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Incidence of schizophrenia lower in people with type I diabetes

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Hannu Juvonen

Correspondence to: Hannu Juvonen, MD, Department of Mental Health and Alcohol Research, National Public Health Institute, Mannerheimintie 166, 00300 Helsinki, Finland;



What is the incidence of schizophrenia in people with type 1 diabetes in Finland?


All individuals born 1950–9 in Finland (896 175 people) identified through the National Population Register. Of these, 5009 were found to have type 1 diabetes based on the Social Insurance Institution of Finland register.


General population, Finland; followed up from 1969–91.


Diagnoses of type 1 diabetes and of schizophrenia (ICD-8 or DSM-III-R) during follow-up were identified through the Social Insurance Institution of Finland register, the National Hospital Discharge Register, and the Pension Register. A broad concept of schizophrenia was used, which included schizoaffective, schizophreniform, and schizotypal personality disorders. To control for reduced sensitivity in the registers, the rate of false positives was assessed in a subsample of 906 individuals in whom DSM-IV diagnoses were made independently by two psychiatrists based on available case note information from hospitals and mental health institutions. All schizophrenia …

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  • Notes: This study did not assess the sequence of events—that is, whether a person developed schizophrenia before or after developing diabetes. Although expert assessment of case notes may give a more accurate diagnosis of schizophrenia than relying on recorded diagnoses, its accuracy will vary depending on accuracy and thoroughness of the case notes. It is possible that the subsample that was checked for false positive diagnoses may not have been representative of register diagnoses as a whole.

  • Source of funding: Millennium Pharmaceuticals and Wyeth-Ayerst.


  • Competing interests: RvW has been a consultant for Eli Lilly Lilly and has received honoraria from Eli Lilly and Janssen-Cilag. MDH has been a consultant for, received grant/research support and honoraria from, and been on the speakers/advisory boards of AstraZeneca, Lundbeck JA, Janssen-Cilag, Eli Lilly, Pfizer, Sanofi and Bristol- Myers Squibb.