[Insulin-dependent diabetes in the county of Funen 1970-2020. An epidemiological description]

We present an epidemiological model applicable to insulin-dependent diabetes mellitus (IDDM), based on which prevalence rates are estimated from assumed rates of incidence and mortality of diabetes. The model is illustrated by analysing epidemiological data on IDDM in Fyn County, Denmark for the period 1970-1990, with predictions of prevalence rates during 1990-2020. The epidemiological model assumes known prevalence rates as well as incidence rates and mortality at a given point of time. Under assumed rates of incidence and mortality of IDDM and its complications, the prevalence rate is the dependent variable which is estimated as a function of calendar time. We used 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 the years 1973 and 1987 in Fyn County, Denmark. During 1970-1990 the prevalence of IDDM increased steadily, due to 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 of mortality, it is estimated that the prevalence rate of IDDM in the year 2020 will be 45-60% higher than the level in 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. We conclude that IDDM will represent an increasing public health problem in Denmark over the next decades, with increasing overall prevalence rates and a rising proportion of patients with nephropathy. The major determinants of this trend are increasing incidence, combined with declining mortality and declining risk of complications. It is recommended that epidemiological modelling techniques be further developed to provide improved data for the planning of the future diabetes care.