The Greater the Amount of Exercise, the Less Risk for Coronary Heart Disease
The Greater the Amount of Exercise One Does, the Less Risk There is for Coronary Heart Disease
Abstract & Commentary
Synopsis: In the Nurses’ Health Study of 72,488 female nurses, greater amounts of exercise were associated with greater reductions in coronary heart disease.
Source: Manson JE, et al. N Engl J Med 1999;341:650-658.
There have been a number of studies demonstrating that physical activity was associated with a decrease in the risk of coronary heart disease but as Manson and colleagues point out, the data on women have been sparse. The Nurses’ Health Study, which was initiated in 1976, has provided an opportunity to examine the progression and associations of various diseases in an unprecedented manner.
This study examined the association between the score for total physical activity, walking, and vigorous exercise and the incidence of coronary events among 72,488 female nurses who were 40-65 years of age in 1986. During eight years of follow-up, 645 coronary events occurred (nonfatal myocardial infarction [MI], or death from coronary disease).
There was a strong inverse association between physical activity and the risk of coronary events. As compared with women in the lowest quintile group for energy expenditure, women in increasing quintile groups had age-adjusted risks of 0.77, 0.65, 0.54, and 0.46 for coronary events (P < 0.001). Sedentary women who became active in middle adulthood or later had a lower risk of coronary events than their counterparts who remained sedentary.
Physical activity was inversely related to the risk of coronary events in all strata for smoking (never, previously, and currently), for both obese and nonobese women, and for women with and without a parental history of premature MI. Women who smoked and had a parental history of MI, although benefiting from exercise, still had an increase in coronary heart disease despite their exercise.
The conclusion stated that the data indicate that brisk walking and vigorous exercise are associated with similar reductions in the incidence of coronary events among women.
Comment by Ralph R. Hall MD, FACP
There seems to be great resistance to conclude that the more vigorous the exercise the greater the benefits for preventing coronary heart disease. The data in the article indicate that the greater the number of Met-hours per week the less the risk for a coronary event. Walking continues to be emphasized because it is easy to do. Apparently, there is a concern that if strenuous exercise is recommended, fewer people will exercise. The walking pace with the greatest benefit is brisk (i.e., > 3 miles per hour). Williams has continually attempted to get out the message that a bit more vigorous exercise may be beneficial.1
Although not in the conclusion, Manson et al note that 1 ½ hours of vigorous exercise is equivalent to three hours of brisk walking. This is important information for those who are pressed for time during a busy work week. My own formula is: time × intensity = level of fitness.
This study is important for a number of reasons. It is the first large study that includes an adequate number of females. Their data also demonstrate the significant benefit of stopping smoking. Although exercise tended to decrease the risk of MI in smokers, there was a dramatic benefit for the women who stopped smoking and exercised. Another finding in this study was that beginning exercise later in life was beneficial and resulted in a decreased number of MI. This confirms the finding in the classic article by Blair and associates, which included predominantly men.2
The women who were physically active were leaner and had a lower prevalence of hypertension, diabetes, and hypercholesterolemia. They were also more likely to use hormone replacement therapy, multivitamin and vitamin E, and alcohol. When these factors were corrected for statistically, the correlation with exercise and a decreased incidence of MI was just as strong.
Manson et al end with the statement, "Although vigorous exercise should not be discouraged for those who choose a higher intensity of activity, our results indicate the enormous public health benefits would accrue from the adoption of a regular moderate-intensity exercise by those who are currently sedentary."
References
1. Williams PT. N Engl J Med 1996;334:1298-1303.
2. Blair SN, et al. JAMA 1989;262:2395-2401.
Which of the following statements is false?
a. Exercise did not decrease the incidence of MI in women who smoked.
b. When corrected for body mass index, exercise did not decrease the incidence of MI.
c. Women who began exercising after 50 years of age decreased their chances of having a coronary event.
d. None of the above
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