Declining Incidence of Nephropathy in Insulin-Dependent Diabetes Mellitus

BACKGROUND: The high relative mortality among patients with insulin-dependent diabetes mellitus results mainly from diabetic nephropathy. The cumulative incidence of nephropathy of 25 to 30 percent among patients who had had diabetes for 25 years remained stable from 1950 to the early 1980s. In a population study, we assessed recent trends in the incidence of diabetic nephropathy. METHODS: We studied all 213 patients in whom insulin-dependent diabetes mellitus was diagnosed before the age of 15 years between 1961 and 1980 in a district in southeastern Sweden. Ninety-two percent of the patients were followed from the onset of diabetes to 1991 or to death. Patients with persistent albuminuria (positive Albustix test) were considered to have diabetic nephropathy. Glycosylated hemoglobin was measured periodically in all patients, beginning in 1980. RESULTS: The cumulative incidence of persistent albuminuria after 25 years of diabetes decreased from 30.0 percent among the patients in whom diabetes developed in the period 1961 to 1965 to 8.9 percent among those in whom it developed from 1966 to 1970 (P = 0.01). After 20 years of diabetes, the cumulative incidence decreased from 28.0 percent among the patients in whom diabetes developed from 1961 to 1965 to 5.8 percent among those in whom it developed from 1971 to 1975 (P = 0.01). Persistent albuminuria has not yet developed in any patient in whom diabetes was diagnosed in the period 1976 to 1980. The average glycosylated hemoglobin value decreased from 7.4 percent in the period 1980 to 1985 to 7.0 percent from 1986 to 1991 (P < 0.001). The mean glycosylated hemoglobin value was higher in the patients with persistent albuminuria than the patients with no albuminuria (8.1 percent vs. 7.1 percent, P < 0.001). CONCLUSIONS: During the past decade the cumulative incidence of diabetic nephropathy, as manifested by persistent albuminuria, among patients who have had diabetes for 25 years has decreased substantially, probably as a result of improved glycemic control.