Ethnic differences in the incidence of type 1 diabetes in Norway: a register-based study using data from the period 2002-2009

Abstract

Background: Few studies have looked at variation in type 1 diabetes incidence between immigrant groups within a country.

Objective: To investigate differences in incidence rates of childhood-onset type 1 diabetes between immigrant groups and ethnic Norwegians, and their contribution to the number of incident cases of type 1 diabetes in Norway.

Subjects: The study includes 2221 individuals with newly onset type 1 diabetes diagnosed during 2002-2009 in children of 0-14 yr in Norway registered in the nationwide and population-based Norwegian Childhood Diabetes Registry.

Methods: Incident cases were classified in seven groups based on country of maternal birth and three age groups. Statistics Norway provided the corresponding population sizes. Incidence rates were compared by Poisson regression.

Results: The overall incidence rate was 34.0 cases per 100,000 person-years (95% CI: 32.6, 35.5). There were large variations in incidence across the immigrant groups (p < 0.001), ranging from 6.8 per 100,000 person-years (95% CI: 1.9-17.5) for South/East Asians to 26.0 cases per 100,000 person-years (95% CI: 11.9-49.3) for sub-Saharan Africans. The differences remained significant after adjusting for age and gender.

Conclusions: There are large variations in the rate of incidence of type 1 diabetes across the ethnic groups, and several immigrant groups have significantly lower incidence than ethnic Norwegians. Immigrant groups contributed ca. 5% of the total cases of type 1 diabetes and influence the overall incidence in Norway only to a small extent.

Keywords: country of maternal birth; ethnicity; immigrants; incidence; type 1 diabetes mellitus.