Workers who do not work the standard 9-to-5 may suffer from unique sleeping problems like shift work disorder. New research offers insight into whether workplace naps help or hurt such employees.
In America, being caught napping on the job is often grounds for dismissal. However, in some countries, sleeping on the job is somewhat acceptable. For example, in Japan there is the practice of inemuri (literally, “sleeping while present”) in which workers are allowed to doze—as long as they remain in an upright position. Such dozing is seen in a positive light: It indicates the employee is so dedicated to the job that he or she has worked to exhaustion, but remains ready to work. As studies continue to show that sleepy workers are more likely to make mistakes, attitudes are changing. For example, the Japanese Ministry of Health, Labour, and Welfare (Tokyo) recently published Sleep Guidelines for Health Promotion 2014.1 These guidelines are intended to improve the sleep, safety, and health of Japanese people and may ultimately discourage inemuri. (For example, the guidelines encourage individuals to get sufficient sleep at night or, if this is not possible, to take a 30-minute nap in the afternoon.)
In America, many industries have implemented rules with the goal of reducing fatigue in their shift workers. Examples include allowing workers to have more “off time” between shifts, rotating shifts forward (ie, from first shift to second shift to third shift), and allowing longer or more breaks during a shift. Some recent research indicates that allowing shift workers to nap on their shift may help to combat fatigue. However, industries are hesitant to allow workers to nap on the job since implementing a napping policy could be problematic logistically: How long should workers be allowed to sleep? How often should a worker be allowed to nap during a shift? Should the naps occur at a scheduled time or only when the worker is sleepy? These and other questions are being addressed by scientists with some conflicting results.
People working the night shift or rotating shifts struggle with sleepiness for several reasons: insufficient sleep resulting from efforts to maintain social activities or attend to obligations; sleep disruption during a sleep period because of environmental factors such as excessive noise or bright lighting; and disruption of the circadian rhythmicity of biological processes.
In a normal circadian rhythm, body temperature is normally highest at 4 PM to 6 PM and lowest at approximately 3 AM to 4 AM. The nadir normally takes place during sleep. It is around the time of the nadir that a night shift worker can struggle most with sleepiness. Therefore, some research has focused on this time when examining various aspects of napping at work.
One issue that has been explored is whether it would be more beneficial for a worker to nap around this time (3 AM to 4 AM) in the shift or only when the worker feels sleepy. To investigate the impact of workers selecting their nap time during a shift, researchers Jonathan Davy and Matthias Gobel allowed student volunteers to nap for 1 hour at a self-selected time during a simulated 3-day night shift schedule.2 The participants were 18- to 23-year-old university students who had not previously worked the night shift. These results were compared to the effects of a simulated “standard” night shift in which the volunteers had a 1-hour break, but did not nap.
The results showed that when the students were allowed a flexible nap schedule, they had better performance, improved physiological responses, and reduced sleepiness for each night shift and collectively over the 3-night cycle. Sleep diaries maintained by the students revealed that napping during the simulated third shift did not significantly reduce daytime sleep. The researchers therefore suggest that allowing flexible napping may be beneficial in a workplace.
Concerning the best timing of a nap during a night shift, Davy told me, “Typically, napping too early [between 7 PM and 10 PM] or slightly later will limit the quality and length of the nap because individuals may not be tired then or their circadian rhythm may not favor sleep then. Napping too late [4 AM to 6 AM] is good from the perspective that the quality of sleep will be good because individuals would have been awake for a long time, but this will interfere with recovery sleep during the day.” He further cautions, “Waking up in the nadir of the circadian rhythm [between 4 AM and 6 AM] may result in sleep inertia, which will negatively affect alertness and performance on awakening.”
The length of a nap can be problematic. If too long, sleep inertia (grogginess immediately after an abrupt awakening) can impair work performance if a worker immediately tries to resume work after a nap. Because sleep inertia can occur after a long nap, Cassie Hilditch and colleagues examined the effect of a 10-minute nap versus a 30-minute nap on sleep inertia in volunteers who underwent a simulated night shift.3
Thirty healthy female women (21–35 years old) underwent a baseline study night (10 PM to 7 AM) in which they slept normally. They were then randomized to one of three conditions for another simulated night shift: total sleep deprivation (“NO-NAP”), 10-minute nap (“10-NAP”), or 30-minute nap (“30-NAP”). The naps ended at 4 AM. Fatigue and vigilance were measured by the Samn-Perelli Fatigue Scale and 3-minute psychomotor vigilance tests, respectively, at 3 AM (before the nap) and then at 2, 17, 32, and 47 minutes after the nap.
In the NO-NAP group, fatigue increased throughout the postnap period. In the 10-NAP group, fatigue initially decreased at 2 minutes postnap and then steadily increased throughout the postnap period. In the 30-NAP group, the prenap fatigue level and the 2-minute postnap fatigue level were similar, but the fatigue level thereafter remained stable throughout the postnap period.
Performance deteriorated steadily throughout the postnap period in the NO-NAP group. In the 10-NAP group, performance was slightly reduced at 2 minutes, and then stabilized. In the 30-NAP group, the postnap performance degraded considerably from the prenap level and was worse than the performance level in the 10-NAP condition throughout the postnap period. Hilditch concluded that during a night in which a person must remain awake, a short (ie, 10-minute nap ending at 4 AM) may help reduce impaired performance—at least up to 47 minutes postnap—with minimal sleep inertia upon awakening; by contrast, a 30-minute nap may significantly impair performance after awakening.
For employers interested in implementing a napping protocol, Hilditch told me the following: “Naps can be very beneficial for managing fatigue on shift, but employers and workers need to be aware of the risk of sleep inertia and manage it appropriately. What the best timing/duration of a nap should be will, to some extent, be determined by the operational environment. Even the best-planned naps may have different benefits/sleep inertia depending on the prior sleep/wake history of the individual.
“I think a buffer zone [ie, the time after a person awakens from a nap until the person returns to work] is a good idea, even if the nap has been planned to minimize sleep inertia. The problem is that, even with best nap planning, prior sleep/wake history of the individual can influence the depth of sleep in the nap and the potential resulting sleep inertia upon waking. So it’s always best to have a buffer zone to make sure you’re fully recovered.”
Acknowledging that maintaining worker performance after a nap is important to consider when a company is weighing the benefits and risks of workers napping in the workplace, Hannah Mulrine and colleagues evaluated the effectiveness of naps of various durations (20 minutes, 40 minutes, or 60 minutes) on alertness and performance at 1.5 to 6 hours postnap in volunteers who underwent simulated night work or an extended wake period.4 After polysomnographically recording a baseline 8-hour time-in-bed, healthy young males underwent either 20 hours or 30 hours of sleep deprivation on four separate occasions. The sleep deprivation period was followed by a nap of 0, 20, 40, or 60 minutes. Subjective sleepiness, memory, and vigilance were measured at 1.5, 2, 2.5, 3, 4, 5, and 6 hours after the nap. Vigilance significantly improved after the 40-minute and 60-minute naps, compared to the 20-minute nap or no nap. Subjective sleepiness was significantly less after the 60-minute nap than after no nap. Mulrine concluded that naps of 40 minutes or 60 minutes show more prolonged benefits 1.5 to 6 hours after the nap, compared to a 20-minute nap or no nap. Mulrine recommends naps of 40–60 minutes for sustained improvement in cognitive performance.
The Davy, Hilditch, and Mulrine studies were all performed in a controlled laboratory setting in which the idealized “worker” had 20 or more minutes to sleep. In a real world setting, how can a business that wants to implement a napping program allow workers to nap 40–60 minutes if it is impractical? Sanae Oriyama and colleagues have investigated a possible solution: providing two short naps during a shift.5 Oriyama’s study took place in a real setting: a hospital. In the study, one group of night shift nurses worked their shift without a nap and a second group took two short (15-minute) naps. Temperature, certain other physiological factors (eg, heart rate variability), and fatigue were measured hourly. In both groups, subjective sleepiness and fatigue increased similarly between 4 AM and 5 AM. However, the heart rate was more reduced (indicating less sympathetic activation) in the nap group than in the no nap group. Therefore, napping physiologically had a positive impact.
Businesses that have established rules to combat sleepiness in their workers have focused on fatigue reduction strategies, which involve practices that decrease the likelihood that a person will be working while fatigued (eg, by restricting the hours of work, increasing the hours between shifts, and rotating shifts forward from first to second to third rather than vice versa).
Napping could be another approach to reduce sleepiness and fatigue. However, on implementing a protocol, various factors will need to be considered such as avoiding sleep inertia, the amount of time that workers will be allowed to nap, whether a “buffer zone” will be allowed to enable a worker to fully awaken before resuming work, whether to allow a worker to do less safety-critical tasks on coming back from a nap. Because conditions differ from workplace to workplace, designing a “universal” napping plan is not possible. As Hilditch says, “Sorry, there’s not a magic answer! But each study builds our knowledge on the benefits and side effects of naps so that we can better advise shift workers. Giving blanket advice is harder than [giving] specific advice for an operator. This ties into the idea a FRMS [Fatigue Risk Management System] needs to be adapted to individual operators and is not one-size-fits-all.”
Regina Patrick, RPSGT, is a freelance medical editor/writer for the Regina Patrick Writing Service. As a result of having worked the night shift off and on during her 30 years as a sleep tech, she enjoys reporting on new approaches to improving circadian rhythmicity.
1. Japanese Ministry of Health, Labour and Welfare. Sleep Guidelines for Health Promotion 2014. Tokyo, Japan: Japanese Ministry of Health, Labour and Welfare; 2014:11. (In Japanese). Available at: http://www.mhlw.go.jp/file/04-Houdouhappyou-10904750-Kenkoukyoku-Gantaisakukenkouzoushinka/0000042751.pdf. Accessed February 6, 2015.
2. Davy J, Gobel M. The effects of a self-selected nap opportunity on the psychophysiological, performance and subjective measures during a simulated industrial night shift regimen. Ergonomics. 2013;56:220-234.
3. Hilditch C, Centofanti S, Dorrian J, et al. Performance and fatigue after waking from 10 min and 30 min night-time naps. Sleep and Biological Rhythms. 2014;12(Suppl 1):2-3 (abstract #8).
4. Mulrine HM, Signal TL, van den Berg MJ, et al. Post-sleep inertia performance benefits of longer naps in simulated nightwork and extended operations. Chronobiology International. 2012;29:1249-1257.
5. Oriyama S, Miyakoshi Y, Kobayashi T. Effects of two 15-min naps on the subjective sleepiness, fatigue and heart rate variability of night shift nurses. Industrial Health. 2014;52:25-35.