Schizophrenia, which is linked to a range of physical health conditions, might share intrinsic inflammatory disease pathways with type-two diabetes mellitus (T2DM). Psychotropic medication has presented a major confounder in examining this association. First-episode psychosis (FEP) patients present an interesting cohort to study this potential association, being generally younger with less comorbidity, and with limited exposure to antipsychotic medication.

To assess whether FEP, which could be described as ‘developing schizophrenia’, is associated with prediabetes, or ‘developing diabetes’, to determine whether intrinsic disease links could cause the conditions to develop in unison.

Using PRISMA criteria, we searched Embase, Medline, PsychInfo, Web of Science, and Google Scholar to 6th January 2016. We assessed case-control studies with biochemical assessment of prediabetic states in FEP patients alongside matched controls.

Twelve studies were included, involving 1137 participants. Several measurements examined prediabetes, including fasting plasma glucose, impaired glucose tolerance, and insulin resistance. Pooled analysis found FEP to be related to impaired glucose tolerance (mean difference 1.31 [0.37, 2.25]), insulin resistance (mean difference 0.30 [0.18, 0.42]), and the number of patients with impaired glucose tolerance (odds ratio 5.44 [2.63–11.27]).

Our findings suggest a potential link between prediabetic markers, in particular impaired glucose tolerance and insulin resistance, and FEP. However, we cannot establish causality, and the studies contributing to this review were at some risk of bias. Nevertheless, the findings might help to explain the increased prevalence of T2DM in patients with schizophrenia and could have implications for the management of schizophrenia patients.

The authors have not supplied their declaration of competing interest.