"Finger on the Pulse of Longevity"
Immanuel Kant, the 18th century philosopher
described the chemistry of his day as a science,
but not really science,
because it wasn’t grounded in mathematics -
at least not until a century later.
The same could be said for biology,
the study of life.
In math, physics, quantum physics, etc.,
there are constants:
physical quantities thought to be both
universal and unchanging.
Biology, though, was considered too complex,
too messy to be governed by simple, natural laws,
but in 1999, a theoretical high energy physicist
from Los Alamos joined up with two biologists
to describe universal scaling laws
that appear to apply across the board.
Are there any clinical implications
of these types of theories?
Well a fascinating observation was published.
The number of heartbeats per lifetime
is remarkably similar,
whether you’re a hamster all the way up to a whale.
So even though mice only live less than two years,
their heartrate is like 5 to 600 beats a minute—
up to ten beats a second,
whereas the heart of a galopagos tortoise
beats 100 times slower,
but they live about a 100 times longer.
There’s such a remarkable consistency in the number
of heartbeats animals get in their lifetimes,
that a provocative question was asked,
“Can human life be extended by cardiac slowing?”
In other words, if humans are predetermined
to have about three billion heart beats period,
in a lifetime,
then would a reduction in average heart rate
extend life?
This is not just some academic question.
If that’s how it worked, then one might estimate
that a reduction in heart rate
from more of an average 70 beats per minute
down to what many athletes have,
60 beats per minute could theoretically
increase life span over a decade.
Seems a bit off the wall,
but that’s how the scientific method works:
you start out with an observation,
like this striking heartbeat data,
and then you make an educated guess, or hypothesis,
that you can then put to the test.
How might one demonstrate a life-prolonging effect
of cardiac slowing in humans?
Well perhaps a first attempt in this direction
would be to see if people with slower hearts
live longer lives,
lamenting the fact that there was no drug
that just lowered heartrate they could give to people,
since drugs like beta blockers lower heart rate,
but also lower blood pressure,
so wouldn’t be ideal for testing the question at hand,
but at least we can do that first part,
about do people with slower heart live longer lives.
And indeed, from the evidence accumulated so far,
we know that a high resting heart rate,
meaning how fast our heart beats
when we’re just sitting at rest,
is associated with an increase in mortality
in the general population,
as well as those with disease.
A faster heart rate may lead to a faster death rate.
Faster resting heart rates, (RHRs) are associated
with shorter life expectancies,
considered a strong independent risk factor
for heart disease and heart failure.
You can see how those with the higher heart rates
were about twice as likely over the next 15 years
to experience heart failure.
In middle-aged people, and older people, in men, and women.
And what’s critical is that this link
between how fast our heart goes,
and how fast our life goes
is independent of physical activity.
At first I was like duh,
of course lower resting heart rates are associated
with a longer lifespan.
Who has a really slow pulse?
Athletes.
As you can see, the more physically fit we are,
the lower our resting pulse.
But no, they found that irrespective of level
of physical fitness people with high resting heart rates
fare worse than people with lower heart rates,
so it appears it’s not just a marker of risk,
but a bona fide risk factor,
independent of how fit we are
or how much we exercise.
Why?
Well, if our heart rate is up 24 hours a day,
even when we’re sleeping,
all that pulsatile stress may break some of the elastic fibers
within the arterial wall,
causing our arteries to become stiff.
It doesn’t allow enough time
for our arteries to relax between beats,
and so the faster our heart,
the stiffer our arteries,
but there are all sorts of theories
how an increased resting heart rate could decrease
our time on Earth.
Regardless, this relationship is now well recognized.
It’s not just a marker of an underlying pathology…
It’s not merely a marker of inflammation...
The reason it’s important to distinguish a risk factor
from a risk marker,
is that if you control the risk factor,
you control the risk,
but if it’s just a risk marker,
it wouldn’t matter if we brought our heart rate down.
But now we even have evidence from drug trials—
now that there actually are medications
that just affect heart rate,
that lowering our heart rate lowers our death rate.
It’s now been shown in at least dozen trials so far.
Basically we don’t want our heart to be beating more
than about one beat per second at rest.
You can measure your pulse right now!
For the maximum lifespan, the target is like
one beat a second, to beat the clock.
But don’t worry if you’re too fast;
heart rate is a modifiable risk factor.
Yes, there are drugs,
but there are also lifestyle regimens
that can bring our resting pulse down…
which I'll cover next.