We Don’t Just “Die from Old Age.”
Some research suggests a more active youth leads to less wasted energy later in life.
Good Morning!
Today’s newsletter isn’t meant to scare you. Like many other Friday newsletters, it simply serves as a reminder to move more, and to move with intention.
I found some time this week to dig into some research papers on health, aging and resting metabolic rate (RMR). RMR is the a fancy term for the amount of energy your body spending on basic functions while it’s resting.
These functions include (but aren’t limited to) circulating blood, regulating body temperature, and maintaining organ function (more on this later).
The factors that influence RMR are many (also more on this later), but the main factors I want to focus on today are resting heart rate and body composition.
Resting heart rate is the amount of heart beats per minute (bpm) someone experiences at complete rest, and body composition is the makeup (muscle, body fat, water, skeletal mass) of one’s entire body that equals their weight.
How We Got Here: A Study on Frailty in Old Age
The study that piqued my interest for this newsletter came while re-reading Why Zebras Don’t Get Ulcers by Robert Sapolsky, a book about the microscopic workings of stress and how stress influences our physiology.
Sapolsky cites a Max Rubner in his chapter about cardiac events, who made quite the proposal back in 1908. Rubner’s Rate of Living Theory asserted that animals with slower metabolisms (typically the largest of them) enjoy longer life spans than those with fast metabolisms (small ones).
He came to this conclusion after observing the total amount of heartbeats in elephants and rats.
This probably seems silly. It was, because even though smaller animals use up their oxygen faster and “tire out” their bodies quicker than larger animals, it was a bit premature to suggest that animals could have a finite number of heartbeats.
Imagine guessing the over-under on how many heartbeats you’ll have in this lifetime!
Sorry, that’s way too existential. So how does this tie into dying of old age?
Rubner’s theory set off a larger discussion about the metabolic demands for humans across our lifespans, and what kinds of things can pre-indicate a long life.
It was Rubner who effectively started the conversation around RMR being a determinant for living into the 80’s, 90’s and beyond.
The Journal of the American Geriatrics society (JAGS) published research in 2013 that showed that in pre-frail and frail older women, those with a history of poorer health (obesity, inactivity and respiratory issues, namely) had higher RMR’s in old age and were more at risk for health deterioration for premature death.
Whereas those individuals with high RMR needed more energy to stay alive — more blood pumping to their organs, more fluids flowing to them to detoxify, and more pressure through vessels to and from the heart — those with lower RMR’s were the equivalent of an iPhone battery on airplane mode; energy efficient and longer lasting.
Whoa, Whoa, Whoa. WHAT!?!
Okay, let’s not freak out too much. Those last few sentences basically make it sound like an unhealthy youth can lead to a shorter life. While that’s pretty obvious, RMR is not a perfect indicator for lifespan.
RMR is also influenced by genetics (largely out of our control), weather (mostly out of our control), and muscle mass (very much within our control). Here’s where it gets interesting.
Typically, we associate a “fast metabolism” as being a good thing, right? It means your body is working hard to convert food into energy. But what we don’t want is for it to be TOO fast. This probably seems counterintuitive.
“But shouldn’t we have a great metabolism all our lives to prevent an early death?”
Technically, yes, but metabolism is going to decline as we age whether we like it or not.
As hard as you might want to train all your life, it might not be smart to be vigorously exercising well into your seventies because you could run the risk of hijacking your homeostasis.
How’s that for some anatomical alliteration?
In all seriousness, we have to allow metabolism to slow down in old age, or else RMR can become elevated. And we now know what can (possibly) happen with elevated RMR in old age.
Tried and (Mostly) True: Solutions for Old Age
Let’s return to the factors for Resting Metabolic Rate that are largely in our control before we become old and decrepit: Body composition and resting heart rate.
In the above study, while we’re UNSURE, that high RMR is an absolute risk factor for early death, the authors acknowledged that research RMR still has the potential to be the scientific breakthrough that helps us better understand longevity.
Knowing this, we can avoid testing our luck against high RMR by strength training in our youth to develop lean muscle, losing fat, and engaging in mildly challenging cardio to strengthen capillaries, blood vessels and our heart.
Even though the study fell short of proving RMR’s causality, the iPhone theory/Runner’s hypothesis still holds some weight: a body that’s working hard just to sustain itself in old age won’t last as long as one that can maintain homeostasis on autopilot.
Lower resting heart rate has been associated with longer life spans, which also tracks with Rubner’s theory and the greater message of more exercise; fitter, healthier individuals who exercise regularly enjoy lower resting heart rates than their non-exercising counterparts.
Just to entertain the Rate of Living Theory once more…
Even if we did have a finite number of heartbeats, wouldn’t it make sense to exercise more so that we could use less of our allotted beats while we’re resting (which by the way, makes up more than two-thirds of our waking lives)?
I still don’t think Rubner was totally correct, since he didn’t seem to account for the excess heartbeats we experience during exercise.
Some athletes achieve max heart rates of 190-200 bpm during sports, which begs the question of whether or not those bouts of exertion offset their lower resting heart rates.
The point I’m trying to make here is this: While we don’t know for sure whether or not our bodies have a clock, we do know that larger amounts of fat tissue and constricted blood vessels will make our bodies work harder to keep us alive in old age.
Which makes me think…
Maybe the phrase “dying of old age” is underscoring something else. “Old age” is usually mid-70’s or older. But it doesn’t have to be. If we take action on our health and make sure our bodies aren’t working too hard to keep us alive by that age, “old age” might not kill us as fast.
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