(Circulation. 1999;100:2-4.)
© 1999 American Heart Association, Inc.
Editorial |
Physical Inactivity
An Easily Modified Risk Factor?
From the Moss Heart Center, University of Texas Southwestern Medical Center, Dallas, Tex.
Correspondence to Peter G. Snell, PhD, Department of Internal Medicine, University of Texas Southwestern Medical Center, 5323 Harry Hines Blvd, Dallas, TX 75235-9034. E-mail psnell{at}mednet.swmed.edu
Key Words: Editorials • risk factors • exercise • mortality
The classic modifiable risk factors for the development of coronary heart disease (CHD), derived from the Framingham Heart Study and other long-term epidemiological studies, are increased blood pressure, elevated plasma cholesterol, and cigarette smoking. However, evidence has been accumulating for many years suggesting that physical inactivity or the lack of exercise is also a potent force in this field. The pioneering studies by Morris et al from England1 2 and Paffenbarger et al from the United States3 4 were the first to strongly suggest that increased physical activity, either at work or during leisure time, was a deterrent to the development of CHD. In 1953, Morris et al1 studied transportation workers in London, England, and found that sedentary bus drivers had a greater incidence of CHD than the more active conductors on double-decker buses. Later, this group showed that vigorous leisure time activity also decreased the incidence of CHD.2 In 1970, Paffenbarger et al3 examined the prevalence of CHD in San Francisco, Calif, longshoremen according to their levels of physical activity. They found that coronary death rates were lower in the middle- and high-activity groups than in the low-activity group.3 Subsequently, Paffenbarger et al4 used a questionnaire to determine the activity index of a large sample of Harvard University alumni and found a progressive decline in both fatal and nonfatal coronary events with an increasing activity index up to 2000 kcal/wk. Further activity had little additional effect on the incidence of CHD. For their similar independent studies, these 2 investigators were awarded the first International Olympic Committee (IOC) Olympic Prize in 1996. Since their seminal findings, numerous epidemiological studies comparing groups of physically inactive subjects with active subjects have been published. Most of these studies have been reviewed5 and subjected to meta-analysis.6 Powell et al5 examined all studies published in the English language that contained adequate data to determine a relative risk or odds ratio for CHD at different amounts of physical activity. From this analysis, they concluded that "physical activity is inversely and causally related to the incidence of CHD." Berlin and Colditz6 performed a meta-analysis on the studies reviewed by Powell et al5 and included results from studies published after that article. They found a summary relative risk of death from CHD of 1.9 (95% CI 1.6 to 2.2) for physically inactive compared with active occupations.
In 1992, the American Heart Association published a position statement on exercise that stated, "There is a relation between physical inactivity and cardiovascular mortality, and inactivity is a risk factor for the development of coronary artery disease."7 Also in 1995, the Centers for Disease Control and Prevention (CDC) and the American College of Sports Medicine (ACSM) came to a similar conclusion that increased physical activity had a protective effect against the development of CHD. In a joint statement, they recommended that "Every US adult should accumulate 30 minutes or more of moderate-intensity physical activity on most, preferably all days of the week."8 In 1996, the first Surgeon General's report to address physical activity and health was published by the US Department of Health and Human Services.9 The effort for producing this consensus document was led by the CDC and the President's Council on Physical Fitness, with contributions from the Office of Chronic Disease Prevention, the National Heart, Lung, and Blood Institute (NHLBI), the AHA, the ACSM, and the American Alliance for Health, Physical Education, Recreation, and Dance. In this report,9 it is stated that "regular physical activity or cardiorespiratory fitness decreases the risk of cardiovascular disease mortality in general and of coronary heart disease in particular." The Surgeon General's report also stated that most adults who performed a moderate amount of physical activity (eg, 30 minutes of brisk walking or raking leaves, 15 minutes of running, or 45 minutes of playing volleyball) on a daily basis could significantly improve their health and quality of life.
The Honolulu Heart Program was established in the mid-1960s with the Framingham Heart Study used as a model. The first major study10 to emerge from the Honolulu Heart Program was on the increasing prevalence of heart disease and stroke in Japanese men living in Japan, Hawaii, and California and demonstrated the importance of lifestyle in development of CHD. From this same cohort, it was recently reported that walking in nonsmoking retired men (61 to 81 years old) carried a reduced risk of death from all causes.11 In addition, there was a trend for decreased mortality from CHD and stroke. The latest article from this program is published in this issue of Circulation12 and examines the effects of walking on morbidity and mortality from CHD in older men 71 to 93 years of age. The distance walked was determined at baseline in the Honolulu Heart Program, and the men were followed up for the development of CHD over a 2- to 4-year period. It was found that men who walked <0.25 mile/d had a 2-fold greater risk of CHD than those who walked >1.5 mile/d. Also men who walked 0.25 to 1.5 mile/d had a greater risk than men who walked longer distances. In addition, when distance walked was modeled as a continuous variable, the risk of CHD was reduced by 15% for every 0.5-mile/d increase in walking distance. The findings were not changed when adjusted for age and other risk factors, including smoking, total and HDL plasma cholesterol, hypertension, and diabetes. Adjustments were also made for medications such as aspirin and ß-blockers and for an index of functional capacity derived from various measures of physical function, including hand strength, balance, and agility.
Evidence that genetic factors do not account for mortality differences
with physical activity has been provided from a prospective cohort
study in Finland, where a large group of twins were followed up for 17
years.13 Among the entire group, those who at baseline did
the equivalent of 30 minutes of vigorous walking 
6 times per month
(conditioning exercisers) had a 43% reduction in age- and sex-adjusted
death compared with the sedentary group. An even greater reduction
(56%) was observed among twin pairs in which 1 twin was a conditioning
exerciser.
The studies from the Honolulu Heart Program emphasize the importance of
physical activity (participation in regular exercise) in contrast to
physical fitness as determined by maximal oxygen uptake
(
O2max) during graded
treadmill testing. In a large cohort study in Dallas, Tex, those in the
lowest quintile for physical fitness had a higher rate of all-cause
mortality,14 and those who improved from the lowest
age-related quintile of physical fitness to a higher quintile reduced
their mortality risk by 44%.15 It has been suggested that
cardiovascular fitness is a better indicator of regular
physical activity than self-reported data. However, a 17-year follow-up
of 4999 men aged 40 to 59 years in 1970/1971 in Copenhagen, Denmark,
found that being very fit (highest
O2max quintile) but sedentary
provided no protection against CHD or all-cause
mortality.16 Conversely, a lower risk of mortality was
associated with being unfit (lowest
O2max quintile) but active
than with being unfit and sedentary.16 In the Harvard
alumni, Paffenbarger et al17 found that there was a 4-fold
increase of CHD in former varsity athletes whose physical activity
dropped to <500 kcal/wk and was no better than inactive nonathletes
(<5 h/wk intramural sports). These observations on fitness verses
activity may be particularly relevant in elderly subjects. Data from a
population of >2000 people >55 years from Sonoma, Calif, indicate
that self-reported physical activity is poorly correlated with
O2max.18 This
suggests that the beneficial effect of physical activity in the elderly
may be the result of metabolic changes, which are not
always reflected by improvements in cardiovascular
performance.
Recently, increased physical activity has been shown to be a key factor in enabling people to attain old age without disability or becoming institutionalized.19 Among the aged, concerns about disability or institutionalization may be greater than their fear of death. Leveille et al20 found that among the most physically active of 1097 elderly adults studied at baseline and followed prospectively for 10 years, there was a 2-fold increase in the likelihood of dying without disability compared with those who were sedentary.
Four broad categories of possible mechanisms for the beneficial effects of exercise have been identified. The first is an antiatherogenic effect that includes an improved plasma lipid profile (increased HDL and decreased LDL and triglycerides), loss of body fat, increased sensitivity to insulin, and reduced blood pressure. The second is a reduced risk of thrombosis due to favorable changes in platelet adhesiveness, fibrinolysis, fibrinogen levels, and blood viscosity. The third is a reduced risk of myocardial ischemia due to a decreased myocardial oxygen demand and an increase in coronary blood flow during exercise.21 The increased coronary flow results from an increased vasodilator capacity.22 Also, recent evidence on reversal of endothelial dysfunction and improved exercise capacity with low-intensity exercise training (<4 METS) in patients with chronic heart failure may be quite relevant in the primary prevention of CHD.23 The fourth mechanism is a reduced occurrence of lethal ventricular arrhythmias due to increased vagal tone and reduced adrenergic activity during rest and exercise.24 Such adaptations of the autonomic nervous system with increased physical activity may account for an overall reduction in the risk of sudden death with habitual exercise.25
The numerous articles in popular health magazines, the proliferation of health clubs, and the large numbers of participants in marathons and triathlons give the impression that the proportion of the US adult population deriving adequate physical activity is increasing markedly. However, for the majority, the opposite trend seems to be the case. According to the 1996 report of the Surgeon General,9 it is estimated that as many as 250 000 deaths per year in the United States are attributable to a lack of regular physical activity. The report found that 25% of all adults are sedentary, and >60% do not achieve the recommended amount of regular physical activity. The latest figures (1996) from the CDC showed that for the older (65 to 74 years old) population, the proportions who were inactive ranged seasonally from 33% in July to 56% in February.26 The adoption of exercise habits by the patient is a major challenge for physicians and other health professionals. It is a well-known problem that the intent to exercise often does not translate into adoption of exercise behavior. Physicians are in a strong position to influence the physical activity of their patients. In a survey conducted by the Perrier Corporation in 1979,27 43% of inactive adults stated that a recommendation from their doctor would have influenced their involvement in sport.
These important behavioral issues led to the first NHLBI funding of a
multicenter activity counseling trial to test the efficacy of 3
different interventions, delivered in clinical settings by a healthcare
educator, to sustain an increase in physical activity by patients for
2 years.28 Participants in the standard-care group
received physician advice consistent with national
recommendations for physical activity counseling by physicians. The
other 2 interventions were simplified from several empirically tested
psychological theories of health behavior change. The staff-assisted
program included an interactive, mail-based component linked to a
low-cost incentive system. The staff-counseling program provided
substantially more interpersonal contact and counseling. This study of
874 sedentary adults without serious health problems concluded last
month, and final results will be published later this year.
From a public health standpoint, the findings that exercise is beneficial at any age, does not need to be strenuous or prolonged, includes activities at work and at home, and does not have to be done every day are extremely encouraging. As personal computers invade our lives and society becomes increasingly successful at reducing our need to move, opportunities for everyone to become more physically active should be given a high priority. Encouragement from physicians is of particular importance in this endeavor. Physical activity may not add many years to life but, more importantly, may add life to years. Thus, increasing the level of moderate physical activity may be a simple and low-cost solution to the spiraling costs of caring for our burgeoning elderly population.
Footnotes
The opinions expressed in this editorial are not necessarily those of the editors or of the American Heart Association.
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