Highlights
id795552082
Routinely sleeping less than six or seven hours a night demolishes your immune system, more than doubling your risk of cancer. Insufficient sleep is a key lifestyle factor determining whether or not you will develop Alzheimer’s disease. Inadequate sleep—even moderate reductions for just one week—disrupts blood sugar levels so profoundly that you would be classified as pre-diabetic. Short sleeping increases the likelihood of your coronary arteries becoming blocked and brittle, setting you on a path toward cardiovascular disease, stroke, and congestive heart failure.
id795552083
sleep disruption further contributes to all major psychiatric conditions, including depression, anxiety, and suicidality
id795552084
Too little sleep swells concentrations of a hormone that makes you feel hungry while suppressing a companion hormone that otherwise signals food satisfaction
id795552085
the shorter your sleep, the shorter your life span
id795552086
the World Health Organization (WHO) has now declared a sleep loss epidemic throughout industrialized nations
id795552087
Scientists such as myself have even started lobbying doctors to start “prescribing” sleep
id795552088
After twelve to eighteen months of no sleep, the patient will die. Though exceedingly rare, this disorder asserts that a lack of sleep can kill a human being.
id795552089
It is disquieting to learn that vehicular accidents caused by drowsy driving exceed those caused by alcohol and drugs combined.
id795552090
Astonishing, but until very recently, this was reality: doctors and scientists could not give you a consistent or complete answer as to why we sleep
id795552091
Addressing the question of why we sleep from an evolutionary perspective only compounds the mystery. No matter what vantage point you take, sleep would appear to be the most foolish of biological phenomena. When you are asleep, you cannot gather food. You cannot socialize. You cannot find a mate and reproduce. You cannot nurture or protect your offspring. Worse still, sleep leaves you vulnerable to predation. Sleep is surely one of the most puzzling of all human behaviors.
id795552092
On any one of these grounds—never mind all of them in combination—there ought to have been a strong evolutionary pressure to prevent the
id795552093
emergence of sleep or anything remotely like it. As one sleep scientist has said, “If sleep does not serve an absolutely vital function, then it is the biggest mistake the evolutionary process has ever made.”III Yet sleep has persisted. Heroically so. Indeed, every species studied to date sleeps.IV This simple fact establishes that sleep evolved with—or very soon after—life itself on our planet. Moreover, the subsequent perseverance of sleep throughout evolution means there must be tremendous benefits that far outweigh all of the obvious hazards and detriments.
id795552094
There does not seem to be one major organ within the body, or process within the brain, that isn’t optimally enhanced by sleep (and detrimentally impaired when we don’t get enough)
id795552095
Dreaming provides a unique suite of benefits to all species fortunate enough to experience it, humans included. Among these gifts are a consoling neurochemical bath that mollifies painful memories and a virtual reality space in which the brain melds past and present knowledge, inspiring creativity.
id795552096
A balanced diet and exercise are of vital importance, yes. But we now see sleep as the preeminent force in this health trinity. The physical and mental impairments caused by one night of bad sleep dwarf those caused by an equivalent absence of food or exercise
id795552097
There are two main factors that determine when you want to sleep and when you want to be awake
id795552098
The first factor is a signal beamed out from your internal twenty-four-hour clock located deep within your brain. The clock creates a cycling, day-night rhythm that makes you feel tired or alert at regular times of night and day, respectively. The second factor is a chemical substance that builds up in your brain and creates a “sleep pressure.” The longer you’ve been awake, the more that chemical sleep pressure accumulates, and consequentially, the sleepier you feel. It is the balance between these two factors that dictates how alert and attentive you are during the day, when you will feel tired and ready for bed at night, and, in part, how well you will sleep.
id795552099
It is no coincidence that the likelihood of breaking an Olympic record has been clearly tied to time of day, being maximal at the natural peak of the human circadian rhythm in the early afternoon
id795552100
In the seventy-plus years since Kleitman and Richardson’s seminal experiment, we have now determined that the average duration of a human adult’s endogenous circadian
id795552101
clock runs around twenty-four hours and fifteen minutes in length
id795552102
Sunlight acts like a manipulating finger and thumb on the side-dial of an imprecise wristwatch. The light of the sun methodically resets our inaccurate internal timepiece each and every day, “winding” us back to precisely, not approximately, twenty-four hours.IV
id795552103
Yet daylight isn’t the only signal that the brain can latch on to for the purpose of biological clock resetting
id795552104
It is the reason that individuals with certain forms of blindness do not entirely lose their circadian rhythm. Despite not receiving light cues due to their blindness, other phenomena act as their resetting triggers. Any signal that the brain uses for the purpose of clock resetting is termed a zeitgeber, from the German “time giver” or “synchronizer
id795552105
An adult’s owlness or larkness, also known as their chronotype, is strongly determined by genetics
id795552106
melatonin helps regulate the timing of when sleep occurs by systemically signaling darkness throughout the organism. But melatonin has little influence on the generation of sleep itself: a mistaken assumption that many people hold. To make clear this distinction, think of sleep as the Olympic 100-meter race. Melatonin is the voice of the timing official that says “Runners, on your mark,” and then fires the starting pistol that triggers the race. That timing official (melatonin) governs when the race (sleep) begins, but does not participate in the race. In this analogy, the sprinters themselves are other brain regions and processes that actively generate sleep. Melatonin corrals these sleep-generating regions of the brain to the starting line of bedtime. Melatonin simply provides the official instruction to commence