Does Exercise Extend Your Lifespan or Just Your Healthspan?

Below is an approximation of this video’s audio content. To see any graphs, charts, graphics, images, and quotes to which Dr. Greger may be referring, watch the above video.

Whether 6 percent of premature mortality is related to physical inactivity, 9 percent, or even 15 percent, these estimates are all predicated on the presumption that the associations found linking inactivity to death rates in observational studies constitute cause and effect. I was surprised by how much controversy there is in the medical literature over whether or not the apparent longevity benefits of exercise are even real.

A classic study from the 1950s entitled “Coronary Heart-Disease and Physical Activity of Work” illustrates how difficult it can be to tease out causality between physical activity and longevity. London bus drivers appeared to have twice the risk of dying from heart disease compared to bus conductors, who were presumed to be protected by their climbing up and down 500 to 700 steps a day in the famous double deckers. However, it was later revealed, in a follow-up paper “Physique of London Busmen,” that based on the measurements of their starting uniforms, the bus drivers started out significantly heavier.

Similar issues surrounding reverse causality continue to haunt observational exercise studies to this day. Is exercising enabling good health, or is good health enabling exercise in the first place? Is inactivity leading to chronic disease, or is chronic disease leading to inactivity?

Then there are the confounding factors––the archetypical one being less smoking among active individuals. With the exception of elite male power athletes, who may die at nearly five times the normal rate (perhaps due to use of anabolic steroids), athletes tend to live longer than their sedentary counterparts, as much as four to eight years longer. But think of all the complicating elements, especially among professionals. Major league baseball players, Tour de France cyclists, and champion skiers all live longer than the general population. But that doesn’t mean that necessarily has anything to do with home runs, bicyclettes, or the slopes. Maybe it’s partly the superior genetic constitution that allow for such physical feats in the first place, or the socioeconomic status bestowed upon the winner. Yes, Olympic medalists live longer than the general population, but so do grandmasters of chess, as revealed by a study subtitled “Mind versus muscle,” suggesting it’s the afforded status rather than muscular exertion. Winners of a Nobel Prize and Oscar award similarly have superior life expectancy.

To try to tease out these factors, researchers have compared the effects of leisure time physical activity to occupational physical activity. If the link between exercise and longevity were truly causal, then the context within which you get the same exertion shouldn’t matter. As you can probably guess, though, manual labor can sometimes be associated with a shorter, not longer, life, again suggesting the primacy of confounders like socioeconomic factors. Is it possible that a genetic predisposition to physical fitness is what accounts for the exercise/longevity link, rather than the physical activity itself? In other words, is it just genetic selection bias? We know exercise and longevity are associated with one another, but instead of exercise causing the longevity, maybe the same genetic predisposition to exercise also leads to longevity, whether or not you actually exercise at all.

This question was raised by a pair of mind-blowing studies. The first involved a comparison of two strains of rats, one bred to have a high intrinsic running capacity, and the other bred to have a low running capacity. Then they were randomized to either get a running wheel or not. Even without exercising, the high-fitness ability rats lived longer than those with the low fitness ability, but unexpectedly the provision of running wheels so they could all exercise voluntarily cut the lives of both strains short. Running reduced their life expectancy.

Using twin studies, we can show that there are also genetic predispositions to exercise in humans too. When identical twins leave home to start their separate lives, their exercise habits are much more likely to be “concordant” than fraternal twins. This means if one twin vigorously exercises, then the other twin is more likely to do the same if they share 100 percent of their DNA, instead of just 50 percent like regular brothers and sisters. How could we tell if it’s this genetic predisposition to exercise, rather than the actual exercise, that accounts for athletic longevity? Well, what about the rare cases of identical twins whose exercise habits diverge? With the same DNA, would intense physical activity make a difference? Apparently not. The same mortality rates were found in identical twins whether they exercised vigorously or not.

A critical analysis on whether physical activity is a cause of longevity concluded “the undisputed health-related benefits of exercise have yet to translate into any proven causal relationship with longevity.” This was based on the fact that the randomized controlled trials in clinical populations, suffering mostly from neurological conditions, have shown a drop in premature death rates. Exercise interventions have failed to show exercise extends life among apparently healthy individuals. However, these are difficult studies to run.

Take the largest such study, where more than 1,500 older men and women (average age 73) were randomized to one of three groups for five years: a recommendation to just follow the national guidelines of 30 minutes a day, five days a week, or to replace two of those weekly sessions with 50-minute sessions, or to replace two of those weekly sessions with four four-minute bursts of high intensity interval training at 90 percent of peak heart rate. And there ended up being no difference in mortality rates between the two extra exercise groups and the control group. This may be because the control group ended up exercising so much. The control group advised to exercise for just 30 minutes ended up exercising more than the group told to boost weekly sessions up to 50 minutes. All participants had the potential to be randomized to the high-intensity group, so the enrollees had to be pretty fit at baseline. And with expectations of health checks at years one, three, and five, the control group stepped it up so much it blurred the distinctions between the three groups.

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• exercise
• longevity
• mortality