The number of heartbeats per lifetime is remarkably similar whether you’re a hamster all the way up to a whale. So, mice, who typically live less than two years, have a heart rate of about 500 to 600 beats a minute—up to 10 beats a second. In contrast, the heart of a Galapagos tortoise beats 100 times slower, but they live about 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 heartbeats 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 works, then one might estimate that a reduction in heart rate from an average of more than 70 beats per minute down to what many athletes have, 60 beats per minute, could theoretically increase life span by more than a decade.
How might one demonstrate “a life-prolonging effect of cardiac slowing in humans”? Perhaps a first attempt would be to see if people with slower heart rates live longer lives. Unfortunately, researchers couldn’t just give subjects drugs that only lower heart rate. Drugs like beta blockers at the time lowered both heart rate and blood pressure, so they weren’t ideal for testing the question at hand. We can, however, do that first part and look at whether people with slower heart rates live longer.
“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 in those with chronic disease. A faster heart rate may lead to a faster death rate. Indeed, faster resting heart rates are associated with shorter life expectancies and are considered a strong independent risk factor for heart disease and heart failure. Researchers found that those with higher heart rates were about twice as likely over the next 15 years to experience heart failure. This was seen in middle-aged people, as well as observed in older people. It was also found in men and women. 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 thought this was painfully obvious. Of course lower resting heart rates are associated with a longer lifespan. Who has a really slow pulse? Athletes. The more physically fit we are, the lower our resting pulse. But, no: Researchers “found that irrespective of level of physical fitness subjects with higher resting heart rates fare worse than people with lower heart rates,” so it appears a high resting heart rate is not just a marker of risk, but a bona-fide risk factor independent of how fit we are or how much we exercise.
Why? 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, so the faster our heart, the stiffer our arteries. There are all sorts of theories about how an increased resting heart rate can decrease our time on Earth. Regardless, this relationship is now well recognized.
It is not just a marker of an underlying pathology nor can it be said to be 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 were just a risk marker, it wouldn’t matter if we brought down our heart rate. We now have evidence from drug trials—indeed, there are now medications that just affect heart rate—that lowering our heart rate lowers our death rate.
It’s been shown in at least a dozen trials so far. Basically, we don’t want our heart to be beating more than about one beat per second at rest. (Measure your pulse right now!) For the maximum lifespan, the target is about one beat a second to beat the clock. Don’t worry if your heart’s beating too fast: Heart rate is a modifiable risk factor. Yes, there are drugs, but there are also lifestyle regimens, like eating beans, that can bring down our resting pulse.
But then, there is always this…
Written by Dr. Michael Greger, M.D. and published by Care 2 ~ January 17, 2018.
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