The Prevalence of Glucose Intolerance in Japanese Schizophrenic Patients With a Normal Fasting Glucose Level

Background: The prevalence of diabetes in patients with schizophrenia is 2- to 3-fold higher than in the general population. Glucose abnormalities were detected in 11.9% of Japanese schizophrenic patients in a recent cross-sectional study that included fasting glucose monitoring. However, detailed studies of glucose intolerance using the glucose tolerance test have been limited in Japanese patients with schizophrenia. We investigated the prevalence of abnormal glucose tolerance after glucose loading among Japanese inpatients with schizophrenia, with normal fasting glucose levels. Method: A total of 258 inpatients with schizophrenia participated in this study after giving their written informed consent. A 75-g oral glucose tolerance test was conducted in the morning after a 12-hour overnight fast. Results: Among patients with normal fasting glucose, 81.3% had normal glucose tolerance, 17.3% had impaired glucose tolerance, and 1.3% were diagnosed with diabetes. Conclusions: This study showed that the frequency of impaired glucose tolerance in patients with schizophrenia with normal fasting glucose levels might be higher than in the general population. Careful monitoring and screening of patients with schizophrenia for abnormal glucose metabolism might therefore be necessary.