Who do you think would have more artery clogging in the heart: (A) a group of sedentary, overweight men; or (B) a group of men who are slightly older, much leaner, and have run at least one marathon annually for 25 years?

If you picked (A), you would be wrong, at least according to a new report in the March/April 2014 issue of Missouri Medicine. Its supporters believe the new study adds weight to the “excessive endurance exercise hypothesis,” which posits that too much exercise, like marathon training and racing, has negative effects on the heart.

The article, “Increased Coronary Artery Plaque Volume Among Male Marathon Runners,” was authored by a large group of contributors including the father/son cardiologists Robert and Jonathan Schwartz; cardiologist James O’Keefe, perhaps the leading voice in the excessive exercise movement; and Runner’s World “sports doc” William Roberts, who has been reporting on marathon-race fatalities for several decades.

The “artery plaque” paper investigated 50 men (average age 59) who had run at least one marathon a year for 25 years vs. a sedentary control group (average age 55). The marathoners had significantly lower weight, BMI, hypertension, lipids, diabetes, and resting heart rates. In fact, none of the 50 marathoners had diabetes vs. 17 percent of the sedentary men. The marathoners also had significantly higher HDL cholesterol levels. All good so far.

But, “Male marathon runners however had paradoxically increased total plaque volume, calcified plaque volume, and non-calcified plaque volume.” The non-calcified plaque is a particularly troublesome finding, since this is the kind of softer cholesterol deposit that can become dislodged from the artery wall, and cause a heart attack or stroke.

The investigators used coronary calcium scans to measure the degree of atherosclerotic plaque in subjects. Studies have shown that high calcium scores, sometimes called Agatson scores, are linked to higher future mortality rates, even among those with no symptoms of heart disease.

The new “artery plaque” study did not look for mortality rates or longevity, but only at a measure of heart health, i.e., the calcium score. "This clearly was not an outcomes study," principal author Robert Schwartz told Runner's World Newswire. "In the general population, coronary calcium is unequivocally the best predictor of cardiac events, but is the same true for marathoners? No one knows. There's simply no data now. We need followup studies over time to get the answer."

Coauthor William Roberts, who's also medical director of the Twin Cities Marathon, notes: "When the sedentary group starts shoveling snow or racing after a bus, they're going to be at much higher risk than the runners. We don't see marathon runners dropping dead on a regular basis at Twin Cities. I'd rather be a marathoner than one of the sedentary guys."

The marathoners in the Schwartz et al study included a surprising number of former or current smokers, 52 percent vs. 39 percent among the controls. Since smoking is known to influence heart and other health outcomes, this could confound the results of the study.

Additionally, as with all observational studies, there is always the chicken and egg question. Runners might call it the “Jim Fixx dilemma.” Did Fixx die of a heart attack while running because he liked to log 10 miles a day and run marathons? Was he “excessive?” Or did he die because he was an overweight smoker for many years before he changed his habits?

Observational studies can’t answer these questions; they can’t unravel cause and effect. In their conclusion, the Schwartz et al authors note that the perfect experiment on marathoners and heart health “is practically impossible, and will never be done.”

It's also possible that the marathoners would have "wider pipes" than the sedentary controls. This has been a frequent finding since a 1961 autopsy report of seven-time Boston Marathon champ Clarence DeMar found his coronary arteries to be "two or three times the normal size." DeMar died of cancer at age 70 in 1958.

"Until we have more and better information, the bulk of data still suggests that you're better off running than not running," says Boston Marathon cardiologist Aaron Baggish, co-author of the RACER (Race Associated Cardiac Arrest Event Registry) that concluded, "Marathons and half-marathons are associated with a low overall risk of cardiac arrest and sudden death." Baggish adds: "I'd never suggest that anyone needs to log 26.2 miles regularly to maximize their health, but we have no reason to believe there is any danger in doing so."

Lacking better information, we know that running and occasional marathoning is healthy for the vast majority of participants who don’t have the time, desire, or talent to chase Olympic fame. We also realize that runners can die while jogging to the mailbox and back, or while running marathons. The most important guideline is: Listen to your body, and take action when you note symptoms such as unusual shortness of breath, or chest and arm tightness.

We likewise know that lifestyle is a substantial contributor to health — diet, smoking, stress, and more. They can make a big difference. Nonetheless, 30 to 50 percent of your risk for many diseases resides in your genes.

With the huge growth in running’s popularity, and the aging of the “first boom” runners, it seem likely that we will hear more stories about runners dying on the run. We just won’t know whether running shortened their lives, or added more joy and more years.

[Added March 26: A similar look at 25-year women marathoners vs controls found that the controls had a "significantly higher" prevalence of coronary plaques. However, the volume of plaque between controls and marathoners (who had plaque) was equivalent.]

Below are some other important study results for runners looking for reassurance.

High coronary calcium scores associated with less heart disease in the highly fit.

Veteran ultramarathoners (13 years x 2,500 miles/year) exhibit greater coronary artery expansion than controls.

Tour de France cyclists live 17 percent longer than normal population.

Vasaloppet (54-miles) cross-country skiers in Sweden have roughly 50 percent lower mortality risk across all age groups.

This content is created and maintained by a third party, and imported onto this page to help users provide their email addresses. You may be able to find more information about this and similar content at piano.io