The incidence of childhood-onset type 1 diabetes, time trends and association with the population composition in Sweden: a 40 year follow-up

Abstract

Aims/hypothesis: During the 1980s and 1990s, the incidence of childhood-onset type 1 diabetes more than doubled in Sweden, followed by a plateau. In the present 40 year follow-up, we investigated if the incidence remained stable and whether this could be explained by increased migration from countries reporting lower incidences.

Methods: We used 23,143 incident cases of childhood-onset type 1 diabetes reported between 1978 and 2019 to the nationwide, population-based Swedish Childhood Diabetes Registry and population data from Statistics Sweden. Generalised additive models and ANOVA were applied to analyse the effects of onset age, sex, time trends and parental country of birth and interaction effects between these factors.

Results: The flattening of the incidence increase seems to remain over the period 2005-2019. When comparing the incidence of type 1 diabetes for all children in Sweden with that for children with both parents born in Sweden, the trends were parallel but at a higher level for the latter. A comparison of the incidence trends between individuals with Swedish backgrounds (high diabetes trait) and Asian backgrounds (low diabetes trait) showed that the Asian subpopulation had a stable increase in incidence over time.

Conclusions/interpretation: In Sweden, the increase in incidence of childhood-onset type 1 diabetes in the late 20th century has been approaching a more stable albeit high level over the last two decades. Increased immigration from countries with lower incidences of childhood-onset type 1 diabetes does not provide a complete explanation for the observed levelling off.

Keywords: Children; Immigration; Incidence; Time trend; Type 1 diabetes.

Fig. 1

Incidence of type 1 diabetes per 100,000 by calendar years 1978–2019 for the total population of children below 15 years of age in Sweden and the subgroup of the population where the child and both parents were born in Sweden

Fig. 2

Incidence of type 1 diabetes per 100,000 by calendar years 1978–2019. (a) Total and Swedish population of boys. (b) Total and Swedish population of girls. Lines represent predicted incidence from GAM model

Fig. 3

(a) Incidence of type 1 diabetes per 100,000 by calendar year for total and Swedish population for age at onset group 0–4 years. (b) Incidence of type 1 diabetes per 100,000 by calendar year for total and Swedish population age at onset group 5–9 years. (c) Incidence of type 1 diabetes per 100,000 by calendar year for total and Swedish population age at onset group 10–14 years. Lines represent predicted incidence from GAM model

Fig. 4

Incidence of type 1 diabetes in children below 15 years of age per 100,000 by calendar years 1980–2019 for subgroups Swedish (i.e. child and both parents born in Sweden) and Asian (i.e. at least one parent born in an Asian country)