HbA1c and Cognitive Functioning Across Bipolar Disorder, Recurrent Major Depressive Disorder, and Schizophrenia: Findings from a Non-Diabetic Sample

Objective: This study examined the association between glycemic status, indexed by HbA1c, and cognitive functioning in individuals with bipolar disorder (BD), recurrent major depressive disorder (rMDD), schizophrenia (SZ), and healthy controls (HCs). Methods: In this cross-sectional study, 215 participants (45 HCs, 64 BD, 62 rMDD, 44 SZ) were assessed. Cognitive performance was evaluated using a comprehensive neuropsychological battery measuring attention, processing speed, memory, executive functions, and social cognition. Sociodemographic characteristics, chlorpromazine-equivalent antipsychotic doses (CEDA), and metabolic variables (body mass index, waist circumference, lipid profile, fasting glucose, and HbA1c) were collected. Group differences, correlation analyses, and multiple regression models were performed. Results: All patient groups showed significantly poorer cognitive performance compared with HCs. HbA1c levels were highest in the SZ group; however, associations between HbA1c and cognitive performance were strongest in the BD group and less consistent in rMDD. In regression analyses, HbA1c was associated with cognitive performance in BD and HCs, with weaker effects in rMDD. CEDA was associated with HbA1c levels and partially attenuated the relationship between HbA1c and cognitive outcomes. Conclusions: HbA1c levels were associated with cognitive performance in non-diabetic individuals, particularly in BD and rMDD. These findings suggest that subclinical variation in glycemic regulation may be relevant to cognitive functioning in psychiatric disorders. Further longitudinal studies are needed to clarify the influence of metabolic factors and psychotropic medication on cognitive outcomes.