Heart attack survivors may not reduce their risk of dying from another heart attack if they run or walk excessively, according to a study released Tuesday.
Out of a sample of 2,377 people, the study found that heart attack survivors who ran between 23 and 30 miles per week had a 63 percent less risk of dying from a heart attack than survivors who did not exercise often. But the study also found that survivors who ran more than 30 miles a week or walked more than 46 miles a week did not significantly decrease their risk of dying.
Lawrence Berkeley National Laboratory scientist Paul T. Williams and the chief of cardiology at Hartford Hospital, Paul D. Thompson, co-authored the study, which will appear in an upcoming issue of the Mayo Clinic Proceedings, an academic journal sponsored by the Mayo Clinic.
Thompson and Williams said they decided to conduct the research after reading several studies suggesting that excessive exercise negatively impacts the body.
“Our mission is really to provide the best exercise prescription,” Williams said. “If people have heart attacks and then go running as far as possible and do as many marathons as possible, it may be prudent for them to be aware of their risk and consult a cardiologist.”
According to Thompson, the individuals in the study had all experienced heart attacks due to plaque buildup in their arteries caused by high cholesterol levels.
Researchers recruited runners for the study between 1991 and 1994 and again between 1998 and 2001. Researchers recruited people who walked for exercise between 1998 and 2001 and followed the participants until 2008. During the study, 526 participants died, and 376 of the deaths were related to cardiovascular disease.
According to Thompson, researchers followed individuals of varying ages. He suggested that a correlation between being a younger heart attack survivor and exercising more may explain the study’s results.
“It could be that the people who were younger and ran the most miles could have had worse heart disease,” Thompson said. “They probably had their first heart attack when they were younger.”
Ethan Weiss, an associate professor in the Cardiovascular Research Institute at UCSF, said some researchers have hypothesized that extreme exercise can deprive heart cells of oxygen. Researchers have said this could lead to the buildup of scar tissue, causing heart attacks. But Weiss said he believes that hormones released during extreme exercise could be the culprit.
“My guess is that it has something to do with adrenaline,” Weiss said. “Exposing heart muscles to high levels of stress hormones can have adverse effects on the heart muscle.”
Williams said he hopes to receive additional funding to continue his study of heart attack survivors.