Why We Sleep: Difference between revisions

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== Introduction ==

 

'''''{{Tooltip|Why We Sleep}}''''' is a popular-science book on the neuroscience and physiology of sleep. {{Tooltip|Scribner}} published it in the {{Tooltip|United States}} on 3 October 2017 (368 pages; ISBN 978-1-5011-4431-8).<ref name="S&S9781501144318" /><ref name="OCLC975365716" /> Neuroscientist {{Tooltip|Matthew P. Walker}}, a professor at the {{Tooltip|University of California, Berkeley}}, synthesizes laboratory, clinical, and epidemiological findings on how sleep and {{Tooltip|circadian biology}} shape learning, memory, emotion, immunity, metabolism, and long-term health.<ref name="UCBProfile">{{cite web |title=Matthew P. Walker |url=https://psychology.berkeley.edu/people/matthew-p-walker |website=UC Berkeley Department of Psychology |publisher=University of California, Berkeley |access-date=6 November 2025}}</ref><ref name="S&S9781501144318" /> The book explains {{Tooltip|NREM}}/{{Tooltip|REM sleep}} and {{Tooltip|circadian rhythms}}, outlines the consequences of insufficient sleep, and discusses practical topics such as caffeine, {{Tooltip|jet lag}}, {{Tooltip|melatonin}}, {{Tooltip|sleep disorders}}, and when behavioral therapy is preferable to sleeping pills.<ref name="S&S9781501144318" /><ref name="UCB2017">{{cite web |title=Everything you need to know about sleep, but are too tired to ask |url=https://news.berkeley.edu/2017/10/17/whywesleep/ |website=UC Berkeley News |publisher=University of California, Berkeley |date=17 October 2017 |access-date=6 November 2025 |last=Anwar |first=Yasmin}}</ref> It is arranged in four parts—what sleep is, why it matters, how and why we dream, and how society might change—written for general readers.<ref name="OCLC1001968546">{{cite web |title=Why we sleep : unlocking the power of sleep and dreams (table of contents) |url=https://www.worldcat.org/oclc/1001968546 |website=WorldCat |publisher=OCLC |access-date=6 November 2025}}</ref><ref name="Kirkus2017">{{cite web |title=Why We Sleep |url=https://www.kirkusreviews.com/book-reviews/matthew-walker/why-we-sleep/ |website=Kirkus Reviews |date=21 August 2017 |access-date=6 November 2025}}</ref> According to the publisher, it is a {{Tooltip|New York Times}} bestseller and an international sensation. It was named one of {{Tooltip|Publishers Weekly}}’s Best Books of 2017, and {{Tooltip|The Sunday Times}}’ year-end list recorded 162,125 {{Tooltip|UK}} copies sold in 2018.<ref name="S&S9781501144318" /><ref name="PWBest2017">{{cite web |title=Best Books 2017 |url=https://best-books.publishersweekly.com/pw/best-books/2017 |website=Publishers Weekly |access-date=6 November 2025}}</ref><ref name="STimes2018">{{cite news |title=Books: The Sunday Times Bestsellers of the Year, 2018 |url=https://www.thetimes.com/culture/books/article/books-the-sunday-times-bestsellers-of-the-year-2018-k9wn67tw6 |work=The Sunday Times |date=30 December 2018 |access-date=6 November 2025}}</ref>

 

== Part I – This Thing Called Sleep ==

=== Chapter 5 – Changes in Sleep Across the Life Span. ===

👶 Irwin Feinberg’s team wired children aged six to eight and re-measured their sleep every six to twelve months for a decade, amassing more than 3,500 all-night recordings—about 320,000 hours—to show how deep {{Tooltip|NREM}} swells, then recedes through adolescence as synapses are pruned and the {{Tooltip|frontal lobes}} mature. Before birth, the fetus cycles between {{Tooltip|NREM}} and REM by the second trimester and spends much of the day in REM-like sleep; in the third trimester, with no {{Tooltip|REM paralysis}} yet, REM commands kick arms and legs that mothers feel. After birth, sleep starts polyphasic: a six-month-old averages ~14 hours with a 50/50 {{Tooltip|NREM}}–REM split; by age five it shifts toward ~70/30, then to biphasic, and in late childhood becomes largely monophasic. In {{Tooltip|autism}}, {{Tooltip|circadian rhythms}} are flatter, nighttime {{Tooltip|melatonin}} surges weaker, total sleep reduced, and REM deficient by 30–50%, aligning with known differences in neural development. Puberty pushes the clock later: melatonin rises later, teenagers fall asleep and wake later than parents, and early school start times collide with that biology. Through midlife, the ability to generate deep {{Tooltip|slow-wave sleep}} deteriorates—by the mid- to late-forties, 60–70% of youthful deep {{Tooltip|NREM}} is gone; by seventy, 80–90% is lost—while sleep fragments. Aging also advances melatonin’s evening peak, pulling bedtimes earlier, and frequent nighttime bathroom trips add fall risk and fractures. Older adults still require a full night of sleep; the difficulty lies in production, not demand. Across development, REM helps build the brain early, deep {{Tooltip|NREM}} sculpts and stabilizes circuits in adolescence, and later-life fragmentation plus reduced {{Tooltip|slow-wave sleep}} power undermine sleep even as need persists. ''That older adults simply need less sleep is a myth.''

 

== Part II – Why Should You Sleep? ==

=== Chapter 8 – Cancer, Heart Attacks, and a Shorter Life: Sleep Deprivation and the Body. ===

❤️ Daylight saving time functions as a one-hour global experiment: when clocks steal an hour in spring, heart attacks spike the next day; when an hour returns in autumn, rates fall. Controlled studies show why: short nights accelerate heart rate and raise blood pressure, while deep {{Tooltip|NREM}} normally applies a nightly brake to the sympathetic nervous system. In a {{Tooltip|University of Chicago}} cohort of ~500 healthy midlife adults, routinely sleeping five to six hours (or less) made coronary-artery calcification 200–300% more likely within five years. A week of four hours a night left young adults 40% less effective at clearing a standard glucose dose, with tissue biopsies showing {{Tooltip|insulin resistance}}—the path toward type 2 diabetes. Appetite signaling tilts too, as {{Tooltip|leptin}} drops and {{Tooltip|ghrelin}} rises, biasing intake toward more food and weight gain. Immunity pays an immediate price: at {{Tooltip|UCLA}}, one night of four hours (3 a.m. to 7 a.m.) cut circulating {{Tooltip|natural killer cells}} by 70%, undermining frontline cancer surveillance. Shift work that breaks {{Tooltip|circadian rhythms}} is linked to higher rates of breast, prostate, endometrial, and colon cancers; {{Tooltip|Denmark}} has compensated affected night-shift workers, and European cohorts (~25,000 participants) show ~40% higher cancer risk with six hours or less. In mice, partially disrupted sleep at the {{Tooltip|University of Chicago}} drove a 200% increase in tumor growth and more metastasis. Across cardiovascular, metabolic, and immune systems, short sleep helps create the conditions for illness. Restoring full-night sleep eases pressure on the heart, improves glucose control, and strengthens immune defense. ''the shorter your sleep, the shorter your life.''

 

== Part III – How and Why We Dream ==

 

''—Note: The above summary follows the {{Tooltip|Scribner}} hardcover first edition (3 October 2017; ISBN 978-1-5011-4431-8).''<ref name="S&S9781501144318">{{cite web |title=Why We Sleep |url=https://www.simonandschuster.com/books/Why-We-Sleep/Matthew-Walker/9781501144318 |website=Simon & Schuster |publisher=Simon & Schuster |date=3 October 2017 |access-date=6 November 2025}}</ref><ref name="OCLC975365716">{{cite web |title=Why we sleep : unlocking the power of sleep and dreams |url=https://www.worldcat.org/oclc/975365716 |website=WorldCat |publisher=OCLC |access-date=6 November 2025}}</ref>

 

== Background & reception ==

 

🌍 '''Impact & adoption'''. Walker promoted the book’s themes in mainstream media, including an interview on {{Tooltip|NPR}}’s ''{{Tooltip|Fresh Air}}'' on 16 October 2017.<ref>{{cite web |title=Sleep Scientist Warns Against Walking Through Life ‘In An Underslept State’ |url=https://www.freshair.com/topics/health-medicine/sleep |website=Fresh Air Archive |publisher=WHYY/NPR |date=16 October 2017 |access-date=6 November 2025}}</ref> He discussed practical {{Tooltip|sleep hygiene}} on ''{{Tooltip|CBS This Morning}}'' the same week.<ref>{{cite news |title=The health costs of losing sleep and tips for getting a good night’s rest |url=https://www.cbsnews.com/news/lack-of-sleep-health-effects-and-tips-for-good-nights-rest/ |work=CBS News |date=11 October 2017 |access-date=6 November 2025}}</ref> In April 2019 his {{Tooltip|TED}} talk, “{{Tooltip|Sleep is your superpower}},” amplified the message globally, followed by {{Tooltip|TED}}’s ''{{Tooltip|Sleeping with Science}}'' series.<ref name="TED2019">{{cite web |title=Matt Walker: Sleep is your superpower |url=https://www.ted.com/talks/matt_walker_sleep_is_your_superpower |website=TED.com |date=2019 |access-date=6 November 2025}}</ref><ref name="TEDSeries2020">{{cite web |title=Sleeping with Science |url=https://www.ted.com/series/sleeping_with_science |website=TED.com |access-date=6 November 2025}}</ref>

 

== Related content ==

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