Key studies linking sleep and napping with productivity, health and safety
Key Productivity Studies
Sleep Deficit: The Performance Killer, C.A. Czeisler, B. Frye, Harvard Business Review, 22nd October 2006
Dr Charles Czeisler, Professor of Sleep Medicine at Harvard Medical School, points out that a week of sleeoing four or five hours a night impairs performance to the same extent as legal drunkenness. “We know that 24 hours without sleep or a week of sleeping four or five hours a night induces an impairment equivalent to a blood alcohol level of .1%. We would never say ‘This person is a great worker! He’s drunk all the time!’ yet we continue to celebrate people who sacrifice sleep.”
See PDF attached
The Restorative Effect of Naps on Perceptual Deterioration, Mednick, S., Nakayama, K., et. al., Nature Neuroscience, published online 28th May 2002,
“Here, we tested human subjects four times in one day and found that with repeated, within-day testing, perceptual thresholds actually increased progressively across the four test sessions. This performance deterioration was prevented either by shifting the target stimuli to an untrained region of visual space or by having the subjects take a mid-day nap between the second and third sessions.”
See PDF attached
Key Health Studies
The Association Between Sleep Duration and Weight Gain in Adults. A 6-year Prospective Study from the Quebec Family Study, J-P. Chaput, J-P. Despres, C. Bouchard, A. Tremblay, Sleep, Vol. 31, No. 4, 2008
In this study of 276 adults between the ages of 21 and 64 over the course of six years the study split subjects into three groups: short sleepers (5 to 6 hours), average sleepers (7 to 8 hours) and long sleepers (9 to 10 hours). They found that over the six years short sleepers were 35% more likely to experience a weight gain of 5 kgs and that short sleepers were 27% more likely to develop obesity.
See attached PDF
Siesta in Health Adults and Coronary Mortality in the Gerneral Population, A. Naska, E. Oikonomou, A. Trichopoulou, T. Psaltopoulou, D. Trichopoulou, Arch Intern Med, Vol. 167, 12th February 2007
In this collaboration between the University of Athens Medical School, Hellenic Health Foundation and Harvard School of Public Health researchers found that after eliminating other health factors, such as diet, exercise and smoking, those who took a regular mid-day nap were 37% less likely to die of heart disease. This rose to 64% in working men.
See attached PDF
Key Safety Studies
Behavioral and Physiological Consequences of Sleep Restriction, S. Banks and D. Dinges, Journal of Clinical Sleep Medicine, Vol. 3, No.5, 2007
In this study of healthy adults individuals were split into groups who were allowed either 4 hours of night time sleep, 6 hours or 8 hours. When tested after 14 days of sleep restriction those in the 4 hours sleep group were 14 times more likely to make an error in testing versus their baseline performance when well rested. The six hour group made 11 times more errors versus baseline, whilst the 8 hours group performed consistently well, despite some decrement.
See attached PDF
Alertness Management: Strategic Naps in Operational Settings, M. Rosekind et al, J. Sleep Research Society, 4, 62-66
Rosekind et al examined the beneficial effects of a brief nap in a group of airline pilots. The group was split into two groups – a rest group who were allowed a brief in-flight nap and a non-rest group who were required to maintain their usual in-flight activities. The Rest Group maintained consistent performance night and day, at the end of flights, and after multiple flight legs. The Rest Group demonstrated vigilance performance improvements from 16% in median reaction time to 34% in lapses compared to the No-Rest Group.
See attached PDF
| Other Studies highlighting the benefits of a controlled rest |
|---|
| 1. Naps as integral parts of the wake time within the human sleep-wake cycle. |
|
ASCHOFF J. |
| 2. The effects of a 20 min nap in the mid-afternoon on mood, performance and EEG activity. |
| HAYASHI M, WATANABE M, HORI T. Clin Neurophysiol 1999;110(2):272-9. Department of Behavioral Sciences, Faculty of Integrated Arts and Sciences, Hiroshima University, Higashi-hiroshima, Japan Objective: The aim of the study is to examine the effects of a 20 min nap in the mid-afternoon on mood, performance and EEG activities. Methods: Seven young adults who had normal sleep-wake habits without habitual daytime napping participated in the study. They underwent Nap and No-nap conditions at intervals of 1 week. After a nocturnal sleep recording (00:00-08:00 h), their EEG recordings during relaxed wakefulness, and their mood, performance and self-ratings of performance level were measured every 20 min from 10:00 to 18:00 h. For the nap condition, they went to bed at 14:00 h and were awakened when 20 min had elapsed from the onset of sleep stage 1. For the No-nap condition, they took a rest without sleep by sitting on a semi-reclining chair Results: All of the subjects were awakened from sleep stage 2 during the nap. The 20 min nap improved the subjective sleepiness, performance level and self-confidence of their task performance. The nap also suppressed EEG alpha activity during eyes-open wakefulness. Conclusions: The results suggest that a short 20 min nap in the mid-afternoon had positive effects upon the maintenance of the daytime vigilance level. |
| 3. The effects of a short daytime nap after restricted night sleep. |
| GILLBERG M, KECKLUND G, AXELSSON J, AKERSTEDT T. Sleep 1996;19(7):570-5. Karolinska Institute, Stockholm, Sweden Study: Eight subjects participated on three occasions in a study investigating the effect of a 30 minute daytime nap opportunity on alertness/sleepiness. Protocols: The baseline condition was a normal home sleep (7.5 hours, with bedtime at 2300 hours). Sleep during the other two conditions was between 2400 hours and 0400 hours. During one of the two 4-hour conditions, a short nap was allowed (between 1045 hours and 1115 hours). Self-ratings of sleepiness/alertness (Karolinska Sleepiness Scale) were recorded every hour. At 10, 12, and 15 hours, the subjects performed a 28-minute visual vigilance task. Electroencephalograms (EEG) and electrooculograms (EOG) were recorded continuously, including during a 10-minute standardized recording procedure at the beginning of each day. Mean total sleep time during the nap was 19.8 (standard error 2.4) minutes. Results: Compared to baseline, EEG/EOG sleepiness and subjective sleepiness were significantly higher and vigilance performance at 10 hours lower, respectively, after the two short sleeps. Conclusions: The nap brought performance to baseline levels, and subjective sleepiness decreased significantly. It was concluded that the short nap had a clear positive effect on alertness. |
| 4. The role of a short post-lunch nap in improving cognitive, motor, and sprint |
|
WATERHOUSE J, ATKINSON G, EDWARDS B, REILLY T. |
| 5. The use of prophylactic naps and caffeine to maintain performance during a continuous operation. |
| BONNET MH, ARAND DL. Ergonomics 1994;37(6):1009-20. Dayton VA Hospital, Wright State University, OH 45428. Protocol: After a normal baseline night of sleep and a morning of baseline test performance, 24 young adult male subjects returned to bed from 16:00-20:00 prior to a 24 h period of sleep loss. Twelve subjects received caffeine 200 mg at 01:30 and 07:30. Results: Performance tests (correctly completed addition problems, vigilance sensitivity, and logical reasoning correct responses) all indicated maintenance of baseline performance levels in the caffeine group after administration of caffeine while performance declined in the placebo group. Similar results were found for the Multiple Sleep Latency Test and Oral Temperature, which both remained near baseline levels throughout the observation period in subjects receiving caffeine. Conclusions: The results indicated that the combination of a prophylactic nap and caffeine was more effective in maintaining nocturnal alertness and performance than was the nap alone. Of more interest was the fact that the group which was given the combination of nap and caffeine was able to maintain alertness and performance at very close to baseline levels throughout a 24 h period without sleep. |
| 6. Short nap versus short rest: recuperative effects during VDT work. |
| HAYASHI M, CHIKAZAWA Y, HORI T. Ergonomics 2004;47(14):1549-60. Department of Behavioral Sciences, Faculty of Integrated Arts and Sciences, Hiroshima University, Higashi-hiroshima, Japan. Study: The effects of a 20-min nap during 2 h of visual display terminal (VDT) work were examined. Methods: Ten young healthy adults took a 20-min nap or a 20-min rest I h after VDT work, followed by another 1 h of VDT work. Results: A 20-min rest temporarily restored subjective sleepiness, but it deteriorated during the additional 1 h of work. In contrast, a 20-min nap maintained subjective alertness and performance level at a higher level and mental fatigue at a lower level for the additional 1 h of work. Conclusions: These results suggest that a short nap would be useful to both fatigue recovery and fatigue prevention during continuous VDT work. The present findings may provide a new work/rest strategy. |
| 7. Habitual napping moderates motor performance improvements following a short daytime nap. |
| MILNER CE, FOGEL SM, COTE KA. Biol Psychol 2006 Mar 13 Brock University, Sleep Research Laboratory, St. Catharines, Ont., Canada Study:The effect of napping on motor performance was examined in habitual and non-habitual nappers who were randomly assigned to a nap or reading condition. Motor procedural learning and auditory discrimination tasks were administered pre- and post-condition. Results: Both groups reported improved alertness post-nap, but not post-reading. Non-habitual nappers fell asleep faster and tended to have greater sleep efficiency, but did not differ from habitual nappers on other sleep architecture variables. Habitual nappers had greater alpha and theta EEG power in stage 1, and greater delta, alpha and sigma power in stage 2 sleep. Motor performance deteriorated for non-habitual nappers who napped, but improved for all others. The number of sleep spindles and sigma power (13.5-15Hz) significantly predicted motor performance following the nap, for habitual nappers only. Conclusions: Results indicate that motor learning was consolidated in a brief nap and was associated with stage 2 spindles, but only for those who habitually take naps. |
