, Volume 52, Issue 12, pp 2531-2535
Date: 11 Oct 2009

The incidence of type 1 diabetes is increasing in both children and young adults in Northern Italy: 1984–2004 temporal trends

Abstract

Aims/hypothesis

A shift towards younger age at onset of diabetes in susceptible people has been suggested as a possible explanation for the increasing temporal trend in incidence of type 1 diabetes. We aimed to test this hypothesis by assessing trends in incidence rates in the period 19842004 in children and young adults in Northern Italy.

Methods

The study bases were: (1) children resident in the Province of Turin in the period 19842004 and in the remaining areas of the Piedmont Region in the period 19902004; and (2) young adults (1529 years) resident in the Province of Turin in the period 19842003. Temporal trends in rates were analysed using Poisson regression models.

Results

A total of 1,773 incident cases were identified. Overall incidence rates/100,000 person-years in the age groups 014 and 1529 years were 11.3 (95% CI 10.712.0) and 7.1 (95% CI 6.67.7), respectively, with sex differences among young adults only (incidence rate ratio [IRR] in males vs females 1.41 [95% CI 1.201.64]). Average annual increases in incidence rates were similar in children and young adults at 3.3% (95% CI 2.54.1). Compared with the period 198489, in 20002004 a 60% higher risk was found in both age 014 years (IRR 1.60, 95% CI 1.311.95) and 1529 years (IRR 1.57, 95% CI 1.261.96) groups. The Poisson modelling showed no interaction between calendar period and age at onset.

Conclusions/interpretation

Incidence of type 1 diabetes in Northern Italy is increasing over time in both children and young adults, not supporting the hypothesis of a shift towards younger age as the main explanation for the increasing temporal trend in children.