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Since Hippocrates first advised us more than 2000 years ago that exercise-though not too much of it--was good for health, the epidemiology of physical activity has developed apace with the epidemiological method itself. It was only in the mid-20th century that Professor Jeremy N Morris and his associates used quantitative analyses, which dealt with possible selection and confounding biases, to show that vigorous exercise protects against coronary heart disease (CHD). They began by demonstrating an apparent protection against CHD enjoyed by active conductors compared with sedentary drivers of London double-decker buses. In addition, postmen seemed to be protected against CHD like conductors, as opposed to less active government workers. The Morris group pursued the matter further, adapting classical infectious disease epidemiology to the new problems of chronic, non-communicable diseases. Realizing that if physical exercise were to be shown to contribute to the prevention of CHD, it would have to be accomplished through study of leisure-time activities, presumably because of a lack of variability in intensities of physical work. Accordingly, they chose typical sedentary middle-management grade men for study, obtained 5-minute logs of their activities over a 2-day period, and followed them for non-fatal and fatal diseases. In a subsequent study, Morris et al. queried such executive-grade civil servants by detailed mail-back questionnaires on their health habits and health status. They then followed these men for chronic disease occurrence, as in the earlier survey. By 1973 they had distinguished between 'moderately vigorous' and 'vigorous' exercise. In both of these civil service surveys, they demonstrated strong associations between moderately vigorous or vigorous exercise and CHD occurrence, independent of other associations, in age classes 35-64 years. In the last 30 years, with modern-day computers, a large number of epidemiological studies have been conducted in both sexes, in different ethnic groups, in broad age classes, in a variety of social groups, and on most continents of the world. These studies have extended and amplified those of the Morris group, thereby helping to solidify the cause-and-effect evidence that exercise protects against heart disease and averts premature mortality.

Context: Recent guidelines for treatment of overweight and obesity include recommendations for risk stratification by disease conditions and cardiovascular disease (CVD) risk factors, but the role of physical inactivity is not prominent in these recommendations., Objective: To quantify the influence of low cardiorespiratory fitness, an objective marker of physical inactivity, on CVD and all-cause mortality in normal-weight, overweight, and obese men and compare low fitness with other mortality predictors., Design: Prospective observational data from the Aerobics Center Longitudinal Study., Setting: Preventive medicine clinic in Dallas, Tex., Participants: A total of 25714 adult men (average age, 43.8 years [SD, 10.1 years]) who received a medical examination during 1970 to 1993, with mortality follow-up to December 31, 1994., Main Outcome Measures: Cardiovascular disease and all-cause mortality based on mortality predictors (baseline CVD, type 2 diabetes mellitus, high serum cholesterol level, hypertension, current cigarette smoking, and low cardiorespiratory fitness) stratified by body mass index., Results: During the study period, there were 1025 deaths (439 due to CVD) during 258781 man-years of follow-up. Overweight and obese men with baseline CVD or CVD risk factors were at higher risk for all-cause and CVD mortality compared with normal-weight men without these predictors. Using normal-weight men without CVD as the referent, the strongest predictor of CVD death in obese men was baseline CVD (age- and examination year-adjusted relative risk [RR], 14.0; 95% confidence interval [CI], 9.4-20.8); RRs for obese men with diabetes mellitus, high cholesterol, hypertension, smoking, and low fitness were similar and ranged from 4.4 (95% CI, 2.7-7.1) for smoking to 5.0 (95% CI, 3.6-7.0) for low fitness. Relative risks for all-cause mortality in obese men ranged from 2.3 (95% CI, 1.7-2.9) for men with hypertension to 4.7 (95% CI, 3.6-6.1) for those with CVD at baseline. Relative risk for all-cause mortality in obese men with low fitness was 3.1 (95% CI, 2.5-3.8) and in obese men with diabetes mellitus 3.1 (95% CI, 2.3-4.2) and as slightly higher than the RRs for obese men who smoked or had high cholesterol levels. Low fitness was an independent predictor of mortality in all body mass index groups after adjustment for other mortality predictors. Approximately 50% (n = 1674) of obese men had low fitness, which led to a population-attributable risk of 39% for CVD mortality and 44% for all-cause mortality. Baseline CVD had population attributable risks of 51% and 27% for CVD and all-cause mortality, respectively., Conclusions: In this analysis, low cardiorespiratory fitness was a strong and independent predictor of CVD and all-cause mortality and of comparable importance with that of diabetes mellitus and other CVD risk factors.

The authors investigated the relation between physical activity and cardiovascular disease (CVD) in women by following 1,564 University of Pennsylvania alumnae (mean age, 45.5 years), initially free of CVD, from 1962 until 1993. Energy expenditure was estimated from the daily number of flights of stairs climbed and blocks walked as well as the sports played and was categorized into approximate thirds (<500, 500-999, > or = 1,000 kcal/week). During 35,021 person-years, 181 CVD cases were identified. After adjustment for coronary risk factors, the relative risks of CVD were 0.99 (95% confidence interval (CI): 0.69, 1.41) and 0.88 (95% CI: 0.62, 1.25) for women who expended 500-999 and > or = 1,000, respectively, compared with <500 kcal/week (p for trend = 0.45). Only walking was found to be inversely related to CVD risk (p for trend = 0.054). Compared with women who walked <4 blocks/day, the relative risks of CVD were 0.84 (95% CI: 0.59, 1.19) and 0.67 (95% CI: 0.45, 1.01) for women who walked 4-9 and > or = 10 blocks/day, respectively. Finally, an interaction (p = 0.023) between body mass index and physical activity on CVD risk was observed, with an inverse association only for leaner (<23 kg/m2) women. These data showed no overall association of physical activity with CVD risk in women. However, walking > or = 10 blocks/day (approximately 6 miles (9.7 km)/week) was associated with a 33% decreased risk. One explanation for this finding may be that walking was reported more precisely than other kinds of activities.

Purpose: This investigation quantifies the relation between cardiorespiratory fitness levels and cardiovascular disease (CVD) mortality within strata of other CVD predictors., Methods: Participants included 25,341 male Cooper Clinic patients who underwent a maximal graded exercise test. CVD death rates were determined for low (least fit one-fifth), moderate (next two-fifths), and high (top two-fifths) cardiorespiratory fitness categories by strata of smoking habit, blood cholesterol level, resting blood pressure, and health status. There were 226 cardiovascular deaths during 211,996 man-years of follow-up., Results: For individuals with none of the major CVD predictors (smoking, elevated resting systolic blood pressure, elevated blood cholesterol), there was a strong inverse relation (P = 0.001) between fitness level and CVD mortality. An inverse relation between CVD mortality and fitness level was seen within strata of cholesterol levels and health status. No evidence of a trend (P = 0.60) for decreased mortality was seen across fitness levels for individuals with elevated systolic blood pressure; however, a strong inverse gradient (P < 0.001) was seen across fitness levels for individuals with normal systolic blood pressure. There was a tendency for association between high levels of fitness and decreased CVD mortality in smokers compared with low and moderately fit smokers (P < 0.076). There was no significant association between level of fitness and CVD mortality for individuals with multiple (two or more) predictors (P = 0.325). Approximately 20% of the 226 CVD deaths in the population studied were attributed to low fitness level., Conclusions: Moderate and high levels of cardiorespiratory fitness seem to provide some protection from CVD mortality, even in the presence of well established CVD predictors.

Longitudinal observations on the sports play, social habits and health status of 52,000 men who entered Harvard College or the University of Pennsylvania between 1916 and 1950 have afforded means of identifying causes of disease and death. These observations were then translated into the eff ect of sports and physical exercise on health and longevity. Student sports play in college predicted a decreased risk of developing cardiovascular disease (CVD) at least up to age 50 years. Questionnaire surveys showed physical exercise (sports play, walking and stair climbing) in middle age to be inversely related to the later development of CVD and early death. In a 10-year follow-up between 1962 and 1972, alumni aged 35-74 years who expended greater than or equal to ≥ 2000 kcal week(-1) (8.4 MJ week -1 ) in such activities had a 25% reduced risk of CVD and death compared with less active men. But, the 'protective eff ect' of early athleticism waned unless a physically active life was maintained. In contrast, sedentary students who took up an active life were at a lower risk of CVD and death than former student athletes who gave up or reduced their physical activities in middle age. A total of 17,815 Harvard alumni aged 45-84 years were followed from a 1977 questionnaire survey through 1992, with 4399 deaths occurring. Death rates declined with increased levels of total activity (estimated in kilocalories), and declined also with increased intensity of effort measured as from none, to light, to moderately vigorous or vigorous sports play. Death rates at any given quantity of physical exercise were lower for men playing moderately intense sports than for less vigorous men. Over the age range, in the 16-year follow-up, Harvard alumni playing moderately vigorous or more intense sports gained 1.5 years by age 90 compared with less active men.

Objective: To quantify the relation of cardiorespiratory fitness to cardiovascular disease (CVD) mortality and to all-cause mortality within strata of other personal characteristics that predispose to early mortality. DESIGN--Observational cohort study. We calculated CVD and all-cause death rates for low (least fit 20%), moderate (next 40%), and high (most fit 40%) fitness categories by strata of smoking habit, cholesterol level, blood pressure, and health status., Setting: Preventive medicine clinic., Study Participants: Participants were 25341 men and 7080 women who completed preventive medical examinations, including a maximal exercise test., Main Outcome Measures: Cardiovascular disease and all-cause mortality., Results: There were 601 deaths during 211996 man-years of follow-up, and 89 deaths during 52982 woman-years of follow-up. Independent predictors of mortality among men, with adjusted relative risks (RRs) and 95% confidence intervals (CIs), were low fitness (RR, 1.52;95% CI, 1.28-1.82), smoking (RR, 1.65; 95% CI, 1.39-1.97), abnormal electrocardiogram (RR, 1.64;95% CI, 1.34-2.01), chronic illness (RR, 1.63;95% CI, 1.37-1.95), increased cholesterol level (RR, 1.34; 95% CI, 1.13-1.59), and elevated systolic blood pressure (RR, 1.34; 95% CI, 1.13-1.59). The only statistically significant independent predictors of mortality in women were low fitness (RR, 2.10; 95% Cl, 1.36-3.21) and smoking (RR, 1.99; 95% Cl, 1.25-3.17). Inverse gradients were seen for mortality across fitness categories within strata of other mortality predictors for both sexes. Fit persons with any combination of smoking, elevated blood pressure, or elevated cholesterol level had lower adjusted death rates than low-fit persons with none of these characteristics., Conclusions: Low fitness is an important precursor of mortality. The protective effect of fitness held for smokers and nonsmokers, those with and without elevated cholesterol levels or elevated blood pressure, and unhealthy and healthy persons. Moderate fitness seems to protect against the influence of these other predictors on mortality. Physicians should encourage sedentary patients to become physically active and thereby reduce the risk of premature mortality.

Longitudinal study of 16,936 Harvard alumni, followed for life-style experiences as related to cardiovascular disease (CVD) and longevity, identified 572 first coronary heart disease (CHD) attacks, 1962-1972, and 1,413 all-cause deaths, 1962-1978. Men expending 8.4+ MJ (2,000+ kcal) per week in walking, stair-climbing, and sports play were at 39% lower risk of developing CHD than less active classmates. Attributable risk estimates suggested: there might have been 16% fewer CVD deaths in the alumni population if every man had exercised 8.4+ MJ per week; 25% fewer from total cigarette abstinence; 9% fewer from abolition of hypertension; 6% fewer with less obesity; and 11% fewer CVD deaths in the absence of parental CHD. Discounting the influence of blood pressure status, cigarette habit, net weight gain since college, and parental history of early death, the more active alumni (39% of the population) are estimated to have lived on average one and one-quarter years longer than less active men.

The relation of resting heart rate on biennial ECG examinations to mortality rates over 30 years of follow-up of the Framingham cohort was examined based on 1876 total deaths and 894 cardiovascular deaths, evolving out of 5070 subjects free of cardiovascular disease at entry into the study. In both sexes, at all ages, all-cause, cardiovascular, and coronary mortality rates increased progressively in relation to antecedent heart rates determined biennially. A more impressive association to cardiovascular disease was observed in men than in women, which was independent of associated cardiovascular risk factors. Case fatality rates following coronary events also increased with antecedent heart rate and the fraction of coronary deaths as sudden death increased strikingly with heart rate in men 35 to 64 years of age. There was also a substantial excess of noncardiovascular deaths at high heart rates, and the proportion of all deaths resulting from cardiovascular disease did not increase with heart rate. The excess cardiovascular deaths with more rapid heart rates were also noted, excluding those with interim overt cardiovascular disease, suggesting an effect independent of preexisting cardiac damage.

That cigarette smoking is causally associated with development of cardiovascular disease is recognized unequivocally. Epidemiological studies worldwide have documented the many pathways of influence and synergism by which this ubiquitous but artificial habit exerts its ill effects on cardiorespiratory and other body systems, leading not only to cardiovascular disease but to cancer and other ailments. Current investigations among college alumni, women, elderly, and other subgroups provide data on how various independent influences combine with smoking to establish risk and promote pathogenesis of cardiovascular disease. Their findings also confirm that cigarette smoking is one of the strongest instigators. All of this knowledge has implications for the design and implementation of effective intervention programmes.