Adults 45 years old or older who sleep fewer than six hours a night are 200 percent more likely to have a heart attack or stroke during their lifetime, as compared with those sleeping seven to eight hours a night.
This finding impresses how important it is to prioritize sleep in midlife, which is unfortunately the time when family and professional circumstances encourage us to do the exact opposite.
Part of the reason the heart suffers so dramatically under the weight of sleep deprivation concerns blood pressure.
Have a quick look at your right forearm and pick out some veins. If you wrap your left hand around that forearm, just below the elbow, and grip it, like a tourniquet, you will see those vessels start to balloon. A little alarming, isn’t it?
The ease with which just a little sleep loss can pump up pressure in the veins of your entire body, stretching and distressing the vessel walls, is equally alarming.
High blood pressure is so common nowadays that we forget the deathly toll it inflicts. This year alone, hypertension will steal more than 7 million people’s lives by way of cardiac failure, ischemic heart disease, stroke, or kidney failure.
Deficient sleep is responsible for many of these lost fathers, mothers, grandparents, and beloved friends.
One night of modest sleep reduction, even just one or two hours, will promptly speed the contracting rate of a person’s heart, hour upon hour, and significantly increase the systolic blood pressure within their vasculature.
You will find no solace in the fact that these experiments were conducted in young, fit individuals, all of whom started out with an otherwise healthy cardiovascular system just hours before.
Such physical fitness proves no match for a short night of sleep; it affords no resistance. Beyond accelerating your heart rate and increasing your blood pressure, a lack of sleep further erodes the fabric of those strained blood vessels, especially those that feed the heart itself, called the coronary arteries.
These corridors of life need to be clean and open wide to supply your heart with blood at all times. Narrow or block those passageways, and your heart can suffer a comprehensive and often fatal attack caused by blood oxygen starvation, colloquially known as a “massive coronary.”
One cause of a coronary artery blockage is atherosclerosis, or the furring up of those heart corridors with hardened plaques that contain calcium deposits.
Researchers at the University of Chicago studied almost five hundred healthy midlife adults, none of whom had any existing heart disease or signs of atherosclerosis. They tracked the health of the coronary arteries of these participants for a number of years, all the while assessing their sleep.
If you were one of the individuals who were obtaining just five to six hours each night or less, you were 200 to 300 percent more likely to suffer calcification of your coronary arteries over the next five years, relative to those individuals sleeping seven to eight hours.
The deficient sleep of those individuals was associated with a closing off of the critical passageways that should otherwise be wide open and feeding the heart with blood, starving it and significantly increasing the risk of a coronary heart attack.
Although the mechanisms by which sleep deprivation degrades cardiovascular health are numerous, they all appear to cluster around a common culprit, called the sympathetic nervous system.
The sympathetic nervous system is resolutely activating, inciting, even agitating. If needed, it will mobilize the evolutionarily ancient fight-or-flight stress response within the body, comprehensively and in a matter of seconds.
Like an accomplished general in command of a vast military, the sympathetic nervous system can muster activity in a vast assortment of the body’s physiological divisions, from respiration, immune function, and stress chemicals to blood pressure and heart rate.
An acute stress response from the sympathetic nervous system, which is normally only deployed for short periods of time lasting minutes to hours, can be highly adaptive under conditions of credible threat, such as the potential of real physical attack.
Survival is the goal, and these responses promote immediate action to accomplish just that. But leave that system stuck in the “on” position for long durations of time, and sympathetic activation becomes deeply maladaptive. In fact, it is a killer.
With few exceptions over the past half century, every experiment that has investigated the impact of deficient sleep on the human body has observed an overactive sympathetic nervous system.
As your sleep-deprived heart beats faster, the volumetric rate of blood pumped through your vasculature increases, and with that comes the hypertensive state of your blood pressure. Occurring at the same time is a chronic increase in a stress hormone called cortisol, which is triggered by the overactive sympathetic nervous system.
One undesirable consequence of the sustained deluge of cortisol is the constriction of those blood vessels, triggering an even greater increase in blood pressure.
Making matters worse, growth hormone, a great healer of the body, which normally surges at night, is shut off by the state of sleep deprivation. Without growth hormone to replenish the lining of your blood vessels, called the endothelium, they will be slowly shorn and stripped of their integrity.
Adding insult to real injury, the hypertensive strain that sleep deprivation places on your vasculature means that you can no longer repair those fracturing vessels effectively.
When Mathew Walker, author of this amazing book called Why We sleep, communicates science to the general public in lectures or writing, he is always wary of bombarding an audience with never-ending mortality and morbidity statistics, lest they themselves lose the will to live in front of him.
It is hard not to do so with such compelling masses of studies in the field of sleep deprivation. Often, however, a single astonishing result is all that people need to apprehend the point.