The legend states that Pheidippides ran slightly less than 26 miles from Marathon to Athens to announce that the Athenian army had conquered the Persians and immediately fell over dead.  The truth of this story is in doubt, but it has fueled speculation that marathons can kill you.  Jim Fixx, author of the bestseller “The Complete Book of Running,” died during a training run after having completed several marathons.  He did, however, have a family history of heart problems and was an overweight smoker before becoming a marathon runner.

There are occasional deaths during marathons, but the rate is very low:  between 0.5 and 1 in 100,000.  A study of 11 million marathoners in a ten-year span showed 59 cardiac events leading to 42 deaths.  This is 1/259,000 participants.  The rate in triathlons is much higher: 1/52,630.

A study from Barts and University College London followed 138 novice runners training for the London marathon.  Over the six-month period, their arteries regained youthful elasticity.  This is believed to reduce the risk of heart disease and stroke.  Their “vascular age” was reduced by an estimate of four years.  Blood pressure was also reduced.  When they ran the marathon, they took between four and a half and five and a half hours.

On the negative side, another study found that men who had run at least one marathon per year for 25 years, showed higher artery plaque than a group of sedentary, overweight men.  Plaque builds up in coronary arteries and occasionally breaks off at unpredictable times.  The plaque then travels down to a narrower part of the artery and blocks it off.  This is a coronary occlusion or heart attack.  If the arteries are wider, there is less chance of blockage.  At autopsy, seven-time Boston Marathon winner Clarence DeMar was found to have coronary arteries two to three times wider than normal.  Did all those marathons make the arteries wider or did wide arteries make him a better athlete?

Another potential problem is generalized inflammation that occurs during a marathon.  (This may contribute to the well-known delayed onset muscle soreness.) Some researchers were particularly troubled by inflammation occurring in the kidneys.  The changes appeared similar to serious kidney damage, but, thankfully, reversed the next day.  These kidney changes are common when the runner becomes dehydrated or overheated.  There is concern about the long-term effect of repeated bouts of this situation.

Most experts believe there are diminishing returns when running more than 20 miles per week, more than 5 days a week, and faster than 7:30 per mile.  But, you can’t prepare for a marathon on 20 miles per week.  The bottom line, on which most authorities agree, is that running is beneficial in the long term, but during a run, especially an all-out effort like a marathon, the risk is heightened.  If one of those nasty plaques breaks off while the heart is operating at maximum effort it is likely to result in a major heart attack versus that same event occurring at rest and resulting in a minor attack.

The good news from the research is that almost anyone who is healthy, motivated, and well-trained can safely run a marathon.