Risk of Developing Insulin-Dependent Diabetes Mellitus (IDDM) before 35 Years of Age: Indications of Climatological Determinants for Age at Onset

This study analyses data from two nationwide prospective diabetes registries now covering about 3400 cases from 19 million person-years of follow-up in the age group 0-34 years. The risk of developing insulin-dependent diabetes mellitus (IDDM) per 100000 individuals before 15 years was 386 (95% confidence intervals (Cl) : 362–410) for boys and 391 (95% Cl: 367–415) for girls and by 35 years 701 (95% Cl: 671–731) for men and 562(95% Cl: 534–690) for women. The incidence rate showed a maximum for both boys and girls in early puberty. After pubertal years a sharp increase in the male to female incidence ratio of IDDM was notable. At 10–14 years it was 0.94, at 15–19 years 1.59 and at 20–24 years 2.08. A Cox regression model was used to analyse the effects on age at onset of sex, population density and climatological factors as measured by north-south area of residence and season at onset. The effect of sex was confirmed (P