In patients with diabetes, coronary artery disease is the most common cause of death. Lipid abnormalities are commonly associated with diabetes, particularly in those with type 2 diabetes (formerly known as non–insulin-dependent diabetes). The most common lipid abnormalities in these patients include hyper-triglyceridemia and reduced high-density lipoprotein (HDL) cholesterol levels. While lipid abnormalities typically improve with better glycemic control, normalization does not usually occur. Because there is a strong relationship between all forms of vascular disease in patients with type 2 diabetes and hyperlipidemia, it is important to screen for and treat these lipid abnormalities. O'Brien and associates review recent studies of the evaluation and management of this problem.
Annual screening for lipid abnormalities in adults with diabetes is recommended. Such screening should include measurements of total cholesterol, HDL, low-density lipoprotein (LDL) and triglyceride levels. An acceptable LDL level is less than 130 mg per dL (3.35 mmol per L); triglycerides should be less than 200 mg per dL (2.25 mmol per L). In patients with clinically evident vascular disease, LDL levels should be less than 100 mg per dL (2.60 mmol per L), and triglycerides should be less than 150 mg per dL (1.70 mmol per L). Whether these lower values should be the target for all patients with diabetes, regardless of whether they manifest vascular disease, has been debated. An HDL level of greater than 45 mg per dL is recommended (1.15 mmol per L).
Management of hyperlipidemia should begin with improving glycemic control and losing weight. Exercise should be incorporated into a weight-loss program, as it has been shown to enhance weight loss and facilitate weight maintenance. Weight loss will result in a decrease in triglyceride levels and an increase in HDL levels. Before an exercise program can be recommended, concomitant medical conditions that would increase the risks of exercise should be taken into consideration, including the presence of proliferative retinopathy, neuropathy and foot problems. It is prudent to recommend an exercise tolerance test to rule out silent myocardial ischemia, particularly in patients older than 35 years.
If the goals for lipid levels have not been reached after three to six months of diet, exercise and improved glycemic control, drug therapy should be initiated. However, drug therapy should be used at the outset in patients with severe hypertriglyceridemia (triglyceride level greater than 1,000 mg per dL [11.30 mmol per L]). The type of drug chosen should be based on the lipid abnormality that is present. In patients with hypercholesterolemia without hypertriglyceridemia, an HMG-CoA reductase inhibitor should be used; in patients with hypercholesterolemia with hypertriglyceridemia, an HMG-CoA reductase inhibitor or gemfibrizol can be used; in patients with hypertriglyceridemia, gemfibrizol can be used. A patient with decreased HDL levels may benefit from taking an HMG-CoA reductase inhibitor or niacin; however, niacin should be used with caution because of a possible adverse effect on glycemic control. Omega-3 fatty acids (fish oils) have been shown to reduce lipid levels in healthy patients. However, when fish oils have been used in patients with type 2 diabetes, some adverse effects have been reported, including elevation of fasting and postprandial glucose levels. Combination drug therapy can be used if hyperlipidemia is unresponsive to monotherapy. An extremely useful example is the combination of low-dose bile acid sequestrants and HMG-CoA reductase inhibitors. The use of an HMG-CoA reductase inhibitor with fibrates or niacin is associated with an increased risk of myopathy. While not contraindicated, this combination should be used with caution.
The authors conclude that hyperlipidemia is partly responsible for the increased vascular disease that occurs in patients with diabetes. Hypertriglyceridemia and reduced LDL levels should be aggressively managed in these patients. Effective treatment includes a combination of pharmacologic and nonpharmacologic therapy. All adults with diabetes should receive an annual fasting lipoprotein profile.