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In reply—Cardiovascular Disease Mortality and Excessive Exercise in Heart Attack Survivors

      We thank Hung et al for their letter. We agree that these novel results should be approached with caution, and we wish to emphasize that there was a substantial reduction in mortality with increasing exercise up to 30 miles (48 km) per week in our cohort. We suspect that the contrasting findings between The FIT (Henry Ford ExercIse Testing) Project and the National Runners’ Health Study and National Walkers’ Health Study are due to differences in study design.
      The FIT Project measured treadmill exercise performance and found that the most-fit heart attack survivors had the largest reduction in mortality, whereas we found an increase in mortality among our most active runners and walkers who had diagnosed coronary heart disease. Fitness, as measured by treadmill exercise performance, is often equated with habitual physical activity, but these 2 parameters are not identical. Elsewhere we have reported that cardiorespiratory fitness and physical activity have very different relationships to cardiovascular disease.
      • Williams P.T.
      Physical fitness and activity as separate heart disease risk factors: a meta-analysis.
      This is especially important in heart attack survivors because cardiorespiratory fitness may be strongly influenced by the severity of the initial heart attack, and the severity of the attack likely affects both exercise capacity and survival. We have not directly measured cardiorespiratory fitness in our cohort but have used 10-km race performance as a surrogate measure because this factor correlates well with maximum oxygen consumption.
      • Cooper K.H.
      A means of assessing maximal oxygen intake: correlation between field and treadmill testing.
      The correlation between 10-km performance and exercise dose in our study was only r=0.29 (or 9% of the variance), documenting that exercise performance and habitual physical activity are not tightly related. In our cohort, 15% of the runners exceeded 7.2 metabolic equivalent of task-h/d (MET-h/d) of running and constituted our high-mileage runners, but these individuals were not the fittest runners. Specifically, 70% of the high-mileage runners were in the slowest 85% of the 10-km performance times. Consequently, the differences in results between The FIT Project and our report is likely due in part to our measuring habitual exercise and Hung et al’s measuring cardiorespiratory fitness.
      In addition, the greater risk we observed may be specific to cardiovascular disease mortality rather than morbidity and may involve mechanisms other than the traditional heart disease risk factors. We have reported no increased risk for nonfatal coronary heart disease
      • Williams P.T.
      Reductions in incident coronary heart disease risk above guideline physical activity levels in men.
      or coronary heart disease risk factors with greater exercise through running at least 39 miles (63 km) per week.
      • Williams P.T.
      Relationship of distance run per week to coronary heart disease risk factors in 8283 male runners: the National Runners' Health Study.
      • Williams P.T.
      Vigorous exercise, fitness and incident hypertension, high cholesterol, and diabetes.
      In fact, 2 other epidemiological cohorts reporting greater risk at higher exercise levels used mortality as their end point.
      • Mons U.
      • Hahmann H.
      • Brenner H.
      A reverse J-shaped association of leisure time physical activity with prognosis in patients with stable coronary heart disease: evidence from a large cohort with repeated measurements.
      • Wannamethee S.G.
      • Shaper A.G.
      • Walker M.
      Physical activity and mortality in older men with diagnosed coronary heart disease.
      Finally, we do not know what percentage of the patients in the studies cited by Hung et al ran more than 30 miles (48 km) per week, but we suspect it was not many. Because time-based estimates tend to overestimate exercise energy expenditure, participants reporting 7.2 MET-h/d or more of exercise in other studies (calculated from exercise duration and intensity) may actually be expending considerably less energy exercising than those who ran or walked 7.2 MET-h/d or more in our study (calculated from distance run or walked).
      • Williams P.T.
      Non-exchangeability of running vs. other exercise in their association with adiposity, and its implications for public health recommendations.

      References

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        Physical fitness and activity as separate heart disease risk factors: a meta-analysis.
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        A means of assessing maximal oxygen intake: correlation between field and treadmill testing.
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        • Williams P.T.
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        Atherosclerosis. 2010; 209: 524-527
        • Williams P.T.
        Relationship of distance run per week to coronary heart disease risk factors in 8283 male runners: the National Runners' Health Study.
        Arch Intern Med. 1997; 157: 191-198
        • Williams P.T.
        Vigorous exercise, fitness and incident hypertension, high cholesterol, and diabetes.
        Med Sci Sports Exerc. 2008; 40: 998-1006
        • Mons U.
        • Hahmann H.
        • Brenner H.
        A reverse J-shaped association of leisure time physical activity with prognosis in patients with stable coronary heart disease: evidence from a large cohort with repeated measurements.
        Heart. 2014; 100: 1043-1049
        • Wannamethee S.G.
        • Shaper A.G.
        • Walker M.
        Physical activity and mortality in older men with diagnosed coronary heart disease.
        Circulation. 2000; 102: 1358-1363
        • Williams P.T.
        Non-exchangeability of running vs. other exercise in their association with adiposity, and its implications for public health recommendations.
        PLoS One. 2012; 7: e36360

      Linked Article

      • Cardiovascular Disease Mortality and Excessive Exercise in Heart Attack Survivors
        Mayo Clinic ProceedingsVol. 90Issue 1
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          In an in-depth study of 2377 patients (mean age, 62.9 years; 32% women) published in the September 2014 issue of Mayo Clinic Proceedings, Thompson et al1 reported that higher levels of physical activity up to 7.2 metabolic equivalent of task-h/d were associated with survival benefits in heart attack survivors. Notably, physical activity beyond this level was found to be associated with poorer prognosis—a 2.6- and 3.2-fold increase in risk for all-cause and ischemic heart disease–related mortality, respectively.
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