Exercise: How Much and What Type to Prevent Heart Disease?

Source: Tufts University
December 20, 2002 (Reviewed: December 16, 2004)

Studies have shown regular physical activity to be associated with a lower risk for coronary heart disease (CHD), but relatively little is known about exactly how much and what type of exercise is most beneficial.

In a recent study published in JAMA, Harvard researchers found that running, rowing, weight-training, and walking were all associated with a reduced risk for heart disease, and that increased intensity and duration of exercise lowered the risk even further.

Assessing exercise type and CHD risk in men

Researchers studied a cohort of 44,452 men aged 40-79 from the Health Professionals' Follow-up Study. Subjects completed detailed lifestyle questionnaires at baseline (1986) and again every two years until 1998. The primary end points studied were fatal and nonfatal myocardial infarction.

Men with a history of CHD and cancer were excluded from the analysis, and potential confounding factors, such as body mass index (BMI), history of diabetes or hypertension, diet, alcohol use, and smoking status were controlled for.

The results

During 475,755 person-years of follow-up, 1700 new cases of CHD occurred. The types of exercise that were associated with lower CHD risk included the following:

• Running for an hour or more per week (compared with no running) was associated with a 42% risk reduction (RR, 0.58; 95% CI 0.44-0.77, p<.001).
• Weight-training for 30 minutes or more per week (compared with no weight-training) was associated with a 23% risk reduction (RR, 0.77; 95% CI 0.61-0.98, p=0.03).
• Rowing for an hour or more per week (compared with no rowing) was associated with an 18% risk reduction (RR, 0.82; 95% CI 0.68-1.00, p=0.04).
• Brisk walking for 30 minutes or more a day (compared to no walking) was associated with an 18% risk reduction (RR, 0.82; 95% CI 0.67-1.00, p=0.04).

Compared with men who walked at slower paces, men who walked at a very brisk pace (4 mph or greater) had the greatest risk reduction (49%) (RR, 0.51; 95% CI 0.31-0.84, p<.001), suggesting, say the authors, that "walking pace is related to reduced CHD risk over and above the effect of walking volume."

Other activities, such as swimming and cycling, did not produce statistically significant risk reductions, but the researchers caution that it may be because only a very small percentage of the cohort engaged in these activities.

The potential benefits of exercise

While the exact mechanisms by which exercise may have lowered heart disease risk in this study are unknown, the authors offer several suggestions, including improved oxygen supply to the heart, improved lipid profiles, decreased blood pressure, and increased insulin sensitivity.

Although these finding are encouraging, the study has some limitations that are important to consider. Among these are the potential for subjects to report their activity levels inaccurately, and for unknown confounding factors to affect the results. In addition, the results cannot necessarily be generalized to women.

Practical advice for patients

Still, the results underscore current US guidelines recommending at least 30 minutes of moderate-level activity on most, if not all, days of the week. While the runners in this study had the greatest risk reductions, the study also shows that brisk walking may protect against CHD - good news for patients who find the prospect of more intense activity daunting.

This study also adds more evidence of the benefits of strength-training. While weight-training lowered CHD risk in this study, evidence already exists for its protective effects on the musculo-skeletal system.

Source

• Exercise type and intensity in relation to coronary heart disease in men. M. Tanasescu, MF. Leitzmann, EB. Rimm,  et al., JAMA, 2002, vol. 288, pp. 1994--2000

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