# The science behind SleepShred

SleepShred is built on the sleep segment of Dr Andy Galpin's appearance on The Diary Of A CEO, cross-referenced with the peer-reviewed literature. This library lists every study the app cites, grouped by topic, with the finding in plain language.



## Sleep duration & health
How much sleep adults actually need, what happens below seven hours, and why you stop noticing the impairment long before it stops happening.
- **Recommended amount of sleep for a healthy adult: a joint consensus statement of the American Academy of Sleep Medicine and Sleep Research Society** (Watson NF, Badr MS, Belenky G, et al., 2015, Sleep 38(6):843–844) — Adults should sleep ≥7 h per night on a regular basis; <7 h is associated with weight gain, diabetes, hypertension, depression and mortality. [Read the paper](watson2015)
- **National Sleep Foundation's sleep time duration recommendations: methodology and results summary** (Hirshkowitz M, Whiton K, Albert SM, et al., 2015, Sleep Health 1(1):40–43) — 7–9 h recommended for adults 26–64; 7–8 h for 65+. [Read the paper](hirshkowitz2015)
- **The cumulative cost of additional wakefulness: dose-response effects on neurobehavioral functions and sleep physiology from chronic sleep restriction and total sleep deprivation** (Van Dongen HP, Maislin G, Mullington JM, Dinges DF, 2003, Sleep 26(2):117–126) — Two weeks at 6 h/night produced deficits equal to two nights of total deprivation — while subjects felt only mildly sleepy. You adapt to feeling tired, not to being impaired. [Read the paper](vandongen2003)
- **Trends in self-reported sleep duration among US adults from 1985 to 2012** (Ford ES, Cunningham TJ, Croft JB, 2015, Sleep 38(5):829–832) — Population sleep has shortened; the share of adults sleeping ≤6 h rose to ~29%. [Read the paper](ford2015)
- **Sleep duration and all-cause mortality: a systematic review and meta-analysis of prospective studies** (Cappuccio FP, D'Elia L, Strazzullo P, Miller MA, 2010, Sleep 33(5):585–592) — Both short (<7 h) and long (>8–9 h) habitual sleep are associated with higher mortality — a U-shaped curve. [Read the paper](cappuccio2010)
- **The effects of sleep extension on the athletic performance of collegiate basketball players** (Mah CD, Mah KE, Kezirian EJ, Dement WC, 2011, Sleep 34(7):943–950) — Extending sleep to ~10 h improved sprint time, shooting accuracy, reaction time and mood. [Read the paper](mah2011)

## Regularity & circadian
Going to bed and waking at consistent times predicts mortality better than total duration — and social jet lag is the version of this most people live with.
- **Sleep regularity is a stronger predictor of mortality risk than sleep duration: a prospective cohort study** (Windred DP, Burns AC, Lane JM, et al., 2024, Sleep 47(1):zsad253) — In ~60,000 UK Biobank participants, how regular sleep was predicted mortality better than how long it was. [Read the paper](windred2024)
- **Social jetlag: misalignment of biological and social time** (Wittmann M, Dinich J, Merrow M, Roenneberg T, 2006, Chronobiology International 23(1–2):497–509) — Defines social jet lag — the shift in sleep midpoint between work and free days — and links it to evening chronotypes and stimulant use. [Read the paper](wittmann2006)
- **Social jetlag and obesity** (Roenneberg T, Allebrandt KV, Merrow M, Vetter C, 2012, Current Biology 22(10):939–943) — Each hour of social jet lag was associated with ~33% higher odds of being overweight. [Read the paper](roenneberg2012)
- **Irregular sleep/wake patterns are associated with poorer academic performance and delayed circadian and sleep/wake timing** (Phillips AJK, Clerx WM, O'Brien CS, et al., 2017, Scientific Reports 7:3216) — Irregular sleepers had delayed melatonin onset and worse outcomes even at equal total sleep. [Read the paper](phillips2017)

## Sleep apnea
The most under-diagnosed sleep disorder there is: roughly 936 million adults have it and the large majority have never been told.
- **Estimation of the global prevalence and burden of obstructive sleep apnoea: a literature-based analysis** (Benjafield AV, Ayas NT, Eastwood PR, et al., 2019, Lancet Respiratory Medicine 7(8):687–698) — ~936 million adults aged 30–69 have OSA worldwide; ~425 million moderate-to-severe. [Read the paper](benjafield2019)
- **Estimation of the clinically diagnosed proportion of sleep apnea syndrome in middle-aged men and women** (Young T, Evans L, Finn L, Palta M, 1997, Sleep 20(9):705–706) — ~82% of men and ~93% of women with moderate-to-severe apnea were undiagnosed — the numbers Galpin quotes. [Read the paper](young1997)
- **Increased prevalence of sleep-disordered breathing in adults** (Peppard PE, Young T, Barnet JH, Palta M, Hagen EW, Hla KM, 2013, American Journal of Epidemiology 177(9):1006–1014) — Prevalence in US adults 30–70: ~26% of men and ~9–17% of women; rising with obesity. [Read the paper](peppard2013)
- **STOP questionnaire: a tool to screen patients for obstructive sleep apnea** (Chung F, Yegneswaran B, Liao P, et al., 2008, Anesthesiology 108(5):812–821) — Origin of the STOP-Bang screen; ≥3 'yes' answers = high sensitivity for moderate-severe OSA. [Read the paper](chung2008)
- **Relationship between overnight rostral fluid shift and obstructive sleep apnea in nonobese men** (Redolfi S, Yumino D, Ruttanaumpawan P, et al., 2009, American Journal of Respiratory and Critical Care Medicine 179(3):241–246) — Fluid moving from the legs to the neck when lying down narrows the airway — apnea without obesity (Galpin's tipped-glass analogy). [Read the paper](redolfi2009)
- **Defining phenotypic causes of obstructive sleep apnea. Identification of novel therapeutic targets** (Eckert DJ, White DP, Jordan AS, Malhotra A, Wellman A, 2013, American Journal of Respiratory and Critical Care Medicine 188(8):996–1004) — OSA has anatomical and non-anatomical phenotypes (muscle responsiveness, arousal threshold, loop gain) — the basis of precision treatment. [Read the paper](eckert2013)
- **Long-term cardiovascular outcomes in men with obstructive sleep apnoea-hypopnoea with or without treatment with continuous positive airway pressure: an observational study** (Marin JM, Carrizo SJ, Vicente E, Agusti AG, 2005, Lancet 365(9464):1046–1053) — Untreated severe OSA tripled fatal and non-fatal cardiovascular events over ~10 years; CPAP normalised the risk. [Read the paper](marin2005)

## Insomnia, RLS & instruments
Insomnia, restless legs and the validated instruments used to measure them — plus what treatment guidelines actually recommend first.
- **Horne & Östberg morningness-eveningness questionnaire: a reduced scale** (Adan A, Almirall H, 1991, Personality and Individual Differences 12(3):241–253) — The 5-item rMEQ chronotype scale used in the Check tab. [Read the paper](adan1991)
- **A new method for measuring daytime sleepiness: the Epworth sleepiness scale** (Johns MW, 1991, Sleep 14(6):540–545) — The 8-item Epworth scale; ≥11 suggests excessive daytime sleepiness. [Read the paper](johns1991)
- **Validation of the Insomnia Severity Index as an outcome measure for insomnia research** (Bastien CH, Vallières A, Morin CM, 2001, Sleep Medicine 2(4):297–307) — The 7-item ISI; ≥15 indicates clinical insomnia. [Read the paper](bastien2001)
- **Restless legs syndrome/Willis-Ekbom disease diagnostic criteria: updated International Restless Legs Syndrome Study Group (IRLSSG) consensus criteria** (Allen RP, Picchietti DL, Garcia-Borreguero D, et al., 2014, Sleep Medicine 15(8):860–873) — The four essential criteria plus 'not solely accounted for by another condition' used in the RLS screen. [Read the paper](allen2014)
- **European guideline for the diagnosis and treatment of insomnia** (Riemann D, Baglioni C, Bassetti C, et al., 2017, Journal of Sleep Research 26(6):675–700) — CBT-I is first-line treatment; hypnotics only short term. [Read the paper](riemann2017)
- **Management of chronic insomnia disorder in adults: a clinical practice guideline from the American College of Physicians** (Qaseem A, Kansagara D, Forciea MA, Cooke M, Denberg TD, 2016, Annals of Internal Medicine 165(2):125–133) — Strong recommendation: all adults with chronic insomnia receive CBT-I as initial treatment. [Read the paper](qaseem2016)

## Wearables & tracking
What your tracker measures well (total sleep time), what it measures badly (stages), and what it invents (sleep scores).
- **Orthosomnia: are some patients taking the quantified self too far?** (Baron KG, Abbott S, Jao N, Manalo N, Mullen R, 2017, Journal of Clinical Sleep Medicine 13(2):351–354) — Case series of people whose fixation on tracker data worsened their sleep — Galpin's health-anxiety warning has a name. [Read the paper](baron2017)
- **Performance of seven consumer sleep-tracking devices compared with polysomnography** (Chinoy ED, Cuellar JA, Huwa KE, et al., 2021, Sleep 44(5):zsaa291) — Consumer devices estimated total sleep well but were poor at sleep stages — trust duration, not deep/REM. [Read the paper](chinoy2021)
- **Wearable sleep technology in clinical and research settings** (de Zambotti M, Cellini N, Goldstone A, Colrain IM, Baker FC, 2019, Medicine & Science in Sports & Exercise 51(7):1538–1557) — Review of what wearables can and cannot measure; stage classification and 'sleep scores' lack validation. [Read the paper](dezambotti2019)

## Sleep, appetite & fat loss
The same diet with less sleep produces a different body: less fat lost, more muscle lost, and measurably more hunger.
- **Insufficient sleep undermines dietary efforts to reduce adiposity** (Nedeltcheva AV, Kilkus JM, Imperial J, Schoeller DA, Penev PD, 2010, Annals of Internal Medicine 153(7):435–441) — Same calorie deficit, 5.5 h vs 8.5 h sleep: the short sleepers lost 55% less fat and 60% more lean mass, and were hungrier. [Read the paper](nedeltcheva2010)
- **Effect of sleep extension on objectively assessed energy intake among adults with overweight in real-life settings: a randomized clinical trial** (Tasali E, Wroblewski K, Kahn E, Kilkus J, Schoeller DA, 2022, JAMA Internal Medicine 182(4):365–374) — Extending sleep by ~1.2 h cut energy intake by ~270 kcal/day with no diet advice — participants simply ate less. [Read the paper](tasali2022)
- **Brief communication: sleep curtailment in healthy young men is associated with decreased leptin levels, elevated ghrelin levels, and increased hunger and appetite** (Spiegel K, Tasali E, Penev P, Van Cauter E, 2004, Annals of Internal Medicine 141(11):846–850) — Two nights of 4 h sleep raised ghrelin, lowered leptin and increased appetite ~24%, especially for calorie-dense carbs. [Read the paper](spiegel2004)
- **Impact of sleep debt on metabolic and endocrine function** (Spiegel K, Leproult R, Van Cauter E, 1999, Lancet 354(9188):1435–1439) — Six nights of 4 h sleep impaired glucose tolerance and raised evening cortisol in healthy young men. [Read the paper](spiegel1999)
- **Effects of experimental sleep restriction on weight gain, caloric intake, and meal timing in healthy adults** (Spaeth AM, Dinges DF, Goel N, 2013, Sleep 36(7):981–990) — Sleep-restricted adults gained ~1 kg in 5 days, mostly from late-night eating. [Read the paper](spaeth2013)
- **Meta-analysis of short sleep duration and obesity in children and adults** (Cappuccio FP, Taggart FM, Kandala NB, et al., 2008, Sleep 31(5):619–626) — Short sleep associated with ~55% higher odds of obesity in adults across 30 studies. [Read the paper](cappuccio2008)
- **Influence of sleep restriction on weight loss outcomes associated with caloric restriction** (Wang X, Sparks JR, Bowyer KP, Youngstedt SD, 2018, Sleep 41(5):zsy027) — Restricting sleep 5 nights/week during an 8-week diet: same weight lost, but a smaller share came from fat. [Read the paper](wang2018)
- **Impaired insulin signaling in human adipocytes after experimental sleep restriction** (Broussard JL, Ehrmann DA, Van Cauter E, Tasali E, Brady MJ, 2012, Annals of Internal Medicine 157(8):549–557) — Four nights of 4.5 h sleep made fat cells ~30% less insulin-sensitive. [Read the paper](broussard2012)
- **The effect of sleep restriction, with or without high-intensity interval exercise, on myofibrillar protein synthesis in healthy young men** (Saner NJ, Lee MJ, Pitchford NW, et al., 2020, Journal of Physiology 598(8):1523–1536) — Five nights of 4 h sleep reduced muscle protein synthesis ~18%; HIIT during restriction preserved it. [Read the paper](saner2020)
- **The role of exercise and physical activity in weight loss and maintenance** (Swift DL, Johannsen NM, Lavie CJ, Earnest CP, Church TS, 2014, Progress in Cardiovascular Diseases 56(4):441–447) — Exercise alone yields modest weight loss, but is strongly tied to keeping weight off — matching Galpin's 5-4-3-2-1 rationale. [Read the paper](swift2014)
- **Constrained total energy expenditure and metabolic adaptation to physical activity in adult humans** (Pontzer H, Durazo-Arvizu R, Dugas LR, et al., 2016, Current Biology 26(3):410–417) — Total daily energy expenditure plateaus at high activity — the 'adaptive' compensation Galpin describes. [Read the paper](pontzer2016)
- **Self-monitoring in weight loss: a systematic review of the literature** (Burke LE, Wang J, Sevick MA, 2011, Journal of the American Dietetic Association 111(1):92–102) — Consistent self-monitoring of diet and weight is one of the strongest predictors of weight-loss success — the 'baker' approach. [Read the paper](burke2011)
- **Self-weighing in weight management: a systematic literature review** (Zheng Y, Klem ML, Sereika SM, Danford CA, Ewing LJ, Burke LE, 2015, Obesity 23(2):256–265) — Frequent (daily/weekly) self-weighing is associated with better weight loss and maintenance without psychological harm in adults. [Read the paper](zheng2015)

## Caffeine
Caffeine works on your sleep for far longer than it works on your alertness — the reason a personal cutoff time beats a rule of thumb.
- **Caffeine effects on sleep taken 0, 3, or 6 hours before going to bed** (Drake C, Roehrs T, Shambroom J, Roth T, 2013, Journal of Clinical Sleep Medicine 9(11):1195–1200) — 400 mg caffeine taken even 6 h before bed cut objective sleep by >1 h — while subjects barely noticed. [Read the paper](drake2013)
- **The effect of caffeine on subsequent sleep: a systematic review and meta-analysis** (Gardiner C, Weakley J, Burke LM, et al., 2023, Sleep Medicine Reviews 69:101764) — Caffeine reduced total sleep by ~45 min and efficiency by 7%. To avoid effects, a coffee (~107 mg) should be ~8.8 h before bed; a pre-workout dose (~217 mg) ~13 h. [Read the paper](gardiner2023)
- **Coffee, caffeine, and sleep: a systematic review of epidemiological studies and randomized controlled trials** (Clark I, Landolt HP, 2017, Sleep Medicine Reviews 31:70–78) — Caffeine prolongs sleep latency, reduces total sleep and deep sleep; sensitivity varies with genetics and habitual use. [Read the paper](clark2017)
- **A review of caffeine's effects on cognitive, physical and occupational performance** (McLellan TM, Caldwell JA, Lieberman HR, 2016, Neuroscience & Biobehavioral Reviews 71:294–312) — Caffeine restores performance lost to sleep deprivation but does not exceed the rested baseline — no free passes. [Read the paper](mclellan2016)
- **Sustaining executive functions during sleep deprivation: a comparison of caffeine, dextroamphetamine, and modafinil** (Killgore WDS, Kahn-Greene ET, Grugle NL, Killgore DB, Balkin TJ, 2009, Sleep 32(2):205–216) — Stimulants patch alertness but not higher-order judgement after sleep loss. [Read the paper](killgore2009)
- **Wake up and smell the coffee: caffeine supplementation and exercise performance — an umbrella review of 21 published meta-analyses** (Grgic J, Grgic I, Pickering C, Schoenfeld BJ, Bishop DJ, Pedisic Z, 2020, British Journal of Sports Medicine 54(11):681–688) — Caffeine is ergogenic for endurance, strength and power — which is why timing (not abstinence) is the lever. [Read the paper](grgic2020)

## Alcohol
Alcohol shortens the time it takes to fall asleep and damages nearly everything that happens afterwards.
- **Alcohol and sleep I: effects on normal sleep** (Ebrahim IO, Shapiro CM, Williams AJ, Fenwick PB, 2013, Alcoholism: Clinical and Experimental Research 37(4):539–549) — Alcohol shortens sleep onset but suppresses REM and fragments the second half of the night. [Read the paper](ebrahim2013)
- **Acute effect of alcohol intake on cardiovascular autonomic regulation during the first hours of sleep in a large real-world sample of Finnish employees: observational study** (Pietilä J, Helander E, Korhonen I, Myllymäki T, Kujala UM, Lindholm H, 2018, JMIR Mental Health 5(1):e23) — In 4,098 people, even 'low' alcohol intake cut sleep HRV by ~9%; high intake by ~40%, more so in fit and young people. [Read the paper](pietila2018)
- **Sleep, sleepiness, and alcohol use** (Roehrs T, Roth T, 2001, Alcohol Research & Health 25(2):101–109) — Review: alcohol's sedative effect fades quickly and rebounds into lighter, more disrupted sleep. [Read the paper](roehrs2001)

## Screens & evening arousal
The problem with the phone in bed is mostly arousal, not blue light — and even having the device in the room measurably matters.
- **Evening use of light-emitting eReaders negatively affects sleep, circadian timing, and next-morning alertness** (Chang AM, Aeschbach D, Duffy JF, Czeisler CA, 2015, PNAS 112(4):1232–1237) — Reading on a light-emitting device before bed delayed melatonin, lengthened sleep onset and reduced next-morning alertness vs a printed book. [Read the paper](chang2015)
- **Bedtime mobile phone use and sleep in adults** (Exelmans L, Van den Bulck J, 2016, Social Science & Medicine 148:93–101) — Phone use after lights-out was linked to later bedtimes, longer sleep latency, more fatigue and worse sleep quality in adults. [Read the paper](exelmans2016)
- **"To sleep, perchance to tweet": in-bed electronic social media use and its associations with insomnia, daytime sleepiness, mood, and sleep duration in adults** (Bhat S, Pinto-Zipp G, Upadhyay H, Polos PG, 2018, Sleep Health 4(2):166–173) — In-bed social media use was associated with insomnia symptoms and anxiety — engagement, not just light. [Read the paper](bhat2018)
- **Association between portable screen-based media device access or use and sleep outcomes: a systematic review and meta-analysis** (Carter B, Rees P, Hale L, Bhattacharjee D, Paradkar MS, 2016, JAMA Pediatrics 170(12):1202–1208) — Even access to a device in the bedroom (not just use) doubled the odds of inadequate sleep. [Read the paper](carter2016)
- **The inner clock — blue light sets the human rhythm** (Wahl S, Engelhardt M, Schaupp P, Lappe C, Ivanov IV, 2019, Journal of Biophotonics 12(12):e201900102) — Review of how short-wavelength light drives melanopsin signalling — the (smaller) light component of the screen problem. [Read the paper](wahl2019)

## Light
Light is the main signal setting your clock: bright days and dark nights both count, and modern life inverts the pair.
- **Entrainment of the human circadian clock to the natural light-dark cycle** (Wright KP Jr, McHill AW, Birks BR, Griffin BR, Rusterholz T, Chinoy ED, 2013, Current Biology 23(16):1554–1558) — A week of camping without electric light shifted the internal clock ~2 h earlier and aligned it to sunrise/sunset. [Read the paper](wright2013)
- **The new world atlas of artificial night sky brightness** (Falchi F, Cinzano P, Duriscoe D, et al., 2016, Science Advances 2(6):e1600377) — 80% of the world and 99% of US/European populations live under light-polluted skies — the 'world is physically brighter'. [Read the paper](falchi2016)
- **Artificially lit surface of Earth at night increasing in radiance and extent** (Kyba CCM, Kuester T, Sánchez de Miguel A, et al., 2017, Science Advances 3(11):e1701528) — Satellite data: outdoor lit area and brightness grew ~2%/year 2012–2016. [Read the paper](kyba2017)
- **Day and night light exposure are associated with psychiatric disorders: an objective light study in >85,000 people** (Burns AC, Windred DP, Rutter MK, et al., 2023, Nature Mental Health 1:853–862) — Brighter days and darker nights were each independently linked to lower risk of depression and other disorders — daytime light offsets night light. [Read the paper](burns2023)
- **Effects of light on human circadian rhythms, sleep and mood** (Blume C, Garbazza C, Spitschan M, 2019, Somnologie 23(3):147–156) — Accessible review of how timing, intensity and spectrum of light set the clock and affect sleep. [Read the paper](blume2019)
- **Exposure to room light before bedtime suppresses melatonin onset and shortens melatonin duration in humans** (Gooley JJ, Chamberlain K, Smith KA, et al., 2011, Journal of Clinical Endocrinology & Metabolism 96(3):E463–E472) — Ordinary room light in the hours before bed suppressed melatonin in 99% of people and shortened its duration ~90 min. [Read the paper](gooley2011)

## Sound
Noise fragments sleep at levels far below what wakes you up, which is why the target is a number, not a feeling.
- **Auditory and non-auditory effects of noise on health** (Basner M, Babisch W, Davis A, et al., 2014, Lancet 383(9925):1325–1332) — Night-time noise fragments sleep and raises cardiovascular risk even when people don't consciously wake. [Read the paper](basner2014)
- **Night noise guidelines for Europe** (World Health Organization Regional Office for Europe, 2009, WHO) — Recommends outdoor night noise below 40 dB (L_night) to protect health; effects begin around 30–35 dB indoors. [Read the paper](who2009)
- **Noise as a sleep aid: a systematic review** (Riedy SM, Smith MG, Rocha S, Basner M, 2021, Sleep Medicine Reviews 55:101385) — Evidence for white/pink noise as a sleep aid is weak and low quality — it can mask inconsistent sounds, but keep it quiet. [Read the paper](riedy2021)
- **Environmental noise and sleep disturbances: a threat to health?** (Halperin D, 2014, Sleep Science 7(4):209–212) — Review linking traffic and environmental noise with awakenings, sleep-stage changes and next-day effects. [Read the paper](halperin2014)

## Temperature & air
Sleep starts with a fall in core temperature, so the room's job is to let heat leave your body.
- **Effects of thermal environment on sleep and circadian rhythm** (Okamoto-Mizuno K, Mizuno K, 2012, Journal of Physiological Anthropology 31(1):14) — Heat exposure increases wakefulness and reduces deep and REM sleep; humidity worsens it. [Read the paper](okamoto2012)
- **The temperature dependence of sleep** (Harding EC, Franks NP, Wisden W, 2019, Frontiers in Neuroscience 13:336) — Falling core temperature (via warm skin, cool room) is a trigger for sleep onset. [Read the paper](harding2019)
- **Nighttime ambient temperature and sleep in community-dwelling older adults** (Baniassadi A, Manor B, Yu W, Travison T, Lipsitz L, 2023, Science of the Total Environment 899:165623) — Sleep efficiency was best between ~20–25 °C (68–77 °F) in older adults and dropped 5–10% as rooms warmed — cooler is better, personal range matters. [Read the paper](baniassadi2023)

## Meal timing & diet
When you eat shapes how you sleep: late large meals hurt, the eating window matters, and a few foods have real (small) effects.
- **The role of protein in weight loss and maintenance** (Leidy HJ, Clifton PM, Astrup A, et al., 2015, American Journal of Clinical Nutrition 101(6):1320S–1329S) — Higher-protein diets (~1.2–1.6 g/kg) improve satiety, preserve lean mass and aid maintenance — 'a dedicated protein source every time you eat'. [Read the paper](leidy2015)
- **The health impact of nighttime eating: old and new perspectives** (Kinsey AW, Ormsbee MJ, 2015, Nutrients 7(4):2648–2662) — Large late meals impair sleep and metabolic health; small protein-rich snacks are less problematic. [Read the paper](kinsey2015)
- **Relationship between food intake and sleep pattern in healthy individuals** (Crispim CA, Zimberg IZ, dos Reis BG, Diniz RM, Tufik S, de Mello MT, 2011, Journal of Clinical Sleep Medicine 7(6):659–664) — Higher fat intake close to bedtime correlated with worse sleep efficiency and longer sleep onset. [Read the paper](crispim2011)
- **Effects of diet on sleep quality** (St-Onge MP, Mikic A, Pietrolungo CE, 2016, Advances in Nutrition 7(5):938–949) — Higher fibre and lower saturated fat/sugar predict deeper sleep; kiwifruit and tart cherry show promise. [Read the paper](stonge2016)
- **A smartphone app reveals erratic diurnal eating patterns in humans that can be modulated for health benefits** (Gill S, Panda S, 2015, Cell Metabolism 22(5):789–798) — Most people eat across >15 h/day; restricting to a 10–11 h window led to weight loss and better sleep with no other instruction — the 'eating window' rule. [Read the paper](gill2015)

## Exercise, RHR & energy
Exercise improves sleep, sleep improves exercise, and the loop can be started from either end — the basis of the 5·4·3·2·1 rule.
- **Effects of exercise on the resting heart rate: a systematic review and meta-analysis of interventional studies** (Reimers AK, Knapp G, Reimers CD, 2018, Journal of Clinical Medicine 7(12):503) — Endurance training lowers resting heart rate by ~5 bpm on average; yoga also lowers it. [Read the paper](reimers2018)
- **The effects of physical activity on sleep: a meta-analytic review** (Kredlow MA, Capozzoli MC, Hearon BA, Calkins AW, Otto MW, 2015, Journal of Behavioral Medicine 38(3):427–449) — Regular exercise modestly improves total sleep, efficiency and deep sleep. [Read the paper](kredlow2015)
- **Effects of evening exercise on sleep in healthy participants: a systematic review and meta-analysis** (Stutz J, Eiholzer R, Spengler CM, 2019, Sports Medicine 49(2):269–287) — Evening exercise does not harm sleep — unless vigorous exercise ends within ~1 h of bedtime. [Read the paper](stutz2019)
- **The bidirectional relationship between exercise and sleep: implications for exercise adherence and sleep improvement** (Kline CE, 2014, American Journal of Lifestyle Medicine 8(6):375–379) — Better sleep → more exercise → better sleep: a loop worth starting anywhere. [Read the paper](kline2014)
- **Effects of chronic exercise on feelings of energy and fatigue: a quantitative synthesis** (Puetz TW, O'Connor PJ, Dishman RK, 2006, Psychological Bulletin 132(6):866–876) — Across 70 trials, regular exercise reliably increased feelings of energy and reduced fatigue — Galpin's 'stress inoculation'. [Read the paper](puetz2006)
- **The post-lunch dip in performance** (Monk TH, 2005, Clinics in Sports Medicine 24(2):e15–e23) — The early-afternoon dip is a normal circadian feature, largely independent of lunch — 'that's the point'. [Read the paper](monk2005)
- **Benefits of napping in healthy adults: impact of nap length, time of day, age, and experience with napping** (Milner CE, Cote KA, 2009, Journal of Sleep Research 18(2):272–281) — Short (10–20 min) early-afternoon naps improve alertness with little sleep inertia; long/late naps cut into night sleep. [Read the paper](milner2009)
- **Association between objectively-measured physical activity and sleep, NHANES 2005–2006** (Loprinzi PD, Cardinal BJ, 2011, Mental Health and Physical Activity 4(2):65–69) — 150 min/week of moderate-vigorous activity was associated with ~65% better odds of feeling well rested. [Read the paper](loprinzi2011)

## Supplements & melatonin
Which sleep supplements survive contact with the evidence, at what dose, and why melatonin is a timing signal rather than a sedative.
- **The effect of magnesium supplementation on primary insomnia in elderly: a double-blind placebo-controlled clinical trial** (Abbasi B, Kimiagar M, Sadeghniiat K, Shirazi MM, Hedayati M, Rashidkhani B, 2012, Journal of Research in Medical Sciences 17(12):1161–1169) — 500 mg/day magnesium improved sleep time, efficiency, onset and morning cortisol/melatonin in older adults with insomnia. [Read the paper](abbasi2012)
- **Oral magnesium supplementation for insomnia in older adults: a systematic review & meta-analysis** (Mah J, Pitre T, 2021, BMC Complementary Medicine and Therapies 21(1):125) — Magnesium shortened sleep onset by ~17 min; evidence quality low-to-moderate — cheap and safe, not miraculous. [Read the paper](mah2021)
- **Effect of kiwifruit consumption on sleep quality in adults with sleep problems** (Lin HH, Tsai PS, Fang SC, Liu JF, 2011, Asia Pacific Journal of Clinical Nutrition 20(2):169–174) — Two kiwis one hour before bed for 4 weeks improved onset, duration and efficiency — the study behind Galpin's kiwis. [Read the paper](lin2011)
- **Effect of tart cherry juice (Prunus cerasus) on melatonin levels and enhanced sleep quality** (Howatson G, Bell PG, Tallent J, Middleton B, McHugh MP, Ellis J, 2012, European Journal of Nutrition 51(8):909–916) — Tart cherry juice raised urinary melatonin and modestly increased sleep time and efficiency. [Read the paper](howatson2012)
- **Preliminary examination of the efficacy and safety of a standardized chamomile extract for chronic primary insomnia: a randomized placebo-controlled pilot study** (Zick SM, Wright BD, Sen A, Arnedt JT, 2011, BMC Complementary and Alternative Medicine 11:78) — Chamomile extract showed modest, non-significant improvements in daytime functioning and sleep latency — level-1 design, small effect. [Read the paper](zick2011)
- **Meta-analysis: melatonin for the treatment of primary sleep disorders** (Ferracioli-Oda E, Qawasmi A, Bloch MH, 2013, PLoS ONE 8(5):e63773) — Melatonin shortens sleep onset ~7 min and adds ~8 min of sleep — real but small effects; it is a timing signal, not a sedative. [Read the paper](ferracioli2013)
- **Melatonin treatment for age-related insomnia** (Zhdanova IV, Wurtman RJ, Regan MM, Taylor JA, Shi JP, Leclair OU, 2001, Journal of Clinical Endocrinology & Metabolism 86(10):4727–4730) — 0.3 mg (physiological) melatonin restored sleep efficiency as well as or better than 3 mg — the micro-dose Galpin uses. [Read the paper](zhdanova2001)
- **Melatonin natural health products and supplements: presence of serotonin and significant variability of melatonin content** (Erland LA, Saxena PK, 2017, Journal of Clinical Sleep Medicine 13(2):275–281) — Actual melatonin content ranged from −83% to +478% of the label; 26% contained serotonin — buy third-party tested. [Read the paper](erland2017)
- **Melatonin for the prevention and treatment of jet lag** (Herxheimer A, Petrie KJ, 2002, Cochrane Database of Systematic Reviews (2):CD001520) — Melatonin is remarkably effective for jet lag when taken close to target bedtime — the use case Galpin endorses. [Read the paper](herxheimer2002)
- **Differential effects of DHA- and EPA-rich oils on sleep in healthy young adults: a randomized controlled trial** (Patan MJ, Kennedy DO, Husberg C, et al., 2021, Nutrients 13(1):248) — DHA-rich omega-3 improved sleep efficiency and reduced latency in healthy adults with low fish intake. [Read the paper](patan2021)
- **Natural compounds for Alzheimer's disease therapy: a systematic review of preclinical and clinical studies** (Andrade S, Ramalho MJ, Loureiro JA, Pereira MDC, 2018, International Journal of Molecular Sciences 19(9):2313) — Background on apigenin (chamomile's active flavonoid) as a mild GABA-A modulator — the 'frontal cortex off' switch. [Read the paper](andrade2018)

## Partner, travel & environment
Your bed partner, hotel rooms and the first night anywhere new all change your sleep in measurable, testable ways.
- **It's more than sex: exploring the dyadic nature of sleep and implications for health** (Troxel WM, 2010, Psychosomatic Medicine 72(6):578–586) — Sleep is dyadic: partners' movements, schedules and conflict measurably shape each other's sleep. [Read the paper](troxel2010)
- **Two in a bed: the influence of couple sleeping and chronotypes on relationship and sleep. An overview** (Richter K, Adam S, Geiss L, Peter L, Niklewski G, 2016, Chronobiology International 33(10):1464–1472) — Objective sleep is often worse when sharing a bed, though subjective satisfaction can be higher — hence the 'partial sleep divorce'. [Read the paper](richter2016)
- **Bed-sharing in couples is associated with increased and stabilized REM sleep and sleep-stage synchronization** (Drews HJ, Wallot S, Brysch P, et al., 2020, Frontiers in Psychiatry 11:583) — Counterpoint: in young couples, co-sleeping increased REM — the effect of a partner is individual; test it. [Read the paper](drews2020)
- **Night watch in one brain hemisphere during sleep associated with the first-night effect in humans** (Tamaki M, Bang JW, Watanabe T, Sasaki Y, 2016, Current Biology 26(9):1190–1194) — On the first night in a new place, one hemisphere sleeps lighter and is more responsive to sounds — the first-night effect is a vigilance mechanism. [Read the paper](tamaki2016)
- **Effect of inhaled lavender and sleep hygiene on self-reported sleep issues: a randomized controlled trial** (Lillehei AS, Halcón LL, Savik K, Reis R, 2015, Journal of Alternative and Complementary Medicine 21(7):430–438) — Lavender inhalation plus sleep hygiene improved sleep quality more than hygiene alone — a small, safe 'stackable win'. [Read the paper](lillehei2015)

## Life stages
How sleep changes with age and after having children — and which changes are normal rather than a problem to fix.
- **Meta-analysis of quantitative sleep parameters from childhood to old age in healthy individuals** (Ohayon MM, Carskadon MA, Guilleminault C, Vitiello MV, 2004, Sleep 27(7):1255–1273) — Total sleep time and deep sleep decline modestly across adulthood — some reduction with age is normal. [Read the paper](ohayon2004)
- **Long-term effects of pregnancy and childbirth on sleep satisfaction and duration of first-time and experienced mothers and fathers** (Richter D, Krämer MD, Tang NKY, Montgomery-Downs HE, Lemola S, 2019, Sleep 42(4):zsz015) — Parents' sleep satisfaction and duration did not fully recover for up to 6 years after the first child, most markedly in mothers. [Read the paper](richter2019)
- **Trajectories of maternal sleep problems before and after childbirth: a longitudinal population-based study** (Sivertsen B, Hysing M, Dørheim SK, Eberhard-Gran M, 2015, BMC Pregnancy and Childbirth 15:129) — Insomnia was common in late pregnancy and persisted at 2 years postpartum in a large share of mothers. [Read the paper](sivertsen2015)

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Educational summary of published research, not medical advice. Screening scores are not diagnoses. If a score is elevated or you feel unwell, talk to a clinician.

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