The Impact of Physical Activity (Running) on Cardiovascular Outcomes
The World Health Organization and U.S. government's Physical Activity Guidelines recommend at least 150 minutes of moderate-intensity aerobic exercise per week. The impact of activity levels at either end of this spectrum (i.e., minimal activity or prolonged activity) on cardiovascular outcomes has not been well studied and is an area of active debate.
This study was performed in the context of The Aerobics Center Longitudinal Study, a prospective, observational cohort study designed to examine the effects of physical activity and fitness on various health outcomes. Participants in the study had their clinical evaluations at the Cooper Clinic in Dallas, Texas. Assessment of running or jogging activity during the previous three months was assessed by a physical activity questionnaire by this primarily college-educated, Caucasian cohort.
The association of running with all-cause and cardiovascular mortality risks was examined in 55,137 adults (mean age of 44 years). During a mean follow-up of 15 years, 3,143 all-cause and 1,217 cardiovascular deaths occurred. Compared with non-runners, runners had 30% and 45% lower adjusted risks of all-cause and cardiovascular mortality, respectively, with a three-year life expectancy benefit. In dose-response analyses, the mortality benefits in runners were similar across quintiles of running time, distance, frequency, amount, and speed.
Leisure-time running, even at levels well below the current minimum guidelines for physical activity, is associated with reduced risks of death from all causes and cardiovascular disease.
Lee and colleagues performed an interesting observational study examining the associations between habitual running (as assessed by medical history questionnaire) and mortality. As pointed out by the authors, key findings from this effort include the following: 1) runners had a 45% lower risk of cardiovascular mortality than non-runners; 2) significant mortality reduction was observed even among runners in the lowest "running dose" quintile (<51 minutes per week, i.e. 5-10 minutes per day); and 3) greatest longevity was observed among consistent runners as opposed to those who started or stopped regular running during the study period. This is an important study that reinforces the notion that physical exercise is a key determinant of cardiovascular health and overall longevity. The single most important clinical take-home from this paper is that some exercise, even very modest amounts of daily physical activity such as ~10 minutes of jogging, has the potential to improve health outcomes. Data from this paper reminds health care providers that patients deserve to receive this message from their physicians. In the era of designer medications and complex medical technology, simple physical activity remains among the most powerful tools to prevent cardiovascular disease.
Beyond this simple elegant finding, this paper provides several addition important insights. First, statistical analyses used to examine the relative importance of specific cardiovascular risk factors as they relate to all-cause and cardiovascular death (reported as "decreased life expectancy in years" in Table 2 in the article) indicate that being a non-runner confers similar risk hazard to several well-established traditional risk factors, including obesity, family history, hypertension, and diabetes. Thus, the independent importance of physical activity appears to parallel those associated with the risk factors that clinicians spend most of their time combating. Second, data from this paper advance our understanding of exercise, specifically running, "dose." A consistent and important finding from this paper is that most of the mortality benefit associated with exercise is appreciated among those with low levels of exposure. Put another way, pushing one's running speed or mileage beyond a slow and low baseline does not appear to confer incremental health benefits and accomplishes little more than higher exercise capacity, which is of high importance for some.
From our perspective, within the limitations of an observational questionnaire study, the conclusions from this study can be summarized as follows: 1) running is beneficial; 2) runners are not immune to cardiovascular disease; and 3) running does not substitute for control of other traditional cardiovascular risk factors. All physically active individuals and the doctors who care for them need to be mindful of traditional cardiovascular risk factors (i.e., hypertension, hyperlipidemia, and diabetes), as exercise does not confer complete immunity. Furthermore, even relatively minimal routine physical activity provides substantial physical benefit. This finding should help physicians counsel their patients to be active, and to emphasize that even small amounts of exercise can afford clinical benefits. Finally, it is noteworthy that while the increasing exercise doses examined in this study did not confer incremental benefit, they were not associated with any clear signal of harm. While this study addresses an area deserving of future investigation, data from this study may serve as reassurance to athletes and highly active patients who choose exercise doses above and beyond what is needed to maximize cardiovascular health.
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