WHY WE SLEEP 3 2 9 by forty-two minutes per night on average. Trivial as that may sound, it does translate tO five hours Of extra sleep each week, or seventy-five extra hours ofsleep each semester. But this isn't enough. l'm sure a depressingly large proportion 0f my students returned t0 their shorter, unhealthy sleep habits in the years after. Just as describing the scientific dangers 0f how eating junk f00d leads to obesity rarely ends up with people choosing broccoli over a cookie, knowledge alone is not enough. Additional methods are required. One practice known tO convert a healthy new habit intO a perma- nent way Of ⅱ他 is exposure tO your own data. Research in cardiovascu- lar disease is a good example. lfpatients are given t001S that can be used at home t0 track their improving physiological health ⅲ response t0 an exercise plan—such as blOOd pressure monitors during exercise pro- grams, scales that log b0dy mass index during dieting effortS' or spirom- etry devices that reg1Ster respiratory lung capacity during attempted smoking cessation—compliance rates with rehabilitation programs increase. FOIIOW up with those same individuals after ayear or even five, and more ofthem have maintained their positive change in lifestyle and behavior as a consequence. When it comes tO the quantified self, it's the Old adage of"seeing is believing" that ensures longer-term adherence tO healthy habits. With wearables that accurately track our slumber fast emergmg, we can apply this same approach t0 sleep. Harnessing smartphones as a central hub t0 gather an individual's health data 伝 om various sources— physical activity (such as number Of steps or minutes and intensity Of exercise), light exposure, temperature, heart rate, b0dy weight' f00d intake, work productivity, or mood—we show each individual how their own sleep is a direct predictor oftheir own physical and mental health. lt's likely that, ifyou wore such a device, you would find out that on the nights you slept more you ate less f00d the next day, and 0f a healthy kind; felt brighter, happier, and more positive; had better relationship interactions; and accomplished more in less time at work. Moreover, you would discover that during months ofthe year when you were aver- agmg more sleep, you were sick less; your weight, b100d pressure and medication use were all lower; and your relationship or marriage satis- faction, as well as sex life, were better.

3 3 2 MATTHEW WALKER rent recommendations). Did they receive tutelage on drugs, alcohol, safe sex, and reproductive health? Eighty-seven percent said yes.Was the importance Of exercise impressed upon them at some point dur- ing their schooling, and/or was the practice of physical education activities mandatory on a weekly basis? s ー 100 percent 0f people confirmed it was. This is hardly a scientific data set, but still, some form of dietary, exercise, and health-related schooling appears to be part ofa worldwide educational plan that most children in developed nations receive. When I asked this same diverse set of individuals if they had received any education about sleep, the response was equally universal in the opposite direction: 0 percent received any educational materials or information about sleep. Even ⅲ the health and personal wellness education that some individuals described, there was nothing resem- bling lip service t0 sleep's physical or mental health importance. lfthese individuals are representative, it suggests that sleep holds no place in the education Of our children. Generation after generation, our young minds continue tO remaln unaware Of the imm. ediate dangers and pro- tracted health impacts of insufficient sleep, and I for one feel that is wrong. I would be keen to work with the WorId Health Organization to develop a simple educational module that can be implemented in schools around the world. lt could take many forms, based on age group: an animated short accessible online, a board game in physical or digital form (one that could even be played internationally with sleep pen pals"), or a virtual environment that helps you explore the secrets 0f sleep. There are many options, of them easily translatable across nations and cultures. The go would be twofold: change the lives ofthose children and, by way ofraising sleep awareness and better sleep practice, have that child pass on their healthy sleep values t0 their own children. ln this way, we would begin a familial transmission ofsleep appreciation 仕 om one gen- eration tO the next, as we dO with things like good manners and moral- ity. Medically, our future generations would not only enjoy a longer ⅱ span, but, more importantly, a longer health span, absolved ofthe mid- and late-life diseases and disorders that we ow are caused by (and not

W HY W E S L E E P 7 complex, profoundly more interesting, and alarmingly more health- relevant. We sleep for a rich litany 0f functions, plural—an abundant constellation Of nighttime benefits that service bOth our brains and our bOdies. There does not seem tO be one maJOr organ within the b0dy, or process within the brain, that isn't optimally enhanced by sleep (and detrimentally impaired when we don't get enough). That we receive such a bounty 0f health benefits each night should not be surprising. After all, we are 4 ル 4 ん e for two-thirds Of our lives and we don't just achieve one useful thing during that stretch Of time. Ⅵ厄 accomplish myriad undertakings that promote our own well-being and survival. Why, then, would we expect sleep—and the twenty- five tO thirty years, on average, it takes from our lives—to Offer one function only? Through an explosion Of discoveries over the past twenty years, we have come tO realize that evolution did not make a spectacular blunder in conceiving 0f sleep. Sleep dispenses a multitude 0f health-ensunng benefits, yours tO pick up in repeat prescription every twenty-four hours, should you choose. (Many don't. ) Within the brain, sleep enriches a diversity 0f functions, including our ability tO learn, memorize, and make 10 c 記 decisions and choices. Benev01ently servicing our psychological health, sleep recalibrates our emotional brain circuits, allowing us tO navigate next-day social and psychological challenges with cool-headed composure. We are even beginning tO understand the most impemous and controversial Of all conscious expenences: the dream. provides a unique Of benefits tO all species fortunate enough tO experience it, humans included. Among these gifts are a consoling neurochemical bath that .- 里Ⅱ es painful memories and a virtual reality space in which the brain ー . eldspast and present knowledge, inspiring creativity• Downstairs in the bOdy, sleep restocks the armory Of our immune system, helping fight m 曲 g 具 4n9 当 . 、 preventing infection' and yarding off manner of sickness. Sleep reforms the body's metabolic state by fine-tuning the balance ofinsulin and circulating glucose. Sleep further regulates our appetite, helping control body weight through healthy food selection rather than rash impulsivity. Plentiful sleep maintains a flouri shing microbiome within your gut 伝 om which we know s 0 much

3 3 6 MATHEW WALKER cal care that places sleep at the center Of patient care, or very close tO it. ln one Of my own research studies, we have discovered that pain- related centers within the human brain are 42 percent more sensitive t0 unpleasant thermal stimulation (non-damaging, ofcourse) following a night 0f sleep deprivation, relative t0 a んⅡ , healthy eight-hour night Of sleep. lt is interesting tO note that these pain-related brain reglons are the same areas that narcotic medications, such as morphine, act upon. Sleep appears t0 be a natural analgesic, and without it, pain is perceived more acutely by the brain, and, most importantly, felt more powerfully by the individual. Morphine is not a desirable medication, by the way.. lt has serious safety issues related tO the cessation ofbreath- ing, dependency, and withdrawal, together with terribly unpleas ant side effects. These include nausea, loss Of appetite, cold sweats, itchy skin, and urinary and bowel issues, not tO mention a form Of sedation that prevents natural sleep. Morphine 記 so alters the action 0f other medications, resulting in problematic interaction effects. Extrapolating 仕 om a now extensive set Of scientific research, we should be able t0 reduce the dose 0f narcotic drugs on our hospital wards by improving sleep conditions. ln turn, this would lessen safety risks, reduce the severity Of side effects, and decrease the potential for drug interactions. lmproving sleep conditions for patients would not only reduce drug doses, it would 記 SO bOOSt their immune system. lnpatients could there- fore mount a far more effective battle against infection and accelerate postoperative wound healing. With hastened recovery rates would come shorter inpatient stays, reducing health-care costs and health insurance rates. N0b0dy wants to be ⅲ the hospital any longer than is absolutely necessary. Hospital administrators feel likewise. Sleep can help. The sleep solutions need not be complicated. Some are simple and inexpensive, and the benefits should be immediate. We can start by removing any eqmpment and alarms that are not necessary for any one patient. Next, we must educate doctors, nurses, and hospital administrations on the scientific health benefits 0f sound sleep, help- ing them realize the premium we must place on patients' slumber. We can alSO ask patients about their regular sleep schedules on the stan- dard hospital admission form, and then structure assessments and

WHY WE SLEEP I was used t0 back in England. They stated: open 伝 om nine a. m. to one p. m. , closed 仕 om one tO five p. m. , open five tO nine p. m. Today, few of those signs remain in windows of shops through- Ollt Greece. Prior tO the turn Of the millennium, there was increasing pressure tO abandon the siesta-like practice in Greece. A team Of researchers 仕 om Harvard University's Sch001 0f Public Health decided to quantify the health consequences of this radical change in more than 23 , 000 Greek adults, which contained men and women rangmg ⅲ age from twenty t0 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 ofthem. 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 ofcardiovascular Ⅲ 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 ⅲ workingmen, where the ensumg mortality risk ofnot napping increased by well over 60 percent. Apparent 仕 om this remarkable study is this fact: when we are cleaved 仕 om the innate practice of biphasic sleep, our lives are short- ened. lt is perhaps unsurprising that ⅲ the small enclaves of Greece where siestas still remain intact, such as the island Of lkaria, men are nearly four times as likely t0 reach the age ofninety 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 ofnatural biphasic sleep, and a healthy diet, appear to be the keys to a long-sustained life. WE ARE SPECIAL Sleep, you can now appreciate, is a unifying feature across the animal kingdom, yet within and between species there is remarkable diversity ⅲ amount (). g. , time), form (). g. , half-brain, whole-brain), and pattern (mono- phasic, biphasic, polyphasic). But are we humans special ⅲ our sleep pro-

ー 66 MATTHEW WALKER disease, stroke, or kidney failure. Deficient sleep is responsible for many ofthese lost fathers, mothers, grandparents, and beloved friends. As with other consequences of sleep loss weve encountered, you don't need a 血Ⅱ night 0f total sleep deprivation to inflict a measurable impact on your cardiovascular system. One night ofmodest sleep reduc- tion—even just one or AJO hours—will promptly speed the contracting rate 0f a person's heart, hour upon hour, and significantly increase the systolic b100d pressure within their vasculature. * You ⅶⅡ find no solace in the fact that these experiments were conducted in young, fit individ- uals, ofwhom started out with an otherwise healthy cardiovascular system just hours before. Such physical fitness proves no match for a short night ofsleep; it affords no resistance. Beyond accelerating your heart rate and increasing your blood pres- sure, a lack 0f sleep further erodes the fabric 0f those strained blood vessels, especially those that feed the heart itself, called the coronary arteries. These corridors oflife need to be clean and open wide to supply your hear い Mith b100d at times. Narrow or block those passageways, and your heart can suffer a comprehensive and often fatal attack caused by blOOd oxygen starvation, colloquially k10 、Ⅵ 1 as a massive coronary. One cause Of a coronary artery blockage is atherosclerosis, or the furring up 0f those heart corridors with hardened plaques that con- tain calcium deposits. Researchers at the University 0fChicago studied almost five hundred healthy midlife adults, none ofwhom had any exist- ing heart disease or signs of atherosclerosis. They tracked the health 0f 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 arter- ies over the next five years, relative tO those individuals sleeping seven t0 eight hours. The deficient sleep 0f 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 Ofa coronary heart attack. *O. Tochikubo, A. lkeda, E. MiyaJ ima, and M. Ishii,"Effects of insufficient sleep on blood pressure monitored by a new multibiomedical recorder," / り臾 e e 〃ⅵ 0 〃 27 , no. 6 ( 1996 ) : 1318 ー 24.

ー 7 0 MATTHEW WALKER b100d sugar, or glucose, overweeks or years lnflicts a surprising harm to the tissues and organs ofyourbody, worsens yo 矼 health, and shortens your life span. Eye disease that can end ⅲ blindness, nerve disease that commonly results ⅲ amputations, and kidney failure necessitating dialysis or trans- plant are consequences ofprolonged high b100d sugar, are hyperten- sion and heart disease. But it is the condition Of 与甲 e 2 diabetes that is most commonly and immediately related to unregulated blood sugar. ⅲ a healthy individual, the hormone insulin Ⅱ trigger the cells ofyo body t0 swiftly absorb glucose from the bloodstream should it increase, happens after eating a meal. lnstructed by insulin, the cells of yo body ⅲⅡ open special channels on their surface that operate likewonderfullyeff- cient roadside drains at the height 0f a downpoun They have no problem dealingwith the deluge ofglucose coursing do Ⅷ 1 the transit arteries, avert- ingwhat could otherwise be a dangerous flood ofsugar ⅲ the bloodstream. If the cells 0f your body stop responding to insulin, however, they cannot efficiently absorb glucose 伝 om the blood. Similar t0 roadside drains that become blocked or erroneously closed shut, the rising swell ofblood sugar cannot be brought back down to safe levels. At this point, the body has transitioned int0 a hyperglycemic state. Should this condi- tion persist, and the cells 0fyour b0dy remain intolerant t0 dealing with the high levels Of glucose, you 、ⅵⅡ transition intO a pre-diabetic state and, ultimately, develop full-blown り甲 e 2 diabetes. Early-warning signs of a link between sleep loss and abnormal blood sugar emerged in a series oflarge epidemiological studies spanmng sev- eral continents. lndependent of one another, the research groups found far higher rates oftype 2 diabetes among individuals that reported sleep- ing less than six hours a night routinely. The association remained signif- icant even when adj usting for Other contributing factors, such as bOdy weight, coh smoking, age, gender, race, and caffeine use. Powerful as these studies are, though, they do not inform the direction of causality. Does the state of diabetes impalr your sleep, or does short sleep impair your body's ability t0 regulate b100d sugar, thereby causing diabetes? TO answer this question, scientists had tO conduct carefully con- trolled experiments with healthy adults who had no existing signs 0f diabetes or issues with b100d sugar. ln the first of these studies, par- ticipants were limited to sleeping four hours a night for just six nights.

WHY WE SLEEP 9 7 interventions that a doctor whO is board certified in sleep medicine can provide. The second hallmark 0f altered sleep as we age, and one that older adults are more conscious Of, is, 第 & 〃 e 〃〃 0 〃 . The olderwe get, the more frequently we wake up throughout the night. There are many causes, including interacting medications and diseases, but chief among them is a weakened bladder. OIder adults therefore visit the bathroom more frequently at night. Reducing fluid intake in the mid- and late evening can help, but it is not a cure-all. Due to sleep fragmentation, 01der individuals will suffer a reduc- tion ⅲ sleep efficiency, defined as the percent Of time you were asleep while in bed. If you spent eight hours in bed, and slept for all eight of those hours, your sleep efficiency would be 100 percent. If you slept just four 0f those eight hours, your sleep efficiency would be 50 percent. As healthy teenagers, we enjoyed a sleep efficiency 0f about 95 per- cent. AS a reference anchor, most sleep doctors consider good-quality sleep t0 involve a sleep efficiency 0f 90 percent or above. By the time we reach our eighties, sleep efficiency has 0ften dropped below 70 or 80 percent; 70 t0 80 percent may sound reasonable until you realize that, within an eight-hour period ⅲ bed, it means you ⅵⅡ spend as much as one to one and a halfhours awake. lnefficient sleep is no small thing, as studies assessing tens Of thou- sands 0f older adults show. Even when controlling for factors such as body mass index, gender, race, history 0f smoking, frequency 0f exer- cise, and medications, the lower an Older individual's sleep efficiency score, the higher their mortality risk, the worse their physical health, the more likely they are t0 suffer 仕 om depression, the less energy they report, and the lower their cognitive function, typified by forgetfulness. Any individual, no matter what age, will exhibit physical ailments, men- tal health instability, reduced alertness, and impaired memory if their 物 D. J. FoIey, A. A. Monjan, S. L. Brown, E. M. Simonsick et al., "Sleep complaints among elderly persons: an epidemiologic study 0f three communities," Sleep 18 , no. 6 ( 1995 ) : 425 ー 32. See so D. J. FOIey, A. A. Monj an, E. M. Simonstick, R. B. Wallace, and D. G. Blazer, "lncidence and remission 0f insomnia among elderly adults: an epidemiologic study 0f 6 , 8 開 persons over three years," Sleep 22 (Suppl 2 ) ( 1999 ) : S366 ー 72.

2 ー 4 MATTHEW WALKER tide of noradrenaline within the brain, gving the se p atients healthier REM-sleep quality. With healthy REM sleep came a reduction ⅲ the patients' clinical symptoms and, most critically, a decrease ⅲ the fre- quency oftheir repetitive nightmares. Raskind and I continued our communications and scientific discus- sions throughout that conference. He subsequentlyvisited mylab at UC Berkeley ⅲ the months that followed, and we talked nonstop through- out the day and into the evening over dinner about my neurobiological model 0f overnight emotional therapy, and how it seemed t0 perfectly explain his clinical findings with prazosin. These were hairs-on-the- back-of-your-neck-standing-up conversations, perhaps the most excit- ing I have ever experienced in my career. The basic scientific theorywas no longer in search 0f clinical confirmation. The had found each other one sky-leaking day ⅲ Se attle. Mutually informed by each other's work, and based on the strength of Raskind's studies and now severallarge-scale independent clini- cal trials, prazosin has become the officially approved drug by the VA for the treatment of repetitive trauma nightmares, and has since received approval by the US F00d and Drug Administration for the same benefit. Many questions remain t0 be addressed, including more indepen- dent replication ofthe findings in other types oftrauma, such as sexual abuse or violence. lt is alSO not a perfect medication due tO side effects at higher doses, and not every individual responds tO the treatment with the same success. But it is a start. Ⅵ厄 now have a scientifically informed explanation of one function of REM sleep and the dreaming process inherent in it, and 伝 om that knowledge we have taken the first steps toward treating the distressing and disabling clinical condition 0f PTSD. lt may so unlock new treatment avenues regarding sleep and Other mental illness, including depression. DREAMING TO DECODE WAKING EXPERIENCES Just when I thought REM sleep had revealed it could offer to our mental health, a second emotional brain advantage gifted by REM sleep came tO light—one that is arguably more survival-relevant.

WHY WE SLEEP 3 3 9 I know that may sound unwelcome t0 some ofyou. But it would not if you had lost a loved one tO a fatigue-related accident. FortunateIy, the rise Of semiautonomous-driving features ⅲ cars can help us avoid thiS issue. Cars can use these very same signatures offatigue tO heighten their watch and, when needed, take greater self-control ofthe vehicle 仕 om the driver. At the very highest levels, transforming entire societies ⅷⅡ be nei- ther trivial nor easy. Yetwe can borrowproven methods 仕 om other areas ofhealth to shift society's sleep for the better. I offerjust one example. ln the United States, many health insurance compames provide a financial credit t0 their members forjoimng a 部 , m. Considering the health bene- fits ofincreased sleep amount, why don't we institute a similar incentive for racking up more consistent and plentiful slumber? Health insurance companies could approve valid commercial sleep-tracking devices that individuals commonly own. You, the individual, could then upload your sleep credit score t0 your health-care provider profile. Based on a tiered, pro-rata system, with reasonable threshold expectations for different age groups, you would be awarded a lower insurance rate with increas- ing sleep credit on a month-to-month basis. Like exercise, this ⅲ turn ⅷⅡ help improve societal health en masse and lower the cost ofhealth- care utilization, allowing people t0 have longer and healthier lives. Even with lower insurance paid by the individual, health insurance companies would still gain, as it would significantly decrease the cost burden oftheir insured individuals, allowing for greater profit margms. Everyone wins. Ofcourse,just like a gym membership, some people will start off adhering to the regime but then stop, and some may look for ways tO bend or play the system regarding accurate sleep assessment. However, even ifonly 50 to 60 percent ofindividuals truly increase their sleep amount, it could save tens or hundreds 0f millions 0f dollars in terms Of health costs—not tO mention hundreds ofthousands Of lives. This tour ofideas offers, I hope, some message ofoptimism rather than the tabloid-like doom with which we are so often assaulted in the media regarding things health. More than hope, however, I wish for it t0 spark better sleep solutions 0f your own; ideas that some 0f you may translate intO a non- or for-profit commercial venture, perhaps.