Is Exercise a Magic Bullet for Longevity? | Daniel Lieberman

have you ever wondered why something we've never evolved to do is healthy for us going to the gym playing tennis riding bicycles I couldn't think of anyone more qualified to answer that question than paleoanthropologist Daniel Lieberman he couldn't be at our tedex longevity conference because he was overseas so he let us film his talk in his office in the spectacular peabot Museum hello my name is Dan lman I'm a professor at Harvard University and I study the evolution of physical activity and how it's relevant to health and disease now before we get started let's get

a few definitions under our belt the first thing I want to discuss is the difference between physical activity and exercise so physical activity is just any bodily movement produced by skeletal muscles but exercise is voluntary discretional physical activity for the sake of health and fitness and healthspan is the number of years we live without serious chronic disease but lifespan is just how long we live now wouldn't it be great if we had a Magic Bullet if exercise was one of them to live a long and healthy life right that'd be fantastic right and this idea

actually originates from long time ago from the Middle Ages there's an old German folk tale about called shoots which is about a marksman who makes a deal with the devil and the devil gives him seven Magic Bullets they're silver and six of those bullets that will hit whatever Target The Marksman wants to hit but the trade-off is that the seventh bullet the Magic Bullet will go will hit whatever the devil wants to hit and that's a that's a trade-off that we should keep in mind because the first person to think about magic bullets in medicine

was Dr Paul erck and he came up with this idea around the turn of the century that medicine would come up with you know drugs Magic Bullets that would cure disease with absolutely no side effects and the first Magic Bullet he thought he discovered was something called salver San which was a kind of arsenic that was used to treat um syphilis and the good news was that it did treat syphilis pretty well but the bad news was that people who given solver often had diarrhea they had nausea and sometimes they died remember that seventh magic

bull and now of course nobody uses it anymore now we use penicillin which was invented in 1928 which has turned out to be a better medicine for syphilis and many other diseases so since then people have proposed many many many medicines and various other lifestyle treatments that are supposed to help us live to B 100 these are often touted as Magic Bullets right you've probably heard of caloric restriction the intermittent fasting taking ice baths and there are all kinds of pharmaceuticals like rapamycin and Metformin and nadh and some of these do have benefits um but

the sad fact of the matter is that unless you're a mouse or a fruit fly there's really no compelling evidence that any of them have any substantial effect on human or even for that matter primate longevity and the reason for that has to do with Evolution remember nothing in biology makes sense except in the light of evolution and we evolved to grow old and die sorry that's just the truth right so natural selection cares about one thing and one thing only how many offspring we have who survive and reproduce so natural selection wants us to

live and stay healthy as long as we're reproducing but once we stop reproducing we enter what's called The Selective Shadow now humans have managed to extend that selective Shadow for a while right because grandparents help their children and their grandchildren survive and so they have some selective benefit but eventually that dwindles and natural selection doesn't seem to care about us and it seems that humans evolve to live about seven or eight decades and after that well it's because of good luck now what about exercise and it is true that exercise really is very good for

us but it's also true that exercise is not a Magic Bullet and the argument I'm going to make today is that physical activity improves Health span by slowing aging and decreasing our vulnerability to disease and before medicine think about it life healthspan equaled lifespan because there was no doctor to keep you alive after you got sick now the the reason for this the explanation the why behind this is what we call the active grandparent hypothesis and so my colleagues and I Aaron baggish I Min Lee and others have argued that there's been selection in human

evolution for moderate levels of lifelong physical activity that extend our healthspan and hence our lifespans and it's that for that reason that physical activity exercise is good for us so the active grandparent hypothesis makes two kind of predictions or two parts to the hypothesis and the first is that humans evolve to be moderately physically active and to stay active as we age including after we stop reproducing and the second is that there was selection for physical activity to slow aging and decrease vulnerability to disease thereby extending Health spans which as we've already discussed ex extends

lifespans so let's talk about the first part that humans evolved for lifelong physical activity including as grandparents and it's true humans did evolve to be grandparents take our closest relatives chimpanzees the average chimpanzee in the wild lives to be 33 years old some of them live to be about 50 maybe that's very rare but can happen but for the most part very few animals chimpanzees including included ever survive after they stop reproducing but humans in all kinds of populations all around the world live to be post-reproductive typical hunter gatherers live to be about 20 years

or so after they stop reproducing to be their modal age of death is about 68 to 78 if they survive childhood and importantly those years are not spent just inactive there they're spent to be active right humans evolve to be much more physically active than our ape ancestors typical chimpanzee walks maybe 2 to 3 kilm a day and they take maybe what 3 4,000 steps a day a typical hunter gatherer takes about 15 to 20,000 steps a day per kilo Hunter gathers spend about twice as much energy per kilo on being Physically Active per day

than our ape cousins and importantly that physical activity occurs as we age right so Americans are pretty inactive as we all know a typical American in their 20s might be you know get spend 3040 minutes a day being physically active and by the time most Americans hit the age of 70 they may be doing 10 to 20 minutes a day of moderate to vigorous physical activity hunter gatherers in Tanzania are way more active in their 20s and 30s they're doing three four hours a day of physical activity and although that declines by the time they're

70 or 80 they're still doing two to three hours of physical activity a day that's well more than 10 times more physical activity per day than a typical American so we evolved to stay active as we age and the reason for that is that activity is to is to do stuff it's not like we don't retire we don't go to the beach we don't go to Florida hunter gatherers continue to gather they continue to hunt they continue to take care of children and they produce an energetic Surplus which they Supply to their children and their

grandchildren and that Surplus can amount to somewhere between 250 to a whopping of 3,000 calories per day that's substantial so yes human beings were selected to be moderately physically active and to stay active as we age including after we stop reproducing now the second part of the act of grandparent hypothesis is that there was selection from moderate physical activity to slow aging and decreased vulnerability to disease thereby extending Health spans and as we talked about before also lifespans and if you want proof of this one of the best studies ever done was the Harvard alumni

study done right here in my University Harvard University by Ralph paffenbarger and paffenbarger studied over 20,000 Harvard alumni and he looked at them from all ages and by the way when you do that you're basically correcting for socioeconomic status and what he showed was that alumni below the age of 50 who are getting about 2,000 calories a week of exercise had 21% lower death rates than the alumni who were inactive and that's after correcting for smoking and various other sorts of things like that by the time they got to their 50s the more physically active

alumni had 36% lower death rates and in their 70s and their 80s those exercising alumni had 50% lower death rates than sedentary alumni of the same age that's an amazingly large effect right and what he's showing here is that as we get older exercise not only helps you get you know stay healthy it becomes more important as we get older the reason for that is because exercise causes stress and that stress turns on a whole raft of beneficial effects and there really two kinds of this stress now the first kind is energetic stress like I

went for a run this morning I spent probably about 500 calories running and I can only do so many things with the calories my body has and if I spend 500 extra calories exercising that means I'm not going to spend 500 calories on other activities that my B body might engage in and one of them is fat storage everybody knows I hope they know that physical activi is one of the best ways may be the best way to prevent weight gain so a lack of physical activity is one of the ways that encourages weight gain

and in a famous experiment for example Benta Peterson in Copenhagen took a whole bunch of young healthy Danes right who normally very active and made them sit on a couch for two weeks and eat the same amount of food and she scanned them before and after those two weeks and just in two weeks they gained 7% more body fat including s more per in their bellies and that's concerning because belly fat or visceral fat is highly inflammatory now another study also looked at another kind of energetic stress which is how you allocate energy towards reproduction

remember I can only do so many things with my calories so if I'm spending more energy in physical activity I'm not going to spend as much energy on other on reproduction and in a famous study done here at Harvard my colleague Peter Ellison looked at women who are running 20 kilom a week right that's not a huge amount so that's about 180 calories a day and compared it to sedentary women and the sedentary women were taking that extra energy and they're plowing it into being uh into reproduction by increasing their levels of estrogen and progesterone

50% higher levels in the in the second half of the menstrual cycle and higher levels of progesterone and progest progesterone and estrogen increase rates of cancer so the energetic stress from physical activity decreases inflammation which is involved in everything from metabolic syndrome to cancer to heart disease and it also decreases reproductive hormones which decrease cancer rates now the other kind of stress that physical activity cus is structural stress now when I was running this morning for example my mitochondria were generating all kinds of ATP to fuel my body but my mitochondria were also spewing out

all kinds of reactive oxygen species which cause widespread damage throughout my body I was getting mutations in My DNA those that damage is causing my telr at the end of my chromosomes to shorten it's damaging cells it's causing tears in my muscles causing cracks in my bone and of course if all that damage were un you know you know we did nothing about it right we we we you know we we die soon after exercising but instead exercise turns on a wide range of repair and maintenance mechanisms that repair all that damage and in fact

increase capacity so the next time do a five mile run I might actually be able to do it with more ease right and there are a lot of these right so one of them is you know when I produce all those reactive oxygen species my cells also produce a ton of antioxidants that mop up all that damage when I stress my mitochondria my cells are also being induced by exercise to repair and produce more mitochondria that keep my cells healthy I'm getting DNA damage from all those reactive oxygen species but my but I'm turning on

all kinds of enzymes that repair DNA I o turn on factors that repair my brain and actually cause growth of new brain cells one of them is called brain derived neurotropic growth factor that's turned on my exercise my muscles when I'm exercising are producing molecules that actually suppress inflammation keeping my inflammation levels low and my immune system is getting turned on I produce more natural killer cells and cytotoxic tea cells and antibodies all of which are going to protect me from infectious diseases so the bottom line is that when you exercise you slow rates of

Aging you slow the rate at which you lose muscle you decrease your risk of dementia you decrease inflammation you decrease your risk of infectious disease including by the way covid and there's a and many many more kinds of functions like that that improve our health so the bad news is that exercise really isn't medicine it's not like a pill that you take like salverson or or or you know penicillin that you know that that gets rid of a disease instead it's something is that instead it's really the better way to think about is that we

never evolved not to be physically active and the result of that is that when we're sedentary habitually sedentary that leads to a lack of repair and maintenance so that's the bad news but the good news is that just a little bit of physical activity you don't need to do very much stimulates a wide range of repair and maintenance mechanisms that overshoot any of the damage that the physical activity causes right so I like to think about like imagine spilling coffee on the floor right and then you clean up the floor the floor is going to

be cleaner after you spilled the coffee than before because we overshoot the repair and maintenance so just a 150 minutes of physical activity a week that's 21 minutes a day right that's not very much of just like walking right can lower an average person's risk of heart disease by 20% that's a lot it lowers the average woman's risk of breast cancer by 30 to 50% and it lowers the average person's lifetime risk of Alzheimer's Disease by a whopping 45% and if you look at the overall effect on mortality and I'm showing a graph here of

minutes per week of moderate to vigorous physical activity on the x-axis against the relative risk of all cause mortality just 150 minutes a week of exercise again 21 minutes a day leads to a 30% lifetime reduction or you or yearly reduction in all cause of mortality and getting up to the levels of hunter gatherers results in a 40% reduction that's a massive effects and it's hard to turn those those Health span estimates to longevity estimates but the best best guesses are that adds at least a half a year to as many as seven years to

your life so in short we never evolved not to engage in moderate levels of lifelong physical activity and therefore lack of physical activity or its modern manifestation exercise fails to slow aging and increases our vulnerability to many diseases so in the final analysis exercise is not a Magic Bullet but it sure is a great way to add life to your years and it can also maybe add a few years to your life thank you