Cognitive deficits among people with schizophrenia and prediabetes or diabetes

Both type 2 diabetes mellitus (T2DM) and schizophrenia are known to be associated with cognitive deficits. The impact of the comorbidities of T2DM or prediabetes (PD) on cognition among people with schizophrenia has been poorly researched. We evaluated the cognitive functioning of patients with schizophrenia and PD or T2DM and compared them to patients with schizophrenia with normal blood sugar.

We retrospectively collated data on cognition, fasting blood glucose (FBG), lipids and other selected demographic and clinical variables of 171 patients with schizophrenia and 16 patients with schizoaffective disorder who were admitted to an inpatient rehabilitation facility in Western Australia from 2011 to 2018. The Brief Assessment of Cognition in Schizophrenia (BACS) was used to evaluate cognitive functioning. Parametric and non-parametric analyses were used to examine the study's aims.

Sixty-six percent of the patients had normal blood sugar, 25% had PD and 9% had T2DM. The BACS composite score revealed an increasing gradient of cognitive deficits, ranging from mild to severe, between the normal, PD and T2DM groups, respectively. The T2DM group had a significantly lower composite score compared with the PD (p = 0.026) and normal groups (p < 0.001). On the BACS subtests, the scores of T2DM and PD patients were similar except for the token motor task, in which the T2DM group had significantly lower scores (p < 0.001). The T2DM group also had lower scores on the subtests of BACS, except memory tests, compared with those with normal blood sugar. There was no significant difference in the composite and subtest cognitive scores between the PD and normal groups.

Our study revealed more pronounced cognitive deficits among patients with schizophrenia and dysglycaemia, particularly those with T2DM, compared with those with schizophrenia with normal blood sugar.