Exercise and Cardiovascular Disease
By Dónal P. O'Mathúna, PhD, Lecturer in Health Care Ethics, School of Nursing, Dublin City University, Ireland. Dr. O'Mathúna reports no consultant, stockholder, speaker's bureau, research, or other financial relationships with companies having ties to this field of study.
Everyone agrees that exercise is good for us. most also will agree that they don't get enough exercise. Concern about exercise often comes up in discussions about weight and dieting. But exercise has many other important benefits, both for general health and quality of life. Evidence has been accumulating that exercise helps reduce the risk of Type 2 diabetes, osteoporosis, obesity, depression, and certain types of cancer.1 Cardiovascular disease (CVD) in particular is influenced by exercise, with physical inactivity accepted as an independent risk factor for CVD since 1992.2 CVD is the leading cause of mortality in U.S. women.3 Yet only 33% of U.S. adults engage regularly in moderate exercise and 38% report no leisurely physical activity.4 In these reports, the proportion of women exercising is always lower than men.
For those with CVD, exercise brings many benefits, with research suggesting it reduces subsequent death rates. Yet only 20% of eligible patients are referred to cardiac rehabilitation programs, with referral rates for eligible women and older patients even lower.5 When exercise programs are made available, attendance rates vary between 21% and 53% with uptake particularly poor among women, older patients, and minorities.6 For those who decide to increase their physical activity, many questions remain about how much, how often, how intense, and in what ways exercise helps.
How Does Exercise Bring Cardiac Benefit?
The precise mechanisms by which exercise impacts CVD are not fully understood. The physiological effects of exercise are many, complex, and interrelated (see Table).7 Physical activity has been associated with reduction in obesity, improved distribution of body fat, and lower incidence of Type 2 diabetes. Blood pressure is lower for 8-12 hours immediately after physical activity, and regular exercise results in sustained reductions in blood pressure and heart rate. Studies examining the impact of exercise on lipid profiles have had variable results, but generally show improvements. A meta-analysis of randomized controlled studies involving women found statistically significant reductions in all lipid and lipoprotein levels of between 2% and 5%.3 These lipid level changes occurred at lower exercise intensities than those needed to improve fitness. Numerous studies also show that exercise improves blood-clotting mechanisms.8 Physical activity helps improve muscle strength, which can improve cardiac performance. Muscle blood flow is occluded during exercise which limits cardiac ejection fraction and stroke volume, ultimately leading to improved peak cardiac performance.7 Additionally, physical activity often leads to other beneficial lifestyle changes regarding CVD, such as smoking cessation, weight loss, and improved mood.
| Table |
| Possible biological mechanisms for exercise-induced cardiac benefits7 |
Cardiovascular Influences • Reduction of resting and exercise heart rate • Reduction of resting and exercise blood pressure • Reduction of myocardial oxygen demand at submaximal levels of physical activity • Expansion of plasma volume • Increase in myocardial contractility • Increase in peripheral venous tone • Favorable changes in fibrinolytic system • Increased endothelium-dependent vasodilatation • Increased gene expression for nitric oxide synthase • Enhanced parasympathetic tone • Possible increases in coronary blood flow, coronary collateral vessels, and myocardial capillary density Metabolic Influences • Reduction of obesity • Enhanced glucose tolerance • Improved lipid profile Lifestyle Influences • Decreased likelihood of smoking • Possible reduction of stress • Short-term reduction of appetite • Improved overall well-being |
How Much of What Sort of Exercise?
Early recommendations for exercise were to engage in 20 or more minutes per day of vigorous aerobic exercise such as jogging, swimming, cycling, or aerobics.9 Since the mid-1990s, however, research has reassessed the amount and intensity of activity necessary for cardiovascular benefit. For these purposes, physical activity is defined as any bodily movement produced by skeletal muscles that results in energy expenditure.7 Exercise is defined as those types of physical activities that are planned, structured, repetitive, and designed to improve or maintain physical fitness. Physical activity of lesser intensity is now recommended by most authorities, although debate continues over the specific guidelines.
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Current guidelines generally recommend that people engage in 30 minutes of moderate-intensity physical exercise on most, and preferably all, days of the week, or that people engage in 20 minutes of vigorous exercise at least three times per week.10 The particular type of activity does not appear to be crucial. For example, a randomized controlled trial examined two exercise interventions in 235 sedentary men and women.2 The structured exercise intervention was supervised and individually designed at a fitness center, with attendance increasing from three to five days per week. The lifestyle intervention instructed subjects on how to gradually add 30 minutes of moderately intense physical activity to most or preferably all days. The specific activities were individually selected according to each person's interests and lifestyle. The interventions were monitored actively for six months, with follow-up for another 18 months. Both groups had significantly reduced systolic and diastolic blood pressure and percent body fat, but not body weight. Cardiovascular fitness also increased. Again, the outcomes did not differ with the type of activity. Total cholesterol, low-density lipoprotein, high-density lipoprotein, and triglycerides did not change in either group, probably reflecting the lack of dietary changes. The lifestyle intervention had a mean monthly cost one-third that of the structured intervention due to fitness center costs.11
However, results of a 20-year prospective study in Norway have found that even once-weekly exercise can have cardiovascular benefits.10 Among the women in the study, the greatest reductions in deaths from CVD occurred among those who engaged in intense exercise once weekly. Higher exercise frequency did not bring additional benefit regarding CVD, although it may have had other benefits. This study confirmed earlier findings that men and women differ in the impact of exercise on CVD. In men, exercise imparted greater cardiovascular benefit with increasing age, but this pattern was not found in women. Other studies have found that middle-aged men require vigorous exercise for cardiovascular benefit, while women and older men benefit as much from moderate-intensity exercise. For example, one study among women found that length of time walking was more important than walking pace in reducing risk of coronary heart disease.12
Exercise for People with CVD
A number of studies have shown that patients with stable chronic CVD can benefit from exercise programs. Hence, over the last several years, exercise programs have become standard in cardiac rehabilitation centers. A 2004 meta-analysis examined 48 trials and supported this practice.13 Exercise-based cardiac rehabilitation programs reduced both cardiac and total mortality, but not the risk of heart attack or revascularization. No significant differences were found between exercise-only programs and those where exercise was part of more comprehensive programs. Mortality rates did not differ according to exercise type, frequency, or intensity.
Exercise also has been shown to reduce the risk of developing Type 2 diabetes, which often leads to CVD. One study examined the impact of walking on mortality rates among diabetic patients.14 Compared to sedentary people with diabetes, those who walked at least two hours per week had 39% lower mortality from all causes, and 34% lower CVD mortality. Lower mortality (54%) was found for those who walked 3-4 hours per week, but longer duration afforded no additional benefits. Walking that led to moderate increases in heart and breathing rates gave lower mortality than walking that greatly increased these rates. The researchers estimated that one death per year could be prevented for every 61 diabetic patients who were persuaded to start walking two hours per week.
Adverse Effects
Exercise is not without its risks, although several practical steps can be taken to reduce the risk of injury. The most common type of risk in adults is musculoskeletal injury, with between one-quarter and one-half of adults reporting some sort of musculoskeletal injury within a year of commencing exercise.1 The risk of injury increased with obesity, amount of exercise, and exercise intensity, especially if involving competitive sports. The risk was reduced with higher baseline fitness, supervision, stretching exercises, and wearing protective equipment such as bike helmets. Walking is a low-risk exercise where increased duration does not usually lead to more injuries.15 Increasing the exercise intensity gradually resulted in fewer injuries.
Exercise also can increase the risk of myocardial infarction and sudden cardiac death. A number of highly publicized deaths of high school, college, and professional athletes have drawn attention to this area. The incidence of these sudden deaths is not well documented, but is greatest in those who are least physically active who were performing unaccustomed vigorous exercise.1 Among men, about 6-17% of sudden cardiac deaths are associated with acute exertion.16 The first prospective analysis of the risk of sudden cardiac death among women found the risk exceedingly small (one in 36.5 million hours of exertion).16 The risk was even lower among women who exercised four or more hours per week.
Recommendation
A significant body of evidence supports the cardiovascular health benefits of physical activity and exercise. Exercise has an important role in both preventing CVD and, when medically supervised, assisting in recovery from CVD. Thirty minutes of physical activity per day are recommended, although research is showing that some benefits are obtained with less activity. Therefore, people should be encouraged to gradually increase their activity by manageable amounts. This should help prevent discouragement through failing to attain overly ambitious goals or through injury. At the same time, people can be encouraged by the variety of ways they can include physical activity in their lifestyles. What is most important is that people be encouraged to get active—for their heart's sake.
References
1. Thompson PD, et al. Exercise and physical activity in the prevention and treatment of atherosclerotic cardiovascular disease: A statement from the Council on Clinical Cardiology (Subcommittee on Exercise, Rehabilitation, and Prevention) and the Council on Nutrition, Physical Activity, and Metabolism (Subcommittee on Physical Activity). Circulation 2003;107:3109-3116.
2. Dunn AL, et al. Comparison of lifestyle and structured interventions to increase physical activity and cardiorespiratory fitness: A randomized trial. JAMA 1999;281:327-334.
3. Kelley GA, et al. Aerobic exercise and lipids and lipoproteins in women: A meta-analysis of randomized controlled trials. J Womens Health 2004;13:1148-1164. Erratum in: J Womens Health 2005;14:198.
4. Healthy People 2010. Progress Review 2004. Available at: www.healthypeople.gov/Data/2010prog/focus22/. Accessed Oct. 7, 2006.
5. Thompson PD. Exercise prescription and proscription for patients with coronary artery disease. Circulation 2005;112:2354-2363.
6. Mears S. The importance of exercise training in patients with chronic heart failure. Nurs Stand 2006;20:41-47.
7. Shepherd RJ, Balady GJ. Exercise as cardiovascular therapy. Circulation 1999;99:963-972.
8. Lee KW, Lip GY. Effects of lifestyle on hemostasis, fibrinolysis, and platelet reactivity: A systematic review. Arch Intern Med 2003;163:2368-2392.
9. Pratt M. Benefits of lifestyle activity vs. structured exercise. JAMA 1999;281:375-376.
10. Wisløff U, et al. A single weekly bout of exercise may reduce cardiovascular mortality: How little pain for cardiac gain? 'The HUNT study, Norway'. Eur J Cardiovasc Prev Rehabil 2006;13:798-804.
11. Sevick MA, et al. Cost-effectiveness of lifestyle and structured exercise interventions in sedentary adults: Results of Project ACTIVE. Am J Prev Med 2000;19:1-8.
12. Lee IM, et al. Physical activity and coronary heart disease in women: Is "no pain, no gain" passé? JAMA 2001;285:1447-1454.
13. Taylor RS, et al. Exercise-based rehabilitation for patients with coronary heart disease: Systematic review and meta-analysis of randomized controlled trials. Am J Med 2004;116:682-692.
14. Gregg EW, et al. Relationship of walking to mortality among U.S. adults with diabetes. Arch Intern Med 2003;163:1440-1447.
15. Hootman JM, et al. Epidemiology of musculoskeletal injuries among sedentary and physically active adults. Med Sci Sports Exerc 2002;34:838-844. Erratum in: Med Sci Sports Exerc 2003;35:188.
16. Whang W, et al. Physical exertion, exercise, and sudden cardiac death in women. JAMA 2006;295:1399-1403.
O'Mathuna DP. Exercise and cardiovascular disease. Altern Ther Women's Health 2006;8(11):81-85.You have reached your article limit for the month. Subscribe now to access this article plus other member-only content.
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