Several clinical trials have recently shown that the risk of progression from impaired glucose tolerance to type 2 DM can be markedly reduced (by approximately 50% over several years) through lifestyle modifications such as a combination of diet and exercise therapy. The amount of weight loss and exercise required to achieve this result is surprisingly modest. For instance, in the Diabetes Prevention Program, patients who were asked to perform 150 minutes of brisk walking per week (a little over 20 minutes per day) lost only about 12 pounds of weight on average but reduced their risk of diabetes mellitus development by 50% over 6 months. Other studies have suggested that early pharmacologic intervention with oral hypoglycemic agents also decreases the risk of progression to diabetes mellitus. There are, as yet, no known ways to prevent type 1 DM, but trials of interventions to regulate immune response are under way.
The importance of glycemic control
For patients with either type 1 or type 2 DM, glycemic control is of the utmost importance. The Diabetes Control and Complications Trial showed that intensive therapy aimed at maintaining near-normal glucose levels had a large and beneficial effect on delaying the development and progression of long-term complications for patients with type 1 diabetes mellitus. For example, intensive therapy decreased the risk of the development and progression of retinopathy, nephropathy, and neuropathy by 40%–76%. The beneficial effects increased over time, but they were accompanied by a threefold increased risk of hypoglycemia. Thus, intensive therapy is recommended for most patients with type 1 DM, but these patients should be instructed to self-monitor their blood glucose levels carefully to prevent hypoglycemic episodes. See also BCSC Section 12, Retina and Vitreous.
Tight glycemic control has a profound effect on the development of complications. The risk of retinopathy progression rises almost exponentially as the HbA1c level increases (Fig 2-1). However, patients who decrease their HbA1c by 1 percentage point (eg, from 8.0% to 7.0%) reduce their risk of retinopathy by approximately 30%, and this benefit also holds for other complications of diabetes mellitus, such as nephropathy and neuropathy. When working with patients with diabetes mellitus, health care providers should emphasize the importance of tight control and encourage patients to achieve it.
For patients with type 1 DM, intensive therapy also provides protection against macrovascular complications such as cardiovascular disease. For patients with type 2 DM, however, the role of glycemic control in reducing cardiovascular risk has not been established. In this group, macrovascular disease may be affected more by other risk factors, such as smoking, obesity, and lipid abnormalities.
Action to Control Cardiovascular Risk in Diabetes Study Group; Gerstein HC, Miller ME, Byington RP, et al. Effects of intensive glucose lowering in type 2 diabetes. N Engl J Med. 2008;358(24):2545–2559.
Excerpted from BCSC 2020-2021 series: Section 1 - Update on General Medicine. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.