The other day John Little forwarded me a study from Stanford that concluded that running promoted longevity and preserved functional ability in older age.  He asked me to comment on the study which you can view below:

By ERIN DIGITALE

STANFORD, Calif. — Regular running slows the effects of aging, according to a new study from the Stanford University School of Medicinethat has tracked 500 older runners for more than 20 years. Elderly runners have fewer disabilities, a longer span of active life and are half as likely as aging nonrunners to die early deaths, the research found.

“The study has a very pro-exercise message,” said James Fries, MD, an emeritus professor of medicine at the medical school and the study’s senior author. “If you had to pick one thing to make people healthier as they age, it would be aerobic exercise.” The new findings appear in the Aug. 11 issue of the Archives of Internal Medicine.

When Fries and his team began this research in 1984, many scientists thought vigorous exercise would do older folks more harm than good. Some feared the long-term effect of the then-new jogging craze would be floods of orthopedic injuries, with older runners permanently hobbled by their exercise habit. Fries had a different hypothesis: he thought regular exercise would extend high-quality, disability-free life. Keeping the body moving, he speculated, wouldn’t necessarily extend longevity, but it would compress the period at the end of life when people couldn’t carry out daily tasks on their own.  That idea came to be known as “the compression of morbidity theory.”

Fries’ team began tracking 538 runners over age 50, comparing them to a similar group of nonrunners. The subjects, now in their 70s and 80s, have answered yearly questionnaires about their ability to perform everyday activities such as walking, dressing and grooming, getting out of a chair and gripping objects. The researchers have used national death records to learn which participants died, and why. Nineteen years into the study, 34 percent of the nonrunners had died, compared to only 15 percent of the runners.

At the beginning of the study, the runners ran an average of about four hours a week. After 21 years, their running time declined to an average of 76 minutes per week, but they were still seeing health benefits from running.

On average both groups in the study became more disabled after 21 years of aging, but for runners the onset of disability started later.

“Runners’ initial disability was 16 years later than nonrunners,’” Fries said. “By and large, the runners have stayed healthy.”

Not only did running delay disability, but the gap between runners’ and nonrunners’ abilities got bigger with time. 

“We did not expect this,” Fries said, noting that the increasing gap between the groups has been apparent for several years now. “The health benefits of exercise are greater than we thought.”

Fries was surprised the gap between runners and nonrunners continues to widen even as his subjects entered their ninth decade of life. The effect was probably due to runners’ greater lean body mass and healthier habits in general, he said. “We don’t think this effect can go on forever,” Fries added. “We know that deaths come one to a customer. Eventually we will have a 100 percent mortality rate in both groups.”

But so far, the effect of running on delaying death has also been more dramatic than the scientists expected. Not surprisingly, running has slowed cardiovascular deaths. However, it has also been associated with fewer early deaths from cancer, neurological disease, infections and other causes.

And the dire injury predictions other scientists made for runners have fallen completely flat. Fries and his colleagues published a companion paper in the August issue of the American Journal of Preventive Medicineshowing running was not associated with greater rates of osteoarthritis in their elderly runners. Runners also do not require more total knee replacements than nonrunners, Fries said. 

“Running straight ahead without pain is not harmful,” he said, adding that running seems safer for the joints than high-impact sports such as football, or unnatural motions like standing en pointe in ballet.

“When we first began, there was skepticism about our ideas,” Fries said.  “Now, many other findings go in the same direction.”

Fries, 69, takes his own advice on aging: he’s an accomplished runner, mountaineer and outdoor adventurer.

Hanging on his office wall is a photo he jokingly describes as “me, running around the world in two minutes.” In the dazzling image of blue sky and white ice, Fries makes a tiny lap around the North Pole.

Fries collaborated with Stanford colleagues Eliza Chakravarty, MD, MS, an assistant professor of medicine; Helen Hubert, PhD, a researcher now retired from Stanford, and Vijaya Lingala, PhD, a research software developer.

The research was supported by grants from the National Institute of Arthritis and Musculoskeletal and Skin Diseases and by the National Institute on Aging.

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John asked me to comment on the researchers’ conclusions, but I find commenting on the methods more illustrative of what is wrong with this study.  This study incorporates a very common thinking error that leads many of us to improper conclusions.  It involves embracing a type of bias called survivorship bias.   The methodological flaw in this study is there is no randomization.  The subjects in the experimental group were long-standing runners who were active runners at age 50.  The study ignores the “graveyard” of people who used to run but quit before they turned 50 because of injury or illness that could have been related to the “treatment” being studied.   The study also fails to recognize that the strong survivors are still actually weakened by the activity logging less running time and being more debilitated (though less debilitated than those that self-selected themselves to “the graveyard”).   Author Nassim  Taleb discusses this concept in his book The Black Swan under the heading A Health Club for Rats.  Since Taleb covers the topic so much more elegantly than I could ever hope to, I will quote excerpts below.

…”I came across an article discussing the mounting threat of the Russian Mafia in the United states…The article explained their toughness and brutality as a result of their being hardened by their Gulag experiences.  The Gulag was a network of labor camps in Siberia where criminals and dissidents were routinely deported…Many deportees did not survive these labor camps.

Hardened by the Gulag?The sentence jumped out at me as both profoundly flawed (and a reasonable inference).  It took me a while to figure out the nonsense in it since it was protected by cosmetic wrapping; the following thought experiment will give the intuition.  Assume you’re able to find a large, assorted population of rats: fat, thin, sickly, strong, well-proportioned, etcetera…With these rats you build a heterogeneous cohort…You bring them to my laboratory…and we put the entire collection in a large vat.  We subject the rats to increasingly higher levels of radiation.  At every level of radiation, those that are naturally stronger (and this is the key) will survive; the dead will drop out of your sample.  We will progressively have a stronger and stronger collection of rats.  Note the following central fact: every single rat, including the strong ones will be weaker after the radiation than before.

An observer endowed with analytical abilities, who probably got excellent grades in college, would be led to believe that treatment in my laboratory is an excellent health-club experiment, and one that could be generalized to all mammals (think of the potential commercial success).  His logic would run as follows:  Hey, these rats are stronger than the rest of the rat population.  What do they seem to have in common?  They all came from that Black Swan guy Taleb’s workshop.  Not many people will have the temptation to go look at the dead rats.

Next we pull the following trick on The New York Times:  we let these surviving rats loose in New York City and inform the chief rodent correspondent of the newsworthy disruption in the pecking order in the New York rat population.  He will write a lengthy (and analytical) article on the social dynamics of New York rats that includes the following passage:  “Those rats are now bullies in the rat population.  They literally run the show. Strengthenedby their experience in the laboratory of the reclusive (but friendly) statistician/philosopher/trader Dr. Taleb they…”

Dr. Taleb’s analysis of this article perfectly parallels the flaws in this study.  The study selected long-standing runners who were fairly advanced in age and only then began any longitudinal followup.  In essence only the stronger rats who had already survived significant radiation doses were followed.    The author himself is a dedicated runner and endurance athlete, which could even compound the selection bias and the author’s own blindness to it.  Even more importantly, this sort of bias is most profound when the supposed beneficial intervention is most harmful.  This has been born out in many recent drug cases where medicines that were supposed to improved long-term functioning in survivors and then later investigations of the raw data found that the drug was simply killing the patients with more severe disease, making their survivors appear healthier.  I won’t mention what drugs this has happened with, because you saw what happened to Dr. Richard Kimball (played by Harrison Ford) in the movie The Fugitive.  

Once again, Nassim Taleb drives this point home much more clearly than I in the quote below:

“There is a vicious attribute to the bias: it can hide best when its impact is largest.  Owing to the invisibility of the dead rats, the more lethal the risks, the less visible they will be, since the severely victimized are likely to be eliminated from the evidence.  The more injurious the treatment, the larger the difference between the surviving rats and the rest, and the more fooled you will be about the strengthening effect.

The cognitive errors in this study are so bad that (in my opinion) it should not have passed peer review and been published.  It is always fun to look at a studies funding source.  In this case The National Institute of Arthritis and Musculoskeletal and Skin Diseases.  This institute exists becauseof the existence of arthritis and musculoskeletal disorders.  In BBS we cite studies that show running increases the risk of arthritis, musculoskeletal disorders and skin cancer.  While not a conscious deception I’m sure, this does seem kind of like the dentist that gives out lolly pops to kids after their appointments.  In conclusion, I told John that this study may well prove exactly the opposite of what it suggests.  To any readers of BBS, I would suggest reading Dr. Taleb’s Fooled by Randomness, and The Black Swan.   Both books highlight cognitive errors that are common in research and that can lead your training astray.

Doug McGuff, MD