Incidence of schizophrenia in a nationwide cohort of patients with type 1 diabetes mellitus.

CONTEXT Patients with schizophrenia have an increased risk of type 2 diabetes mellitus. However, very few studies have dealt with the association of type 1 diabetes and schizophrenia. Preliminary evidence points to a possible inverse association. OBJECTIVE To investigate the incidence of schizophrenia in a nationwide cohort of patients with type 1 diabetes born in 1950 through 1959 in Finland. DESIGN A cohort study of individuals born in 1950 through 1959 with a follow-up of 1969 through 1991. SETTING Finland. PATIENTS All individuals born in 1950 through 1959 with type 1 diabetes were identified through nationwide registers. The incidence of schizophrenia until 1992 among the total 1950-1959 cohort and in individuals with type 1 diabetes was calculated using information from 3 health care registers. MAIN OUTCOME MEASURE Incidence of schizophrenia. RESULTS The incidence of schizophrenia was 0.21 per 10 000 person-years in the group with type 1 diabetes and 0.56 per 10 000 person-years in the group without type 1 diabetes (P < .001). CONCLUSION The incidence of schizophrenia is decreased in patients with type 1 diabetes.