Exercise and Modifiable Cardiac Risk Factors

Posted by Blog Sunday, February 20, 2011

Risk FactorsEffect of Exercise
Physical inactivityImproved
Unfavorable cholesterol levelsImproved
C-reactive proteinImproved
Faced with a near epidemic of coronary artery disease, researchers have identified a series of factors that increase risk. People can’t do anything about three risk factors: having relatives with heart disease, being male, and growing older all indicate vulnerability. But other cardiac risk factors can be modified to help prevent heart attacks . Physical inactivity is one of the strongest harbingers of trouble. Researchers at the Centers for Disease Control and Prevention have calculated that sedentary folks are nearly twice as likely to suffer heart attacks as physically active people. Exercise is the only remedy for inactivity, but can it also help correct other risk factors? In the case of seven of the nine remaining major factors, the answer is yes.

 These physiological effects of exercise should do a great job in protecting you from heart disease, but do they actually work? The first modern study of exercise and heart disease dates to 1953. The lead investigator was Professor J. N. Morris; his laboratory was the double-decker London bus. Dr. Morris and his colleagues evaluated thirty-one thousand male London Transport Service employees who were between the ages of thirty-five and sixty-four. They found that bus drivers who sat behind the wheel all day were 30 percent more likely to develop heart disease than the conductors, whose work kept them walking the aisles and climbing the stairs.

 Although it was a landmark report, this early study was naive by today’s standards. Professor Morris himself soon recognized an important limitation of the research: did inactivity lead to heart disease, or did men apply for the driver’s  ob because they were already unwell? In a follow-up investigation on the epidemiology of uniform size, Morris reported that men who signed up to be drivers had larger waists than those who applied to be conductors, implying that they were less healthy to begin with.

 Epidemiologists have now learned how to account for confounding variables, such as obesity, diabetes, smoking, blood pressure, and cholesterol, when they study the impact of exercise on heart disease and health. Professor Morris and his colleagues used these techniques to evaluate British civil servants, executives, and, in a second look, transport workers. In each case, exercise was linked to a 30 to 50 percent reduction in cardiac risk. And the last I heard, Jeremy Morris was active and well at age ninety.

The first major American studies of exercise and health were directed by Dr. Ralph Paffenbarger of Stanford University and the Harvard School of Public Health. In the mid-1970s, Dr. Paffenbarger reported that regular physical exercise was associated with a reduced risk of heart disease in San Francisco longshoremen. But his groundbreaking research of 1978 used quite a different study population: graduates of Harvard College. The results demonstrated clearly the cardiac benefits of exercise. The more that men exercised, the lower their risk of heart attack and death. Men who exercised enough to burn at least two thousand calories per week were 39 percent less likely to suffer heart attacks than their sedentary classmates

Even in its initial report, the Harvard Alumni Study provided additional details about exercise and health. Until then, some doctors argued that, like Professor Morris’s first group of transport workers, people exercise because they are healthy, not the other way around. But the Harvard study showed that the benefits of physical activity are not explained by genetic endowment or selfselection: men who were varsity athletes in college were no better off than their sedentary peers unless they continued to exercise in subsequent years. Much more recently, a major Finnish study of nearly sixteen thousand twins confirmed that the benefits of exercise depend on your muscles, not your DNA. The protection is kinetic, not genetic.

 The Harvard research also showed that people of all ages benefit; men as young as thirty-five and as old as seventy-four were included in the analysis, and all were protected by exercise. And in a follow-up study fifteen years later, the scientists demonstrated that it’s never too late to start. Previously sedentary men who didn’t exercise until after age forty-five clearly benefited, enjoying a 23 percent lower risk of death than their classmates who remained inactive. Substantial benefits were linked to amounts of exercise equivalent to walking for about forty-five minutes a day at a pace of about seventeen minutes per mile.

The original 1978 report of the Harvard Alumni Study also provided important insights into the “dose” of exercise that is best for health. Death rates declined steadily as physical activityincreased  from five hundred to three thousand calories per week, but at very high levels, the rewards of exercise leveled off in a plateaulike fashion. Figure 1.1 shows a graph from the original publication; based on this information, doctors have concluded that about two thousand calories of exercise a week would provide optimal benefits for longevity.

Finally, although the Harvard study demonstrated that the total amount of exercise was the main determinant of benefit, it also  found that vigorous exercise produced somewhat greater rewards than less intense activities. But while these insights remain meaningful and important, they are not the last word on what you need to do to be healthy  We’ll return to this graph and examine new data from the past ten years to help you determine the type and amount of exercise that will work best for you.

As important as it is, the Harvard Alumni Study is limited by the fact that all of its subjects are highly educated men—almost all white and upper-income American men at that. Not to worry. In the past quarter century, more than one hundred studies have evaluated exercise and health in men and women of diverse ethnic and socioeconomic backgrounds. Although the details vary, the conclusions of this vast array of independent studies are in broad agreement: regular exercise is associated with a sharp reduction in the risk of heart attacks and death from cardiovascular disease. Most studies peg protection in the range of 35 to 55 percent.

More About Exercise:

Exercise, your body,and your Health

Exercise and Your Body


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