Incidence of type 1 and type 2 diabetes in adults aged 30-49 years: the population-based registry in the province of Turin, Italy.
OBJECTIVE
Incidence of type 1 diabetes is considered to be low in adults, but no study has been performed in Mediterranean countries.


METHODS
We extended the study base of the registry of the province of Turin, Italy, to subjects aged 30-49 years in the period 1999-2001 to estimate the incidences of type 1 and type 2 diabetes. Diagnosis of type 1 diabetes was based on permanent insulin treatment or a fasting C-peptide level < or =0.20 nmol/l or islet cell (ICA) or GAD (GADA) antibody positivities.


RESULTS
We identified 1,135 case subjects with high completeness of ascertainment (99%), giving an incidence rate of 58.0 per 100,000 person-years (95% CI 54.7-61.5). The incidence of type 1 diabetes was 7.3 per 100,000 person-years (6.2-8.6), comparable with the rates in subjects aged 0-14 and 15-29 years (10.3 [9.5-11.2] and 6.8 [6.3-7.4]). Male subjects had a higher risk than female subjects for both type 1 (rate ratio [RR] 1.70 [95% CI 1.21-2.38]) and type 2 (2.10 [1.84-2.40]) diabetes. ICA and/or GADA positivities were found in 16% of the cohort. In logistic regression, variables independently associated with autoimmune diabetes were age 30-39 years (odds ratio [OR] 2.39 [95% CI 1.40-4.07]), fasting C-peptide <0.60 nmol/l (3.09 [1.74-5.5]), and BMI <26 kg/m2 (2.17 [1.22-3.85]).


CONCLUSIONS
Risk of type 1 diabetes between age 30 and 49 years is similar to that found in the same area between age 15 and 29 years. Further studies are required to allow geographical comparisons of risks of both childhood and adulthood autoimmune diabetes, the latter being probably higher than previously believed.
Bruno
Graziella
G
Department of Internal Medicine, University of Turin; corso Dogliotti 14, I-10126 Turin, Italy. graziella.bruno@katamail.com
Runzo
Cristina
C
Cavallo-Perin
Paolo
P
Merletti
Franco
F
Rivetti
Marina
M
Pinach
Silvia
S
Novelli
Giulia
G
Trovati
Mariella
M
Cerutti
Franco
F
Pagano
Gianfranco
G
D000328:Adult; D015992:Body Mass Index; D002096:C-Peptide / Q000032:analysis; D003922:Diabetes Mellitus, Type 1 / Q000175:diagnosis / Q000453:epidemiology*; D003924:Diabetes Mellitus, Type 2 / Q000175:diagnosis / Q000453:epidemiology*; D005215:Fasting; D005260:Female; D005968:Glutamate Decarboxylase / Q000276:immunology; D006801:Humans; D015994:Incidence; D007328:Insulin / Q000627:therapeutic use; D007515:Islets of Langerhans / Q000276:immunology; D007558:Italy / Q000453:epidemiology; D016015:Logistic Models; D008297:Male; D016017:Odds Ratio; D012042:Registries / Q000706:statistics & numerical data*; D012189:Retrospective Studies; D012306:Risk
D002096:C-Peptide; D007328:Insulin; D005968:Glutamate Decarboxylase