The Impact of Physical Activity on Health

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In terms of mortality, in 1996 a study of over 32,000 men and women demonstrated that "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" [7]. For men, the adjusted relative

Adults

Both Regular Vigorous'

Regular Vigorous'

and Regular Sustained"1"

Inactive

Regular Vigorous'

Inactive

Not Regularly Active

Regular Sustained"

'Regular Vigorous-20 minutes 3 times per week of vigorous intensity f Regular Sustained-30 minutes 5 times per week of any intensity Source: CDC 1992 Behavioral Risk Factor Survey

Figure 4.1. According to the 1996 Surgeon General's report, 60% of the American adult population did not engage in regular physical activity and 25% were not physically active at all. (Report of the Surgeon General. Centers for Disease Control and Prevention, http://www.cdc.gov/nccdphp/sgr/ataglan.htm. Last accessed: February 23 , 2005 [1].)

risk (RR) of all-cause mortality due to low fitness was 1.52, while smoking was 1.65, and for women it was approximately 2.0 for both low fitness and smoking [7].

Another study evaluated the impact of physical activity on mortality among older women. The study consisted of 7753 white women 65 years old and older followed over 5.7 years. The results showed those women who were physically active at both the initial and follow-up visits had a lower all-cause mortality (RR 0.68) and cardiovascular mortality (RR 0.62) compared to sedentary women. These findings were not as strong for women over 75 years old or for those who were already in poor health [8].

Specifically focusing on women, The Women's Health Initiative Observational Study, which includes 73,743 postmenopausal women 50 to 79 years old, reported in 2002 that increasing PA resulted in a reduced relative risk for coronary artery disease. Each increasing quintile of energy expenditure lowered the risk of coronary artery disease from 1.0, 0.73, 0.69, 0.68, and 0.47. These findings were consistent across all races, ages, and BMIs [9].

The Nurses' Health Study consists of 72,488 participants with no cardiovascular disease or cancer in 1986 who complete extensive health questionnaires on a periodic basis. The data show an inverse relationship between the relative risk of ischemic stroke and physical activity level (Figure 4.2). The lowest quin-tile of physical activity had a relative risk of 1.0, and the highest had a relative risk of 0.52. Brisk walking (third quintile with 4.7 to 10.4 metabolic equivalents) was associated with an age-adjusted reduced risk of both total number of strokes (0.68) and ischemic stroke (0.69) [10].

With respect to men, the Health Professionals' Follow-up provides important data regarding heart disease and physical activity. This is a cohort study of 44,452 men surveyed every 2 years since 1986. Recent data from this study show that running for 1 hour or more per week conferred a 42% risk reduction of coronary heart disease compared to men who did not run. Weight training for 30 minutes or more per week resulted in a 23% risk reduction, and rowing for 1 hour or more per week resulted in an 18% risk reduction. Intensity of the PA was also associated with a reduced risk, independent of the duration of the activity [11].

5 10 15 20 25 30 35 Physical Activity Level, METs, h/wk

Figure 4.2. Spline regression model of multivariate relative risks of ischemic stroke according to total physical activity level. Total physical activity level is measured by metabolic equivalent tasks (METs) in hours per week. The solid black line represents point estimates; dotted lines represent 95% confidence intervals. (Reprinted with permission from Hu FB, Stampfer MJ, Colditz GA, et al. JAMA 283:2964 copyright © 2000, American Medical Association. All rights reserved.)

Patients who are physically active have a lower mortality rate and a decrease in the relative risk of cardiovascular disease and stroke. They also experience a reduction in the rate of the metabolic syndrome, which is a risk factor for diabetes and coronary heart disease (CHD) that is found in 23.7% of the US adult population [12]. In 2001, the National Institutes of Health published the Third Report of the National Cholesterol Education Program Expert Panel called the Adult Treatment Panel III (ATP III). This report describes the five components of the metabolic syndrome -elevated blood pressure, low HDL, raised triglycerides, insulin resistance, and abdominal obesity [13]. It lists therapeutic lifestyle change (TLC) as an important treatment modality for the metabolic syndrome and reduction of LDL cholesterol. Increased physical activity is one of the TLC components [13].

The largest study to date evaluating the impact of physical activity on the metabolic syndrome was published in May 2004. The data come from the Aerobics Center Longitudinal Study (ACLS), which includes 7104 women whose cardiorespiratory fitness (CRF) was objectively determined using a treadmill. These data show a metabolic syndrome prevalence of 19% among women in the least fit quartile, and a prevalence of 2.3% among those in the highest quartile of CRF [14]. The study participants were mostly white, educated women and did not represent the US population in terms of ethnicity and socioeconomic background. Also, the prevalence of the metabolic syndrome among this population (19% in the least fit quartile) was less than in the general population (23.7%), which indicates a selection bias in terms of health in this study cohort. Nevertheless, the difference within this population between the least fit and the most fit in terms of the prevalence of the metabolic syndrome is remarkable. A smaller, but more diverse population included African American (N = 49), Native American (N = 46), and white (N = 51) women with the metabolic syndrome. The data showed a trend similar to the ACLS results in terms of a lower rate of metabolic syndrome with a higher level of fitness compared to a lower level of fitness [15].

Physical activity, with or without weight loss, has positive effects on a variety of chronic diseases. These effects include reducing lipoproteins [16] and lowering the risk of glucose intolerance, diabetes [17], and breast cancer [18,19]. Physical activity is possibly as effective as medications in treating older patients with a major depressive disorder [20].

Physical activity has a positive impact on the health of obese patients whether or not weight loss occurs. One study divided premenopausal women into four groups: diet weight loss, exercise weight loss, exercise without weight loss, and control group. After 14 weeks, the data showed women in both the diet weight loss group and the exercise weight loss group lost weight. However, CRF improved only in the two exercise groups, and reduction in both total and abdominal fat occurred only in the exercise weight loss group [21]. Another study has shown a reduction in visceral adipose tissue in both older men and women that was inversely correlated with physical activity [22]. Finally, Ross and Katzmarzyk showed that "high CRF is associated with lower levels of total and abdominal obesity for a given BMI by comparison to those with a low CRF" [23].

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