Early diabetic complications in a population of young patients with type 1 diabetes mellitus despite intensive treatment.

Background/aim. The incidence of microvascular complications has been reported to be unchanged the last decades. However, in randomized clinical trials it has been shown that improved metabolic control can reduce the development of long term complications. It has been debated whether it is possible to achieve the same results in an unselected population. In a previous study we found a decreased incidence of overt nephropathy, but unchanged incidence of severe laser treated retinopathy in a population of patients with type 1 diabetes diagnosed in childhood. The aim of the present study was to investigate the incidence 10 years later in the same population and to analyse the importance of possible risk factors. In another previous study we found a high prevalence of subclinical neuropathy among young diabetic patients despite intensive insulin therapy since diagnosis. The aim of the present study was to examine if intensive treatment is more effective in preventing early diabetic complications other than neuropathy. The incidence of type 1 diabetes has doubled in Sweden the last decades. The reason must be environmental factors. These, as well as more intensive insulin regimens from onset of diabetes, might also lead to different disease process. We wanted to analyse if clinical characteristics at onset had changed the last 25 years and if there was any secular trend of C-peptide secretion. We also intended to investigate if longer persistence of C-peptide secretion could be of importance for prevention of long term complications. Methods. The whole study population consisted of all 478 patients with type 1 diabetes diagnosed before the age of 15 during the years 1961 - 2000, living in the catchment area of the Paediatric Clinic, University Hospital, Linkoping, Sweden. For the statistical analysis the population was divided into five–year cohorts according to time of onset of diabetes. The cumulative proportion of severe retinopathy and overt nephropathy in 269 patients with onset of diabetes 1961 - 1985 was computed with survival analysis. Multivariable regression models were used to analyse the importance of metabolic control, diabetes duration, blood pressure, smoking, BMI, lipids and persisting C-peptide secretion. The prevalence of all grades of retinal changes, nephropathy and neuropathy, defined as abnormal nerve conduction, was estimated in the late 1990s in a subgroup of 80 children and adolescents with mean 13 years of diabetes duration. Clinical characteristics at onset, duration of partial remission and regularly measurements of fasting and stimulated C-peptide secretion the first five years after onset were analysed in 316 patients with onset of diabetes 1976 - 2000. Results. The cumulative proportion of severe laser treated retinopathy showed a significant declining trend the last decades. The decrease was significant between the oldest cohort with diabetes onset 1961 - 1965 and the cohorts with diabetes onset 1971 - 1975 and 1976 - 1980. The cumulative proportion of overt nephropathy also declined with a significant decrease between the oldest cohorts and all the following cohorts. After 25 years of diabetes duration it was 30% and 8% in the two oldest cohorts respectively and remained largely unchanged after 30 years. Diabetes duration and long term HbA1c were the only significant independent risk factors for both retinopathy and nephropathy. The risk of overt nephropathy increased substantially when HbA1c was above 8.5%, while the risk of severe retinopathy increased already when HbA1c exceeded 7.5%. The prevalence of neuropathy was 59%, of retinopathy 27% and of nephropathy 5% in the population of young patients after mean 13 years of diabetes duration. During the last 25 years the clinical characteristics at onset were unchanged as well as duration of partial remission and magnitude and persistence of C-peptide secretion. Conclusions. In this unselected population the cumulative proportion of severe retinopathy and overt nephropathy decreased over the last decades. Diabetic nephropathy has probably been prevented and not just postponed. Good glycaemic control was the most important factor to avoid complications, with the necessity of a lower level of HbA1c to escape retinopathy than nephropathy. Intensive insulin regimens from diabetes onset was not sufficient to entirely escape early diabetic complications after mean 13 years of diabetes duration, even if the prevalence of retinopathy and especially nephropathy was lower than usually reported. The clinical picture at onset of diabetes was unchanged the last 25 years. There was no secular trend of partial diabetes remission or C-peptide secretion during the first years after diagnosis.