Humans are not sleeping the way nature intended. The number of sleep bouts, the duration of sleep, and when sleep occurs have all been comprehensively distorted by modernity.
Throughout developed nations, most adults currently sleep in a monophasic pattern, that is, we try to take a long, single bout of slumber at night, the average duration of which is now less than seven hours.
Visit cultures that are untouched by electricity and you often see something rather different. Hunter-gatherer tribes, such as the Gabra in northern Kenya or the San people in the Kalahari Desert, whose way of life has changed little over the past thousands of years, sleep in a biphasic pattern.
Both these groups take a similarly longer sleep period at night (seven to eight hours of time in bed, achieving about seven hours of sleep), followed by a thirty- to sixty-minute nap in the afternoon.
There is also evidence for a mix of the two sleep patterns, determined by time of year. Pre-industrial tribes, such as the Hadza in northern Tanzania or the San of Namibia, sleep in a biphasic pattern in the hotter summer months, incorporating a thirty- to forty-minute nap at high noon.
They then switch to a largely monophasic sleep pattern during the cooler winter months. Even when sleeping in a monophasic pattern, the timing of slumber observed in pre-industrialized cultures is not that of our own, contorted making.
On average, these tribespeople will fall asleep two to three hours after sunset, around nine p.m. Their nighttime sleep bouts will come to an end just prior to, or soon after, dawn.
Have you ever wondered about the meaning of the term “midnight”? It of course means the middle of the night, or, more technically, the middle point of the solar cycle. And so it is for the sleep cycle of hunter-gatherer cultures, and presumably all those that came before.
Now consider our cultural sleep norms. Midnight is no longer “mid night.” For many of us, midnight is usually the time when we consider checking our email one last time, and we know what often happens in the protracted thereafter.
Compounding the problem, we do not then sleep any longer into the morning hours to accommodate these later sleep-onset times. We cannot. Our circadian biology, and the insatiable early-morning demands of a post-industrial industrial way of life, denies us the sleep we vitally need.
At one time we went to bed in the hours after dusk and woke up with the chickens. Now many of us are still waking up with the chickens, but dusk is simply the time we are finishing up at the office, with much of the waking night to go.
Moreover, few of us enjoy a full afternoon nap, further contributing to our state of sleep bankruptcy.
The practice of biphasic sleep is not cultural in origin, however. It is deeply biological. All humans, irrespective of culture or geographical location, have a genetically hardwired dip in alertness that occurs in the midafternoon hours. Observe any post-lunch meeting around a boardroom table and this fact will become evidently clear.
Like puppets whose control strings were let loose, then rapidly pulled taut, heads will start dipping then quickly snap back upright. I’m sure you’ve experienced this blanket of drowsiness that seems to take hold of you, mid afternoon, as though your brain is heading toward an unusually early bedtime.
Both you and the meeting attendees are falling prey to an evolutionarily imprinted lull in wakefulness that favors an afternoon nap, called the post-prandial alertness dip (from the Latin prandium, “meal”). This brief descent from high-degree wakefulness to low-level alertness reflects an innate drive to be asleep and napping in the afternoon, and not working.
It appears to be a normal part of the daily rhythm of life. Should you ever have to give a presentation at work, for your own sake, and that of the conscious state of your listeners, if you can, avoid the mid afternoon slot.
What becomes clearly apparent when you step back from these details is that modern society has divorced us from what should be a preordained arrangement of biphasic sleep, one that our genetic code nevertheless tries to rekindle every afternoon. The separation from biphasic sleep occurred at, or even before, our shift from an agrarian existence to an industrial one.
Humans need longer bout of continuous sleep at night, followed by a shorter mid afternoon nap.
Accepting that this is our natural pattern of slumber, can we ever know for certain what types of health consequences have been caused by our abandonment of biphasic sleep? Biphasic sleep is still observed in several siesta cultures throughout the world, including regions of South America and Mediterranean Europe.
I am sure we all heard of siesta time in places such as Spain and Greece.
Today most of these countries no longer have these afternoon naps. Prior to the turn of the millennium, there was increasing pressure to abandon the siesta-like practice in Greece.
A team of researchers from Harvard University’s School of Public Health decided to quantify the health consequences of this radical change in more than 23,000 Greek adults, which contained men and women ranging in age from twenty to eighty-three years old.
The researchers focused on cardiovascular outcomes, tracking the group across a six-year period as the siesta practice came to an end for many of them. As with countless Greek tragedies, the end result was heartbreaking, but here in the most serious, literal way.
None of the individuals had a history of coronary heart disease or stroke at the start of the study, indicating the absence of cardiovascular ill health.
However, those that abandoned regular siestas went on to suffer a 37 percent increased risk of death from heart disease across the six-year period, relative to those who maintained regular daytime naps.
The effect was especially strong in workingmen, where the ensuing mortality risk of not napping increased by well over 60 percent.
Apparent from this remarkable study is this fact: when we are cleaved from the innate practice of biphasic sleep, our lives are shortened. It is perhaps unsurprising that in the small enclaves of Greece where siestas still remain intact, such as the island of Ikaria, men are nearly four times as likely to reach the age of ninety as American males.
These napping communities have sometimes been described as “the places where people forget to die.” From a prescription written long ago in our ancestral genetic code, the practice of natural biphasic sleep, and a healthy diet, appear to be the keys to a long-sustained life.
SINCE I HAVE KNOWN ABOUT THIS, I HAVE MADE SURE I GET A MINIMUM OF 7 HOURS SLEEP PER NIGHT AND 30 TO 1 HOUR NAPS EVERY DAY.