Diabetes is associated with lower global cognitive function in schizophrenia

Background: Co-morbidity of schizophrenia (SZ) and metabolic problems such as diabetes mellitus (DM) has been suggested by many studies. Nonetheless, it is still debated whether DM affects cognitive dysfunction associated with SZ and how much treatment for DM is beneficial for cognitive functions in SZ. We addressed these questions by re-assessing the cognitive dataset from the Clinical Antipsychotic Trials of Intervention Effectiveness (CATIE) schizophrenia study. Methods: We identified 1289 SZ patients in which scores for several cognitive domains of verbal memory, vigilance, processing speed, reasoning, and working memory together with the composite score and metabolic characteristics (body mass index, dyslipidemia, hypertension, and DM) were available at baseline of the trial. We performed multiple linear regression analyses to assess the impact of DM on cognitive performance of SZ patients, controlling for a number of other confounding factors including obesity, hypertension, and dyslipidemia. We also conducted analyses of covariance to compare cognitive performance among SZ patients without DM and diabetic SZ sub-groups based on anti-diabetic drugs they were receiving at baseline of the trial. Results: Co-morbid DM with SZ predicted worse overall cognitive performance and lower scores for three cognitive domains (vigilance, processing speed, and reasoning), but none of the other metabolic factors (i.e., obesity, hypertension and dyslipidemia) correlated with cognitive function in SZ. Furthermore, SZ patients with untreated DM showed poorer overall cognitive performance and a significantly lower score in the domain of vigilance compared with SZ patients without DM. Conclusion: Our data suggest that DM negatively affects the overall cognitive function of SZ patients.