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The Key to a Longer, Happier Life

How to make the most of your "activity dividend."

Key points

  • The "use it or lose it" hypothesis is well-known, but the newest approach adds the "active grandparent" to the equation.
  • New research suggests how physical activity's repair and maintenance processes can stave off some of the effects of aging.
  • By being more active, such as playing with grandchildren, you can enjoy not just a longer lifespan but a longer healthspan as well.

The idea of “use it or lose it” can perhaps be traced to the pioneering work of sex researchers Masters and Johnson who concluded that, for women at least, having an “interested and interesting” sex partner was the key to battling the effects of aging on sexual functioning. From a broader perspective, the concept of remaining active to benefit physical if not cognitive functioning has continued to receive extensive support. Physical exercise has beneficial effects on a wide range of physiological functions, and both physical and mental activity are now known to help stave off the effects of aging on such key abilities as response speed and memory.

Indeed, researchers in gerontology now speak of the "longevity dividend" associated with increases in life expectancy. Based on the idea that exercise can help prevent or delay the aging process, might there also be an "activity dividend"? If so, this would suggest that it's time to start investing in yours.

You might be aware of all this research but still not be convinced that exercise is really worth it. You’ve got a busy enough life, and maybe you’re already benefiting from activity because you are so busy. If you work outside the home, you at least get your “steps in” by getting to your workplace, and, once there, you do plenty of moving around. If you are a parent of young children, you also are generally active, either physically picking them up and carrying them around all the time, or just running after them to make sure they are safe. You’re definitely “using it” and so the idea of “losing it” seems remote indeed.

Yes, ideally, you would carve out some piece of your day to devote to even the minimum of 20 to 30 minutes of some form of organized exercise. But if you’re truly doing plenty of walking, running, and lifting weight (including those children), you’re still better off than if you were a completely sedentary couch potato. It’s in this spirit that a newly released publication can inspire anyone of any age to make getting up and moving around a priority.

Why Do People Live Past Their Reproductive Prime?

Evolutionary biologist Daniel Lieberman and colleagues (2021), in an article containing the intriguing lead-in “The active grandparent hypothesis…,” link physical activity with longevity, examining the issue from an evolutionary perspective. This hypothesis proposes that “selection for increased physical activity (PA) in humans was linked to selection for extended lifespans.”

Grandparents factor into the equation because, the Harvard researchers go on to note,

Lengthy postreproductive lifespans have been shown to be a critical component of the unique human life-history strategy in which grandparents enhance their reproductive success not just by imparting knowledge but also by being physically active foragers who gather and hunt for food surpluses that they provide to their children and grandchildren.

Unpacking this novel idea, what might strike you right away is the proposal that grandparents aren’t just some sort of evolutionary accident, the result of medical and social improvements that allow people to live by their “sell-by date” when they no longer can reproduce. Doesn’t this turn your idea of evolution on its head? Indeed, one biological theory of aging maintained that evolution’s main job was to keep people alive long enough to reproduce, and, after that, the species doesn't need you anymore to survive. But if instead older adults (perhaps but not limited to grandparents) continue to make worthwhile contributions to younger generations, then there’s a good evolutionary reason to keep them around.

Next, you might have in your head some imaginary hunter-gatherer to whom this hypothesis would apply. However, given that most “foraging” occurs in grocery stores and other retail establishments, it would seem that the grandparent hypothesis could work in the contemporary sense of the generative grandparent contributing to their younger family members through economic support if not actually literally bringing home the groceries.

What Is the Role of Physical Activity in Promoting Longevity?

Lieberman et al. incorporate what’s now known about the difference between “healthspan” (i.e., years of healthy life) and “lifespan” (i.e., years of life, healthy or not) to suggest that, more than burning calories, “the stresses of PA stimulate investments in health-span preserving somatic repair and maintenance processes that are activated less in the absence of PA.”

To understand this piece of the grandparent hypothesis, think now about the kinds of damage you may do to your body when you exercise. You get muscular aches and pains, you feel physically tired, you have to breathe harder, and you raise your heart rate and blood pressure, at least temporarily. This kind of “damage,” according to Lieberman et al., actually helps contribute to PA’s effect on your healthspan and lifespan. Your body has to do something to repair the damage, which can include restocking your depleted energy, producing antioxidants, clearing away harmful waste products of metabolism, reducing inflammation, and getting your nervous system to turn down some of that autonomic (e.g., breathing rate control) activation. The other changes in your body that occur after you exercise directly promote the growth of muscle tissue and bone strength.

Citing a wide range of data to support their position, the Harvard research team conclude that if PA didn’t stimulate repair and maintenance of physiological functions, it would “shorten, not extend, healthspans.” If you’re thinking “no pain, no gain,” you’ve got the basic idea.

Probing further into the grandparent hypothesis, the question in Westernized societies is whether a mismatch has developed between the factors that favor longevity (i.e., PA) and the sedentary lifestyle that is becoming increasingly prevalent throughout the lifespan. Addressing directly the “use it or lose it” hypothesis, the authors note that modern environments “enable individuals, especially the elderly, to be inactive.” When people aren’t active, their bodies don’t engage in those healthspan-promoting repair and maintenance activities and they suffer changes such as loss of muscle mass. Older individuals then become weaker and less able to perform the kinds of exercise that would keep those muscles stressed and toned. Nevertheless, once they begin to engage in PA, there’s ample evidence to show that many previously lost functions can be regained.

Are You Ready to Claim Your Own Activity Dividend?

After learning about the new insights in the Lieberman et al. article, it should be even harder for you to shove aside those excuses not to put your body through the stresses and strains of regular exercise. However, many good intentions vanish in the face of the realities of jam-packed daily schedules. Good intentions can also be defeated by the lure of a comfortable chair. You may also have trouble seeing yourself as nothing more than a tiny speck in the grand scheme of evolution.

Fortunately, the grandparent hypothesis can give you some concrete ways to make some relatively simple changes in your routine to incorporate more physical activity. If you are actually a grandparent, you can do more than just forage the grocery shelves to put food on your family’s tables. Lieberman et al. frame much of their argument in terms of “energy expenditure,” meaning the number of calories hunter-gathering elders burned to contribute to the welfare of their grandchildren. In modern terms, this can be translated into burning calories in the process of having fun with those young children. There are all kinds of games that involve physical activity (think hide and seek) and activities such as going to playgrounds or just a walk in the park or around the block. Not only do these benefit you, but they can also help the little ones in your life avoid their own trap of a sedentary lifestyle, passing the activity dividend along as part of their inheritance.

The other important takeaway from the study is reinforcement of the concept of healthspan. Wouldn’t you rather spend your money and energy on activities other than sitting around at a physician’s office or, worse, a hospital ward as one of the casualties of inactivity? Several key areas reviewed in the Harvard study pertain to lowered risk through PA of the big threats to health and ultimately lifespan presented by cardiovascular disease and cancer. Who wants to have to deal with these diseases if there’s a way to avoid them?

To sum up, the authors of this groundbreaking study suggest that it is both “useful and empowering” to know that you don’t need a “magic bullet” of extreme exercise to take advantage of the activity dividend. It only takes “moderate levels of PA” to enjoy the benefits of a healthier and, therefore, more fulfilling, longer life.

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Lieberman, D. E., Kistner, T. M., Richard, D., Lee, I.-M., & Baggish, A. L. (2021). The active grandparent hypothesis: Physical activity and the evolution of extended human healthspans and lifespans. Proceedings of the National Academy of Sciences, 118(50), e2107621118. doi:10.1073/pnas.2107621118