Changing Patterns of Type 2 Diabetes Incidence Among Pima Indians

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Abstract
OBJECTIVE— The rising prevalence of obesity and high prevalence of diabetes among Pima Indians suggest that the incidence of diabetes has risen over time. We examined trends in the incidence rate of type 2 diabetes among Pima Indians between 1965 and 2003. RESEARCH DESIGN AND METHODS— Incidence rates were computed independently in three 13-year time periods in Pima Indians aged ≥5 years. Diabetes was defined by the presence of at least one of two criteria: 1) 2-h plasma glucose concentration ≥200 mg/dl (11.1 mmol/l) or 2) hypoglycemic treatment. RESULTS— Among 8,236 subjects without diabetes at baseline, 1,005 incident cases occurred during follow-up. Age- and sex-adjusted incidence rates of diabetes were 25.3 cases/1,000 patient-years (95% CI 22.5–28.0) in 1965–1977, 22.9 cases/1,000 patient years (20.0–25.8) in 1978–1990, and 23.5 cases/1,000 patient years (20.5–26.5) in 1991–2003 (P = 0.3). The incidence rate in subjects aged 5–14 years was 5.7 (1.9–17.4) times as high in the last as in the first period, but the rate declined in those aged 25–34 years (incidence rate ratio 0.6 [0.4–0.8]). Sex-adjusted prevalence increased significantly over time only in those aged 5–24 years (Ptrend < 0.0001). CONCLUSIONS— The overall incidence of diabetes among Pima Indians remained stable over the past four decades, with a significant rise occurring only in the youth.