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Abstract & Commentary
Synopsis: Walking an hour or more per week lowered the risk of coronary heart disease in more than 39,000 women 45 years of age and older.
Source: Lee IM, et al. JAMA. 2001;285:1447-1454.
The purposes of this study were to find out how intense physical activity needs to be in order to reduce coronary heart disease (CHD) events in women, and to determine if physical activity modifies the risk of CHD in women with risk factors. This was a prospective study of 39,372 women aged 45 years or older. They were followed every 6 months for the first year then annually between 1992 and 1995. An extensive battery of variables was recorded at each visit. Participants estimated the average time they spend doing various physical activities per week. The relative risks of CHD for a given caloric expenditure were:
|Kcal/week||Relative Risk (confidence intervals)|
|< 200||1.0 (referent)|
|>1500||0.75 (0.50-1.12) (p for linear trend, 0.03)|
The more vigorous the activity, the lower the risk. However, even walking an hour or more per week reduced CHD risk, and it was the distance, not the pace, that mattered. Physical activity reduced CHD risk in women who were overweight, had elevated cholesterol levels, and who were current or former smokers. For women with hypertension, there was a U-shaped relationship, with increased CHD rates observed in the highest category of exercise. There was an inverse relationship between smoking status and degree of exercise and a direct relationship between alcohol consumption and degree of exercise.
Comment by Barbara A. Phillips, MD, MSPH, FCCP
Lee and associates set out to fill in some notable gaps in our knowledge about the role of exercise in preventing CHD in women. Physically active individuals have about half the rate of CHD than those who are sedentary,1 but few women were included in the studies on which this finding is based. Further, it is not clear how much or what kind of exercise is required to confer benefit. The Surgeon General2 and Centers for Disease Control3 have called for at least 30 minutes of moderate-intensity physical activity most days of the week, replacing an earlier recommendation to engage in vigorous-intensity exercise for at least 20 minutes 3 times a week.4
The current findings are important, because walking is the most popular leisure activity among women.2 Sometimes women are intimidated by the message that they must "exercise" for health. Emphasizing that walking "counts" may be an effective approach to take. Many of our patients have risk factors that they simply are not going to be able to conquer. It may be particularly important to stress the importance of walking to these individuals, since this paper indicates that exercise lowers CHD risk in women with known risk factors.
This paper is just one of many studies produced from the Women’s Health Study, a randomized, double-blind, placebo-controlled trial of low-dose aspirin and vitamin E for the prevention of cardiovascular disease and cancer.5 Since it is prospective and has a huge enrollment, impeccable methods, and intense follow-up (99% complete for this paper), its findings are credible and noteworthy.
1. Berlin JA, Colditz GA. Am J Epidemiol. 1990;132:612-628.
2. US Department of Health and Human Services. Physical Activity and Health: A Report of the Surgeon General. Atlanta, Ga: National Center for Chronic Disease Prevention and Health Promotion; 1996.
3. Pate RR, et al. JAMA. 1995;273:402-407.
4. Guidelines for Graded Exercise Testing and Exercise Prescription. 3rd ed. Philadelphia, Pa: Lea and Febiger; American College of Sports Medicine: 1985.
5. Buring JE, Hennekens CH. J Myocardial Ischemia. 1992;4:27-29.