Background: About 90 percent of the 20 million persons with diabetes in the United States have type 2 disease. The prevalence of diabetes increases with age from 1.4 percent in persons younger than 45 years to 16.7 percent in persons 65 to 74 years of age. Patients with type 2 diabetes have insulin resistance, increased hepatic glucose production, reduced glucose clearance, and impaired beta cell insulin secretion. Visceral fat increases insulin resistance. In the disease course, postprandial glucose levels probably increase before fasting glucose levels increase. Several studies have shown that tight glucose control is associated with a decrease in the development and progression of microvascular complications. The Diabetes Control and Complications Trial, which evaluated patients with type 1 diabetes, found that a 2 percent reduction in A1C level was associated with a delay in the onset and progression of retinopathy and nephropathy. Similar results were found in trials evaluating patients with type 2 diabetes, but no trial has specifically evaluated patients older than 60 years.
Recommendations: Based on these trials, it is recommended that patients achieve an A1C goal of less than 7 percent. Modest weight loss can lower A1C levels by 1 percent, and moderate exercise can lower A1C levels by 0.5 percent. Treatments include medications that increase insulin secretion. Two new secretagogue medications are available: exenatide injection (Byetta); and sitagliptin (Januvia), a dipeptidyl peptidase type IV inhibitor. More established treatment options include metformin (Glucophage) and thiazolidinediones, which decrease insulin resistance; and alpha-glucosidase inhibitors, which delay absorption of carbohydrates from the gastrointestinal tract. Individually, antihyperglycemic medications reduce A1C levels by 0.5 to 2 percent. Combinations of medications with different mechanisms of action have additive effects.
If patients do not achieve A1C goals with oral medications, insulin is initiated. Other indications for insulin therapy include severe symptoms, ketoacidosis, and preconception planning. When the fasting glucose level is elevated, 10 units (or 0.1 units per kg) of nighttime basal insulin is titrated upward until fasting blood glucose is at the desired level. At lower A1C levels, postprandial blood glucose is likely to contribute more to overall glucose control. When postprandial glucose is elevated, patients should use short-acting insulins before meals and should stop using insulin secretagogues while continuing insulin sensitizers.