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 100,000 individuals before 15 years was 386 (95% confidence intervals (CI): 362-410) for boys and 391 (95% CI: 367-415) for girls and by 35 years 701 (95% CI: 671-731) for men and 562 (95% CI: 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 less than 0.001). A significant effect (P = 0.004) of season was shown when the four seasons were classified according to a four stage scale related to mean temperature. When dividing Sweden into 11 regions according to north-south gradient (Latitude 55 degrees, 56 degrees, 57 degrees, ..., 65 degrees) a significant effect (P = 0.038) was also found. However, no effects of population density or living near the coast versus in the interior were found. It is concluded that a large proportion of the young are at risk of developing this chronic disease.(ABSTRACT TRUNCATED AT 250 WORDS)