While the lifespan of people with type 1 diabetes has increased progressively since the advent of insulin therapy, these patients still experience premature mortality, primarily from cardiovascular disease (CVD). However, a subgroup of those with type 1 diabetes survives well into old age without significant morbidity.
Early glycaemic control is an important factor in preventing CVD in type 1 diabetes and it might be expected that hyperglycaemia plays a major role in explaining the increased incidence of CVD and mortality, but it is apparent that good glycaemic control alone cannot explain why some patients with type 1 diabetes avoid fatal CVD events. For example, the Golden Years Cohort Study followed 400 patients with type 1 diabetes who lived for over fifty years with their disease. They had beaten the odds and survived. What was their secret? Well, it certainly was not tight blood glucose control. Their average A1C was 7.6 percent, with some as high as 8.5 to 9.0 percent, which is well above the standard recommended target of 7.0 percent. In fact, not a single Golden Years Cohort patient had an A1C in the normal range, ruling out glucotoxicity as a major player. The entire Golden Years Cohort of survivors had suboptimal blood glucose control and yet their health was excellent.
The common factor was a low insulin dosage. Obesity, high blood pressure, and other manifestations of hyperinsulinemia were notably absent.
In addition, a number of other publications have shown only a weak correlation between long-term glycaemic control, CVD and mortality.