While running, biking, and other endurance training have become popular means of exercise, too much could be hazardous to the heart.

That’s the key finding of a recent study from the Mayo Clinic that has turned the endurance sports and exercise world on its head.

The study, published by Dr. James O’Keefe in the June edition of Mayo Clinic Proceedings found that endurance training that goes over 40-60 minutes per day can cause serious negative effects to the heart and coronary artery, including scarring and remodeling which can result in an increased risk of heart diseases, heart attacks, and death.

How concerned should endurance exercisers and athletes be?

According to Dr. Dennis Humen, a cardiologist with the London Cardiac Institute and former president of the Canadian Nuclear Cardiology Society, it depends on the level of the athlete.

“Think of it as dealing with the engine of a Formula 1 racecar versus something that you’d bring into Jiffy Lube,” said Humen.

“Casual athletes or exercisers are going to be more hampered by other muscles before they are able to reach an intensity level that could cause damage to the heart. The casual athlete, even someone running a single marathon, doesn’t have anything to worry about.”

However, Humen indicated that the same cannot be said for elite level athletes who are pushing themselves too hard.

“High level athletes, the most elite marathon runners or endurance trainers, can reach a point where their bodies start to metabolize free radicals – unattached molecules that bond with, and cause damage to, cells.  The output from this process, combined with increased adrenaline levels is what can endanger the heart.”

Humen also noted that the symptoms indicated in the Mayo study are akin to those found in patients undergoing extreme body stress, including having heart failure.

“Similar damage to the Mayo findings has also been found as a result of takotsubo cardiomyopathy – heart damage as a result of extreme psychological distress,” said Humen.

“For example, autopsies in trauma victims, such as a plane crash victims, show contraction band necrosis – heart muscle cell death – believed to be from a spike in adrenaline and adrenaline-like compounds generated from the extreme stress of the situation.”

The level of endangerment indicated in the study has the potential to be extremely severe, said Humen, particularly the potential scarring of the heart.

“While small scarring won’t be a problem, if that scarring is continuously reaggrivated there can be serious health issues,” said Humen, who emphasized the need for a cool down period between races and training that most elite athletes don’t take.

While Humen supports Mayo’s findings, he also acknowledged the difficulty of making the information useful to athletes.

“The level of total body stress in pursuit of sport has a very real danger to damage the heart,” he said. “However, we still don’t know how frequent or to what extent that damages goes, nor do we know how many instances it takes for damage to cumulate or long-term effects of that damage.”

“There is no test for early signs of damage, we only catch it after it happens,” added Humen.

While the cardiology community is adamant of the dangers of endurance training, the athletic community does not share the same concern.

Alex Hutchinson, a senior editor at Canadian Running magazine, and former Canadian national team long-distance runner has taken issue with Mayo’s findings.

“The study finds there may be dangers from excessive running and exercise, but it fails to acknowledge that there are still several health benefits when going beyond 60 minutes a day,” said Hutchison.

“There’s a big difference between “doesn’t make me healthier” and “makes me less healthy.” I think it’s reasonable to assume that, if you’re already running 60 minutes a day, most people won’t get significant further health benefits by increasing the amount that they run beyond that. But will it make them less healthy? I don’t think so, and that’s what the Mayo study is claiming,” he added.

24-year-old McMaster University biology masters student and competitive triathlete Andrew Bycise shares Hutchinson’s feelings towards the study findings.

“I believe someone could develop scarring of the heart if they pushed themselves too hard and didn’t take the appropriate time to recover.  But so far there have been no long-term negative effects found, so I feel I’ll be all right as long as I take recovery time after training hard or racing.”

Bycise, who spends upwards of 25 hours a week on the track, on the bike, or in the pool added that the study would not influence his training approach in any way.

Still, Dr. Humen emphasizes the need for athletes to keep regular consultations with a doctor. A doctor is in the best place to tell you about your heath, he said.

Environmental Health Perspectives, 2012.

Citation: Tong H, Rappold AG, Diaz-Sanchez D, Steck SE, Berntsen J, et al. 2012 Omega-3 Fatty Acid Supplementation Appears to Attenuate Particulate Air Pollution Induced Cardiac Effects and Lipid Changes in Healthy Middle-Aged Adults. Environ Health Perspect doi:10.1289/ehp.1104472

Omega-3 Fatty Acid Supplementation Appears to Attenuate Particulate Air Pollution Induced Cardiac Effects and Lipid Changes in Healthy Middle-Aged Adults

Haiyan Tong, Ana G. Rappold, David Diaz-Sanchez, Susan E. Steck, Jon Berntsen, Wayne E. Cascio, Robert B. Devlin, James M. Samet

The authors state the background for their study: “Air pollution exposure has been associated with adverse cardiovascular health effects. Findings of a recent epidemiologic study suggested that omega-3 fatty acid (fish oil) supplementation blunted cardiac responses to air pollution exposure.”

The results of the study were as follows: “Fish oil supplementation appeared to attenuate CAP-induced reductions in high-frequency/low-frequency ratio (HF/LF), as well as elevations in normalized LF (nLF) HRV, and prolongation of the QT interval corrected for heart rate (QTc). Very low-density lipoprotein and triglyceride concentrations increased significantly immediately after exposure to CAP in participants supplemented with olive oil, but not in those supplemented with fish oil.”

The authors conclude, “Exposure of healthy middle-aged adults to CAP for 2 hr induced acute cardiac and lipids changes following supplementation with olive oil, but not fish oil. Our findings suggest that omega-3 fatty acid supplements offer protection against the adverse cardiac and lipid effects associated with air pollution exposure.”