Light interventions

Reference

Study participants

Shift system

Intervention

Key endpoints

Key results

Babkoff 2002

11 subjects (females??)

Simulated shift‐work schedule beginning 17:30 and ending 10:00 the next morning

1 hour bright light + placebo; exposure to 3000 lux occurred between 01:30 and 02:30 hours, placebo at 01:40

CRT

Exposure for 1 hour to bright light combined with placebo yielded swifter CRTs immediately after the treatment, but also seemed to result in more sleepiness and greater performance deficit than when the subjects were not exposed to the bright light.

Boyce 1997

16 subjects

(all males)

Graveyard shift (00:00‐07:59); rapidly rotating shift system, having three continuous nights' work followed by three days’ rest

1) Low‐illuminance (250 lux, 3900 K)

2) High‐illuminance (2800 lux, 4050 K)

3) Increasing illuminance condition (200 lux to 2800 lux, 2800 K to 4050 K)

4) Decreasing illuminance condition (2800 lux to 200 lux, 4050K to 2800 K)

Sleep quality (by diary);
arousal measured using the questionnaire developed by Mehrabian 1974

High, increasing, and decreasing illuminance conditions associated with greater subjective arousal than were the low‐illuminance condition. No difference of performing simple cognitive tasks associated with the lighting conditions.

Campbell 1995

26 subjects

(7 females)

3 consecutive night shifts between 24:00 hours until 08:00 hours the following morning

Exposed group: night 1: > 4000 lux between 00:00 hours to 04:00 hours, followed by ambient room illumination < 100 lux;

night 2+3: circa 1000 lux for the duration of each shift

Control group: < 100 lux (night 1‐3)

Levels of alertness during shift assessed using the RTSW

There was little effect on measures of on‐duty alertness and performance or on off‐duty sleep.

Middle‐aged subjects may be less phase‐tolerant than young subjects.

Chinoy 2015

8 subjects

(2 females)

4 day shifts followed by 4 night shifts

Treatment subjects (n = 4) received 2500 lux in the latter half of night shifts + a scheduled 8‐hour evening sleep episode; control subjects were in standard lighting (90 lux)

Subjective sleepiness on‐shift; PVT reaction time

For treatment subjects, by night 2, reaction time was not different from day shifts, and by night 3, subjective sleepiness was not different from day shifts. The preliminary data indicate that a combination treatment of scheduled evening sleep before night shifts and enhanced lighting during night shifts improves on‐shift sleepiness and reaction time.

Czeisler 1990

8 subjects

(all males)

1 week of night work

Treatment study condition: circa 7000‐12,000 Iux at night and nearly complete darkness during the day (had to stay in their bedroom from 9:00‐17:00)

Control study conditions: circa 150 lux; no restriction for the day

Subjective alertness on‐shift assessed with use of a VAS; cognitive performance measured by a test involving calculations

Both alertness and cognitive performance significantly improved in the treatment group during night‐shift hours.

Dawson 1991

13 subjects

(6 females)

3 consecutive simulated night shifts between 00:00 and 08:00

Treatment study condition: circa 6000 Iux between 00:00 and 04:00 on the first night shift + dim light (< 200 Iux) for the remainder of the study

The control group received dim light throughout

Alertness on‐shift assessed using the RTSW; measures of sleep quality included time in bed, total sleep time, sleep efficiency, sleep onset latency, wake after sleep onset

The treatment was associated with significantly higher alertness across the night shift and improved sleep quality during the day. On‐shift alertness was improved relative to the control group. The data indicate that a single 4‐hour pulse of bright light between midnight and 04:00 is effective in ameliorating the sleep and alertness problems associated with transition to night shift.

Dawson 1995

16 subjects

(6 females)

3 consecutive simulated night shifts between 23:00 and 07:00

Treatment group condition: bright light (4000‐7000 Iux between 00:00 and 04:00)

Control group conditions: dim red light < 50 lux

Sleep quality measured by wrist actigraphy; cognitive performance measured using computer‐based divided attention tasks

Sleep quality and cognitive psychomotor performance was improved in the Iight‐treatment group.

Eastman 1995

46 subjects

(21 females)

Simulated night shifts of 8 consecutive night‐work, day‐sleep days

Bright light durations of 6, 3 and 0 hours (i.e. dim light) during simulated night shifts. The bright light (circa 5,000 Iux) was used during all 8 night shifts, and dim light was < 500 Iux

Core body temperature continuously measured; sleep duration assessed by daily sleep log; mood assessed using the POMS

Substantial circadian adaptation (i.e. a large cumulative temperature rhythm phase shift) was produced in many subjects in the bright light groups, but not in the dim light group. Larger temperature rhythm phase shifts were associated with better subjective daytime sleep, less subjective fatigue and better overall mood.

Englund 1990

22 subjects

(all male?)

1 full day shift (08:00‐16:00) + 2 night shifts (19:00‐07:00)

Four treatment groups: bright light (2000 lux) for three hours at 19:00, 22:00, 01:00 or 04:00 during the first night shift

Control group: dim red light during 01:00‐04:00; 200 lux ambient lighting

Core body temperature and wrist activity monitored by a Vitalog PMS‐8; cognitive performance and mood assessed through a battery computerised task battery. Specific measures of mood include: POMS, School of Aerospace Medicine Subjective Fatigue Checklist, SSS

Preliminary analysis indicates equal or better results across all groups on the second night shift as compared to the first night for simple reaction time, logical reasoning, addition/subtraction, sleepiness and fatigue.

Foret 1998

8 subjects

(all males)

Simulated night shift regimen (60‐hour protocol)

Treatment group: during 20:00 to 08:00 (1st night), 4‐hour pulse of bright light (700‐1000 Iux)

Control group: during 20:00 to 08:00 (1st night), dim light (circa 50 Iux); 2nd night: dim light in both groups

Self‐rated alertness assessed using a shortened version of the Activation ‐ Deactivation Adjective Checklist; performance tests were 'search and memory' tests derived from the Memory and Search Task

Self‐assessed alertness and task performance were improved by the exposure to bright light. Subjective alertness and performance continued to show a time course during the subsequent night following exposure only to dim light.

Higuchi 2011

11 subjects

(all males)

Simulated night work

Day 1: dim light (< 15 lux) from 20:00 to 03:00

Day 2: light for four hours from 23:00 to 03:00 with a non‐visor cap (500 lux), red‐visor cap (circa 160 lux), blue‐visor cap (circa 160 lux)

Performance of a PVT as an index of objective sleepiness; subjective sleepiness on‐shift, fatigue, mood, visual comfort and brightness measured using a VAS

The red‐visor cap had no adverse effects on performance of the PVT, brightness and visual comfort, though it tended to increase subjective sleepiness.

Hoppen 2001

Experiment 1: Pilot study:

5 subjects

(4 females)

Experiment 2:

6 subjects

(all females)

Experiment 3:

11 subjects

(all males)

Experiment 1: two seven‐day study periods

Experiment 2: 4 six‐day study periods

Experiment 3: five seven‐day study periods

Experiment 1: ambient lighting in the clinical investigation unit of 50 lux; 2 hours of 10,000 Iux or dim light during 02:00‐04:00

Experiment 2: I‐hour 10,000 Iux at 20:00 or 00:00 or 04:00, or dim light

Experiment 3: 1, 2 or 4 hours of 10,000 lux or dim light in time windows 01:00‐05:00

Subjective fatigue measure on‐shift through Samn‐Perelli scale; alertness and performance measured using digit‐symbol substitution task, CRT, and subjective alertness ratings VAS + G15

A series of experiments established that 2 hours of bright light (broad spectrum white, 02:00‐04:00, 10,000 lux) did improve subjective alertness and performance. Bright light given in the middle of the night (white 00:00‐01:00, 10,000 lux) was more effective than light given at 20:00 or 04:00. Light of 2 hours and 4 hours duration were more effective than 1 hour of light centred at 03:00 (white, 10,000 lux). Light of shorter wavelengths appeared to be more effective than light of Ionger wavelengths at improving nocturnal alertness and performance (01:00‐05:00, 300 lux).

Kretschmer 2011

32 subjects

(16 females)

Three consecutive simulated night shifts between 22:00‐06:00

Treatment group: 4‐hour pulse of bright light (3000 lux) between 22:00 and 02:00 on night 1, 1 hour later in night 2, and 2 hours later in night 3

Control group: dim light (300 Iux)

Objective measures of working memory, selective attention, divided attention, concentration performance, and vigilance recorded by established performance tests (including working memory of the TAP, Go/No‐Go, Divided Attention of the test battery for attention testing; Konzentrations‐Leistungs‐Test; Simple Reaction Time Task)

Bright light Ieads to an improvement in working memory, divided attention and concentration performance in all three night shifts. Bright light leads to better performance for some forms of attention tasks in elderly night workers.

Kretschmer 2012

32 subjects

(16 females)

Three consecutive simulated night shifts between 22:00‐06:00

Treatment group: 4‐hour pulse of bright light (3000 lux) between 22:00 and 02:00 on night 1, 1 hour later in night 2, and 2 hours later in night 3

Control group: dim light (300 Iux)

Objective measures of working memory, selective attention, divided attention, concentration performance, and vigilance recorded by established performance tests (subtest working memory of the TAP, Divided Attention of the test battery for attention testing; Konzentrations‐Leistungs‐Test (KLT‐R); PVT

Bright light exposure results in a better performance for cognitive tasks in older night workers over time. Except for high‐demand tasks, such as sustained attention tasks, bright light induces better performance in working memory and concentration tasks for older night workers.

Kretschmer 2013

32 subjects

(16 females)

Three consecutive simulated night shifts between 22:00‐06:00

Treatment group: 4‐hour pulse of bright light (3000 lux) between 22:00 and 02:00 on night 1, 1 hour later in night 2, and 2 hours later in night 3

Control group: dim light (300 Iux)

Mood (Der Mehrdimensionale Befindlichkeitsfragebogen and sleepiness on‐shift (SSS) questionnaires and a concentration task, a working memory task, and a divided‐attention task by established performance tests (Konzentrations‐Leistungs‐Test (KLT‐R)); subtest working memory of the TAP; Divided Attention of the test battery for attention testing)

Results indicate that sleepiness and mood did not function as mediators in the prediction of concentration, working memory, and/or divided attention by light exposure. Bright light has a strong direct and independent effect on cognitive performance, particularly on working memory and concentration.

Martin 1998

35 subjects

(9 females)

6 days of simulated 8‐hour night shifts

Treatment group 1: 5700 lux 3 hours/day

Treatment group 2: 12:30 lux 3 hours/day

Treatment group 3: < 250 lux

All participants wore dark sunglasses while outside during daylight

Core body temperature continuously measured; sleep duration via daily sleep log; mood and fatigue during day assessed using the POMS

During nights 3‐5, most subjects in the high and medium groups (100% and 85%) exhibited phase delays large enough that their body temperature minima occurred within the daytime sleep/dark period. Larger phase shifts were correlated with more sleep and less fatigue. Extremely 'bright' light may not be necessary for circadian adaptation in specific shift work situations.

Rahman 2011

12 subjects

(5 females)

All subjects exposed to the five lighting conditions between 20:00 and 08:00 over 5 consecutive weeks

Lighting conditions: 1) complete darkness;

2) unfiltered fluorescent white light (380‐730 nm);

3) fluorescent white light with wavelengths < 480 nm filtered'

4) fluorescent white light with wavelengths < 460 nm filtered;

5) fluorescent white light with wavelengths < 480 partially filtered

During each overnight testing session, objective and subjective neuropsychometric tests and saliva samples were collected every 2 hours. The Toronto Hospital Alertness Test, the Digit Vigilance Test, the SSS, the seven‐item Fatigue Scale self‐report questionnaire and a VAS for subjective mood were employed

Subjective alertness, mood, and errors on an objective vigilance task were significantly less impaired at 08:00 by filtering wavelengths < 480 nm compared with unfiltered nocturnal light exposure. The changes were not associated with significantly increased sleepiness or fatigue compared with unfiltered light exposure. The data suggest that spectral modulation may provide an effective method of regulating the effects of light on physiological processes

Samel 1995

4 subject

(all males)

Two sessions of 11 days of simulated microgravity (6° head down tilt bedrest) with 6‐hour extensions of the wake period on 2 days (12‐hour phase delay)

Bright light (> 3500 Iux) for 5 hours on each of the 2 shift days and the following day at times either expected to accelerate the adjustment to the phase delay (treatment condition) or to have no phase shifting effect (control condition)

Sleep recorded polygraphically; circadian system monitored by recordings of heart rate and body temperature, and by collection of urine (electrolyte and hormone excretion); subjective sleep duration assessed via sleep log

5‐hour exposures to bright light finishing at the time of the circadian temperature minimum were not more effective at accelerating adjustment to a 12‐hour schedule delay than exposures coinciding with the temperature maximum. We conclude that, while bright light may accelerate adjustment to work‐rest schedule delays, any such effect seems to be largely independent from the timing of the light exposure. No significant effects in polygraphically measured sleep parameters

Schobersberger 2007

11 subjects

(all males)

Three consecutive simulated night shifts (22:00‐06:00); after a 2‐week rest, a second run of three consecutive night shifts

Treatment group: lighting environment (800 lux) with reduced short‐wavelength components

Control group: unfiltered bright light (800 lux) environment

Circadian markers (including urinary aMT6s), symptoms of lassitude, and personal mood; fatigue (and other parameters) assessed via mood rating inventory before and after the shift; Vienna Test System, including performance testing (reaction time analysis), vigilance testing and evaluation of attentiveness (Continous Attention)

Mood rating inventories did not result in differences in the subjective perception between the two lighting environments with respect to the dimensions of 'activity', 'concentration', 'deactivation', and 'fatigue'. In addition, changes in signs of vigour and weariness in the course of each night of the study were equally pronounced in test light and bright light.

Sletten 2014

71 subjects

(29 females)

after ≥ 2 night shifts in the field, 1 simulated night shift in the laboratory

Treatment group: blue‐enriched white light (17,000 K, 150 lux) from 2300‐0700

Control group: continued background white light (4000 K, 150 lux)

Habitual sleep‐wake patterns monitored for 1‐3 weeks via diaries and actigraphy; urine collected for aMT6s; assessments via KSS, PVT, polysomnography and mood

Exposure to blue‐enriched light was not associated with significant improvements in PVT performance, or electro‐oculogram correlates of alertness. During the biological night, however, blue‐enriched light was associated with improved subjective alertness.

Thessing 1994

30 subjects

(19 females)

2‐night protocol

Lighting conditions:
1) bright light 00:00‐04:00;
2) dim light 00:00‐02:00 + bright light 02:00‐04:00;
3) dim light 00:00‐04:00

Sleep estimated with actigraphy; subjective sleepiness (VAS); throughout night 2, the MSLT, SALT performance

4‐hour exposure to bright light significantly increased MSLT scores and improved SALT performance during the early morning hours on the night following bright‐light exposure. No significant effects were noted with a 2‐hour exposure.
A single exposure to bright light from 00:00 to 04:00 hours significantly decreased objectively measured sleepiness and improved performance on the subsequent night, particularly during the early morning hours. On the contrary, a 2‐hour exposure of essentially equal intensity light produced no change, relative to dim light, in any of the dependent measures.

Weisgerber 2015

19 subjects

(5 females)

no less than 1 week between the interventions 1‐3

Interventions:
1) No sleep deprivation (SD);
2) Overnight SD with 45 min dim light (DL+50 lux);
3) Overnight SD with 45 min BL (+5600 lux)

Body temperature and psychomotor vigilance (PVT); Saliva collected before and after light treatment for melatonin assay

Temperature, subjective alertness and PVT performance decreased significantly across the night. BL significantly suppressed melatonin, but did not improve subjective alertness or PVT performance. SD markedly increased incidents, accidents, and standard deviation of lane position. BL compared to DL did not improve performance during the first 22 min circuit, but across the 2 circuits BL significantly attenuated the effect of time on task on incidents and accidents.

Light and glasses interventions

Reference

Study participants

Shift system

Intervention

Key endpoints

Key results

Eastman 1994

50 subjects (19 females)

8 consecutive simulated night shifts

Four groups in 2 x 2 design: light (bright, dim); goggles (yes, no); exposure to bright light (circa 5000 lux) for 6 hours on the first two night shifts; dim light < 500 lux

Core body temperature continuously measured; sleep duration via daily sleep log; mood and fatigue assessed using the POMS

Both bright light and goggles were significant factors for producing circadian rhythm phase shifts. The combination of bright light plus goggles was most effective; the combination of dim light and no goggles was least effective. Larger temperature‐rhythm phase shifts were associated with better subjective daytime sleep, less subjective fatigue and better mood. There was no significant main effect of goggles on sleep duration, but the main effect of light and the interaction of light and goggles were not significant.

Smith 2008

24 subjects

(14 females)

3 simulated night shifts (2300‐0700), 2 days‐off + 4 more night shifts

Treatment group: five 15 minute bright light pulses during night shifts + sunglasses when outside + sleep in dark bedrooms at scheduled times after night shifts and on days‐off + outdoor afternoon light exposure (the “light brake”)

Control group: remained in normal room light during night shifts + lighter sunglasses + unrestricted sleep and outdoor light exposure

DLMO; daily sleep log + actigraphy, alertness on‐shift, total sleep time assessed using sleep logs and actigraphy; reaction time (SRT) test

The final DLMO of the experimental group was close to our target compromise phase position, and significantly later than the control group. Experimental subjects performed better than controls, and slept for nearly all of the allotted time in bed. Controls demonstrated pronounced performance impairments late in the night shifts, and exhibited large individual differences in sleep duration.

Smith 2008a

31 subjects

(17 females)

3 simulated night shifts (23:00‐07:00) + 2 days‐off

Two treatment groups: intermittent bright light during night shifts (75 and 120 min/night) + dark sunglasses when outside + sleep in dark bedrooms at scheduled times after night shifts and on days‐off + outdoor light exposure upon awakening from sleep

Control group: dim room light during night shifts + lighter sunglasses + unrestricted sleep and outdoor light

DLMO; daily sleep log + actigraphy; simple reaction time (SRT) test

After the days‐off, the DLMO of the experimental groups was in a good position to reach the target after subsequent night shifts with bright light. The DLMO of the control group changed little from baseline. Experimental subjects performed better than control subjects during night shifts on a reaction time task.

Smith 2009

19 subjects

(11 females)

3 simulated night shifts (23:00‐07:00); 2 days‐off, 4 night shifts + 2 days‐off

Treatment group: four 15‐min BL pulses during night shifts + sunglasses when outside + sleep in dark bedrooms at scheduled times + outdoor afternoon light (“light brake”)

Control group: remained in normal room light during night shifts + lighter sunglasses + unrestricted sleep and outdoor light

DLMO; daily sleep log + Actiwatch‐L; Automated Neurophysiological Assessment Metrics test battery (SRT reported)

The final DLMO of the experimental group was close to the target of 03:00, and later than the control group. Subjects who phase‐delayed (whether in the experimental or control group) close to the target phase performed better during night shifts.

Nap interventions

Reference

Study participants

Shift system

Intervention

Key endpoints

Key results

Asaoka 2012

20 subjects

(6 females)

Subjects awakened at 07:00 of the experimental day and were prohibited from sleeping until the end of experiment except for the nap (01:00‐02:00) in the nap group

Participants remained awake for 20 hours ‐ performing cognitive tasks at 21:00, 02:00 and 03:00; experimental chamber below 150 lux, 30 lux during cognitive task period, 0 lux during the nap

Nap condition: 1‐hour nap 01:00‐02:00

Rest condition:1‐hour awake‐rest period 01:00‐02:00

Sleep logs + Actiwatch‐L + polysomnography + EEG; stimulus‐response compatibility (arrow‐orientation task, reaction time

Behavioural performance and amplitude of the error‐positivity declined after midnight (i.e. 02:00 and 03:00) compared with the 21:00 task period in both groups. During the task period starting at 03:00, the participants in the awake‐rest condition reported less alertness and showed fewer correct responses than those who napped.

Bonnet 1994

12 subjects

(all males)

3 consecutive nights and 2 days in the laboratory for 2 consecutive weeks (= session 1+2)

Session 1: 4‐hour afternoon nap + caffeine at 01:30 and 07:30

Session 2: four 1‐hour naps during the night + placebo

In both sessions pills (placebo or caffeine) were administered at 01:30, 07:30, 13:30, 19:30)

MSLT, EEG; performance and mood were assessed with repeated batteries of measures (logical reasoning, WAlS, computer‐modified Williams Word Memory Test of immediate free recall, visual vigilance, subjective sleepiness/alertness, POMS, oral temperature) across the 24‐hour operation

After an afternoon nap, subjects had increased objective and subjective alertness, increased oral temperature, and increased performance on complex tasks like logical reasoning and correct additions when compared to the condition that allowed four night‐time naps.

Bonnet 1994a

24 subjects

(all males)

3 consecutive nights and 2 days in the Iaboratory

Nap condition 1: 16:00‐20:00 prior to a 24‐hour period of sleep loss

Nap condition 2: as in 1 + 200 mg caffeine at 01:30 and 07:30

All subjects received pills at 01:30, 07:30, 13:30, 19:30. For all subjects, the pills received at 13:30 and 19:30 were placebos

MSLT, EEG; visual vigilance, subjective sleepiness/alertness, POMS; performance and mood were assessed with repeated batteries of measures (logical reasoning, WAlS, computer‐modified Williams Word Memory Test of immediate free recall

Performance tests all indicated maintenance of baseline performance Ievels in the caffeine group after administration of caffeine, while performance declined in the placebo group. The combination of nap and caffeine was able to maintain alertness and performance at very close to baseline Ievels throughout a 24‐hour period without sleep.

Bonnet 1995

140 subjects

(all males)

4 consecutive nights and 3 days in the laboratory

1) Nap condition: nap at 12:00, 16:00, 18:00 or not at all

2) Caffeine condition: single 400 mg dose of caffeine at 01:30 each night or repeated doses of 150 mg or 300 mg every 6 hours starting at 01:30 on the 1st night of sleep loss

3) Placebo condition: no‐nap and placebo administered every 6 hours on the repeated caffeine schedule was run for 1) and 2)

During the sleep‐loss period, all subjects were administered placebo capsules every 6 hours starting at 01:30

MSLT, EEG; performance and mood were assessed with repeated batteries of measures (logical reasoning, WAlS, computer‐modified Williams Word Memory Test of immediate free recall, visual vigilance, subjective sleepiness, POMS, oral temperature) across the 24‐hour operation

Naps provided Ionger and less graded changes in performance, mood and alertness than did caffeine, which displayed peak effectiveness and loss of effect within about 6 hours. Neither nap nor caffeine conditions could preserve performance, mood, and alertness near baseline Ievels beyond 24 hours, after which Ievels approached those of placebo.

Bonnet 1995a

12 subjects

(all males)

3 consecutive nights and 2 days in the Iaboratory

Nap condition 1: 4‐hour afternoon nap

Nap condition 2: four 1‐hour naps during the night

Nap condition 3: 0.125 mg of triazolam prior to a prophylactic 4‐hour nap before the 24‐hour operation

MSLT, EEG; performance and mood were assessed with repeated batteries of measures (logical reasoning, WAlS, computer‐modified Williams Word Memory Test of immediate free recall, visual vigilance, subjective sleepiness/alertness, POMS, oral temperature) across the 24‐hour operation

When a series of 1‐hour naps was taken during the normal night period, oral temperature and psychomotor performance also declined. However, performance was relatively improved on the following evening. In contrast, with an effective 4‐hour prophylactic nap, performance remained near baseline Ievels across the night. Fatigue increased over the course of the study, the increases were similar in each group.

Caldwell 1998

18 subjects

(all males)

3 separate 38‐hour periods of continuous wakefulness, each separated by 10 hours of recovery sleep

Nap condition 1: 2‐hour evening nap (at 21:00) induced with 10 mg zolpidem tartrate

Nap condition 2: 2‐hour nap (at 21:00) with placebo;

Condition 3: 2‐hour rest break with no sleep

Following 1) or 2) or 3), subjects remained awake for 23 additional hours

Sleepiness on‐shift, alertness (and others) assessed using VAS; Repeated Test of Sustained Wakefulness; polysomnography of naps; POMS; multiattribute task battery

Results indicated the effectiveness of prophylactic naps for sustaining mood, alertness, and performance throughout the final 23 hours of a 39‐hour period of sustained operations. Both napping conditions attenuated the decrements normally associated with total sleep deprivation, but the zolpidem nap was the most effective because subjects obtained the most sleep.

Della Rocco 2000

59 subjects

(31 females)

4‐day protocol with 3 early morning shifts (07:00‐15:00) followed by a rapid rotation to the midnight shift (23:00‐07:00)

Nap condition 1: long nap of 2 hours

Nap condition 2: a short nap of 45 minutes

Nap condition 3: no‐nap condition

Wrist activity monitors; sleepiness on‐shift via Stanford Sleepiness Scale; Air Traffic Scenarios Test; the Bakan, a test of vigilance

While sleepiness increased across the midnight shift for all groups, ratings were generally lower for the long nap condition and were lower for males in the short nap condition. Both cognitive performance and subjective measures of sleepiness supported the use of naps during the midnight shift.

Gillberg 1984

12 subjects

(all males)

Sleep of 4 hours during the preceding night, work during the day and then kept awake (except for naps) in the laboratory from 17:00 to 08:00 the following morning

Nap condition 1: one‐hour nap (21:00h)

Nap condition 2: one‐hour nap (04:30h)

Nap condition 3: no‐nap

EEG, EOG; self‐ratings of sleepiness on‐shift, sleep latency tests; single choice visual reaction time task

Clear positive effects of naps (especially the 04:30 nap) on performance. The sleep latency measurements showed similar, but less clear tendencies, while ratings of sleepiness did not differentiate between conditions.

Hilditch 2014

30 subjects

(18 females)

3‐day laboratory study including one baseline sleep (22:00‐07:00) and one experimental night

Nap condition 1: total sleep deprivation (NO‐NAP)

Nap condition 2: 10‐min nap (10‐NAP)

Nap condition 3: 30‐min nap (30‐NAP)

Nap opportunities ended at 04:00

Fatigue scale, sleepiness scale, and self‐rated performance scale; psychomotor vigilance test (PVT‐B), digit‐symbol substitution task

In the 30‐NAP condition, performance immediately deteriorated from pre‐nap and was still worse at 47 min postnap. A 10‐min ‐ but not a 30‐min ‐ night‐time nap had minimal sleep inertia and helped to mitigate short‐term performance impairment during a simulated night shift.

Hilditch 2015

21 subjects

(12 females)

3‐day laboratory study; keeping subjects awake for 27 hours for 1 simulated night shift; 40‐min York highway driving task at 07:15 to simulate the commute

Nap condition 1: total sleep deprivation (NO‐NAP)

Nap condition 2: 10‐min nap ending at 04:00 + a 10‐min pre‐drive nap ending at 07:10 (10‐NAP)

Polysomnography; SP‐Fatigue; PVT‐B

In the 10‐NAP condition, PVT‐B performance was worse after the nap (07:12) compared to before the nap (06:30); no change across time was found in the NO‐NAP condition. SP‐Fatigue and driving performance did not differ significantly between conditions.

Kan 2012

79 subjects

(27 females)

10‐day sleep restriction protocol, assignment to one of 18 sleep regimens

Nap condition 1: restricted diurnal sleep + nocturnal nap (0.4‐hour, 0.8‐hour, 1.2‐hour, 1.6‐hour, 2.0‐hour or 2.4‐hour time in bed

Nap condition 2: restricted diurnal sleep + no‐nap

Polysomnography; total sleep time (sleep duration)

Napping on the night shift does not degrade subsequent daytime SE above and beyond SE reduction associated with daytime sleep or increasing overall time in bed

Kubo 2010

12 subjects

(all males)

3‐day experiment with 1 simulated night shift (22:00–08:00 ) and subsequent day (11:30–17:30) and night sleep (00:00–07:00)

Nap conditions: 1) 00:00–01:00 (early 60 min; E60);

2) 00:00–02:00 (E120)

3) 04:00–05:00 (late 60 min; L60)

4) 04:00–06:00 (L120)

5) no‐nap

Polysomnography; rectal temperature; VAS for sleepiness; visual vigilance test; set of tasks, including English transcription task + a performance test battery

Posthoc analyses showed significantly longer RTs and more lapses following the L60 nap compared with no‐nap. In contrast, there was no significant difference in sleepiness between the L60, or any of the other nap conditions, and the no‐nap condition. Findings suggest the effect of sleep inertia on visual vigilance test performance was profound in the L60 condition, although no significant effects on sleepiness were self‐reported by VAS.

Lovato 2009

22 subjects

(13 females)

Simulated night shift environment with a 2‐hour sleep in the afternoon from 15:00–17:00 hours, followed by nap condition 1 or 2 in 02:30–03:00

Nap condition 1: 30‐min nap

Nap condition 2: no‐nap

Sleepiness on‐shift (SSS, KSS), fatigue and vigour subscales of the POMS, and the VAS for sleepiness; symbol–digit substitution task, the letter cancellation task, and the PVT

The 30‐min nap resulted in some impairment of subjective alertness for a brief period (up to 30 min) immediately following the nap when compared to the no‐nap condition. Following this brief period, alertness improved by the 30‐min nap from 04:00 until the end of the testing period at 07:00.

Macchi 2002

8 subjects

(1 female)

Simulated night shift; alertness and performance testing sessions + 2‐hour runs in a driving simulator

From 14:00 to 17:00

Nap condition 1: sleep

Nap condition 2: sedentary activities

Polysomnography, subjective fatigue and sleepiness on‐shift via VAS, sleep quality (Sleep Quality Questionnaire); EEG; 3 computerised tests from the Walter Reed performance assessment battery

In the nap condition, the subjects showed lower subjective sleepiness and fatigue, as measured by VAS, and faster reaction times and less variability on psychomotor performance tasks.

Matsumoto 1981

8 subjects

(all male)

5 Nap conditions between a previous full night's sleep and a day sleep on the day following the night

Nap conditions: a 2‐hour nap between:

1) 22:00‐00:00 (N1)

2) 02:00‐04:00 (N2)

3) 04:00‐06:00 (N3)

4) 06:00‐08:00 (N4)

5) no‐nap(Control group)

EEG, EOG, EMG, ECG, respiratory movement; rectal temperature, oral temperature; flicker fusion frequency, sleepiness, fatigue complaints

Decrease in rectal temperature during the night was more marked for conditions N2, N3 and N4, with a lesser extent of individual differences, than for the Control group and N1. The self‐evaluation of the sleep depth and the rapidness of sleep onset correlated highly with sleep parameters. N3 and N4 were evaluated to have resulted in a better sleep than N1.

Saito 1996

6 subjects

(all female)

3 x 3 days experimental conditions

Day 1+2 daily activities

Day 3: awake from 00:00 until 10:00 with a nap period which started at 03:00

On each of 3 days:
nap condition 1: no‐nap

nap condition 2: 1‐hour nap

nap condition 3: 2‐hour nap

Fatigue Feelings Scale, SSS; EEG, EOG and EMG during the naps

A 1‐hour nocturnal nap gave significantly smaller scores on two subscales of Fatigue Feelings Scale during early morning hours than no napping. A 2‐hour nocturnal nap, which contained significantly Ionger duration of Slow Wave Sleep than a 1‐hour nocturnal nap, did not differ from a 1‐hour nocturnal nap in decreasing scores of fatigue feelings during these hours

Salame 1995

24 subjects

(all males)

5 nights experimental design with one no‐nap condition before the night tests + a nap condition that comprised the 1‐hour nap followed by the test sessions

Nap condition 1: 1‐hour nap at 00:00

Nap condition 2: 1‐hour nap at 03:00

Sleep inertia (spatial memory) and logical reasoning tasks

No effects on accuracy, and no circadian effects of napping were found. Pooled data of intervention groups showed that the performance in the 1‐hour nap condition exhibited significant reductions of speed immediately following awakening, when compared with no‐nap, reflecting sleep inertia effects.

Schweitzer 1992

Study A:

10 subjects

(7 females);

Study B:

12 subjects

(5 females)

Study A&B: Two night‐time work periods separated by at least three normally timed nights of sleep

Study A ‐ Nap condition: 3‐hour nap opportunity on 1 night between 20:00 and 23:00 ;

Study B ‐ Caffeine condition: 4 mg/kg caffeine on 1 night

Polysomnography, sleepiness on‐shift SSS, VAS; alertness (computer‐driven simulated assembly line task)

Performance and subjective alertness improved after both a 2·3‐hour evening nap or ingestion of caffeine prior to the work shift. Although neither napping nor caffeine countered the strong circadian influence on performance and alertness in the early morning hours, both strategies attenuated their sharp decline.

Takeyama 2002

13 subjects

(all male)

Simulated shift work schedules of 9 consecutive days: 2 day (08:00‐16:00) + 3 night (22:00‐08:00) + 3 day shifts; between experimenting with nap condition 1 and 2, rest period of 1 week

Nap condition 1: nap from 02:00‐04:00

Nap condition 2: no‐nap

Fatigue and anxiety questionnaire, heart rate variability, oral temperature, salivary cortisol; two performance tasks: typing figures + performing mental arithmetic; CFF, 3‐choice reaction time

Task performances decreased and subjective fatigue and anxiety increased in proportion to the length of time worked in both M‐types (morningness) and E‐types (eveningness) who had no‐nap. In M‐types, these changes were significantly suppressed by the nap on the first night of duty. Changes for E‐types were smaller than those for M‐types in terms of task performance and psycho‐physiological parameters.

Takeyama 2004

6 subjects

(all male)

5 nap conditions on‐shift for each participant; 3 consecutive days with one night shift (22:00‐08:00) followed by daytime sleep and night sleep; at least 5 days between the experiments

Nap conditions:
1) 00:00‐01:00 (E60)
2) 00:00‐02:00 (E120)
3) 04:00‐05:00 (L60)
4) 04:00‐06:00 (L120)
5) no‐nap (No‐nap)

Polysomnography, questionnaire on subjective fatigue, heart rate variability, rectal temperature; performance task (typing text) and tests (choice reaction time test, a logical reasoning test, a vigilance test, and a CFF test)

Sleep latency was shorter and sleep efficiency was higher in the nap in L60 and L120 than that in E60 and E120. Performance was somewhat improved by taking a 2‐hour nap later in the shift, but deteriorated after a one‐hour nap.

Tremaine 2010

24 subjects

(15 females)

Simulated night‐shift schedules with at least one week intervening between conditions

2‐hour afternoon sleep opportunity + one of two‐nap conditions: 1) 30‐min night‐nap; 2) no night‐nap

Polysomnography, subjective sleepiness on‐shift (SSS, KSS, VAS), objective sleepiness on‐shift (sleep latency tests); objective performance (Symbol Digit Substitution Task) + reaction time (PVT)

Subjective sleepiness was less correlated with objective sleepiness and objective performance when participants were given a 30‐min night nap. However subjective sleepiness and reaction time performance was strongly correlated in both conditions, and there was no significant difference between the nap and no‐nap conditions.

Other interventions

Reference

Study participants

Shift system

Intervention

Key endpoints

Key results

Baehr 1999

33 subjects

(17 females)

Simulated night work study with 8 consecutive night shifts followed by daytime sleep/dark periods

1) Intermittent bright light (6 pulses, 40‐min long each, at 5000 lux) versus dim light (< 500 lux, 20 min )

2) Intermittent exercise (6 bouts, 15‐min long each, at 50%‐60% of maximum heart rate) versus no exercise; bright light and exercise interventions during the first 6 hours of the first 3 night shifts

Core temperature; sleep duration (sleep log)

Intermittent bright light groups had significantly larger phase delays than dim‐light groups, and 94% of subjects who received bright light had phase shifts large enough for the individual rectal temperature minimum to reach daytime sleep. Exercise did not affect phase shifts; neither facilitating nor inhibiting phase shifts produced by bright light. During the last 4 days of the study, subjects in the bright light groups slept more (within the scheduled sleep/dark periods) and napped less than those in the dim light groups.

Kelly 1994

43 subjects

(all male)

5‐day night work study involving a 10‐hour phase delay of the work/rest cycle

1) Bright white light (3500‐4300 Iux) versus dim red light (200‐300 Iux) from 22:00‐02:00 each night

2) Inactive LEET versus active LEET therapy for 20 min prior to the daytime sleep periods

Polysomnography; circadian phase shifting evaluated via core body temperature + urinary 6‐SM excretion; indirect measurement of alertness: complex reaction time, simple reaction time; subjective alertness (VAS); performance examined with a cognitive performance assessment battery

6‐SM data indicate that bright light exposure increased the phase delay seen in this circadian rhythm in the 3 days after the work/rest schedule shift. Bright light treatment shows evidence of improving accuracy on a broad range of cognitive performance, without compensatory decreases in speed. LEET administration before the daytime sleep periods showed little evidence of affecting either performance or 6‐SM. Complex reaction time: bright light‐exposed subjects performed significantly better than did dim light‐exposed on all three postshift testing sessions, with the largest difference the second postshift night (Day 3). Bright light subjects started out slightly less alert at baseline, dropped less the first night after the shift, and rose much more the second night after the shift. On the last night both groups dropped to a similar level.

Kelly 1997

45 subjects

(all male)

5‐day night work study with subjects working and being tested during three 9‐hour night shifts from 18:00‐03:00

1) Bright light (3500‐4300 lux) or dim light (200‐300 lux) from 22:00‐02:00 each night

2) LEET for 20 min prior to daytime sleep

3) Both bright light) + LEET)

4) Placebo treatments

Polysomnography; 6‐SM, VAS of sleepiness; cognitive tests in the performance assessment battery, simple and complex reaction times (simple reaction times + complex reaction times) trials, word memory task

Bright light accelerated phase delay of the circadian melatonin rhythm after the work‐rest schedule shift. Further, subjects who received bright light had greater total sleep time and improved sleep continuity. Some minor improvements in cognitive performance were produced by light treatments but not by LEET.

Neri 2002

28 subjects

(all male)

6‐hour night‐time flight in a flight simulator; a structured sleep/wake schedule for three nights just prior to the study; obtaining their typical amount of night‐time sleep between the hours of 22:00 and 08:00

Treatment condition: 5 breaks spaced hourly during cruise

Control condition: 1 break in the middle of cruise

Questionnaire + interview; EEG/EOG, subjective sleepiness (KSS, VAS); vigilance performance (PVT), subjective sleepiness ratings, electrophysiological measures of drowsiness, continuous video

The treatment group showed significant reductions for 15 min postbreak in slow eye movements, theta‐band activity, and unintended sleep episodes compared with the control group. The treatment group reported significantly greater subjective alertness for up to 25 min postbreak. There was no evidence of objective vigilance performance improvement at 15‐25 min postbreak.

Santhi 2008

35 subjects

(14 females)

10‐day shift work simulation (4 day shifts = 07:00‐15:00 and 3 night shifts = 23:00‐07:00)

1) Morning Sleep (08:00‐16:00) + phase‐delaying light exposure (23:00‐03:00)

2) Evening Sleep (14:00‐22:00) + phase‐advancing light exposure (03:00‐07:00)

Polysomnography; dim light salivary melatonin onset; RT in the PVT; subjective alertness via the KSS

Analysis of the dim light salivary melatonin onset indicated a modest but significant circadian realignment in both sleep groups. Daytime sleep efficiency and total sleep time did not differ between them or from their respective baseline sleep. On the final night shift, the evening sleep subjects had fewer episodes of attentional impairment and quicker responses on the PVT than their morning sleep counterparts.

Sato 2010

8 subjects

(all male)

Simulated night work (22:00‐08:00) with an hourly exercise consisting of 30 min task, 15 min test and 15 min break

Treatment condition: hourly exercise (3 min during breaks)

Control condition: no exercise during breaks

Heart rate variability; a VAS for subjective fatigue + sleepiness, psychomotor vigilance test (PVT)

Work performance in the last 10 min of each 30‐min task was better under the treatment condition than under the control condition. During the second half of the test period, exercise showed an effect on sustained attention. Exercise was not effective in reducing subjective fatigue and sleepiness.

Yamanaka 2010

17 subjects

(all male)

In a temporal isolation facility with dim light conditions (< 10 lux), sleep schedules were phase‐advanced by 8 hours from habitual sleep times for 4 days, followed by a free‐run session for 6 days with no time cues. During the shift schedule, the treatment and control groups performed physical exercise or not

Treatment group: physical exercise with a bicycle ergometer in the early and middle waking period for 2 hours each

Control group: sat on a chair at those times

Polysomnography, bed sensor, wrist activity + light intensity (Actiwatch); plasma melatonin, continuous rectal temperature

Sleep‐onset on the first day of free‐run in the exercise group was significantly phase‐advanced from that in the control and from the baseline. The circadian melatonin rhythm was significantly phase‐delayed in both groups, showing internal desynchronisation of the circadian rhythms.

Cross‐over trial

Outcome

Description of ANOVA strategy

ANOVA results

Correlation coefficient (CC)

Estimates of P values by CC (see Unit of analysis issues)

Sadeghniiat‐Haghighi 2011

Sleepiness on‐shift overall

"A two‐factor repeated measurement ANOVA was used. Factors:

1) treatment; 2) time (of night measurement)

P values were corrected for sphericity (using the Huynh‐Feldt coefficient). Significance was defined at P < 0.05."

Period 1 : Time of night measurement × Treatment: (F = 8.76; P < 0.001)

Time of night measurement: (F = 40.98; P < 0.001)

Period 2 : Time of night measurement × Treatment:

(F = 5.124, P < 0.01)

Time of night measurement: (F = 9.872; P < 0.001)

0.9

0.7

0.0

< 0.0001

< 0.0001

< 0.0001

Karchani 2011

Sleepiness on‐shift overall

"Using the paired t‐test, we compared subjective sleepiness between two conditions (with bright light and with normal light). A repeated measure ANOVA showed interaction between independent variables in this study. The level of significance was defined at P < 0.05. (examined treatment effect, carry‐over effect, and period effect)."

The findings for treatment effect, period effect and carry‐over effect of the study population:

Treatment effect:

t df P value

–21.95 89 0.001

0.9

0.7

0.0

< 0.0001

< 0.0001

< 0.0001

Lowden 2004

Sleep efficiency (actigraph)

"The data obtained during night work were submitted to ANOVA for repeated measures, with correction for unequal variances according to Huynh and Feldt (Huynh 1976). The two‐way ANOVA included the factors of condition (Bright light/Normal light) and day (15 examined night shifts). A third factor, time of day, was added for variables with several measures during 1 day (for melatonin and KSS). A fourth factor, week (three studied night work weeks), was added to give a more detailed analysis of KSS ratings. Posthoc mean comparisons were carried out with contrasts.

KSS ratings during the night shift week (means of 3 weeks): As some workers showed missing data on Fridays, this day was omitted from the analysis. To reflect the many data points, a four‐way analysis of variance including the factors of condition, week (3 weeks), night (night 1–4 of each week) and time of day, were used."

Condition: NS (no P value reported)

Cond./Night Interaction: NS

0.9

0.7

0.0

< 0.0001

0.02

0.20

Total sleep time‐main sleep

(bed time; final awakening)

Condition: NS (no P value reported)

Cond./Night Interaction: NS

0.9

0.7

0.0

0.01

0.14

0.43

Total sleep time‐24‐hr sleep

Condition: (P < 0.05)

Cond./Night Interaction: NS

0.9

0.7

0.0

< 0.0001

0.04

0.24

Sleepiness on‐shift KSS (overall)

Sleepiness: "No main effects were obtained except for time of day showing an increase of sleepiness throughout the night shift (F = 36.46; P = 0.0001; df = 3/45). A significant interaction was obtained (Fig. 2) for the interaction of condition, night and time (F = 2.39; P = 0.0365; df = 9/135). Sleepiness was significantly reduced in the bright light condition at 02:00 hours on Tuesday; at 04:00 hours on Monday, Tuesday and Thursday; and at 06:00 hours on Tuesday and Thursday as shown by the posthoc mean comparisons. The reduction of sleepiness in the bright light condition was further emphasised by the significant interaction of condition and time of day (F = 3.07; P = 0.0429; df = 3/45). The interaction of week + light was insignificant."

0.9

0.7

0.0

< 0.0001

0.06

0.31

Sleepiness on‐shift KSS (postintervention)

0.9

0.7

0.0

< 0.0001

0.09

0.35

Smith 2007

Sleepiness on‐shift – Reaction time – postintervention (03:00 and 04:00 and 05:00 and 06:00)

"For each of the dependent variables, a set of 2 x 2 repeated measures ANOVAs were carried out. In order to control for interindividual variability in baseline performance, scores for all four dependent variables (response speed, M10%RT, lapse frequency and subjective sleepiness) were expressed relative to the baseline test score obtained at 00:00 hours, calculated by subtracting the 00:00 hours’ value from each hourly score. That is, 00:00 hours scores were zeroed and subsequent scores were relative to this point. Relative scores at each hour of shift were then averaged to obtain the mean relative performance across participants. In order to analyse specific time differences in the dependent variables after the nap, parallel ANOVAs were carried out with different levels entered for the time factor (i.e. before nap and 03:00 hours; before nap and 04:00 hours; before nap and 05:00 hours; before nap and 06:00 hours). Before‐nap mean scores were calculated from a combined average of 00:00, 01:00 and 02:00 hours data. As the aim was to compare nap and no‐nap conditions after the nap, the statistics of interest were the nap × time interactions. Significant interactions were observed for response speed at 04:00 and 06:00… and for subjective sleepiness at 03:00 and 04:00. … Participants therefore had faster reaction times, and less subjective sleepiness, after the nap."

Before nap vs 06:00

Nap: P = 0.002

Time: P = 0.011

N x T : P = 0.012

0.9

0.7

0.0

< 0.0001

0.02

0.21

Sleepiness on‐shift – Subjective sleepiness score – postintervention (03:00 and 04:00 and 05:00 and 06:00)

Before nap vs 06:00

Nap: P = 0.16

Time: P = 0.201

N x T : P = 0.095

0.9

0.7

0.0

< 0.0001

< 0.0001

0.05