The Joslin Medalist study of type 1 diabetic patients who have lived 50 years or more with their disease shows that most of them have minimal diabetic vascular and neurological complications. Surprisingly, it was found that this group of patients had an average HbA1c of over 10% — an enormously high blood sugar value. This corresponds to a finding in the DCCT study, which showed that 40% of type 1 diabetics who had an average HbA1c value greater than 9.8% had absolutely no development of retinopathy during 10 years of follow-up. A recent case resport of a patient who had had type 1 diabetes for 69 years but had developed no retinopathy despite very poor blood sugar control is consistent with these findings, which indicate that there are still a number of hidden variables determining whether hyperglycemia has a negative impact on patients or not.
Sources: G. Gill, et al, "Insulin-Dependent Diabetes of Over 50 Years Duration," PRACTICAL DIABETES INTERNATIONAL, vol. 10, no. 2, p. 60 (2005); J. Esteves, "Absence of Diabetic Retinopathy in a Patient who had had Diabetes Mellitus for 69 Years and Inadequate Glycemic Control," DIABETOLOGY AND METABOLIC SYNDROME, vol. 1, no. 13, October 5, 2009.