Seasonal variation in the incidence of Type 1 diabetes mellitus during 1983 to 1992 in the countries around the Baltic Sea

Aim To examine seasonal patterns of incidence of Type 1 diabetes mellitus i ncidence in children aged 0-14 years in Finland, Sweden, Estonia, Latvia an d Lithuania during 1983-1992 (1987-1992 for Finland). Methods The study used a method that models incidence data using combinatio ns of sine waves to model seasonal variation around a possible linear trend . Results In Finland, a significant pattern was found for combined sexes and age groups 0-9 and 10-14 years. A significant pattern was also confirmed fo r 10-14 year-old boys. In Sweden, the best model with significant pattern w as found separately for boys and girls and age groups 0-9 and 10-14 years, however, a significant pattern was confirmed for older girls only. A season al pattern in older boys in Finland and girls in Sweden was characterized b y two cycles with decreased incidence in June and November-December. The pa ttern among younger children (0-9 or 5-9 years) had one cycle with a decrea sed incidence in May-June. In Estonia, a significant pattern was found for the age group 0-14 years and combined sexes. No significant seasonal patter ns were found in Latvia and Lithuania. Conclusions The seasonal pattern with two cycles among older children and o ne cycle only among younger children may indicate different triggers of Typ e 1 diabetes mellitus for different age groups.