How is diabetes related to schizophrenia?

People with schizophrenia may show increased rates of unrelated co-occurring illnesses, one example is diabetes. Diabetes is a state of impaired insulin function, either as a result of reduced insulin production (type I diabetes) or reduced insulin responsiveness (type II diabetes). Insulin regulates blood glucose levels, and reduced insulin function effectively increases blood glucose levels (hyperglycaemia). This is a dangerous state in the long term, and can ultimately damage the retina, kidneys, nerves and blood vessels. Consequently, effective management of diabetes is crucial. It is unclear if any increased risk in people with schizophrenia is purely a consequence of biological risk, the metabolic impact of antipsychotic administration, or unhealthy lifestyle choices, but it is likely a combination of many factors.

What is the evidence for comorbid diabetes?

Moderate quality evidence shows people with multi-episode schizophrenia have increased rates of diabetes compared to age and gender-matched population controls, although when only type 1 diabetes was assessed, there were no increases found. People with multi-episode schizophrenia have similar rates of diabetes as people with first-episode psychosis (9.5% vs. 8.7%), while drug naïve patients have slightly lower rates (6.4%).

Moderate quality evidence finds a medium to large effect of increased odds of type 2 diabetes in patients with a family history of type 2 diabetes compared to patients without a family history of type 2 diabetes.

Moderate to high quality evidence finds a large increase in 2-hour oral glucose tolerance test results in unmedicated patients with first-episode psychosis or first-episode mood disorder compared to controls. There were significant, medium-sized increases in insulin levels and insulin resistance in first-episode psychosis patients compared to controls, but no differences between controls and patients with a first-episode mood disorder. There were no significant differences in fasting glucose or haemoglobin A1c.

High quality evidence finds small effects of more impaired global cognition and memory, and a medium-sized effect of more impaired processing speed in people with schizophrenia and diabetes compared to people with schizophrenia without diabetes.

Moderate to high quality evidence finds second generation antipsychotics clozapine, olanzapine, risperidone and quetiapine may be associated with a small increased risk of diabetes mellitus when compared to first generation antipsychotics.

Moderate to high quality evidence suggests a small effect of greater adherence to diabetes medication in people with schizophrenia than in people without schizophrenia (approximately 17 more days per year). Moderate quality evidence shows access to treatments for diabetes was not significantly different.

June 2020

Last updated at: 4:27 pm, 18th May 2022
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