction of BMI-factor by group (β = -0.8, SE = 0.33, P = .022) and cognition at baseline (β = -0.46, SE = 0.15, P = .004), which explained 27.65% of variance (F₆,₄₀ = 2.548, P = .0349). Generalized estimating equations analysis showed that interaction of group by BMI (Wald χ²₁ = 5.37, P = .02), age (Wald χ²₁ = 22.08, P < .0001), and premorbid IQ (Wald χ²₁ = 25.65, P < .0001) were the significant predictors.

Conclusions: Obesity was significantly associated with cognitive impairment in euthymic bipolar patients, and it also appeared to affect cognition in the long term.