Running Overdose – the heart of the matter

Most people have heard stories of marathon runners dying of heart attacks, the most famous case was Pheidippides, the story goes that he ran from Marathon (the place) to Athens and then died.
Historians are still arguing if this actually occurred or is a myth.

However, there are verified accounts of other people dying while on a run, for example the running guru, Jim Fixx. So, running must be bad for you right? Well no, 2 or 3 data points don’t cut it in science, so I decided to take a look at the medical literature. It turns out that the evidence is not conclusive.   

How running affects your health

Even this is hard to prove, since there are a lot of practical and ethical problems with doing a strict ‘control’ experiment until the participants all die. The best we can do is measure indirect indicators of health and cautiously extrapolate that to general rules. The evidence from such “observational” studies1,2 is overwhelming – running is definitely good for you. Running improves almost all health indicators, the simplest and most powerful of those indicators is BMI – the ratio of height to weight squared. Runners tend to have a BMI in the ideal range of under 30.  

Can you run too much?

The second study2 made the statement that “the longer the length of training, the larger the achieved health benefits”, which is somewhat reminiscent of the hypothesis propounded by Thomas Bassler in the 1970s3 that marathon running confers immunity against coronary atherosclerosis.

Nothing else, not even air or water, is good for humans in unlimited amounts, so these conclusions seem rather unlikely. Have there been any big studies to find out what the ideal ‘dose’ of running is?

Large Studies

The two big studies on heart health were The Copenhagen City Heart Study (CCHS)4, and the Aerobics Center Longitudinal Study (ACLS)5. There have been other smaller scale studies, but at this point in time, most clinical evidence on running and heart health comes from CCHS and ACLS. Both large studies found a U shaped relationship between running amount and mortality. For CCHS, the fourth examination from 2001 had 1098 joggers and 3905 non-joggers. In simple terms they found these groups:

  1. people who did no exercise had the lowest life expectancy
  2. those that did a moderate amount of running (<= 2.5hr / week) had the highest life expectancy
  3. the group that ran furthest and fastest could expect to live a bit longer than the sedentary group but not as long as the moderate exercisers

This was a revelation, and seems to disprove the Bassler hypothesis. The idea that too much running wipes out the initial health benefits seems plausible. However, only 28 joggers and 128 non-joggers actually died, so we are using relatively low sample sizes and extrapolating from health indicators … again.  A simple statistical study in 20126 showed the difficulty in such extrapolations, their conclusion: “Participation in marathons has increased without any change in mortality or average overall performance from 2000 to 2009”. 

We should be careful drawing general conclusions from these sharp cut-offs – it’s hard to believe that a change from 2.5 to 2.6 hours per week abruptly removes health benefits. 

How could it work?

Another real problem with the CCHS conclusion was that no mechanism was proposed for the change in mortality risk. A later paper by O’Keefe et al7 points to an observed increase in coronary plaque among male marathoners and theorises that these plaques could ,burst and lead to heart attacks. Other studies have not supported that theory8, 9, and at least one small study has found that marathon running is associated with low coronary formation in women10.  

Another connection was made between Atrial fibrillation (AF), a sort of quivering of the heart, and physical activity11. That association seems to be real (and it can be alarming to a runner), but like a number of the effects exercise has on the heart, everything returns to normal in a few days12.


The science is somewhat confusing and it’s hard to know what to think. One might expect that a strong connection between too much running and worsening heart health would have been found by the big studies.  I suspect that any such correlation is weak or non existent.  However we shouldn’t be smug about the healthiness of running, a better way to think about it is an enjoyable thing to do.

My favourite articles on running and heart health were interviews with Aaron Baggash13, and Bart Loews14. These gentlemen had a refreshingly practical approach to exercise. They emphasised that running is fun and you should run marathons if you enjoy them. 

I have some risk factors, mainly a family history, so did a treadmill test. After receiving that green light, I intend to continue running as I have before. If you have concerns about your heart health then you could also consider such a test.

Lastly, whatever the correct running ‘dose’ is for you, it is certainly greater than zero.  


  1. Healthy Lifestyle Habits May Be Associated With Reduced Risk Of Chronic Disease — ScienceDaily
  2. Meta-Analyses of the Effects of Habitual Running on Indices of Health in Physically Inactive Adults. – PubMed – NCBI
  3. Marathon Running And Immunity To Atherosclerosis. Thomas J. Bassler: October 1977
  4. The dose of running that best confers longevity
  5. Running and all-cause mortality risk: is more better? Lee J, Lavie CJ et al. Med Sci Sports Exerc 2012; 44:924
  6. Mortality among marathon runners in the United States, 2000-2009. – PubMed – NCBI
  7. Potential Adverse Cardiovascular Effects From Excessive Endurance Exercise
  8. Cardiac Arrest during Long-Distance Running Races — NEJM
  9. Fifty Men, 3510 Marathons, Cardiac Risk Factors, and Coronary Artery Calcium Scores
  10. Long-Term Marathon Running Is Associated with Low Coronary Plaque Formation in Women. – PubMed – NCBI
  11. Long-term endurance sport practice increases the incidence of lone atrial fibrillation in men: a follow-up study Lluis Molina et al EP Europace, Volume 10, Issue 5, 1 May 2008, Pages 618–623
  12. Dose of Jogging and Long-Term Mortality | JACC: Journal of the American College of Cardiology
  13. A Brief Chat with Aaron Baggish, M.D., Author of New England Journal Study | Runner’s World
  14. Is Long-Distance Running Actually Bad For Your Heart?

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