But, adding still more complexity to the issue, other recent studies have indicated that, even if longtime endurance athletes do develop heart problems such as atherosclerosis, their version of the disease may be different from and more benign than the types of heart disease that develop in less active people.
It was in hopes of bringing more clarity to the increasingly tangled question of how endurance training affects hearts that researchers from the University of Minnesota, Stanford University and other institutions decided, for the new study, to zero in on a unique group of runners: men who had participated in at least 25 consecutive Twin Cities marathons in Minneapolis-St. Paul.
These 50 runners, identified by marathon participation logs, turned out to have completed, collectively, 3,510 marathons, with each runner, individually, having finished anywhere from 27 to 171 of the races.
The men obviously were experienced endurance athletes. They had trained for at least 26 years, and some for more than 50. Many had started competing in high school or earlier, but others had come to the sport much later, often, the researchers report, in hopes of ameliorating the effects of past lifestyle choices, such as smoking or junk food diets. Most were lean at the time of the study, but a few qualified as overweight, based on their body mass indexes.
Most ran 30 miles per week or more.
The researchers had each of these runners fill out detailed questionnaires about their training routines, as well as their general health history and habits.
Then they scanned the runners’ hearts to look for atherosclerosis.
Sixteen of the runners proved to have no plaque in their arteries at all. The rest had some deposits, with 12 displaying slight amounts, another 12 moderate levels, and 10 having worrisomely large deposits of plaques.
When the scientists compared the men’s running histories to their scan results, however, they found little relationship between how much they had run overall and how much plaque they had in their arteries. Those men who had run the greatest number of marathons did not tend to have less, or more, arterial plaque than the men who had run fewer races, indicating that extreme running itself had not increased the severity of heart disease.
On the other hand, a history of heavy smoking and high cholesterol was linked to greater levels of plaque, especially in the men who had begun running later in life.
The good news was that these findings suggest that years of hard running had not harmed the men’s hearts, says Dr. William O. Roberts, a professor of family and community medicine at the University of Minnesota, who led the study, which was published in Medicine & Science in Sports & Exercise. Indeed, all that running probably helped to keep some runners’ arteries clear.
But the exercise also had not inoculated those with a history of unwise lifestyle choices, especially smoking, against developing heart disease.
“You can’t just outrun your past,” Dr. Roberts says.
Of course, this study was relatively small and focused on Caucasian men with the physical, economic and psychological wherewithal to run competitively for years. Whether the results apply equally to other people and other sports is unclear. (Dr. Roberts and his collaborators published a small study earlier this year of female marathon runners that found almost no plaques in their hearts.)
This type of study also can show only relationships between running and heart health. It cannot prove that running directly caused any changes in the heart.
Still, the results may help to quell some runners’ and their families’ worries about the cardiac demands of long-term training. But if you misspent your youth smoking and eating poorly or have a family history of cardiac disease, you might want to talk with your physician about having your heart assessed, Dr. Roberts says, even if you have completed a marathon or two, or even 100.