Epidemiologic Evidence Supporting Physical Activity

In the United States alone, it has been estimated that roughly 250,000 deaths per year are attributed to lack of regular physical activity3 (roughly one-quarter of all preventable deaths annually). However, others have suggested that these figures may be significantly underestimated.23 Ongoing longitudinal studies have provided consistent evidence of varying strength documenting the protective effects of activity for a number of chronic diseases, including CHD, chronic heart failure (CHF), type 2 diabetes, hypertension, osteoporosis, and site-specific cancers.2,3,6 In contrast, low levels of physical fitness or activity are consistently associated with higher cardiovascular and all-cause mortality rates.2,3,13,14 Midlife increases in physical activity, fitness level, or both, through change in occupation or recreational activities, are associated with a decrease in mortality rates.24,25 Considering the last few years alone (2000-2004), an impressive volume of data has been published throughout the European Union and the US confirming the association between physical activity and cardiovascular health; some notable examples of these cohorts are presented in Table 13-3.

The landmark epidemiologic work of Paffen-barger and associates among Harvard alumni24,26 has been particularly persuasive in support of physical activity, and thus the development of the CDC, AHA, ACSM, and European Working Group guidelines. Table 13-4 illustrates the rates and relative risks of death over a 9-year period among 11,864 Harvard alumni by patterns of physical activity. Several findings in Table 13-4 are particularly noteworthy. The largest benefits in terms of mortality appear to accrue through engaging in moderate activity levels; moderate is generally defined as activity performed at an intensity of 3 to 6 METs, roughly equivalent to

Table 13-3. Recent cohorts (2000-2004) supporting the role of physical activity in predicting health outcomes

Framingham Heart Study (Boston)

Belgian Physical Fitness Study

Physicians Health Follow-up Study (Boston)

Nurses Health Study (Boston)

VA Health Care System (Palo Alto)

The Whitehall Study (London)

Seven Countries Study (US, Europe, multicenter)

National Center for Chronic Disease Prevention and Health Promotion

(CDC, Atlanta) The SENECA Study (Europe, multicenter) Baltimore Longitudinal Study on Aging Finnish Twin Study

Aerobics Center for Longitudinal Research (Dallas)

Honolulu Heart Study

Canada Health Survey

Harvard Alumni Health Study (Boston)

Copenhagen Male Study

Zutphen Elderly Study (Greece)

Osteoporotic Fractures Research Group (US, multicenter)

Caerphilly Wales Study

Puerto Rico Heart Health Program

Nordic Research Project on Aging (NORA)

Lipid Research Clinics Follow-up (Baltimore)

brisk walking for most adults. Note also that regular, moderate walking or sports participation is associated with 30% to 40% reductions in mortality (relative risk of death 0.60 to 0.70). Likewise, the physical activity index, expressed as kilocalo-ries per week (the sum of walking, stair climbing, and sports participation), suggests that a 40% reduction in mortality occurs by engaging in modest levels of activity (1000 to 2000kcal/week, equivalent to three to five 1-hour sessions of activity), whereas only minimal additional benefits are achieved by engaging in greater-intensity activity. These findings agree closely with earlier results among 16,936 Harvard alumni assessed in the early 1960s and followed for all-cause mortality for nearly 20 years.26 Similar results have been reported from large studies that have followed cohorts for CHD morbidity and mortality in the range of 10 to 20 years among British civil servants, US railroad workers, San Francisco longshoremen, nurses, physicians, other healthcare workers, and other cohorts (for review, see Kohl27 or Lee and Paffenbarger28). Clearly, the evidence linking a physically active lifestyle and cardiovascular health is substantial.

Table 13-4. Rates and relative risks of death* among Harvard alumni, by patterns of physical activity

Relative

P value of trend

Table 13-4. Rates and relative risks of death* among Harvard alumni, by patterns of physical activity

Relative

Deaths

per

Relative

Physical activity

No. of

10,000

risk of

(weekly)

Man-years (%)

deaths

man-years

death

Walking (km)

<5

26

228

86.2

1.00

5-14

42

275

67.4

0.78

15+

32

194

57.7

0.67

Stair-climbing (floors)

<20

37

341

80.0

1.00

20-54

48

293

62.9

0.79

55+

15

80

59.6

0.75

All sportsplay

None

12

156

88.9

1.00

Light only

10

152

97.4

1.10

Light and moderate

36

208

59.7

0.67

Moderate onlyt

42

178

56.4

0.63

Moderate sportsplay (h)

<1

30

308

92.9

1.00

1-2

41

126

58.2

0.63

3+

29

64

43.6

0.47

Index (kcal)§

<500

12

197

110.3

1.00

500-999

18

58

135

69.1

78.9

0.63

1.00

1000-1499

15

111

68.9

0.62

1500-1999

13

73

61.4

0.56

2000-2499

10

51

52.4

0.48

2500-2999

8

42

44

64.6

55.4

0.59

0.70

3000-3400

6

36

74.7

0.68

3500+

18

82

48.1

0.44

METs, metabolic equivalents. *Age-adjusted. +<4.5 METs intensity. +4.5+ METs intensity.

§Sum of walking, stair climbing,and all sportsplay.

Source: From Paffenbarger et al.26© 1994 Human Kinetics, Inc. All rights reserved. Reprinted with permission.

METs, metabolic equivalents. *Age-adjusted. +<4.5 METs intensity. +4.5+ METs intensity.

§Sum of walking, stair climbing,and all sportsplay.

Source: From Paffenbarger et al.26© 1994 Human Kinetics, Inc. All rights reserved. Reprinted with permission.

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