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


METHODS
The study bases were: (1) children resident in the Province of Turin in the period 1984-2004 and in the remaining areas of the Piedmont Region in the period 1990-2004; and (2) young adults (15-29 years) resident in the Province of Turin in the period 1984-2003. 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 0-14 and 15-29 years were 11.3 (95% CI 10.7-12.0) and 7.1 (95% CI 6.6-7.7), respectively, with sex differences among young adults only (incidence rate ratio [IRR] in males vs females 1.41 [95% CI 1.20-1.64]). Average annual increases in incidence rates were similar in children and young adults at 3.3% (95% CI 2.5-4.1). Compared with the period 1984-89, in 2000-2004 a 60% higher risk was found in both age 0-14 years (IRR 1.60, 95% CI 1.31-1.95) and 15-29 years (IRR 1.57, 95% CI 1.26-1.96) groups. The Poisson modelling showed no interaction between calendar period and age at onset.


CONCLUSIONS
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.
Bruno
G
G
Department of Internal Medicine, University of Turin, corso Dogliotti 14, 10126, Turin, Italy. graziella.bruno@unito.it
Novelli
G
G
Panero
F
F
Perotto
M
M
Monasterolo
F
F
Bona
G
G
Perino
A
A
Rabbone
I
I
Cavallo-Perin
P
P
Cerutti
F
F
D000293:Adolescent; D000328:Adult; D000367:Age Factors; D017668:Age of Onset; D002648:Child; D002675:Child, Preschool; D003710:Demography; D003922:Diabetes Mellitus, Type 1 / Q000453:epidemiology*; D005260:Female; D006801:Humans; D015994:Incidence; D007223:Infant; D007558:Italy / Q000453:epidemiology; D008297:Male; D012044:Regression Analysis; D012727:Sex Characteristics; D013997:Time Factors; D055815:Young Adult