Correspondence

The Health Benefits of Exercise

N Engl J Med 1993; 328:1852-1853June 24, 1993

Article

To the Editor:

Two recent articles (Feb. 25 issue)1,2 extend our knowledge of the relation between physical activity and fitness levels and mortality. We disagree with the implication of Dr. Curfman's accompanying editorial that there are insufficient data to recommend public policies promoting physical activity as a way of reducing the risk of coronary heart disease3.

Numerous studies support the association between physical inactivity and coronary heart disease4-7. The effect is independent of the effect of physical activity on other risk factors, such as hypertension, smoking, hypercholesterolemia, and overweight. Therefore, many organizations, including the American Heart Association, the International Society and Federation of Cardiology, and the Public Health Service, have recognized physical inactivity as a major risk factor for coronary heart disease.

We disagree with the premise that the observational nature of the studies of physical activity and coronary heart disease negates our ability to infer causality in this important association. The lack of randomized, controlled trials has not prevented a causal association from being inferred with regard to other public health issues. For example, smoking was determined to cause lung cancer on the basis of observational evidence. The association between physical activity and coronary heart disease should be assessed likewise.

As Dr. Curfman noted, the association between physical inactivity and coronary heart disease is consistent, is supported by multiple studies using different methods, and is biologically plausible. The association is moderately strong: a sedentary lifestyle doubles the risk of coronary heart disease, approximately the same increase as has been found with smoking4. In addition, the evidence that light-to-moderate levels of activity have intermediate but still substantial benefits supports a dose-response effect. As with other conditions that have multiple causes, however, coronary heart disease can and does occur among physically active persons.

The potential bias that persons with incipient coronary heart disease adopt sedentary lifestyles seems to have only limited effect, given the extensive screening for coronary heart disease in most studies, the low initial mortality among all physical-activity and fitness groups, and the long-term follow-up. For example, in the article by Sandvik et al., the protective effect of intermediate fitness levels was not evident until the follow-up extended beyond 10 years1. However, this bias can and should be addressed in ongoing research.

We conclude that the weight of the evidence strongly supports the association between physical inactivity and coronary heart disease and that the link appears to be causal. Public health policies to promote physical activity among all population groups must not be delayed simply because of a lack of randomized, controlled trials on this subject. The promotion of physical activity to prevent coronary heart disease is not hype from a select group of exercise advocates, but a reasoned and appropriate public health response to the accumulated scientific evidence.

John R. Livengood, M.D., M.Phil.
Carl J. Caspersen, Ph.D., M.P.H.
Jeffrey P. Koplan, M.D., M.P.H.
Centers for Disease Control and Prevention, Atlanta, GA 30333

Steven N. Blair, P.E.D.
Cooper Institute for Aerobic Research, Dallas, TX 75230

7 References

1
Sandvik L, Erikssen J, Thaulow E, Erikssen G, Mundal R, Rodahl K. Physical fitness as a predictor of mortality among healthy, middle-aged Norwegian men. N Engl J Med 1993;328:533-537
Full Text | Web of Science | Medline

2
Paffenbarger RS Jr, Hyde RT, Wing AL, Lee I-M, Jung DL, Kampert JB. The association of changes in physical-activity level and other lifestyle characteristics with mortality among men. N Engl J Med 1993;328:538-545
Full Text | Web of Science | Medline

3
Curfman GD. The health benefits of exercise -- a critical reappraisal. N Engl J Med 1993;328:574-576
Full Text | Web of Science | Medline

4
Powell KE, Thompson PD, Caspersen CJ, Kendrick JS. Physical activity and the incidence of coronary heart disease. Annu Rev Public Health 1987;8:253-287
CrossRef | Web of Science | Medline

5
Protective effect of physical activity on coronary heart diseaseMMWR Morb Mortal Wkly Rep 1987;36:426-430
Medline

6
Berlin JA, Colditz GA. A meta-analysis of physical activity in the prevention of coronary heart disease. Am J Epidemiol 1990;132:612-628
Web of Science | Medline

7
Blair SN, Kohl HW III, Paffenbarger RS Jr, Clark DG, Cooper KH, Gibbons LW. Physical fitness and all-cause mortality: a prospective study of healthy men and women. JAMA 1989;262:2395-2401
CrossRef | Web of Science | Medline

Author/Editor Response

Editor's reply:

As one who has logged more than 40,000 miles during 15 years of jogging, I do not need to be convinced of the potential health benefits of physical activity. The principal public health message of my editorial was that there are “compelling reasons” for most people to exercise regularly. It is indisputable that regular exercise can promote weight loss and improve functional capacity. But whereas Livengood et al. are convinced that physical activity can also prevent coronary heart disease and prolong life, I am not. The observational data available, though suggestive, simply do not settle these issues as definitively as Livengood et al. would like us to believe. In observational studies, subjects decide for themselves whether or not to participate in regular exercise, and without random assignment, bias cannot be eliminated. If exercise were a new drug being touted to prevent heart attacks and extend life, the Food and Drug Administration would be hard pressed to sanction it.

Although a large, randomized, controlled trial of exercise in the primary prevention of coronary disease would be extraordinarily difficult to perform, such a trial in secondary prevention would not. Meta-analyses of small trials in secondary prevention 1 are not an acceptable substitute, in my view. At a time when we can find millions of dollars to spend on clinical trials of thrombolytic therapy, coronary angioplasty, and myriad other high-technology interventions in cardiovascular disease, how can we justify not funding a large exercise trial? We are close to having a convincing resolution to the “exercise problem”; we should not demur from taking the next step. In the meantime, responsible health care professionals should continue to encourage regular exercise, but without making claims about exercise that cannot be backed up by rigorous data.

Gregory D. Curfman, M.D.

1 References

1
O'Connor GT, Buring JE, Yusuf S, et al. An overview of randomized trials of rehabilitation with exercise after myocardial infarction. Circulation 1989;80:234-244
CrossRef | Web of Science | Medline

Citing Articles (1)