THE INCIDENCE OF TYPE-1 (INSULIN-DEPENDENT) DIABETES-MELLITUS 15-29 YEARS IN NORWAY 1978-1982

All new cases of Type 1 (insulin-dependent) diabetes mellitus in the 15-29 year age group during the five-year period 1978-1982 were registered using a retrospective technique on a nation-wide basis. A total of 784 newly diagnosed cases were detected, from an average population of 926,192. The degree of ascertainment was almost 90%. The mean yearly incidence for the five-year period was 17.0 per 100,000. The observed incidence is doubled compared to the incidence found in the city of Oslo during the years 1956-1964 (8.8 per 100,000). The male incidence exceeded the female incidence by 12% (p < 0.05). There was a marked geographic variation in incidence, with a higher incidence in the three southern health regions compared to the two northern, 18.3 vs 13.9 per 100,000 (p < 0.01). There was a significant seasonal trend in the incidence data (p < 0.025) with the highest number of new cases detected in the months of January and September and the lowest number in July. In conclusion, the study suggests a two-fold increase of incidence of diabetes mellitus in the age group 15-29 years during the last 2-3 decades and a geographic variation in incidence within the country, pointing to the operation of environmental pathogenic factors.