We analysed Sardinian Registry data to assess time trends in incidence rates of Type 1 diabetes, period 1989-2009 (2371 cases aged 0-14 years). Poisson regression models were used to estimate the effects of sex, age, period of diagnosis and birth cohorts. Incidence rate was 44.8 cases per 100,000 person-years (95% CI 43.1-46.7). The annual increase was 2.12% (1.45-2.80, test for linear trend: p<0.001). For boys, the increasing trend was evident up to 5 years of age, and for girls up to 8 years. Compared with the 1989-94 birth cohort, the relative risk increased from 0.78 (0.61-1.10) in 1974-79 to 1.62 (1.18-2.23) in 2004-09. The increase over period was less striking, with a tendency to regress in more recent years. The best fitting model for boys included age and a linear time trend, for girls age and non-linear effects of calendar period and birth cohort. In conclusion, incidence increased over time, the increase tended to level off in more recent years by calendar period but not by birth cohort, with some evidence of a stronger increase among girls than boys. Should the increase be attributable to the effects of some perinatal environmental factor, this would mean that such a factor has started affecting females before males.
- Received December 15, 2012.
- Accepted June 25, 2013.
- © 2013 by the American Diabetes Association.
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