A low incidence of Type 1 diabetes between 1977 and 2001 in south-eastern Sweden in areas with high population density and which are more deprived.

Aims: To explore how socioeconomic factors and population density may contribute to the geographical variation of incidence of Type 1 diabetes in children in south-eastern Sweden.

Method: All children diagnosed with Type 1 diabetes in south-eastern Sweden during 1977-2001 were defined geographically to their place of residence and were allocated x and y coordinates in the national grid. The population at risk and socioeconomic data were aggregated in 82,000 200-m squares and geocoded likewise. A socioeconomic index was calculated using a signed chi(2) method. Rural-urban gradients were defined by overlay analysis in a geographic information system.

Results: The incidence during the past 25 years has been rising steadily, particularly in the last 6 years. The incidence was highest in areas with a high proportion of small families, of families with a high family income and better education, and this was found both at the time of diagnosis and at the time of birth. In the rural-urban analysis, the lowest incidence was found in the urban area with > 20,000 inhabitants, where there was also a higher frequency of deprivation.

Conclusions: Our findings indicate that geographical variations in incidence rates of Type 1 diabetes in children are associated with socioeconomic factors and population density, although other contributing factors remain to be explained.