Incidence and prevalence of Type 1 (insulin-dependent) diabetes mellitus in Icelandic children 1970–1989

Through use of primary and secondary data sources for registration and validation, the incidence and prevalence of Type 1 (insulin-dependent) diabetes mellitus in children aged 0–14 years in Iceland has been completely ascertained for the years 1970–1989. The age-adjusted mean annual incidence per 100,000 for the 20-year period was 9.4 (95% confidence interval 7.8–11.3); similar for boys (9.9; 7.7–12.7) and girls (8.8; 6.7–11.5). Between 1970–1979 the incidence was 8.0 (6.0–10.6) and between 1980–1989 it was comparable at 10.8 (8.4–13.8) (p>0.10). By Poisson regression analysis the variation in incidence was related to age at diagnosis (p<0.001), while a linear trend for calendar year at diagnosis did not reach statistical significance (p=0.07). A quadratic curve, however, better described the temporal variation in incidence (p<0.05). The total prevalence per 1,000 by the end of 1979 and 1989 was similar, 0.45 (0.30–0.65) and 0.57 (0.40–0.79), respectively. In conclusion, this study confirms that both the incidence and prevalence of childhood Type 1 diabetes in Iceland are low compared to the other Nordic countries. The findings may suggest a causative role for environmental factors that are not related to latitude or ambient temperature.