The Heart of the Matter: Diabetes and Cardiovascular Disease
The Heart of the Matter: Diabetes and Cardiovascular Disease
By Om P. Ganda, M.D.
Director, Lipid Clinic, Joslin Diabetes Center; Associate Clinical Professor of Medicine, Harvard Medical School
There is a clear-cut relationship between diabetes and cardiovascular disease. Studies from Joslin Diabetes Center many years ago showed a two- to threefold increased incidence of heart disease in patients with diabetes compared with people without diabetes who were being followed in the Framingham Heart Study. Women with diabetes have an even greater risk of heart disease compared with those of similar age who do not have diabetes. In fact, cardiovascular disease (leading to heart attack and stroke) is by far the most frequent cause of death in both men and women with diabetes. Another major component of cardiovascular disease is poor circulation in the legs, which contributes to a greatly increased risk of foot ulcers and amputations.
Several advances in treating heart disease over the past two decades have improved the chances of surviving a heart attack or stroke. However, as the incidence of diabetes steadily increases, so does the number of new cases of heart disease and cardiovascular complications. Unfortunately, in people with diabetes, improvement in survival after a heart attack has been less than half as much as in the general population.
Not Just One Risk Factor
Diabetes by itself is now regarded as the strongest risk factor for heart disease. However, most likely the risk is not just due to high blood glucose levels, but a variety of mechanisms that interact. The blood vessels in patients with diabetes are more susceptible to other well-established risk factors such as smoking, high cholesterol and high blood pressure. More than 90 percent of patients have one or more of these additional risk factors.
There is evidence that smoking hastens the chance of premature heart disease by an average of 10 years. Some of this increased susceptibility could be due to the long-term effects of inadequate control of blood glucose levels on the tissues; it could also be due to other cell damage related to diabetes. In addition, there is evidence that being overweight, having a sedentary lifestyle and poor blood glucose control contribute to the increased chance of high blood pressure and abnormalities in blood lipids (high cholesterol, high triglycerides, and a low level of HDL, known as the “good cholesterol”).
Research on the role of additional risk factors is being studied. There is evidence that patients with diabetes have an increased level of low-grade inflammation of their arterial lining, a process that initiates the blood vessel changes leading to heart disease. Some of the new tests to assess this inflammation are being evaluated, including C-reactive protein.
Good News About Preventing or Delaying Heart Disease
The increased risk for heart disease often begins years before diabetes is diagnosed. With more than 60 million adults in the U.S. currently at increased risk for developing diabetes, the best way to prevent or delay the development of cardiovascular disease is to prevent diabetes itself. People with increased risk for diabetes can be identified. A large National Institutes of Health-sponsored study, the Diabetes Prevention Program, and other studies have proven that modest weight reduction and a 30-minute exercise routine five days a week can reduce the development of type 2 diabetes over three years by more than 50 percent. Moreover, even people at risk for diabetes or those with pre-diabetes, in addition to those with diabetes, frequently have abnormalities in blood pressure and lipid levels that can be detected and treated to prevent cardiovascular disease.
Weight control and smoking cessation are two important lifestyle measures that have an impact on preventing heart disease. Studies show that even in overweight people, regular physical activity has major cardiovascular benefits.
Over the past 12 years, large-scale research studies around the world show that optimal control of LDL cholesterol (the so-called “bad cholesterol”) and blood pressure can prevent adverse cardiovascular outcomes by 30 to 50 percent. The American Diabetes Association and the American Heart Association recommend an LDL cholesterol goal in all adults with diabetes of less than 100 mg/dl. In people who already have heart disease, a more desirable LDL cholesterol goal should be less than 70 mg/dl, based on more recent studies. The blood pressure goal in all patients with diabetes is less than 130/80. In most people with diabetes, reaching these blood pressure targets may require two or more medications. Fortunately, we have safe and effective medications to help patients meet these lipid and blood pressure goals.
In addition, good control of blood glucose levels and the use of low-dose aspirin can add to these benefits. For A1C tests—a measure of average blood glucose levels over the preceding two to three months—the goal is less than 7 percent. Current studies are investigating if the ideal cut-off should be even lower, such as 6.5 percent. This is particularly important for the increasing number of younger people developing diabetes.
In spite of much progress, less than 30 percent of people with diabetes are achieving the proper blood pressure and lipid goals, and less than 50 percent of patients are at the A1C goal of less than 7 percent. Although this can be partly related to access to medical care and cost of medications, a major factor is lack of proper communication and patient education.
What Other Measures Are Good for the Heart?
Evidence exists that diabetes is associated with a state of what is called “increased oxidative stress,” a chemical process reflecting subtle injury to body tissues over time. However, studies carried out so far offer no proof that taking antioxidants such as vitamins E or C, or beta-carotene, has any beneficial role in preventing cardiovascular disease. Similarly, reducing homocysteine levels through folic acid and other vitamin supplements has not yet been proven beneficial. What is important is that one should consume a balanced, nutritious, fiber-rich diet that includes naturally available nutrients from fruits and vegetables in adequate amounts, and pay more attention to the proven benefits from the treatment goals outlined above. Eating fish twice a week or taking two or three omega-3 fish oil pills daily also appears to be protective. Taking a multi-vitamin daily may be appropriate until we have evidence of benefits for any additional supplements.
A number of studies suggest that alcohol in moderate amounts may be good for the heart. However, excessive use of alcohol is a major cause of liver disease, accidents and cancer in our society. It is prudent for women to limit their daily intake to one alcoholic beverage, and for men, two.
This article first appeared in the Nov. 13, 2006 issue of TIME.
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