August 15, 2014
Heart attack survivors who exceed 30 miles of running per week may lose the health benefits accrued by running less, according to new research by the Department of Energy’s Lawrence Berkeley National Laboratory life sciences researcher Paul T. Williams. His work appears in an upcoming issue of the Mayo Clinic Proceedings. Similar results were found for walkers who expended 46 miles per week, the energy equivalent of running 30 miles. The study was co-authored by Paul D. Thompson, cardiologist at Hartford Hospital, CT.
The study included 2377 subjects who reported having had a prior heart attack when they enrolled in the National Runners’ and Walkers’ Health Study. During the average 10.4 years of follow-up there were 376 deaths due to cardiovascular disease. The risk of dying from a cardiovascular disease decreased progressively through about 30 miles run or 46 miles walked per week. Those achieving this level were at 70% lower risk than those who neither walked nor ran. But at higher exercise levels, the risk of a cardiovascular death was about 2.6-times greater. This wiped out all of the risk reduction accrued below 30 miles run or 46 miles walked, so much so that cardiovascular disease mortality in these patients was similar to those that hardly exercised.
“The results are surprising,” said Williams. “Our previous research has shown that heart disease risk factors and the risk for nonfatal heart attacks improved with greater running distance through at least 40 miles per week, with no indication that things got worst at higher mileages. Like other medical treatments, there appears to be a level that can be excessive.” Williams cautions that his findings were specific to heart attack survivors.
High intensity, life long endurance exercise has been previously associated with myocardial scarring, which could give rise to cardiac arrhythmias. Vigorous exercise is also known to acutely increase the risk for a heart attack during and immediately after exercise.
The results also showed that the current public health recommendations of 150 minutes of moderate intensity exercise (such as brisk walking) or 75 minutes of vigorous intensity exercise (such as running) may not be optimal in heart attack survivors. Those that met the recommendations decreased their mortality risk by 21%.
“The current finding underscores the importance of precisely defining the dose-response relationship between exercise and its health benefits,” said Williams. The National Runners’ and Walkers’ Health Study is a unique resource of Lawrence Berkeley National Laboratory that began in 1991 specifically for this mission.
Funding for this project came from the National Heart, Lung, and Blood Institute of the National Institutes of Health.