Health & Medical Heart Diseases

Jogging Dose and Long-term Mortality: Copenhagen Heart Study

Jogging Dose and Long-term Mortality: Copenhagen Heart Study

Discussion


In this prospective, observational study, which included 1,098 healthy joggers between 20 and 86 years of age who were followed up for 12 years, we compared the long-term all-cause mortality rates of light, moderate, and strenuous joggers with the long-term mortality rate of sedentary nonjoggers. We found a U-shaped association between jogging and mortality. The lowest mortality was among light joggers in relation to pace, quantity, and frequency of jogging. Moderate joggers had a significantly higher mortality rate compared with light joggers, but it was still lower than that of sedentary nonjoggers, whereas strenuous joggers had a mortality rate that was not statistically different from that of sedentary nonjoggers (Central Illustration).

It should be emphasized that even slow jogging (6 METs) corresponds to vigorous exercise and strenuous jogging corresponds to very heavy vigorous exercise (≥12 METs), which when performed for decades could pose health risks, especially to the CV system.

A recently published study of 55,000 adults between 18 and 100 years of age who were followed up for a mean of 15 years, using comprehensive analyses that controlled for potential confounding factors, reported that runners as compared with nonrunners had 30% and 45% lower risks of allcause and CV mortality, respectively, with a mean improvement in life expectancy of 3 years. Again, however, maximal CV longevity benefits were noted with moderate doses of running (specifically 6 to 12 miles per week), running durations of approximately 50 to 120 min per week, a running frequency of approximately 3 times per week, and a modest pace of approximately 6 to 7 miles per hour. Our findings are aligned in that a U-shaped or reverse J-shaped relationship was noted, whereas higher doses of running were associated with loss of approximately one-third to one-half of the CV mortality benefits linked to moderate doses of running. In fact, the most favorable running regimen for reducing CV mortality in that study was 6 miles per week, 3 running days per week, and a pace of 7 miles per hour.

Other studies that did not focus solely on joggers but instead on cumulative doses of exercise have also reported U-shaped or reverse J-shaped curves depicting the relationship between leisure-time physical activity and mortality. A number of large studies have found an inverse association between physical activity in leisure time and morbidity/mortality from CHD and all-cause mortality. However, even the first such landmark study by Paffenbarger et al. found that death rates declined steadily as energy expended on physical activity increased from <500 kcal per week to 3,500 kcal per week, beyond which mortality rates increased again. A weekly energy expenditure of 3,500 kcal is approximately equivalent to that required for running 35 miles, which is in the range of the upper limits for incremental health benefits from strenuous exercise identified by several recent large epidemiological reports. These studies found that a weekly cumulative dose of approximately 30 miles of running or 46 miles of walking is approximately the safe upper limit for optimizing long-term CV health and life expectancy.

Over the past 35 years, the number of Americans who jog has risen 20-fold. In 2013, the number of U.S. joggers was estimated to be 54 million. The number of marathon finishers has risen from 25,000 in 1976 to 541,000 in 2013, and approximately 1,960,000 people completed a half-marathon in 2013. The incidence of sudden cardiac death in these endurance races was very low in absolute numbers, although the rate was significantly higher (almost 4-fold) in marathons (1.01 per 100,000; 95% CI: 0.72 to 1.38) than in half-marathons (0.27; 95% CI: 0.17 to 0.43). Triathlons, which can involve even higher doses of strenuous exercise than marathons, also have been growing rapidly in popularity. In 1999, there were 127,824 members of USA Triathlon; this number grew to 510,859 in 2012.

Long-term strenuous endurance exercise may induce pathological structural remodeling of the heart and large arteries. Emerging data suggest that long-term training for and competing in extreme endurance events such as marathons, ultra-marathons, ironman distance triathlons, and very long distance bicycle races can cause transient acute volume overload of the atria and right ventricle, with transient reductions in right ventricular ejection fraction and elevation of cardiac biomarker levels. Months to years of repetitive injury in some people may lead to patchy myocardial fibrosis, particularly in the atria, interventricular septum, and right ventricle, creating a substrate for atrial and ventricular arrhythmias. Additionally, long-term excessive exercise may be associated with coronary artery calcification, diastolic dysfunction, and large artery wall stiffening. To our knowledge, there has been no study of the longevity of marathon, half-marathon, or triathlon participants, but such studies would clearly be informative.

Higher doses of running are associated with progressively better cardiorespiratory fitness as well as dose-dependent improvements in many CV risk factors, such as abdominal adiposity, glucose metabolism, and high-density lipoprotein cholesterol level, along with preservation of youthful levels of left ventricular compliance. Even so, accumulating evidence suggests that activity patterns that are ideal for promoting long-term CV health and enhancing life expectancy may differ from the high-intensity, high-volume endurance training regimens used for developing peak cardiac performance and maximum cardiorespiratory fitness.

Study Limitations


The strengths include the random population sample, prospective design, detailed information about potential confounding variables, and almost 100% complete follow-up. The limitations include the fact that the information about jogging used in the present analyses was solely obtained at the fourth examination (between 2001 and 2003); repeated assessments of jogging during follow-up would have strengthened the design. Even so, previous analyses suggest that jogging seems to be a fairly stable habit among Copenhagen residents. However, because our study was observational and not randomized, we can only show associations and not casual relationships. Through exclusion of all participants who had CHD, stroke, or DM, we partly ruled out a self-selection bias against jogging among sick subjects. Furthermore, we repeated the analyses after excluding all deaths within the first 2 years of follow-up and found similar results.

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