Trends in the epidemiology of IDDM during 1970-2020 in Fyn County, Denmark

OBJECTIVE - To present an epidemiological model applicable to diabetes based on which prevalence rates are estimated from assumed rates of incidence and mortality of diabetes. Furthermore, this study illustrates the model by analyzing epidemiological data on IDDM in a Danish population during 1970-1990, with predictions of prevalence rates for 1990-2020. RESEARCH DESIGN AND METHODS - The epidemiological model assumes known prevalence rates as well as incidence rates and mortality at a given time. Under assumed rates of incidence and mortality of IDDM and its complications, the prevalence rate is the dependent variable, estimated as a function of calendar time. We use epidemiological data on IDDM (operationally defined as insulin-treated diabetes with onset before age 30 years), blindness, and nephropathy, as well as mortality, as reported for 1973 and 1987 in Fyn County, Denmark. RESULTS - During 1970-1990, the prevalence of IDDM increased steadily because of increasing incidence and decreasing risk of complications and mortality. The relative prevalence of patients with nephropathy increased, whereas that of blind patients decreased considerably. Under specified assumptions regarding the future levels of incidence of disease, complications, and mortality, it is estimated that the prevalence rate of IDDM in the year 2020 will be 45-60% higher than the level in the year 1990. The relative prevalence of patients with nephropathy will increase further, whereas the relative prevalence of blind patients will remain constant at a low level. CONCLUSIONS - IDDM will represent an increasing public health problem in Denmark during the next decades, with increasing overall prevalence rates and a rising proportion of patients with nephropathy. The major determinant of this trend is increasing incidence, combined with declining mortality and declining risk of complications. It is strongly recommended that epidemiological models like the one presented here be further developed and implemented at regional levels to provide data for the dimensioning of the current and future diabetes care systems.