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📖 Sleep & Recovery Sources

Sources for sleep science, recovery, and rest optimization.

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Key Research Findings Summary​

Sleep Duration and Mortality​

  • U-shaped relationship confirmed: Both short (<7h) and long (>9h) sleep associated with increased mortality
  • Short sleep (<7h): 12-14% increased mortality risk (multiple meta-analyses)
  • Long sleep (>8-9h): 30% increased mortality risk (may indicate underlying illness)
  • Optimal duration: 7-8 hours/night for lowest all-cause mortality
  • 2025 meta-analysis (79 cohorts): Short sleep = 14% increased mortality; imbalanced sleep = 14-34% increased risk

Sleep Regularity (Major 2024 Finding)​

  • Sleep regularity is a stronger predictor of mortality than sleep duration
  • Regular sleepers (±1 hour window): 22-57% lower cardiometabolic mortality risk
  • Irregular sleepers (±3 hour window): Significantly elevated mortality
  • Sleep Regularity Index (SRI) predicts cardiometabolic, cancer, and other-cause mortality

Sleep Stages and Health (2024 Research)​

  • REM and deep sleep inversely associated with atrial fibrillation (Nature Medicine, 2024)
  • Sleep irregularity is an independent risk factor after adjusting for average duration
  • Circadian rhythm disruptions linked to reduced insulin sensitivity, increased inflammation
  • 4-6 cycles per night (90 min each); deep sleep dominates early night, REM dominates late

Cognitive Effects of Sleep Deprivation​

  • Simple attention most affected by short-term sleep deprivation (meta-analysis)
  • Effect sizes: Attention lapses (g = -0.776) to reasoning accuracy (g = -0.125)
  • Sleep restriction selectively impairs: Sustained attention, executive function, long-term memory
  • Chronic effects may be irreversible: Night shift workers show cognitive impairment even with adequate sleep

Light Exposure and Circadian Health (2024)​

  • Brighter nights + darker days = higher mortality risk (PNAS, ~89,000 individuals)
  • Morning light exposure advances circadian clock; evening light delays it
  • Blue light from screens suppresses melatonin and disrupts sleep
  • Light therapy can stabilize sleep-wake rhythm (2024 RCT)

Sleep Hygiene Interventions (2024 Meta-Analyses)​

  • CBT-I remains gold standard for insomnia treatment
  • Sleep hygiene education shows modest effectiveness (MD = 3.4 ISI improvement)
  • Exercise interventions highly effective — resistance training particularly beneficial
  • Multicomponent interventions work best — CBT-I, stimulus control, sleep restriction

Key Sources​

Source Tier Definitions
  • Tier A: Peer-reviewed meta-analyses and systematic reviews from top journals
  • Tier B: Institutional guidelines, high-quality single studies, comprehensive reviews
  • Tier C: Expert sources, popular science books with good scientific basis
  • Tier D: Emerging research, specialized theories, lower evidentiary support

Sleep Duration and Mortality​

Meta-Analyses​

  • Imbalanced sleep mortality meta-analysis — GeroScience (2025) — Tier A
    • 79 cohort studies; short sleep = 14% increased mortality; data through Oct 2024
  • Sleep duration and all-cause mortality — Cappuccio et al., Sleep (2010) — Tier A
    • Foundational meta-analysis; U-shaped curve; short = 12%, long = 30% increased risk
  • Sleep duration and CVD — J Am Heart Assoc (2017) — Tier A
    • U-shaped; 7h optimal; <7h RR 1.06/hour reduction; >7h RR 1.13/hour
  • Sleep in older adults — BMC Public Health (2020) — Tier A
    • Long sleep HR = 1.24; short sleep marginal in elderly

Sleep Regularity​

  • Sleep regularity vs duration mortality — Windred et al., SLEEP (2024) — Tier A
    • Landmark study: regularity stronger predictor than duration; 60,977 participants
  • Sleep Regularity Index and mortality — SLEEP Editorial (2024) — Tier A
    • Commentary confirming regularity findings
  • Sleep regularity and cardiometabolic mortality — PMC (2023) — Tier A
    • 22-57% lower risk in regular sleepers

Sleep Stages and Architecture​

  • Sleep patterns and chronic disease — Nature Medicine (July 2024) — Tier A
    • Wearable data; REM/deep sleep inversely associated with AFib; irregularity independent risk
  • Physiology of sleep stages — StatPearls (2024) — Tier B
    • Comprehensive review of NREM/REM stages
  • REM sleep and brain connectivity — Transl Psychiatry (July 2024) — Tier A
    • REM loss impacts brain networks

Cognitive Effects​

  • Sleep deprivation cognitive meta-analysis — Lim & Dinges (2010) — Tier A
    • 147 tests; attention most affected (g = -0.776)
  • Sleep restriction meta-analysis — Neurosci Biobehav Rev (2017) — Tier A
    • 61 studies; g = -0.383; attention, executive function, long-term memory
  • Sleep deprivation and cognitive performance — PMC (2023) — Tier B
    • Review of consequences
  • Insufficient vs adequate sleep cognition — Sleep Health (2024) — Tier A
    • 7+ hours enhances working memory and response inhibition

Light and Circadian Rhythm​

  • Light exposure and mortality — PNAS (2024) — Tier A
    • ~89,000 individuals; brighter nights = higher mortality risk
  • Effects of light on circadian rhythms — PMC (2019) — Tier A
    • Comprehensive review of light mechanisms
  • Light therapy in older diabetics — Front Endocrinol (2024) — Tier A
    • RCT: bright light improves sleep-wake rhythm
  • Blue light and sleep in students — Chronobiol Med (2024) — Tier B
    • Blue light suppresses melatonin; disrupts sleep
  • Circadian-informed lighting interventions — SLEEP (2024) — Tier A
    • Shift work; circadian adaptation with light
  • Light recommendations for circadian health — Brown et al. (2022) — Tier B
    • Expert recommendations

Sleep Hygiene and Interventions​

  • Nonpharmacological sleep hygiene NMA — PLOS One (June 2024) — Tier A
    • Resistance training most effective for nonelderly
  • Sleep hygiene education for insomnia — Sleep Med Rev (2024/2025) — Tier A
    • 42 RCTs; SHE inferior to CBT-I but shows improvement
  • CBT-I systematic review — JCSM (2021) — Tier A
    • AASM GRADE assessment; CBT-I gold standard
  • Sleep improvement and mental health — PMC (2021) — Tier A
    • RCTs: improving sleep improves mental health

Sleep Deprivation Health Effects​

  • Short sleep and health outcomes — Itani et al. (2017) — Tier A
    • Systematic review of health consequences
  • Sleep and immune function — Prather et al. (2015) — Tier A
    • Cold study: <7h = 4.5× more likely to develop cold
  • Sleep and athletic performance — Vitale et al. (2019) — Tier A
    • Sleep critical for performance and recovery
  • Sleep deprivation meta-analysis — Van Dongen et al. (2003) — Tier A
    • Cumulative cognitive deficits; subjective vs objective diverge

Sources by Topic​

Click to expand sources organized by content page

Sleep Science (sleep-science.md)​

  • Sleep physiology (StatPearls)
  • Sleep stages and architecture
  • Circadian rhythm mechanisms
  • Why We Sleep (Walker)

What Sleep Does (what-sleep-does.md)​

  • Physical restoration (deep sleep)
  • Cognitive restoration (REM)
  • Memory consolidation research
  • Immune function studies

Requirements (requirements.md)​

  • Sleep duration meta-analyses (Cappuccio)
  • Sleep regularity research (Windred 2024)
  • Individual variation
  • Age-related changes

Sleep Deficiency (deficiency.md)​

  • Cognitive impairment meta-analyses
  • Metabolic effects research
  • Immune function (Prather)
  • Long-term health risks

Sleep Hygiene (sleep-hygiene.md)​

  • Intervention effectiveness (2024 NMA)
  • CBT-I research
  • Light exposure studies
  • Environment optimization

Disorders (disorders.md)​

  • AASM clinical guidelines
  • Insomnia treatment research
  • Sleep apnea epidemiology
  • Clinical assessment
Best Places to Start
  1. For mortality evidence: Sleep regularity study (Windred, SLEEP 2024)
  2. For comprehensive understanding: Why We Sleep (Walker) — with caveats
  3. For cognitive effects: Lim & Dinges meta-analysis
  4. For interventions: AASM CBT-I guidelines
  5. For light exposure: PNAS 2024 mortality study

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