Background: The risk of proteinuria in Type 1 diabetes declined > or = 30% over the past 50 years, and improvements in metabolic control are believed to be largely responsible. Little is known about secular changes in the risk of proteinuria in Type 2 diabetes.
Methods: We examined trends in the incidence rate of proteinuria in Pima Indians > or = 20 years of age with diabetes diagnosed between January 1, 1955 and December 31, 1994.
Results: Among 1305 initially non-proteinuric diabetic subjects, 433 developed proteinuria during a median follow-up of 8.0 years (range 0.8 to 30.2 years). With subjects with diabetes diagnosed between 1955 and 1964 serving as the reference group, the rate of proteinuria was similar (rate ratio 1.0; 95% confidence interval, 0.79 to 1.3) in the cohort diagnosed between 1965 and 1974, 1.5 times as high (95% confidence interval, 1.1 to 2.0) in the cohort diagnosed between 1975 and 1984, and 1.9 times as high (95% confidence interval, 1.1 to 3.0) in the cohort diagnosed between 1985 and 1994, after adjusting for potential confounders in a generalized additive proportional hazards model. Between the first and last cohorts, plasma glucose concentration declined, on average, by 17% (P = 0.0001) and the mean arterial pressure declined by 11% (P = 0.0001).
Conclusions: The incidence rate of proteinuria in Pima Indians with Type 2 diabetes increased nearly twofold in the last 40 years, despite improvements in plasma glucose and blood pressure. Rapidly changing environmental or behavioral factors must play an important role in the pathogenesis of diabetic renal disease in this population.