Cardiovascular Disease / Exercise / running

Matters of the Heart: Marathons and Cardiovascular Health

Linear

LINEAR RELATIONSHIP

J curve

J-SHAPED “SWEET SPOT” CURVE

Running (or any chronic physical activity) reduces your risk of cardiovascular morbidity and mortality (disease and death). We know this to be true. However, a source of passionate disagreement among cardiologists, researchers and epidemiologists has been the nature of the relationship between exercise training and cardiovascular risk. Is it a direct, linear relationship, meaning that the more exercise you do each day (either in duration and/or intensity), the greater the cardiovascular health benefits? Or, is it a J-shaped curve (similar to a bell curve), meaning there’s a “sweet spot” for improved cardiovascular outcomes that occurs with moderate daily exercise, beyond which greater exercise has increasingly fewer or even negative health benefits?

Exponential

EXPONENTIAL DOSE-RESPONSE

Most scientists think the answer lies somewhere in between the two viewpoints.  There is an established dose-response with exercise such that more exercise is generally better with respect to lowering cardiovascular disease risk, but the greatest benefits are incurred on the lower to middle portion of the curve, such that avid, high-intensity endurance training doesn’t evoke as substantial a benefit as simply “not being sedentary.” In contrast to this view, however, some researchers have publically warned against extreme exercise, suggesting that there may actually be cardiac risks associated with long-term endurance exercise such as marathon running, cycling or triathlon training.  For example, some reports indicate that the risk of death is lowest in moderate exercisers, and there are even a few troubling reports of surprisingly high atherosclerosis prevalence in marathon runners. All of this has led to emerging speculation that perhaps excessive endurance exercise evokes cardiovascular damage and adverse effects.

Well, I’ve got something new to add to that argument! My colleagues and I in Hartford and Boston recently published this article on the impact of long-term endurance training (i.e., marathon running) on cardiovascular risk markers and atherosclerotic progression in healthy adults.  We took 42 runners competing in the 2012 Boston Marathon and their non-running (control) spouses, and assessed traditional cardiovascular markers such as cholesterol, blood pressure, body weight and inflammatory markers. We also measured carotid intima medial thickness (IMT), which estimates atherosclerotic progression in the carotid artery and can predict the risk of future cardiovascular events. Our rationale for comparing runners to their cohabitating partners was to try and isolate the effect of endurance training on cardiovascular risk markers, since presumably couples that live together have somewhat similar lifestyle habits. We found that while the runners had improved cardiovascular risk profiles for the traditional measurements (i.e., lower body weight, lower inflammatory factors, higher good cholesterol), their carotid IMT was no different than the non-runners. In other words, chronic endurance exercise doesn’t necessarily protect against atherosclerosis, but it also doesn’t appear to exacerbate it. And these results support what many researchers and clinicians have thought all along: strenuous running is neither panacea nor poison for perfect cardiovascular health.  Avid exercisers shouldn’t be scared of high-dose exercise, but neither should they use it as an excuse to ignore other beneficial lifestyle practices such as following a healthy diet and treating abnormal cardiovascular risk factors.

By the way, if this post finds you interested and wanting more, Amby Burfoot of Runner’s World wrote a  much better review  of the published article than I’ve presented here, and I urge you to visit his post to get a nice summary of the study results.

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2 thoughts on “Matters of the Heart: Marathons and Cardiovascular Health

  1. Thanks for the timely information. I think this is and will be an emerging area of interest for endurance athletes. The implications, however, should be of interest to the general public.

    In my limited and un-scientific research (aka reading articles), it appears that chronic inflammation is taking the center stage as the underlying cause of many long-term illnesses, including heart disease and cancer. This, of course, is contrary to the conventional wisdom that spurred a low fat, low cholesterol diet craze.

    It’s not about lowering fat and cholesterol intake (though moderation is always good); it’s about fueling our bodies better with raw fruits and vegetables–and those with intact nutritional value. Much of the conventional produce has been reduced to a fraction of it’s former value through mass production, poor soil conditions, and a no-stress growing environment.

    Couple the low nutritional value of conventional produce with the low intake of most Americans. Most of us are getting 1-2 servings *at the most* daily, when we need 9-12 fist-sized servings. The average marathon runner probably needs much more.

    It’s my assertion that the marathon runner would probably remain on the linear benefit-dose relationship–if s/he fueled correctly.

    If we marathon runners and endurance athletes are not taking measures to compensate for the oxidative stress we’re incurring, we will do damage to our cardiovascular systems.

    So, we either need to run less, or fuel more and better.

    *Sent from personal email address of: * Marc A. Scrivener, BSBM, MM, 26.2 PO Box 106 Willimantic CT 06226 860.933.5144 (Cell)

    Twitter: mascrivener http://www.facebook.com/marc.scrivener http://www.willimanticdowntown.org http://www.willimanticathleticclub.org/

    Be miserable. Or motivate yourself. Whatever has to be done, it’s always your choice – Wayne Dyer

  2. Good points! Chronic or acute inflammation can both exacerbate and evoke cardiac events, and diet certainly plays a large role in modulating inflammation. Unfortunately, we know very little about the long-term effects of sustained, high-intensity endurance training in combination with healthy, unprocessed dietary intake…because so few people would qualify for such a study!

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