Protocol · graded by use, six uses
Daytime napping (length and timing)
Graded on: alertness and cognitive performance on objective tests (reaction time, attention lapses, sleep latency, task scores) in the 1 to 3 hours after a nap.
At a glance
This page is about naps. In lab studies, a nap of about 10 minutes made people more alert right away. Naps of 30 minutes or more left people groggy for a while before they did better. A nap during a night shift helped staff stay sharp, but it did not make the drive home safer. Studies of large groups link naps of an hour or more a day to more heart disease. They cannot show whether long naps cause harm or whether sick people nap more.
The A is shared by three of the six uses graded on this record, each on its own evidence. The other three carry their own letters.
This record carries a separate letter for each thing it has been measured on. The headline grade is the best of them, and it does not transfer to the others.
Brooks and Lack (2006; PMID PubMed ID: the permanent number the US National Library of Medicine gives a published paper. Each one links to that paper's record on PubMed. 16796222), 24 adults after about 5 hours of sleep: 10 minutes of nap sleep improved sleep latency, sleepiness and cognitive performance at once, for up to 155 minutes; 20 minutes helped from 35 minutes after waking; 30 minutes was followed by sleep inertia before the benefit; 5 minutes did little. Tietzel and Lack (2002; PMID 12220317) repeated the 10-minute benefit and found none from 30 or 90 seconds. Takahashi and Arito (2000; PMID 11007448), an independent group in Japan, found a 15-minute post-lunch nap after 4 hours of sleep shortened P300 latency and raised logical-reasoning accuracy against no nap. Dutheil et al. (2021; PMID 34639511) pooled 11 laboratory studies from several groups, 381 adults: effect size How large a difference the treatment made, as distinct from whether the difference could be detected at all. 0.18 overall and 0.29 for alertness, holding in randomized trials alone. Leong et al. (Sleep Med Rev, 2022; PMID 36041284) pooled 60 samples from 54 studies: naps improved the aggregate of cognitive tests (Cohen's d 0.38) and vigilance (d 0.61), with no moderation by age, nap length or nap start time. Mesas et al. (2023; PMID 36690376) pooled 22 randomized trials from other groups and found cognitive performance improved after a nap in men aged 18 to 35 (SMD 0.69). Hayashi et al. (1999; PMID 10210616) found a 20-minute nap at 2 PM improved subjective sleepiness and self-rated performance; self-report does not count toward the letter. Objectively measured performance, replicated The same finding reproduced by a separate research group. A result seen once can be chance or bias; a replicated one is harder to explain away. across independent groups: A. The pooled studies were almost all laboratory studies; workplace effects were not tested.
Dutheil et al. (2020; PMID 32492169) pooled 18 studies, 6 in real work, 494 participants: performance improved after the nap (effect size 0.25), mainly from 30 minutes after waking, with memory worse immediately on waking. Smith-Coggins et al. (2006; PMID 17052562), a randomized trial in 49 emergency staff: fewer attention lapses at 7:30 AM after a 3 AM nap. Hilditch et al. (2016; PMID 26715234): a 10-minute night nap prevented the decline seen without a nap and produced minimal sleep inertia; a 30-minute nap impaired performance for at least 47 minutes. Patterson et al. (2023; PMID 37347968): inertia after 30-minute and 2-hour naps resolved by 10 minutes. Objective performance, replicated by independent groups: A. Not covered: workplace safety, which no study measured (PMID 23411360), and driving home, where a nap did not help (PMID 17052562, PMID 26589387).
Mesas et al. (2023; PMID 36690376) pooled 22 randomized trials in 291 men aged 18 to 35: physical performance improved after a nap (SMD 0.99), largest for naps of 30 to under 60 minutes tested more than an hour after waking, with high heterogeneity How much the results of the pooled trials differ from each other. High heterogeneity makes a combined estimate less reliable. (I2 89 percent). Boukhris et al. (2024; PMID 37700141): after normal night sleep, napping improved the 5-meter shuttle run test but had no effect on muscle force, and most other measures rest on one to three studies. Zheng et al. (Front Physiol, 2026; PMID 42558951) pooled 12 randomized trials in 179 team-sport athletes: endurance improved (SMD 0.96) and agility modestly (SMD 0.55), while power and strength did not reach significance. WHY NOT A: the benefit is consistent on one test but absent on muscle force and untested or single-study on most others, and no trial included women: B.
Mednick et al. (2008; PMID 18554731): a 60 to 90 minute nap improved word recall against 200 mg of caffeine and against placebo An inactive substitute made to look like the real treatment, so participants cannot tell which one they received.. Scullin et al. (2017; PMID 28329381): a 90-minute nap opportunity improved word retention against quiet wakefulness in 50 young adults. Leong et al. (2022; PMID 36041284) pooled 52 memory samples: naps improved declarative memory (Cohen's d 0.38) and procedural memory (d 0.49), with no moderation by age. Objective memory tests, replicated across independent groups: A. Not covered: Scullin found no benefit in 45 adults aged 58 to 83, so the benefit in older adults is less certain than the pooled result suggests.
Reyner and Horne (1997; PMID 9401427): in 12 sleepy adults, 200 mg of caffeine plus a nap under 15 minutes cut simulated driving incidents to 9 percent of placebo levels, against 34 percent for caffeine alone. Hayashi et al. (2003; PMID 14652086): in 10 young adults, caffeine before a 20-minute nap was the most effective of five conditions for sleepiness and performance level. Two small controlled trials of 10 and 12 people: C.
Dourte et al. (2026; PMID 41973339) randomized 58 habitual nappers aged 59 to 82 to coaching to nap less or to their usual routine for 12 months; the usual-routine group lost more verbal episodic memory than both the nap-reduction group and non-nappers. One small trial, not repeated: C. It points the other way from Campbell et al. (2011; PMID 21314644), in which 22 adults aged 50 to 88 napped 45 minutes or 2 hours daily for a month and cognitive performance improved with no harm to nighttime sleep; that trial compared two nap lengths with no no-nap arm.
Alertness and performance on objective tests in the hours after an afternoon nap (A) and after a nap taken during a night shift (A). Memory retention after an afternoon nap is A; physical performance in athletes is B. Heart disease, mortality and dementia rest on population studies and carry no letter.
Why this letter
Why this gradeThe reasoning, and what the grade does not cover.
Grade A, the record's best use: alertness and cognitive performance on objective tests in the hours after an afternoon nap, in healthy adults. Brooks and Lack (Sleep, 2006; PMID 16796222) found a 10-minute nap improved sleep latency and cognitive performance at once, with benefits up to 155 minutes, after nights restricted to about 5 hours; Takahashi and Arito (2000; PMID 11007448), an independent group, found a 15-minute post-lunch nap improved P300 latency and reasoning accuracy against no nap; Tietzel and Lack (2002; PMID 12220317) repeated the 10-minute benefit and found none from 30 or 90 seconds; Dutheil et al. (2021; PMID 34639511) pooled 11 laboratory studies from several research groups and found cognitive performance improved after a nap, with the result holding in randomized trials alone; Leong et al. (2022; PMID 36041284), pooling 54 studies, found the same (Cohen's d 0.38 across cognitive tests, 0.61 for vigilance); and Mesas et al. (2023; PMID 36690376), pooling 22 randomized trials from other groups, found cognitive performance improved after a nap in young men (SMD 0.69). Reaction time and test scores are objectively measured by instrument, which qualifies the endpoint The outcome a trial measures to decide whether the treatment worked, such as heart attacks, blood pressure or a symptom score. for A, and the effect replicates across independent groups. Memory retention after an afternoon nap is a second A (Leong et al., 2022; PMID 36041284), and performance during night shifts after an on-shift nap a third (Dutheil et al., 2020; PMID 32492169; Smith-Coggins et al., 2006; PMID 17052562).
WHAT THIS GRADE DOES NOT COVERperformance in the first minutes after naps of 30 minutes or more, when trials measured grogginess instead of benefit; driving after a night shift, where a nap did not help in two trials (PMID 17052562, PMID 26589387); workplace safety, which no night-shift trial measured (PMID 23411360); and heart disease, stroke, dementia and death, where no randomized trial exists and the cohort associations with long naps, listed under excluded evidence, carry no letter.
Shared endpoint: Objectively measured alertness and cognitive performance after an early-afternoon nap against no nap, healthy adults after short night sleep
- Flinders University, Adelaide, Australia (Brooks, Lack): A 10-minute nap at 3 PM improved sleep latency and cognitive performance at once, for up to 155 minutes, after about 5 hours of sleep; 24 young adults, crossover A trial design in which each participant receives both the treatment and the comparison, one after the other, and serves as their own control.. PMID 16796222 · Funding: not stated in the indexed record
- National Institute of Industrial Health, Kawasaki, Japan (Takahashi, Arito): A 15-minute post-lunch nap shortened P300 latency and raised logical-reasoning accuracy at 13:15 against no nap, after 4 hours of sleep; 12 students, counterbalanced crossover; other performance measures did not differ. PMID 11007448 · Funding: government research institute
What the replication does not cover: Both trials are small laboratory crossovers in young adults after restricted sleep. Pooled replication across many more groups is in Dutheil 2021 (PMID 34639511) and Leong 2022 (PMID 36041284). Participants cannot be blinded to sleeping, and workplace effects were not tested.
Shared endpoint: Objectively measured reaction-time performance during a night shift after an on-shift nap against no nap
- Stanford University, Palo Alto, USA (Smith-Coggins): A 40-minute nap opportunity at 3 AM gave fewer attention lapses at 7:30 AM; 49 emergency physicians and nurses, randomized. PMID 17052562 · Funding: not stated in the indexed record
- University of South Australia, Adelaide, Australia (Hilditch): A 10-minute nap ending at 4 AM prevented the reaction-time decline seen with no nap, with minimal sleep inertia; 31 adults, randomized, simulated night shift. PMID 26715234 · Funding: not stated in the indexed record
What the replication does not cover: Neither trial measured workplace errors or injuries (PMID 23411360), and the nap did not improve driving home in either relevant trial (PMID 17052562, PMID 26589387). Pooled across 18 studies in Dutheil 2020 (PMID 32492169).
Shared endpoint: Objectively measured word recall after a nap against no nap, young adults
- University of California, San Diego, USA (Mednick): A 60 to 90 minute nap improved word recall against 200 mg caffeine and placebo. PMID 18554731 · Funding: US National Institutes of Health
- Emory University and Baylor University, USA (Scullin): A 90-minute nap opportunity improved word retention against quiet wakefulness in 50 young adults; no benefit in 45 adults aged 58 to 83. PMID 28329381 · Funding: US National Institute on Aging
What the replication does not cover: The two trials used different memory tasks and comparators, and the older-adult arm of Scullin 2017 showed no benefit. Pooled replication across 52 memory samples is in Leong 2022 (PMID 36041284).
A grade describes the human evidence for a named use. It is not advice, and it is not a judgment on any individual prescription. How the letters are decided →
Evidence notes: randomized trial, meta-analysis A study that pools the numbers from several trials into one combined estimate.
Endpoint graded: Alertness and cognitive performance on objective tests (reaction time, attention lapses, sleep latency, task scores) in the 1 to 3 hours after a nap (functional)
Last reviewed: October 2026
Dose, form and timing
Measured outcome: in the trials, a 3 to 10 minute computerized reaction-time test (psychomotor vigilance) before the nap and at intervals up to about 2.5 hours after waking. Nap length in the trials was counted from sleep onset, not from lying down. No trial has measured heart disease, stroke, dementia or death, so these short-term performance measures are the only endpoints the letters rest on.
As studiedDose, form, population and duration for every use.
A grade describes the intervention that was tested. Where the product on the shelf differs from it, this says so.
Safety
Grogginess after waking (sleep inertia): after naps of 30 minutes or more, reaction time and performance were worse for a period after waking, still measurable 47 minutes later after a 30-minute night-shift nap (Hilditch 2016; PMID 26715234), and participants rated their own performance as better while it was worse. Driving: a nap during or at the end of a night shift did not improve simulated driving home in two trials (Smith-Coggins 2006, PMID 17052562; Hilditch 2017, PMID 26589387). Nighttime sleep: afternoon naps shortened same-day nighttime sleep in a 7-day diary study (Häusler 2019; PMID 31300205). A growing need for long or frequent daytime sleep: in older adults, longer and more frequent naps preceded Alzheimer's dementia, and worsening cognition was followed by more napping (Li 2023; PMID 35297533); habitual long naps can reflect an underlying condition as well as cause one.
Sources
The evidence, in full28 papers, each linked to its PubMed record.
Nap length, afternoon: Brooks and Lack (Sleep, 2006; PMID 16796222) compared no nap with naps of exactly 5, 10, 20 and 30 minutes of sleep at 3 PM in 24 healthy young adults after nights restricted to about 5 hours. The 5-minute nap did little; the 10-minute nap improved sleep latency, sleepiness, fatigue, vigor and cognitive performance at once, with some benefits lasting 155 minutes; the 20-minute nap's benefits emerged 35 minutes after waking and lasted up to 125 minutes; the 30-minute nap was followed by impaired alertness and performance (sleep inertia) and then benefits lasting up to 155 minutes. Tietzel and Lack (J Sleep Res, 2002; PMID 12220317): 30-second and 90-second naps produced no measurable benefit, a 10-minute nap did. Takahashi and Arito (Sleep, 2000; PMID 11007448): in 12 students after 4 hours of sleep, a 15-minute nap at 12:30 shortened P300 latency, lowered sleepiness and raised logical-reasoning accuracy at 13:15 against no nap; other performance measures did not differ. Hayashi et al. (Clin Neurophysiol, 1999; PMID 10210616): a 20-minute mid-afternoon nap at 2 PM improved subjective sleepiness and self-rated performance against rest without sleep; the same group's 20-minute nap at 12:20 improved sleepiness but not measured task performance (Int J Psychophysiol, 1999; PMID 10380949). Dutheil et al. (Int J Environ Res Public Health, 2021; PMID 34639511) pooled 11 laboratory studies, 381 working-age adults, mean nap 55 minutes: overall cognitive performance improved after the nap (effect size 0.18), most for alertness (0.29), mainly up to 120 minutes after the nap; the result held when only randomized trials were pooled; naps before 1 PM trended better, with a confidence interval The range the true effect probably falls in. A wide interval means the estimate is uncertain. crossing zero. Night shifts: Dutheil et al. (Sleep, 2020; PMID 32492169) pooled 18 studies, 494 participants, mean nap 42 minutes at about 2 AM: performance improved (effect size 0.25), mainly from 30 minutes after waking, with memory worse immediately on waking. Smith-Coggins et al. (Ann Emerg Med, 2006; PMID 17052562) randomized 49 emergency department physicians and nurses to a 40-minute nap opportunity at 3 AM or none; nappers slept about 25 minutes and at 7:30 AM had fewer attention lapses, more vigor and less fatigue and sleepiness, with memory worse immediately after the nap and no better driving on a simulated drive home. Hilditch et al. (Sleep, 2016; PMID 26715234), 31 adults on a simulated night shift: a 10-minute nap ending at 4 AM produced minimal sleep inertia, a 30-minute nap impaired reaction-time performance that was still worse 47 minutes later, and participants rated their own performance better in every condition. Patterson et al. (Prehosp Emerg Care, 2023; PMID 37347968), 28 mostly emergency medical workers: sleep inertia after 30-minute and 2-hour naps at 2 AM had resolved by 10 minutes. Hilditch et al. (Accid Anal Prev, 2017; PMID 26589387): a 10-minute nap before a simulated commute after a night shift did not improve driving. Ruggiero and Redeker (Biol Res Nurs, 2014; PMID 23411360): 13 night-shift nap studies, none measuring workplace safety outcomes. Sleep inertia review: Hilditch et al. (Sleep Med, 2017; PMID 28366332). Physical performance: Mesas et al. (Br J Sports Med, 2023; PMID 36690376) pooled 22 randomized trials in 291 men aged 18 to 35; naps between 12:30 and 4:50 PM improved cognitive (SMD 0.69) and physical performance (SMD 0.99) and reduced perceived fatigue, with larger benefits for naps of 30 to under 60 minutes tested more than an hour after waking. Boukhris et al. (Sports Med, 2024; PMID 37700141): after normal night sleep, napping improved the 5-meter shuttle run test but had no effect on muscle force. Leong et al. (Sleep Med Rev, 2022; PMID 36041284) pooled 60 samples from 54 afternoon-nap studies: aggregate cognitive benefit d 0.38, declarative memory 0.38, procedural memory 0.49, vigilance 0.61, speed of processing 0.21, with no moderation by age, nap length, start time, habit or prior sleep restriction. Zheng et al. (Front Physiol, 2026; PMID 42558951): 12 randomized trials in 179 team-sport athletes, endurance SMD 0.96, agility 0.55, power and strength not significant. Memory: Mednick et al. (Behav Brain Res, 2008; PMID 18554731): a 60 to 90 minute nap improved word recall against 200 mg of caffeine and placebo, and caffeine impaired motor learning. Scullin et al. (Sleep, 2017; PMID 28329381): a 90-minute nap improved word retention in 50 young adults but not in 45 adults aged 58 to 83. Caffeine with a nap: Reyner and Horne (Psychophysiology, 1997; PMID 9401427): in 12 sleepy drivers, 200 mg of caffeine plus a nap under 15 minutes cut simulated driving incidents to 9 percent of placebo levels, against 34 percent for caffeine alone. Hayashi et al. (Clin Neurophysiol, 2003; PMID 14652086): caffeine before a 20-minute nap was the most effective of five conditions against mid-afternoon sleepiness. Older adults: Campbell et al. (J Am Geriatr Soc, 2011; PMID 21314644): 22 healthy adults aged 50 to 88 assigned to a daily 45-minute or 2-hour nap for a month, with no no-nap arm; nighttime sleep was not harmed, 24-hour sleep rose, cognitive performance improved, and adherence was better to 45 minutes. Dourte et al. (Geroscience, 2026; PMID 41973339): 58 habitual nappers aged 59 to 82 randomized to coaching to nap less or to their usual routine for 12 months; the usual-routine group lost more verbal episodic memory than the nap-reduction group and non-nappers. Souabni et al. (Front Aging Neurosci, 2022; PMID 36337699): 15 studies, 326 older adults, minimal evidence that napping harms nighttime sleep. Timing and nighttime sleep: Häusler et al. (Sleep Med, 2019; PMID 31300205): in 683 adults over 7 days, afternoon naps shortened same-day nighttime sleep, morning and evening naps did not. Population studies on heart disease, stroke, mortality, dementia and weight are listed under excluded evidence on this record and carry no letter. Zaregarizi et al. (J Appl Physiol, 2007; PMID 17641220): in 9 adults, blood pressure fell about 4 to 5 mmHg systolic between lights out and sleep onset during an afternoon nap. Children: Souabni et al. (Sleep Med, 2025; PMID 40592247), 27 studies: naps improved declarative memory in early childhood (Hedges g 0.35; 0.60 in preschoolers); Kurdziel et al. (Proc Natl Acad Sci U S A, 2013; PMID 24062429).
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(nap[tiab] OR naps[tiab] OR napping[tiab] OR siesta[tiab]) AND (performance[tiab] OR alertness[tiab] OR cognitive[tiab] OR memory[tiab] OR "sleep inertia"[tiab]) AND (randomized controlled trial[pt] OR meta-analysis[pt] OR randomized[tiab] OR crossover[tiab])Disclosure
Educational use only · Not medical advice · EBL grades published human evidence and does not recommend treatment. Stopping a prescription is a decision for your physician.
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