 Manuel 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 and physics, quantum physics, 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 kind of theories? Well, a fascinating observation was published. The number of heartbeats per lifetime is remarkably similar. Either you're a hamster, or all the way up to a whale. So even though mice only live less than two years, their heart rate is like 5 to 600 beats a minute, up to 10 beats a second, whereas the heart of a colapa ghost 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 3 billion heartbeats 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, would theoretically increase lifespan 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's no drug that just lowered heart rate that they could give to people, since drugs like beta blockers lower heart rate, but also lower blood pressure, so it wouldn't be ideal for testing the question at hand. But at least we could do that first part about do people with slower hearts 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 you're just sitting at rest, is associated with an increased immortality in the general population, as well as those with chronic disease. A fasting heart rate may lead to a faster death rate. Faster resting heart rates 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 are 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. I mean, at first I was like, well 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 higher 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, our heart rate is, 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 though 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, but lowering our heart rate lowers our death rate. It's now 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. 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.