Some of the same blood markers that spike following a heart attack also skyrocket in amateur long-distance runners, especially those who do a full marathon, researchers say.
The small study in Spain tested non-professional runners before and after 10K, half-marathon and full-marathon races and found that a protein called troponin, which indicates damage to the heart muscle, surges to many times its normal level after a full marathon. It's not clear if this represents long-term damage, however, the study team writes in the journal Circulation.
"The main conclusion is that cardiac stress during a marathon is higher than the cardiac stress produced by competing in shorter-distance events, at least in athletes with low experience and low training background," the study's senior author Juan Del Coso, director of the exercise physiology laboratory at Camilo Jose Cela University in Madrid, told Reuters Health in an email.
The new study grew out of previous work that looked at the impact of endurance events on other muscles in the bodies of amateurs who are not able to train as hard as professionals prior to competitions, Del Coso said.
"We have found a relationship between the lack of training and high levels of muscle damage and we started to believe this 'damage' in skeletal muscle could also happen in the (heart's muscle fibers)," Del Coso said. "If we look at the practical applications of our investigation, (this suggests) potential marathon runners should prepare the race with a professional coach, decide to compete in the race after an adequate training background and with planned nutrition and hydration strategies."
Del Coso and his colleagues measured several biomarkers in the blood of 63 volunteers, whose mean age was 37, before races and again 10 minutes after the competitions were finished. Two types of biomarkers showed small increases, but cardiac troponins rose dramatically with increasing race distance.
While deaths in long distance races are relatively rare, we shouldn't forget that the runner who sparked the marathon competitions, the Greek herald, Pheidippides, who in 490 BC ran a distance of about 26 miles from Marathon to Athens with the news of the victory his people had over the Persians died shortly after delivering that news, said Dr. James Glazier, a cardiologist at Detroit Medical Center and a clinical professor of medicine at Wayne State University in Michigan, who wasn't involved in the study.
The increase in troponin levels "suggests that marathons put quite a strain on the heart," Glazier said. "Other studies that looked at MRIs of the hearts of runners showed that they can become very enlarged after a race and we worry that with competitive running you might get some scarring of the heart and then maybe some rhythm problems."
Large increases in troponin levels are "generally associated with irreversible cardiac damage," said Alan Wu, a professor of laboratory medicine at the University of California, San Francisco and laboratory director of San Francisco General Hospital. Wu's lab is responsible for testing the troponin levels of patients who show up at the hospital with a suspected heart attack.
Still, exercise is good for heart health, said Wu, who was not involved in the new research. "But on this occasion the runners may have exceeded what is acceptable for them. And maybe there was some cardiac injury. But the heart is one of the few organs that remodels. I think the lessons here are that conditioning and exercise are always good things and would far outweigh the injury that might have occurred in one event, and as with anything in life, you have to take things in moderation."
The new study should spark more research in the area to determine whether there are any long-term effects, said Dr. Ali Nsair, co-director of the Sports Cardiology Program at the University of California, Los Angeles. "Studies have shown increased rates of fibrosis in marathon runners, but what that means clinically remains to be determined," said Nsair, who was not involved in the new study.
"The one take-home message from all of this is that these athletes should be screened for any baseline cardiac abnormalities - inherited weaknesses that could progress over time. Hypertrophic cardiomyopathy (an abnormal thickening of the heart), for example, is something we see in athletes with sudden cardiac death," Nsair said.