Decreased Incidence of Type 1 Diabetes in Young Finnish Children

The incidence of type 1 diabetes has been rising for decades, particularly among young children. Between 2006 and 2011, the incidence rate (IR) reached a plateau in Finland. In this observational, register-based cohort study, we assess recent trends in the disease rate in Finnish children. Based on data from the Finnish Pediatric Diabetes Register, we studied the incidence of type 1 diabetes among children younger than 15 years of age between 2003 and 2018. We assessed sex-specific IRs per 100,000 person-years (PY) by 4-year time periods in three age-groups (0.50-4.99, 5.00-9.99, and 10.00-14.99 years). Among the 7,871 children with newly diagnosed type 1 diabetes, the median age at diagnosis increased from 7.88 to 8.33 years ( = 0.001), while the overall IR decreased from 57.9/100,000 PY in 2003-2006 to 52.2/100,000 PY in 2015-2018, yielding an IR ratio (IRR) of 0.90 (95% CI 0.85-0.96, = 0.001). This decline was mainly due to the decrease in the youngest age-group (IRR 0.77 [95% CI 0.68-0.87]; < 0.001), being significant both among boys and girls. In the middle age-group, a significant decrease was observed only among girls. No changes were observed in the oldest children. The incidence of type 1 diabetes decreased among young Finnish children between 2003 and 2018. Current findings imply that environmental factors driving the immune system toward islet autoimmunity are changing in young children.