ArticlesTime trends in the incidence of type 1 diabetes in Finnish children: a cohort study
Introduction
A steady increase in the incidence of type 1 diabetes has been reported worldwide;1 it seems to have been most pronounced in children aged 4 years and younger.2 The average increase per year was 2·5–3·0% worldwide.3 The incidence of this disease varies considerably among countries—eg, it is lowest in China and Venezuela and highest in Finland and Sardinia.3 In Europe—the high-risk continent—the incidence of type 1 diabetes differs between countries by more than ten-fold.
The increase in the incidence of type 1 diabetes is thought to be due to clinical manifestation at a younger age, rather than to a worldwide increase in the lifetime number of patients with the disease.4, 5 Results of studies have been contradictory, suggesting that the incidence of this diabetes in young adults has increased,6 remained constant, or even decreased.5, 7, 8 Thus, whether the overall cumulative incidence has increased or whether the age at onset has only shifted towards a younger age is difficult to judge.
A previous report showed a steady increase in the incidence of type 1 diabetes in Finland from 1965 to 1996.9 We aimed to investigate the present trends in the incidence of disease in Finland and to predict the number of Finnish children who will have this disease in the future.
Section snippets
Study design
Children who were newly diagnosed with type 1 diabetes during 1980–2005 at or before the age of 14 years were selected from the diabetes register in the National Public Health Institute during 1986–2001,9 and from the national Central Drug Register and Hospital Discharge Register during 1980–2005. The date of first entry in one of these registers was used as the date of diagnosis of type 1 diabetes. To estimate the trend during a longer period and to ensure consistency between the registers,
Results
11 148 children who had any type of diabetes at or before 14 years of age were listed on the Hospital Discharge Register during 1980–2005. Ineligible patients included 33 with Down's syndrome, 14 with another secondary form of diabetes, 27 with either maturity-onset diabetes in the young, type 2 diabetes, impaired glucose tolerance, or latent diabetes, 234 patients who were falsely coded as having diabetes, and others excluded for other reasons such as a wrong or changed personal identifier.
Discussion
From 1980 to 2005, the overall incidence rate of type 1 diabetes in Finnish children doubled. The increase was particularly large in the youngest (0–4 years) age-group. The peak incidence occurred in children aged 5–9 years at the end of the study period (2005), whereas at the beginning of the study period it was recorded in children aged 10–14 years. The increase in incidence was non-linear and was greater than 50 per 100 000 per year at the start of this millennium. The cumulative incidence
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