Elsevier

Mayo Clinic Proceedings

Volume 89, Issue 9, September 2014, Pages 1187-1194
Mayo Clinic Proceedings

Original article
Increased Cardiovascular Disease Mortality Associated With Excessive Exercise in Heart Attack Survivors

https://doi.org/10.1016/j.mayocp.2014.05.006Get rights and content

Abstract

Objective

To test whether greater exercise is associated with progressively lower mortality after a cardiac event.

Patients and Methods

We used Cox proportional hazard analyses to examine mortality vs estimated energy expended by running or walking measured as metabolic equivalents (3.5 mL O2/kg per min per day or metabolic equivalent of task-h/d [MET-h/d]) in 2377 self-identified heart attack survivors, where 1 MET-h/d is the energy equivalent of running 1 km/d. Mortality surveillance via the National Death Index included January 1991 through December 2008.

Results

A total of 526 deaths occurred during an average prospective follow-up of 10.4 years, 376 (71.5%) of which were related to cardiovascular disease (CVD) (International Statistical Classification of Diseases, 10th Revision codes I00-I99). CVD-related mortality compared with the lowest exercise group decreased by 21% for 1.07 to 1.8 MET-h/d of running or walking (P=.11), 24% for 1.8 to 3.6 MET-h/d (P=.04), 50% for 3.6 to 5.4 MET-h/d (P=.001), and 63% for 5.4 to 7.2 MET-h/d (P<.001) but decreased only 12% for ≥7.2 MET-h/d (P=.68). These data represent a 15% average risk reduction per MET-h/d for CVD-related mortality through 7.2 MET-h/d (P<.001) and a 2.6-fold risk increase above 7.2 MET-h/d (P=.009). Relative to the risk reduction at 7.2 MET-h/d, the risk for ≥7.2 MET-h/d increased 3.2-fold (P=.006) for all ischemic heart disease (IHD)–related mortalities but was not significantly increased for non–IHD-CVD, arrhythmia-related CVD, or non–CVD-related mortalities.

Conclusion

Running or walking decreases CVD mortality risk progressively at most levels of exercise in patients after a cardiac event, but the benefit of exercise on CVD mortality and IHD deaths is attenuated at the highest levels of exercise (running: above 7.1 km/d or walking briskly: 10.7 km/d).

Section snippets

Patients and Methods

Subjects self-identified as having had a previous heart attack on their baseline survey questionnaires were identified from the National Runners' Health Study (recruited between 1991 and 1994 and between 1998 and 2001) and the National Walkers' Health Study (recruited between 1998 and 2001).2, 23, 24, 25 Walking energy expenditure (metabolic equivalent of task-h/d [MET-h/d]) was calculated by converting the usual distance walked per week into duration (ie, distance/mph) and then calculating the

Results

We excluded 25 of the original 2402 subjects because they survived less than 1 year since their baseline survey, leaving 942 male and 631 female heart attack survivors from the National Walkers' Health Study and 678 male and 126 female heart attack survivors from the National Runners' Health Study (Table 1). Greater energy expended by running or walking was associated with more marathons run per year, less red meat consumption, more fruit consumption, lower body mass index, greater education,

Discussion

These analyses show that greater exercise energy expenditure by walking and running was associated with a significantly lower risk for CVD-related mortality in proportion to the exercise dose through 7.2 MET-h/d, an energy expenditure approximately equivalent to running 30 miles or 50 km per week,27 or walking briskly 46 miles or 75 km per week.30 Those who expended 3.6 to 5.4 MET-h/d (equivalent to 15-23 miles/wk or 25-37 km/wk run) had 50% lower risk for CVD-related mortality than did those

Conclusion

These analyses provide what is to our knowledge the first data in humans demonstrating a statistically significant increase in cardiovascular risk with the highest levels of exercise. Moreover, we demonstrated the increased risk prospectively. These data were obtained in heart attack survivors and require confirmation in cohorts of healthy subjects before concerns about excessive exercise can be extended to the general public. Fewer than 6% of the heart attack survivors actually exceeded 7.2

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    For editorial comment, see page 1171; for a related article, see page 1195

    Grant Support: This research was supported by grant HL094717 from the National Heart, Lung, and Blood Institute and was conducted at the Ernest Orlando Lawrence Berkeley National Laboratory (Department of Energy DE-AC03-76SF00098 to the University of California). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

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