SHIFT WORK DISORDER - myCME.com

Shift-work disorderThe timing of shifts and changes to the shift schedulehave been shown to significantly affect sleep, withindividuals on rotating shifts experiencing the greatestdetriments to their sleep quality. 8 In one study, workerson rotating shifts experienced significantly more difficultysleeping than those on a stable shift schedule:20.4% of rotating-shift workers reported a sleep latency>30 minutes vs 11.5% of fixed- or night-shift workers(P < .001). 8 Furthermore, while rotating-shift workersexperienced a similar frequency of disrupted nights’sleep to that of other shift workers, they also reporteda significantly higher number of night-time awakeningsduring each disrupted night’s sleep (P < .05). In addition,approximately one-third of rotating-shift workersreported experiencing ES compared with 19% of nightorother shift workers and 12% of daytime workers(P < .001). Therefore, it is probably not surprising thatrotating-shift workers were absent from work significantlymore often than individuals on fixed day-shiftschedules (62.8% vs 38.5%, respectively; P < .001) andhad a significantly higher annual frequency of workrelatedaccidents (19.5%) than those on fixed daytime(8.8%) or night-time shifts (9.6%) (P < .001). 8Advancing the rest period is reportedly more difficultthan delaying sleep and is thought to be responsiblefor making counterclockwise shift rotation a risk factorfor maladaptation to shift-work conditions. 9 Forwardrotatingshift patterns have long been considered morebeneficial to workers than backward-rotating patterns. 9A rapidly forward-rotating shift system has been shownto have positive effects on sleep, to reduce ES, and toimprove overall perceptions of general well-being comparedwith a slower backward-rotating shift pattern. 10However, this study did not elucidate whether the newshift pattern reduced the negative effects of shift work tothe level of those experienced by day workers. 10 The forward-rotatingsystem was found to be particularly helpfulto older workers, who experienced larger improvementsin ES compared with younger workers. 10Shift timing in relation to “zeitgebers”Bright light is the strongest “zeitgeber”—a cue responsiblefor the entrainment (synchronization) of the circadianclock. The body’s natural circadian rhythms,and therefore the likelihood of developing ES and/orinsomnia, will persist as long as shift workers continueto expose themselves to light at times that areinappropriate for re-entrainment (for example, exposureto light in the morning in night-shift workers). 11,12One study found that workers who ensured that theyslept in a darkened bedroom, wore dark glasses whencommuting home, and avoided bright light on theirdays off were least affected by a night-shift schedule. 13There is some evidence that shift workers respond torelative changes in light intensity over a 24-hour periodrather than absolute light intensity, and bright light onthe commute home in the morning from a night shift isenough to prevent re-entrainment of the circadian clocktoward night working. 13 Interestingly, any degree of reentrainmentto the new rhythm is sufficient to confersignificant benefits. Patients who either completely orpartially re-entrained their circadian phase with respectto their night shift through the use of a fixed dark daytimesleep episode, sunglasses, melatonin, and brightlight at night experienced substantial benefits in ES, performance,and mood (see “Managing the patient withshift-work disorder” on page S24 of this supplement).Job satisfactionPoor job satisfaction is associated with higher levels ofES in shift workers 14,15 and may therefore predispose anindividual to SWD. Workers on rapidly rotating shiftswho had poor job satisfaction did not have shorter sleeptimes but were sleepier at work compared with theirsatisfied colleagues (P < .001) and had poorer quality ofsleep. 14 In a 3-year study, workers on a backward-rotatingshift schedule who had poor job satisfaction had ahigher likelihood of experiencing ES than individualswho were satisfied with their work (P = .026). 15 In addition,ES significantly increased in dissatisfied workers(P < .05) over the duration of the study compared withworkers who were content with their jobs. 15Individual physiological and lifestyle factorsAge. There is some disagreement in the literature as tothe degree to which age affects adjustment to shift-workconditions, but the weight of current evidence suggeststhat advancing age is a risk factor for developing an intoleranceto shift work. 2,3,16-19 Older individuals (ages53–59 years) appear to adapt better initially to acutesleep deprivation than younger individuals (ages 19–29years); however, older individuals show a reduced capacityfor circadian adaptation when exposed to a seriesof night shifts. 17 Thus, although younger individuals areinitially sleepier in response to a new shift pattern, theyare capable of rapidly adapting to these changes. After3 consecutive night shifts, younger workers were lesssleepy than older workers 17 ; therefore, older workers aremore likely to experience impairment while workingnight shifts even if they do not meet all of the ICSD-2criteria for a diagnosis of SWD.S20 January 2010 / Vol 59, No 1 • Supplement to The Journal of Family Practice