SHIFT WORK DISORDER - myCME.com

Gender. Shift work may affect men and women differently.In a study of crane operators, women workingnight shifts or afternoon shifts slept approximately 30minutes less than their male counterparts, 20 althoughthis is unlikely to translate into an increased propensityto develop SWD in women. However, less sleep infemale shift workers may reflect differences in the familialand/or social obligations of the male and femalemembers of this worker population. The tendency forfemale shift workers to sleep less also emphasizes thatextrinsic factors, such as childcare requirements, mayhave an impact on sleep during a shift-work scheduleeven in the absence of any innate circadian issues. 20 Amore recent study found few gender-related differencesin sleepiness and performance in workers on rapidlyrotating shifts. 14 More detailed epidemiologic data areneeded before any firm conclusions can be drawn onthe influence of gender in SWD; currently it does notappear that gender is a risk factor for SWD.Circadian preference. It has been suggested that adultscan be divided into “morning” or “evening” types 21 andthe Morningness–Eveningness Questionnaire (MEQ)can be used to assess into which category an individualfalls. 21 Morning-type individuals, or “larks,” are most alertearly in the day and are thought to be more susceptibleto SWD, as they obtain less sleep (on average 86.8 minutesfewer) after a night shift than evening-type workers,or “night owls.” 22 However, use of the MEQ is unprovenin the evaluation of SWD. 23 Currently, there are no studiesregarding whether there is a genetic component toSWD susceptibility 19 ; however, a number of reports haveindicated that a preference for “morningness” or “eveningness”is genetically determined (see “The characterizationand pathology of circadian rhythm sleep disorders”on page S12 of this supplement). In addition, aninherent vulnerability to insomnia or sensitivity to sleeploss may also lead to an innate susceptibility to SWD.Lifestyle factors. A number of lifestyle factors andchoices can cause ES and insomnia in shift workers.These include the presence of other people in the homewho may disrupt the attempted rest period; social obligationsduring the normal waking day that require thepatient to be awake when he or she should be resting;patients attempting to sleep at “normal” times duringdays off and the weekend, thus lowering the chances ofadapting to the shift-work pattern during the week; anddeliberately staying awake or being unable to sleep duringtransitions between shift patterns, leading to sleepdeprivation. These factors should be discussed with thepatient at presentation, with a view to improving sleephygiene. Such factors may trigger SWD in patients whoare predisposed to developing this sleep/wake disorder;addressing poor sleep habits in patients who do nothave SWD may help resolve their sleep problems.Shift work can prevent individuals from enjoying ahealthy lifestyle, with lower levels of physical exerciseand higher levels of smoking seen in shift workers comparedwith non–shift workers. 15,24 Poor diet and lack ofexercise as a result of social constraints or coping mechanismsassociated with shift work may lead to metabolicimbalance, which can exacerbate symptoms of ES andinsomnia. 24Habits adopted to cope with shift work may actuallyexacerbate the problems associated with night- or rotating-workschedules. For example, consumption of caffeinateddrinks to enhance wakefulness or napping atinappropriate times may worsen insomnia when tryingto rest. 25 Consumption of alcohol to induce sleep mayincrease ES during the next shift. 25 Alcohol also interactswith certain shift characteristics to increase the risk ofdeveloping SWD and was found to be particularly detrimentalto workers on a 3-shift rotation, with 51% vs 42%of regular alcohol consumers and nondrinkers experiencinginsomnia, respectively. Although alcohol didexacerbate insomnia in the other shift workers studied,the effect was not as pronounced, with 48% of workerson a 2-shift rotation who consumed alcohol experiencinginsomnia compared with 46% of their nondrinkingcounterparts. 24Differential diagnosis of SWDin the primary care settingThe American Academy of Sleep Medicine notes that theboundary between a “normal” response and a pathologicresponse to shift work is not clearly defined and thatthe validity and reproducibility of diagnostic criterianeed testing. 19 To add to the challenges inherent in definingSWD, ES, insomnia, and a number of their sequelae(see “Symptoms of SWD” on page S18 of this article)are also indicative of a variety of disorders other thanSWD. For example, ES and/or insomnia are also symptomsof other sleep/wake disorders, sleep deprivation,pre-existing medical conditions (including mood disordersand central nervous system issues such as narcolepsyand brain injury), the use of sedative or stimulantmedications, and substance abuse. The discussion of apatient’s full medical history should assist in ruling outother potential causes for his or her symptoms, but it isalso vital to generate a differential diagnosis to excludeSupplement to The Journal of Family Practice • Vol 59, No 1 / January 2010 S21