June 6, 2012 (San Francisco, California) — What doesn't kill you is supposed to make you stronger, an adage that many a long-distance runner has clung to, but intriguing findings from a new study presented last week suggest the mortality benefits of running are best accumulated in shorter distances, specifically at less than 20 miles per week . In fact, at longer distances, the researchers observed a U-shape relationship between all-cause mortality and running, with longer weekly distances trending back in the wrong direction, toward less mortality benefit.
"We were thinking that at some dose of running, things would level off, that we'd see that runners would have a reduction in mortality at certain distances and then it would kind of level off," Dr Carl Lavie (Ochsner Health System, New Orleans, LA), one of the study investigators, told heartwire . "The fact that it reached its plateau at such a low level is surprising, as is the fact that it didn't level off but actually went the other way. We never had a point where runners did worse than nonrunners, but really, if you put it in almost a joking way, it showed that if you ran enough you got yourself back to the level of a couch potato. You lost the survival advantage."
The results of the study were presented last week at the American College of Sports Medicine 2012 Annual Meeting by lead researcher Dr Duck-chul Lee (University of South Carolina, Columbia). Lavie stressed that while the study is one of the largest performed to date, including data on more than 52 000 men and women participating in the Aerobics Center Longitudinal Study (ACLS), it is a retrospective analysis and that results will likely vary among individuals with differing athletic abilities or different ages.
"There is not going to be a set cut point where we say this is the magical amount of running," said Lavie. "But certainly, it looks like you get the benefits at relatively low, modest amounts. If you shoot for superhigh amounts of running, you're certainly not getting more benefit, and it actually appears from our data that you could be getting less benefit."
Running linked with a 19% lower risk of death
In the ACLS, participants were free from cardiovascular disease, cancer, electrocardiographic abnormalities, and diabetes at baseline. Running and other physical activities were self-reported on the medical history questionnaire, and patients were followed for an average of 15 years. During this time, 2984 deaths occurred and approximately 27% of the men and women participated in running as a form of exercise.
Overall, running was associated with a 19% lower risk of all-cause mortality when compared with individuals who did not run (hazard ratio [HR] 0.81; 95% CI 0.73–0.89). As noted, the researchers observed a U-shaped relationship with all-cause mortality, with faster paces, longer distances, and increasing frequency suggestive of a diminishing mortality benefit.
Regarding pace, individuals who ran six and seven miles per hour had a significant 21% and 27% lower risk of all-cause mortality, whereas those who ran eight or more miles per hour had a nonsignificant 7% lower risk of all-cause mortality. Running up to 20 miles per week was associated with a significantly reduced risk of death, with the largest benefit observed in those who ran between 10 to 15 miles weekly (HR 0.73; 95% CI 0.60–0.89). For those who ran 20 to 25 miles and more than 25 miles per week, however, there was a nonsignificant 10% and 5% reduction in all-cause mortality. Similarly, the mortality benefit was observed in individuals who ran two to five days per week, but the benefit began turning in the other direction when subjects ran six or seven days per week. At six and seven days, the reduction in all-cause mortality was not statistically significant.
"Honestly, my weekly running mileage is above the level where we're seeing the benefit," Lavie told heartwire . "I average 35 to 40 miles a week, and in many previous years have probably averaged more than 45 or 50 miles per week. I've done a few marathons and a ton of half-marathons, so I sure would have liked to have seen the benefit leveling off rather than going the other way."
Lavie noted that it is impossible to say definitively that more running is making the reduction in all-cause mortality go in the other direction, as it's possible that unmeasured variables might have influenced the results. That said, the group corrected for the usual variables--age, gender, hypertension status, lipid levels, smoking status, and alcohol intake, among others. It's possible that runners might not be taking care of themselves in other ways, offered Lavie by way of explanation, although he didn't think that was plausible. "I would have thought that runners are more likely to be more health conscious," he said.
Review article highlights the running risk
As for the underlying mechanisms, Lavie highlighted a review paper published this week in the Mayo Clinic Proceedings by lead author Dr James O'Keefe (Mid America Heart Institute of St Luke's Hospital, Kansas City, MO), of which he was a coauthor, highlighting the potential for adverse cardiovascular remodeling among individuals who participate in long-term endurance exercise, such as marathons, ultramarathons, Ironman-distance triathlons, and long-distance cycling races . Regular and intense endurance exercise such as these events might lead to myocardial fibrosis, particularly in the atria, interventricular septum, and right ventricle, which in turn can lead to atrial or ventricular arrhythmias. Endurance exercise may also be associated with coronary artery calcification, diastolic dysfunction, or arterial stiffening.
Despite the potential for harm with long-distance endurance events, Lavie noted that the ACLS analysis does not include participants engaged in this type of "excessive" activity and that running 25 or 30 miles per week would not be considered cardiotoxic. It is possible, however, running longer and further might result in some low-grade inflammatory processes.
"From a health standpoint, you don't have to do an hour-and-a-half of exercise," said Lavie. "You get the extra calorie burning, and some people get some relaxation from that extra amount, but really from a cardiovascular standpoint you're going to get all the benefit in the first 30 or 40 minutes. Is it possible that by going extra you're actually hurting yourself? I think it is possible."
Heartwire from Medscape © 2012 Medscape, LLC
Cite this: The Not-So-Long Run: Mortality Benefit of Running Less Than 20 Miles per Week - Medscape - Jun 06, 2012.