Poor blood glucose control (A1C > 9.0 percent) is associated with symptoms that can include frequent urination, thirst, blurred vision, fatigue, and recurring infections. Treatment of adults with type 2 diabetes with poor glucose control to lower A1C to a mean of 7.5 percent has been shown to improve quality of life and work productivity. 1 Beyond relief of immediate symptoms associated with poor control, the goal of blood glucose control is to reduce long-term complications of diabetes.
The Diabetes Control and Complications Trial (DCCT) 2 found that measures of early microvascular complications were reduced 50 to 76 percent in participants with type 1 diabetes randomized to intensive control. The intensively controlled group achieved an average A1C of about 7 percent compared with controls with an average A1C of about 9 percent. The Epidemiology of Diabetes Interventions and Complications (EDIC) 3 follow-up observational study of the DCCT showed that participants also had benefits that endured and grew over the following 2 decades despite equivalent subsequent A1C levels. During EDIC, the treatment group had major reductions in eye, nerve, kidney, and heart complications and less than half the number of cardiovascular disease (CVD) events than in the conventionally treated group.
Similarly, in people with newly diagnosed type 2 diabetes, the United Kingdom Prospective Diabetes Study 4 and its 10-year follow-up observational study 5 found that reduced complications persisted for at least a decade after a finite period of intensive glycemic control (average A1C of 7 percent compared with 7.9 percent with standard treatment). As in DCCT/EDIC, significant microvascular benefits persisted, and macrovascular benefits emerged with reduced myocardial infarction.
Three randomized trials designed to test the benefits of near-normalization of blood glucose on CVD in participants with long-standing type 2 diabetes found no benefit in the primary macrovascular outcome, 6, 7, 8 and one found increased mortality. 6 These trials did demonstrate reduction in some early microvascular disease measures, such as albuminuria, with lowering of A1C below 7 percent.