exercise and heart disease

The latest research on exercise and heart disease

Heart disease has a number of risk factors. We have no control over some, like our family history. But there are several heart disease risk factors we can eliminate or at least modify. They include cigarette smoking, high blood pressure, high cholesterol levels, diabetes, obesity and physical inactivity. In fact, recent evidence shows that levels of physical activity are much more closely related to risk of death from heart disease than is food intake. A study published in the American Journal of Preventive Medicine surveyed data from nearly 10,000 participants obtained in the 1970s. The authors found that caloric intake was unrelated to heart disease mortality. Instead, persons who ate more but also exercised more were less than half as likely as those who exercised less and ate less to die of cardiovascular disease.

Becoming physically fit can reduce the impact of many risks for heart disease.

Exercise and high blood pressure
Doctors almost always recommend life-style changes as the first step in controlling high blood pressure. Researchers from Duke University performed a study of patients with mild high blood pressure, enrolling 133 sedentary, overweight men and women in an exercise program, an exercise and weight management program, or a control group. In this study, all of those who exercised achieved a lowering of their blood pressure readings, but those in the weight management plus exercise group had greater improvements. The weight management plus exercise subjects also had better blood sugar control than those in the exercise-only or control groups.

Another study at Duke looked at 99 men and women with mild, untreated high blood pressure. The subjects were assigned to either an exercise program (aerobic, strength and flexibility training) or to a control group. At the end of four months, there was no difference in the blood pressure readings between the two groups. Thus, it may be that weight loss is necessary to achieve an exercise-induced improvement in blood pressure.

Exercise and high cholesterol
Elevated total cholesterol, high levels of LDL (often called the "bad" cholesterol) and low levels of HDL ("good" cholesterol) are risk factors for heart disease. While the new lipid-lowering drugs have had a real impact on reducing risk of heart disease, patients occasionally express reluctance to take medications to lower their cholesterol.

Several studies have looked at the benefits of exercise in reducing cholesterol levels. Investigators at the University of Minnesota enrolled 675 sedentary men and women, African-American and white, into a 20-week exercise program. All the subjects had normal cholesterol levels to start. At the end of the 20 weeks, total cholesterol and LDL were unchanged, but the protective HDL levels had gone up an average of 3.6%. This improvement was consistent across race, gender and age.

Another study at the University of Southern California assigned 100 postmenopausal women to one of four groups: no exercise or estrogen, estrogen replacement, exercise, or both estrogen and exercise. Cholesterol levels were measured at three and six months. With exercise alone, the women reduced their total cholesterol by 5%, their LDL by 10% and they raised their HDL by 17%. The estrogen and estrogen plus exercise groups had similar changes, but no advantage was seen to combining the two methods.

Judging from these and other studies, exercise is at least somewhat effective at improving blood cholesterol levels, and thus reducing heart disease risk.

Exercise and glucose metabolism
The form of diabetes most commonly seen in the older population is marked by insulin resistance, the reduced ability of circulating insulin to properly move glucose (blood sugar) out of the bloodstream and into cells where it can be used. Insulin resistance is a risk factor for heart disease. Exercise improves insulin sensitivity in those with insulin resistance and those without. A small Canadian study of 52 obese men, for example, showed that those who exercised with the aim of losing weight had a significant improvement in their insulin sensitivity, thus reducing their risk of heart disease.

Exercise and heart failure
Heart failure is a disease in which the heart fails to pump enough blood per minute to meet the body's metabolic needs. Heart failure can result from damage to the muscle of the heart, as from long-standing high blood pressure or in the aftermath of a heart attack. While advances in the drug treatment of heart failure have significantly improved its prognosis in the last couple of decades, it remains a debilitating disease. In March 2003, the American Heart Association issued a statement in the journal Circulation, based on a review of the medical literature, that recommended exercise programs for heart failure patients. Exercise seems to improve patients' ability to perform activities of daily living and increase the amount of time they are symptom-free.

In one German study, 73 men with chronic heart failure were assigned to either 20 minutes per day of regular exercise or to no exercise and followed for 6 months. At the end of that time, the exercise group experienced a number of improvements in their health. They had greater exercise capacity and exercise time. They had fewer heart failure symptoms. Sophisticated measurements of their heart function showed a 14 times greater increase in stroke volume (amount of blood pumped by the heart with each beat) than the non-exercisers. The exercisers also had less enlargement of their hearts by the end of six months than the non-exercisers.

Another review of the literature, a meta-analysis of data from nine previously published trials of exercise in heart failure patients, concluded that exercise programs significantly reduced the rate of death and hospital admissions among participants. The authors also noted in the study, published in the January 24, 2004 issue of the British Medical Journal, that there was no evidence exercise was dangerous for heart failure patients.

Exercise and abnormal heart rhythms
Obituaries sometimes mention that a person died during some form of exercise. These deaths have usually been attributed to abnormal heart rhythms. In a small Swedish study that examined the frequency of abnormal heart rhythms among exercising elderly, 11 older men with lifelong histories of strenuous exercise were compared to a control group of 12 sedentary men. Both groups underwent 48-hour electrocardiogram monitoring. Abnormal and potentially dangerous heart rhythms were found in 9 of the 11 athletes, versus 5 of the 12 controls. Seven of the athletes also had episodes of significant slowing of the heart rate, although none of the controls had these. Though exercise has largely positive effects on heart function, some researchers caution that it can increase the risk of potentially lethal abnormal rhythms.

Other clinicians and researchers disagree. They point out that studies like that Swedish one look at very strenuous exercise, not the more commonly practiced moderate exercise in which most older adults engage. The long-term benefits of regular, moderate exercise typically outweigh the small risk of abnormal heart rhythms. A great many doctors recommend formal exercise stress testing for older adults starting new exercise programs, though few studies have demonstrated large benefits to such stress testing. Still, it is prudent to check with your own doctor before starting any new exercise program, to make sure that it is safe for you.

Exercise and stroke
Many people who suffer strokes develop weakness on one side of their bodies that affects their ability to walk. Physical therapy is performed in the first few months after a stroke, but patients and physicians generally believe that little further physical gains can be made after this initial period. Recent, relatively small studies have shown that appropriate, regular exercise can improve cardiovascular function and physical strength well beyond those first few months. More research is necessary to fully understand the ultimate effects and benefits of exercise on stroke recovery.

Exercise and peripheral arterial occlusive disease
People with atherosclerosis or hardening of the arteries of their legs can experience claudication, a grabbing pain in their legs or buttocks that occurs with exertion. Exercise rehabilitation can actually improve their symptoms. Investigators in Baltimore enrolled 63 people with claudication in a six-month treadmill exercise program. At the end of their rehabilitation program, the subjects could walk 115% longer before experiencing claudication. Their daily physical activity levels improved 31%. Blood flow to their calves increased 27%. Thus, exercise improved their circulation and their symptoms.