Why We Sleep: Unlocking the Power of Sleep and Dreams

by Matthew Walker

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.

During deep NREM sleep specifically, the brain communicates a calming signal to the fight-or-flight sympathetic branch of the body’s nervous system, and does so for long durations of the night.

For cardiovascular health, I believe that finding comes from a “global experiment” in which 1.5 billion people are forced to reduce their sleep by one hour or less for a single night each year.

The less you sleep, the more you are likely to eat.

Precisely how a lack of sleep sets you on a path toward diabetes and leads to obesity is now well understood and incontrovertible.

research groups found far higher rates of type 2 diabetes among individuals that reported sleeping less than six hours a night routinely.

scientists had to conduct carefully controlled experiments with healthy adults who had no existing signs of diabetes or issues with blood sugar. In the first of these studies, participants were limited to sleeping four hours a night for just six nights. By the end of that week, these (formerly healthy) participants were 40 percent less effective at absorbing a standard dose of glucose, compared to when they were fully rested.

After participants had been restricted to four to five hours of sleep for a week, the cells of these tired individuals had become far less receptive to insulin.

Chronic sleep deprivation is now recognized as one of the major contributors to the escalation of type 2 diabetes throughout first-world countries.

When your sleep becomes short, you will gain weight.

Using precisely this experimental design in a group of healthy, lean participants, Van Cauter discovered that individuals were far more ravenous when sleeping four to five hours a night.

When short sleeping, the very same individuals ate 300 calories more each day—or well over 1,000 calories before the end of the experiment—compared to when they were routinely getting a full night of sleep.

Scale that up to a working year, and assuming one month of vacation in which sleep miraculously becomes abundant, and you will still have consumed more than 70,000 extra calories. Based on caloric estimates, that could cause 10 to 15 pounds of weight gain a year, each and every year.

Sleep, it turns out, is an intensely metabolically active state for brain and body alike.

Three-year-olds sleeping just ten and a half hours or less have a 45 percent increased risk of being obese by age seven than those who get twelve hours of sleep a night.

When you are not getting enough sleep, the body becomes especially stingy about giving up fat.

men who report sleeping too little—or having poor-quality sleep—have a 29 percent lower sperm count than those obtaining a full and restful night of sleep,

that

Males with low testosterone often feel tired and fatigued throughout the day. They find it difficult to concentrate on work tasks, as testosterone has a sharpening effect on the brain’s ability to focus. And of course, they have a dulled libido, making an active, fulfilling, and healthy sex life more challenging. Indeed, the self-reported mood and vigor of the young men described in the above study progressively decreased in lockstep with their increasing state of sleep deprivation and their declining levels of testosterone.

Does this relate at all to what seems like more common and prominent tendencies toward homosexuality more recently?

those working irregular nighttime hours resulting in poor-quality sleep, such as nurses who performed shift work (a profession occupied almost exclusively by women at the time of these earlier studies), had a significantly higher rate of abnormal menstrual cycles than those working regular daytime hours.

the women working erratic hours were 80 percent more likely to suffer from issues of sub-fertility that reduced the ability to get pregnant.

Women who do become pregnant and routinely sleep less than eight hours a night are also more likely to suffer a miscarriage in the first trimester, relative to those con...

The faces pictured after one night of short sleep were rated as looking more fatigued, less healthy, and significantly less attractive, compared with the appealing image of that same individual after they had slept a full eight hours.

He measured the sleep of more than 150 healthy men and women for a week using a wristwatch device. Then he quarantined them, and proceeded to squirt a good dose of rhinovirus, or a live culture of the common cold virus, straight up their noses.

The less sleep an individual was getting in the week before facing the active common cold virus, the more likely it was that they would be infected and catch a cold.

doctors and governments would do well to stress the critical importance of sufficient sleep during the flu season.

sleep impacts your response to a standard flu vaccine.

those in the sleep-restricted group mustered a paltry response, producing less than 50 percent of the immune reaction their well-slept counterparts were able to mobilize.

Even if an individual is allowed two or even three weeks of recovery sleep to get over the assault of one week of short sleeping, they never go on to develop a full immune reaction to the flu shot.

As with the effects of sleep deprivation on memory, once you miss out on the benefit of sleep in the moment—here, regarding an immune response to this season’s flu—you cannot regain the benefit simply by trying to catch up on lost sleep. The damage is done, and some of that harm can still be measured a year later.

fighting immune cells. Examining healthy young men in a careful study that controlled for spurious factors, such as physical activity, Irwin demonstrated that a single night of four hours of sleep—such as going to bed at three a.m. and waking up at seven a.m.—swept away 70 percent of the natural killer cells circulating in the immune system, relative to a full eight-hour night of sleep.

The

Modern medicine is increasingly adept in its treatment of cancer when it stays put, but when cancer metastasizes—as was encouraged by the state of sleep disruption—medical intervention often becomes challenging, and death rates escalate.

Sleep disruption may therefore increase the risk of cancer development and, if cancer is established, favor its rapid and more rampant growth.

The scientific evidence linking disrupted sleep-wake rhythms and cancer is now so damning that the World Health Organization has officially classified nighttime shift work as a “probable carcinogen.”

Deprive a mouse of sleep for just a day, as researchers have done, and the activity of hundreds of these genes becomes significantly impaired.

During dreamless, deep NREM sleep, overall metabolic activity shows a modest decrease relative to that measured from an individual while they are resting but awake. However, something very different happens as the individual transitions into REM sleep and begins to dream.

these emotional regions of the brain are up to 30 percent more active in REM sleep compared to when we are awake!

REM sleep can therefore be considered as a state characterized by strong activation in visual, motor, emotional, and autobiographical memory regions of the brain, yet a relative deactivation in regions that control rational thought.

we could predict with confidence the form of someone’s dream—would it be visual, would it be motoric, would it be awash with emotion, would it be completely irrational and bizarre?—before the dreamers themselves reported their dream experience to the research assistant.

Stickgold did find a strong and predictive daytime signal in the static of nighttime dream reports: emotions.

Concentrations of a key stress-related chemical called noradrenaline are completely shut off within your brain when you enter this dreaming sleep state. In fact, REM sleep is the only time during the twenty-four-hour period when your brain is completely devoid of this anxiety-triggering molecule.

Those who slept in between the two sessions reported a significant decrease in how emotional they were feeling in response to seeing those images again.

results of the MRI scans showed a large and significant reduction in reactivity in the amygdala, that emotional center of the brain that creates painful feelings.

those who remained awake across the day without the chance to sleep and digest those experiences showed no such dissolving of emotional reactivity over time.

it was the dreaming state of REM sleep—and specific patterns of electrical activity that reflected the drop in stress-related brain chemistry during the dream state—that determined the success of overnight therapy from one individual to the next.

Sleep, and specifically REM sleep, was clearly needed in order for us to heal emotional wounds.

Cartwright demonstrated that it was only those patients who were expressly dreaming about the painful experiences around the time of the events who went on to gain clinical resolution from their despair, mentally recovering a year later as clinically determined by having no identifiable depression.