Seasonal Variation in the Time of Disease Manifestation in Finnish Children with Type 1 Diabetes

Abstract We tested the hypothesis of a more aggressive disease process at diagnosis of type 1 diabetes during autumn and winter, the colder seasons with consistently observed higher incidence of type 1 diabetes, compared to spring and summer. Seasonality in the manifestation of type 1 diabetes was examined in 4993 Finnish children and adolescents participated in the nationwide register. Clinical and metabolic characteristics, beta cell autoantibodies and HLA class II genetics were analysed at clinical diagnosis. Significant seasonality was observed with higher number of new cases during autumn and winter (n=1353/27.1% and n=1286/25.8%) compared to spring and summer (n=1135/22.7% and n=219/24.4%) (p<0.001). The youngest children (aged 0.5-4 years) differed from the older ones (aged 5-14 years) as their frequency of diagnoses was highest in autumn and the fewest cases were found in winter (p=0.019) while the older children followed the same pattern as that seen in the total series. Ketoacidosis was more frequent in children diagnosed during spring or summer compared to those diagnosed in autumn (18.8% and 19.9% vs. 15.8%, respectively; p=0.036) and weight loss was highest if diagnosed in summer (6% vs. 4.7˗5.4%; p<0.001). No relationship was observed between the season of disease presentation and diabetes-associated autoantibodies or HLA genotypes.Conclusions: Contrary to our working hypothesis, more severe metabolic decompensation was seen during seasons with lower number of new cases. The heterogeneity in the seasonality of diabetes manifestation between younger and older children suggests that there could be different environmental factors triggering the disease at different ages.Trial registration number: 454/E//2001Date of registration: 19.9.2001