Age and sex differences in the incidence of diabetes mellitus in a population-based Spanish cohort.

BACKGROUND: The prevalence of diabetes mellitus (DM) in Spain ranges between 10% and 20%. However, very little is known about the incidence of DM because of difficulties involved in estimating it and its apparent lack of usefulness in practice. The aim of the present study was to describe the incidence of type 1 and type 2 DM (T1DM and T2DM, respectively) in the Castilla y León diabetes cohort (CODICyL). METHODS: New diabetes cases, were registered on a standard form that included diagnostic criteria, background, symptoms, results of clinical examination, complications, other cardiovascular risk factors, and treatment. There were 1 354 619 person-years monitored between 2000 and 2013. We estimated the incidence of DM and calculated the relative risks adjusted for age, gender, and year of diagnosis with Poisson regression models. RESULTS: The incidence of DM in individuals aged ≥15 years was 196.9 per 100 000 person-years (95% confidence interval [CI] 188.4-205.7), whereas in those aged <15 years the incidence was 10.8 per 100 000 person-years (95% CI 7.8-14.8). Men had a 36% higher risk than women of developing T2DM (95% CI 25%-49%). The greatest incidence of T2DM was found in 55-64-year-old men and 65-69-year-old women. CONCLUSIONS: The annual incidence of T2DM is approximately 2 per 1000 person-years, higher in men, and peaks in middle age. Although specific tests to differentiate between the two types of DM are not available in this study, the estimation of incidence in those <15 years of age (10.8 per 100 000 person-years) represents a close approximation of the incidence of T1DM.