Moderate sleep deprivation produces impairments in cognitive and motor performance equivalent to legally prescribed levels of alcohol intoxication

The study addresses how much sleep deprivation leads to performance deficits comparable to legally defined alcohol intoxication limits for safe driving. Fatigue is common with long or irregular hours and contributes substantially to accidents. Alcohol provides a benchmark for acceptable performance standards. The research aim was to compare cognitive and motor performance after known durations of wakefulness with performance after graded alcohol doses, to identify hours awake at which deficits match those seen at BAC 0.05% and 0.1%.

Prior work highlights substantial societal costs and risks of fatigue-related accidents and calls for better information on fatigue’s performance consequences. Legal BAC limits for driving are based on laboratory and on-road evidence of speed and accuracy impairments. Earlier related research examined only a single eye–hand coordination test; broader test batteries are needed to set standards across work settings. The paper references studies on sleep-related vehicle accidents, economic costs, public policy reports, and a meta-analysis showing sleep deprivation effects on performance, as well as considerations of circadian influences.

Design: Randomised crossover controlled design with counterbalanced order; all subjects completed both alcohol and sleep deprivation conditions, separated by an afternoon break and overnight rest in a motel. Practice: Three practice sessions (~4 hours) the afternoon before testing. Participants: 39 volunteers (37 male, 2 female), 30 from a large road transport company and 9 from the Australian army (drivers and administrative staff), mostly aged 30–49; consent obtained; no selection beyond employment and willingness. Pre-assessments: Demographics, health, recent work/sleep, Epworth Sleepiness Scale; screening for sleep apnoea via questionnaire (none showed evidence). Self-rated tiredness collected at the start and end of each session. Tests: Computer-administered tasks—Mackworth clock (passive vigilance), simple reaction time, tracking (hand–eye coordination), dual task (divided attention combining reaction time and tracking), symbol digit (perceptual coding), spatial memory search, memory and search, and grammatical reasoning (logical reasoning). Alcohol condition: Baseline performance then four hourly alcohol doses targeting BACs of 0.025%, 0.05%, 0.075%, and 0.1%; doses individualized by body fat, weight, sex, and age; tests performed 30 minutes after each dose; BAC measured with a breathalyzer (Drager Alcotest 7110) immediately before and after each test session and hourly thereafter until BAC <0.05%; five performance sessions total; subjects’ preferred spirits/mixer used. Sleep deprivation condition: Hourly tests from baseline to hour 5, then every 2 hours for the next 20 hours; last test at 28 hours after waking; 15 sessions total; order of tests randomized within sessions; grammatical reasoning, spatial memory search, and memory and search were omitted from sessions 2–4 to match alcohol condition timing. Timing: Testing started ~0800, ~2 hours after waking (~0544 average wake time). Statistical analysis: For alcohol, pre- and post-session BACs averaged per session; individual BAC vs. session plots used to interpolate exact performance at 0.025%, 0.05%, 0.075%, and 0.1% BAC for each subject, then averaged across subjects. For sleep deprivation, performance across sessions 8–13 (1900–0500; ~13–23 hours since waking) was examined. Time treated continuously across midnight. The earliest session where sleep-deprived performance became worse than performance at BAC 0.05% and 0.1% was identified per subject; interpolation used to estimate hours since waking at equivalence; averages computed across subjects per measure. Only subjects showing deterioration over the window contributed to equivalence estimates; percentages reflect contributors by measure.

• Alcohol effects: At BAC 0.05%, response speed slowed ~8%–15% across tasks (e.g., reaction time 489→534 ms; dual task 662→725 ms; Mackworth 958→1094 ms; symbol digit 2233→2415 ms). Hand–eye coordination difficulty levels deteriorated ~10%. Accuracy declined notably: reaction time misses increased ~200% (0.36→1.17), Mackworth false alarms rose >50% (1.05→1.63), Mackworth targets detected decreased ~13% (12.64→10.91), spatial memory recalled series length decreased ~13% (5.34→4.65). Subjective tiredness ratings increased ~77% (17.84→31.63).
• At BAC 0.1%, impairments were larger: reaction time misses nearly 7× baseline (0.36→2.81), Mackworth false alarms ~3× baseline (1.05→4.48), hand–eye coordination in tracking and dual-task deteriorated ~50%, Mackworth speed slowed ~42% (958→1361 ms). Higher cognitive tests (grammatical reasoning, memory and search) showed smaller changes (~10%).
• Sleep deprivation effects (13–23 hours awake): Progressive decrements observed. By ~22 hours awake: Mackworth speed ~1511 ms (vs. ~1010 ms earlier), reaction time speed ~540 ms (from ~497 ms at ~14 h), dual task speed ~775 ms (from ~627 ms at ~14 h), symbol digit speed ~2577 ms (from ~2282 ms at ~14 h). Tracking/hand–eye coordination difficulty deteriorated (e.g., tracking ~33.37 at ~22 h vs. ~49.11 at ~14 h). Accuracy declines: reaction time misses increased ~187% (from ~0.98 at ~14 h to ~3.10 at ~22 h), Mackworth targets detected fell ~40% (12.00→7.04), Mackworth false alarms rose ~200% (1.28→4.24). Grammatical reasoning and memory-and-search showed modest changes (~5%–10%).
• Equivalence of sleep deprivation to alcohol (Table 6): Performance matched BAC 0.05% after ~17–19 hours awake (means ranged ~16.91–18.55 h depending on measure; e.g., reaction time speed 18.04 h; dual task speed 17.73 h; Mackworth speed 17.08 h; symbol digit speed 18.55 h; spatial memory sequence length 18.05 h). Equivalence to BAC 0.1% occurred after ~17.74–19.65 h awake (e.g., dual task speed 19.65 h; reaction time speed 18.71 h; Mackworth speed 18.10 h). Across many measures, over half the subjects reached BAC 0.1% equivalence; for several speed measures at BAC 0.05%, ≥75% reached equivalence.

Commonly experienced wake durations (17–19 hours) led to performance decrements equivalent to or worse than the legal BAC limit (0.05%) for driving. The earliest equivalence was seen in passive vigilance (Mackworth), with relatively consistent timing across tasks; dual-task measures reached equivalence slightly later. Longer wakefulness produced impairments equivalent to BAC 0.1% in most measures. These wake durations align with typical daily schedules, implying that extending wakefulness beyond the usual 16–17 hours significantly increases risk. While circadian lows likely compound deficits overnight, equivalence to BAC 0.05% occurred between 2200 and 0000—before the major circadian trough—implicating sleep loss as the primary driver of impairment, with circadian effects adding further deterioration later. The results support using alcohol-based standards as benchmarks for fatigue-related performance risk and argue for considering fatigue limits in safety-critical contexts.

The study demonstrates that moderate sleep deprivation (about 17–19 hours awake) produces cognitive and motor performance impairments comparable to those at legally significant alcohol intoxication levels (≥0.05% BAC), and longer wakefulness approximates BAC 0.1% effects. These findings suggest that extended wakefulness can compromise safety in driving and industrial operations. Policymakers should consider establishing fatigue standards analogous to BAC limits to reduce risk in safety-critical tasks. Future research should disentangle circadian versus sleep loss effects and evaluate chronic partial sleep deprivation’s impact on performance.

• Circadian effects were not independently isolated from sleep loss; the maximum sleep loss period coincided with expected circadian troughs, potentially enhancing observed deficits.
• Chronic partial sleep deprivation was not examined; findings pertain to a single extended wake period following a normal night’s sleep.
• Sample composition was predominantly male transport/army personnel, which may limit generalizability.
• Certain tests (grammatical reasoning, memory and search) showed limited sensitivity; some measures exhibited ceiling effects, affecting equivalence estimates (e.g., Mackworth accuracy, symbol digit symbols inspected).
• Not all subjects showed deterioration for every measure within the analysis window; equivalence estimates were based on subsets who deteriorated.
• Some tests were omitted from early sessions to accommodate alcohol absorption, potentially affecting within-day comparability across tasks.