SLEEP COMPLAINTS AND POLYSOMNOGRAPHIC FINDINGS:

A STUDY OF NUCLEAR POWER PLANT SHIFT WORKERS

Samantha L. Paim,1 Maria Laura N. Pires,2 Lia Rita A. Bittencourt,1

Rogerio S. Silva,1 Ruth F. Santos,1 Andrea M. Esteves,1 Amaury T. Barreto,1

Sergio Tufik,1 and Marco Tulio de Mello1

1Department of Psychobiology, Universidade Federal de Sao Paulo (UNIFESP),Sao Paulo, Brazil2UNESP—Sao Paulo State University, Assis, Sao Paulo, Brazil

The literature widely recognizes that shift workers have more health complaints thanthe general population. The objective of this study was to describe the prevalence ofsleep complaints and verify the polysomnographic (PSG) variables of shift workersin two Brazilian nuclear power plants. We carried out a subjective evaluation with asleep questionnaire. Based on these results, the interviewees that reported sleep-related complaints were referred for polysomnographic evaluation. Of the 327volunteers initially evaluated by the sleep questionnaire, 113 (35%) reported sleepcomplaints; they were significantly older, had higher body mass index (BMI), andworked more years on shifts than those without sleep complaints. Of these 113, 90met criteria for various sleep disorders: 30 (9%) showed obstructive sleep apnea(OSA), 18 (5.5%) showed limb movement, and 42 (13%) evidenced both sleep pro-blems and had a significantly higher proportion of sleep stage 1 and arousals com-pared with the 23 shift workers that had no indices of sleep problems. The presentstudy found that 90 (27.5%) of the evaluated participants met the PSG criteria ofsome type of clinical sleep disorder. This high proportion should be investigated forassociations with other aspects of work, such as working hours, working schedule,years performing shift work, and access to health services. Due to the strong associationbetween sleep disorders and the incidence of fatigue and sleepiness, the evaluation ofthe sleep patterns and complaints of shift workers is essential and should be consideredto be one of the basic strategies of industry to prevent accidents. (Author correspon-dence: tmello@psicobio.epm.br)

Keywords Sleep complaints, Sleep disorders, Shift work, Polysomnography, Nuclearpower plant

Address correspondence to Marco Tulio de Mello, Department of Psychobiology, UniversidadeFederal de Sao Paulo—UNIFESP, Rua: Marselhesa, 535, Vila Clementino, Sao Paulo, SP 04020-060,Brazil. Tel.: 55(11) 5572 0177; Fax: 55(11) 2149 0155; E-mail: tmello@psicobio.epm.br

Chronobiology International, 25(2&3): 321–331, (2008)Copyright # Informa HealthcareISSN 0742-0528 print/1525-6073 onlineDOI: 10.1080/07420520802107197

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INTRODUCTION

Epidemiological studies have demonstrated that chronic sleep depri-vation and the presence of sleep disorders, especially obstructive sleepapnea syndrome (OSAS) and insomnia, are estimated to occur in 2–4%of the population (Liu et al., 2000; Young et al., 1993). Furthermore,the consequences of the sleep disorders can be mental and physicalfatigue, lapses of attention, loss of concentration, compromised quality oflife, and accidents at work or while driving (Costa, 1996; Pandi-Perumalet al., 2006). In this regard, a number of investigators have demonstratedthat shift workers have excessive health complaints (Akerstedt, 2003, 2007;Costa et al., 2006; Fisher et al. 2006; Raediker et al., 2006). The mostcommon complaint is loss of subjective sleep quality. Others havesuggested that sleep problems are the most important reason of quittingshift work (Folkard & Tucker, 2003).

Some industrial processes require special characteristics in the wayworkers must execute their job, such as those in nuclear power plants.To prevent accidents, the maintenance of the security of the oper-ational system depends on precision and attention in performingwork-related tasks (Bobko et al., 1998; Folkard et al., 2005; Gillberget al., 2003). Smith and Folkard (1993) conducted an exploratorysurvey study to examine the impact of shift work on several generalaspects of the health of nuclear power plant workers, such as alertness,fatigue, sleep, and social issues, and concluded that the night shift isthe most problematic in terms of decreases in all these variables.Looking for differences between shifts, Smith et al. (1995) carriedout a study using hand-held computers to record alertness levels,cognitive task performance, and workload ratings. The authors foundsignificantly lower levels of alertness and poorer performance innight-shift workers.

Recently, Takahashi et al. (2005) demonstrated that shift workers withgood adaptation to work on shifts are those who had fewer health pro-blems and who took frequent and long naps. Complementing this work,Smith et al. (2005) used subjective measures to evaluate the health of609 shift workers in a nuclear power plant in Japan. The results demon-strated that the way the worker perceived his mental and physicalfatigue, levels of stress, and general health influenced his tolerance ofshift work.

As far as we are aware, no studies have yet used both subjective (ques-tionnaire) and objective (polysomnography [PSG]) to investigate sleepcomplaints and disorders in shift workers at nuclear power plants. Accord-ingly, the objective of the present study is to describe the prevalence ofsleep complaints and verify sleep problems in shift workers at two Braziliannuclear power plants.

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METHODS

Sample and Experimental Design

This study was approved by the Ethics Research Committee of theFederal University of Sao Paulo (UNIFESP, process number 1556/03),Brazil, and was conducted according to the ethical guidelines rec-ommended by the journal (Touitou et al., 2006). All participants gavewritten informed consent for their participation in the research protocol,which was conducted in two consenting Brazilian nuclear power plants.Recruitment of the volunteers was conducted after the presentation oflectures designed to explain the protocol and the importance of sleephygiene, sleep disorders, and work schedule. After the lectures, theworkers were interviewed individually during the first 2 h of themorning or afternoon shift. Approximately 340 workers were on rotatingshifts at the two power plants, and a total of 327 (96%) agreed to participatein the study. Only those workers who experienced sleep complaintsaccording to the criteria of the UNIFESP Sleep Questionnaire (Pireset al., 2007) were referred for PSG evaluation. This involved 113 of theworkforce. To perform the PSG recordings, a sleep laboratory wasspecially built in rooms of a hotel located near the power plant, followingthe standard criteria the American Academy of Sleep Medicine (2005).

Shift System

One shift system was worked at both plants. Each shift lasted 8 h, andthe number of successive shifts was the same for all job types: six days onthe evening shift (15:00–23:00 h), four days off; six days on the morningshift (07:00–15:00 h), four days off; and six days on the night shift(23:00–07:00 h), six days off.

Questionnaire

The UNIFESP Sleep Questionnaire (Pires et al., 2007) was used, as itwas previously validated by the Brazilian Sleep Institute. In its fullversion, it comprises a number of standard measures typically used inshift work and sleep research.

In this study, the data analyzed consisted of: descriptive data of thesample; questions about socio-demographic characteristics, such as age,marital status, schooling, and salary; and characteristics and complaintsrelated to sleep habits, such as time of going to bed and getting up, thenature of the sleep problems, and the frequency of their occurrence.The interviewees were asked about the frequency with which they experi-enced these sleep problems and the answers were rated on a seven-point

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scale: 1) never; 2) less than once a month; 3) once a month; 4) two to threetimes a month; 5) one to two times a week; 6) three to six times a week;7) daily.

Insomnia was assessed through complaints of difficulty initiating andmaintaining sleep, or awakening earlier than desired and not being ableto resume sleep. Excessive daytime somnolence was assessed through com-plaints of diurnal sleepiness with impairment of daytime activities andbouts of extreme sleepiness. Snoring and sleep apnea were assessedthrough complaints of gasping or choking, and limb movements (LM)were assessed by episodes of repetitive, highly stereotyped, limb move-ments occurring during sleep. Insomnia, excessive daytime sleepiness,snoring, and apnea were considered as sleep complaints when they weredescribed daily or more than three times per week. LM was considereda complaint when described at least one or two times per week. The inter-viewees were also asked if they had already sought the help of a physicianfor their sleep problems, and if they had used medication to help sleep(with no distinction being made between prescribed, over-the-counter,or herbal medicines).

Polysomnographic Records

Overnight PSG was performed and visually scored by a trained sleeptechnician according to the method of Rechtschaffen and Kales (1968)using an EMBLA digital system (EMBLA A10, Embla Systems Inc.Broomfield, Colorado, USA) The following variables were monitored:electroencephalogram (C3–A2, C4–A1, O1–A2, O2–A1), electrooculo-gram (LOC–A2, ROC–A1), electromyogram (submental and anteriortibialis muscles) using surface electrodes, and electrocardiogram.Snoring and body position were detected with EMBLA sensors. Airflowwas detected by a thermocouple and by a pressure-flow transducer.Chest and abdominal XactTrace sensors monitored respiratory effort.Arterial oxygen saturation (SaO2) and pulse were recorded by a pulse oxi-meter (EMBLA). The following parameters were analyzed from the PSGresults: total sleep time (TST, min); sleep latency (min); sleep efficiency(%); wake after sleep onset (WASO, min); stages 1 (S1%), 2 (S2%), 3(S3%þ S4%), and REM sleep (REM%) as the percentage of TST andlatency to REM (min). Arousal, abnormal respiratory events, and periodiclimb movements (PLM) were scored according to standard criteria (Amer-ican Academy of Sleep Medicine Task Force [AASMTF], 1999; AmericanSleep Disorders Association Atlas Task Force, 1992, 1993). The cutoff pointfor obstructive sleep apnea (OSA) was defined as an Apnea HypoapneaIndex (AHI) of 5/h; a AHI of between 5 and 15/h was considered mildOSA, between 16 and 29 moderate OSA, and .30 events severe OSA(AASMTF, 1999). The cutoff point for abnormal LM was 5; a LM between

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6 and 25 was considered mild LM, between 26 and 49 was considered mod-erate, andaLMabove50was consideredsevereLM(AASMTF,1999).All vol-unteers that met the PSG criteria for some type of sleep disturbance werereferred to a sleep specialist for treatment.

Statistical Analysis

Based on the questionnaire results, the workers were divided intothose with and without sleep complaints. The descriptive data areexpressed as the number of workers per group and percentage of thetotal sample. The PSG results were also used to divide the total sampleinto two groups, those with and without sleep problems. Statistical com-parisons between the groups were achieved by Student’s t or chi-squared tests, with differences of 5% being considered statisticallysignificant.

RESULTS

Questionnaire

A total of 327 shift workers answered the UNIFESP sleep question-naire (Pires et al., 2007). Of these, 214 (65%) were classified as withoutsleep complaints, and 113 (35%) were classified with sleep complaints.Table 1 reports their socio-demographic characteristics. There were stat-istically significant differences between the two groups (with/withoutsleep complaints) in terms of age, BMI, and years working shifts.

Of the 113 (35%) that met the questionnaire criteria for sleep com-plaints, 29 (8.8%) workers reported difficulty initiating sleep, 56 (17.1%)reported difficulty maintaining sleep, and 27 (8.2%) reported earlymorning awakenings. Thirteen (3.9%) shift workers reported excessivedaytime sleepiness, and 11 (3.3%) reported bouts of extreme sleepiness.Seventy-seven (23.5%) reported snoring, and 82 (25.0%) reportedgasping or chocking. Limb movements were reported by 17 participants(5.1%). Table 2 summarizes the subjective sleep patterns of the shiftworkers. There were no statistically significant differences between thetwo groups.

Polysomnography

A total of 113 shift workers were referred for PSG: 23 showed normalsleep parameters, and 90 met the criteria for OSA, LM, or both. This lattergroup of 90 subjects showed a significantly higher proportion of sleepstage 1, arousals, and both indices of OSA and LM, and then could bedivided into 30 (9%) individuals with OSA, 18 (5.5%) with LM, and 42

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(13%) with both OSA and LM. Table 3 shows the sleep parameters of the113 subjects who underwent PSG, based on their replies to the sleep ques-tionnaire. Using the indices of sleep disorder severity, 41 shift workers metthe criteria for mild, 20moderate, and 11 severe OSA; 51 shift workers metthe criteria for mild, 6 for moderate, and 3 severe LM.

DISCUSSION

The objective of this study was to examine sleep complaints amongshift workers employed in two Brazilian nuclear power plants using asleep questionnaire followed by PSG evaluation. The data obtained fromthe questionnaire showed that 113 (35%) of the 327 shift workers fulfilledthe criteria for insomnia, excessive sleepiness, snoring, sleep apnea, andlimb movement. Overall, we expected to find that shift workers wouldreport more sleep complaints than the general population. However,

TABLE 1 Socio-demographic Characteristics

Totaln ¼ 327

Without sleepcomplaintsn ¼ 214

With sleepcomplaintsn ¼ 113 p

Age (yrs), mean+ SD 38.2+ 8.8 37.4+ 8.5 40.0+ 9.2 0.02BMI (kg/m2),

mean+ SD26.3+ 4.0 26.0+ 3.4 27.2+ 5.0 ,0.01

Yrs of shift work,mean+SD

12.0+ 9.9 11.0+ 9.1 14.0+ 11.0 0.02

Marital status N (%) N (%) N (%) nsMarried 241 (74.0) 156 (73.0) 85 (75.2)Single 69 (21.0) 47 (22.0) 22 (19.4)Divorced 17 (5.2) 11 (5.1) 06 (5.3)

Financial dependents nsYes 274 (83.8) 178 (83.1) 96 (85.0)No 53 (16.2) 36 (17.0) 17 (15.0)

Schooling nsIncomplete highschool

40 (12.2) 20 (11.0) 20 (18.0)

Completed highschool

137 (42.0) 87 (40.0) 50 (44.2)

University educationnot completed

95 (29.0) 68 (31.0) 27 (23.8)

University educationcompleted

41 (13.0) 29 (13.0) 12 (10.6)

Post-graduate study 14 (4.3) 10 (5.1) 4 (3.5)Salary� ns

2–3 Salaries 1 (0.3) 0 (0) 1(0.8)3–5 Salaries 40 (12.2) 27 (12.6) 13 (11.5)5–10 Salaries 162 (49.5) 105 (49.3) 57 (50.4)10–20 Salaries 92 (28.1) 61 (28.6) 31 (27.4)�20 Salaries 31 (9.4) 20 (9.3) 11 (9.7)

�Salary is defined inmultiples of theminimumsalary used as a reference for the general public studied.

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when we compared our findings with those for the general population ofSao Paulo, Brazil, obtained by Pires et al. (2007), our hypothesis was not con-firmed. For example, in this study of nuclear power plant employees, 8.8%of the shift workers reported difficulty initiating sleep vs. 13.1% of thegeneral population; 17.1% vs. 24.6% reported difficulty maintaining sleep,and 8.2% vs. 11.3% reported early awakenings. For excessive daytime slee-piness, the percentages were similar: 3.9% of the shift workers and 3.3% ofthe general population. The percentages were also similar for the OSAsymptom of snoring: 23.5% of the shift workers and 26.3% of the generalpopulation. Although these results seems to differ from those reported inthe medical literature (Akerstedt, 2003; De Mello et al., 2000; Menezeset al., 2004), this cannot be attributed to the methods of the respectivestudies. Perhaps other aspects of shift work, or even the specificity of thestudy sample of nuclear power plant workers, play a role.

One possibility is the socio-economic characteristics of this sample,such as the number of workers that have a higher degree of schooling(e.g., 150 [46%] had at least some university education) and higherincome (e.g., 285 [86%] earned more than five-fold the averagemonthly salary) compared to the general population studied by Pireset al. (2007), of which 37% had low salary income. Other studies havereported a positive correlation between social problems and sleep

TABLE 2 Subjective Sleep Patterns

Total n ¼ 327

Without sleepcomplaintsn ¼ 214

With sleepcomplaintsn ¼ 113 p

Sleep time (h) 7.3+ 1.3 7.4+ 1.3 7.2+ 1.2 nsSleep enough? ns

Yes 208 (66.4) 138 (67.3) 70 (64.8)No 105 (33.6) 67 (32.7) 38 (35.2)

Have 11 h of restbetween shifts?

ns

Yes 232 (74.1) 158 (77.0) 74 (68.5)No 81 (25.9) 47 (23.0) 34 (31.5)

Take naps? nsYes 168 (54.0) 94 (46.7) 50 (45.0)No 144 (46.0) 107 (53.3) 61 (55.0)

Doze off at the wheel? nsYes 134 (41.0) 87 (40.6) 47 (41.6)No 193 (59.0) 127 (59.4) 66 (58.4)

Medication used forsleep?

ns

Yes 40 (12.8) 23 (11.2) 17 (15.6)No 274 (87.2) 182 (88.8) 92 (93.4)

Physician consulted? nsYes 47 (14.8) 26 (12.6) 21 (19.0)No 269 (85.2) 180 (87.4) 89 (81.0)

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complaints. Hyppa et al. (1997) demonstrated people who were continu-ously unemployed during a period of economic recession in Finland suf-fered more with insomnia and used more hypnotic drugs than thosecontinuously employed. Indeed, Travassos et al. (2002) showed thatfamilies with a higher income are more likely to use health services. Fur-thermore, in our study, 15% of shift workers had consulted a physicianfor a sleep problem, which is higher than the 6% found in the generalpopulation (Pires et al., 2007) and 12% of the shift workers reportedusing sleeping pills. It is also higher than the findings of previousstudies on professional bus drivers, such as the 4% reported byHoward et al. (2004) and 7.5% reported by De Mello et al. (2000).

Based on the sleep questionnaire, we found that shift workers whoreported sleep complaints were older, which is consistent with the find-ings of many other studies (Buysse et al., 2005; Dijik et al., 1999; Younget al., 1993); with aging, the sleep architecture changes, especiallyshowing more fragmented and superficial sleep. Another importantresult is that shift workers with sleep complaint assessed by the question-naire had high BMI. Recent studies (Drake et al., 2004; Moreno et al.,2004, 2006; Taheri, 2006; Van Dongen et al., 2003) suggest that subjectswho must assume a different sleep-wake cycle from that programmed bytheir circadian rhythm are more likely to consume fast foods, therebyincreasing their BMI, which is related with hypertension, cardiovascularrisk, and sleep problems (Stoohs et al., 1994; Viegas & Oliveira, 2006).

The PSG tests and findings enabled us to better characterize the sleepparameters of those 113 shift workers who reported sleep complaints bytheir answers to the sleep questionnaire. Ninety (27.5%) of these 113persons met the criteria for a higher proportion of sleep stage 1, increasedindices of arousal, OSA, and LM. Interestingly, 23 shift workers who

TABLE 3 PSG Sleep Parameters in the Two Groups with and without Sleep Disorders

Without sleep disordern ¼ 23

With sleep Disordern ¼ 90 p

WASO (min) 36.9 +29.5 52.0+ 38.9 nsTotal sleep time (min) 393.6 +50.1 381.6+ 57.8 nsSleep latency (min) 10.2+ 9.5 10.4+ 12.3 nsSleep eficiency (%) 89.1+ 7.4 86.1+ 9.2 nsREM latency (min) 84.7 +32.1 87.9+ 33.4 ns% S–1 3.3 +1.5 4.9+ 3.4 0.03% S–2 52.9 +10.0 54.16+ 8.1 ns% S–3 (S3þ S4) 20.7+ 7.5 19.7+ 6.6 ns% REM 22.9+ 6.3 21.3+ 5.3 nsArousal index (h) 9.6+ 5.5 16.7+ 9.4 ,0.01IAH 2.3+ 1.3 16.0+ 15.9 ,0.01LM 2.2 +1.3 11.8+ 14.7 ,0.01

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complained of a potential sleep problem through their responses to thesleep questionnaire showed normal sleep parameters. These results arehigher than those reported by Young et al. (1993) for the general popu-lation (24%), but lower than those reported by Santos et al. (2004).Santos compared the day and night-time sleep parameters of a small(n ¼ 32) but complete sample of professional bus drivers and concludedthat 38% met the criteria for both OSA and LM by a night-time PSGstudy. Our findings can be attributed to the limited (i.e., 75%) sensibilityof the questionnaire when it was first developed by Braz et al. (1987),and/or perhaps (as suggested by Takahashi et al., 2005) the difficulty ofshift workers to adequately perceive the quality of their sleep, as theymust continuously alter their sleep-wake schedule with each change inthe work shift.

The PSG results show that most of the workers who were diagnosedwith a sleep disorder met the criteria for mild sleep disorder, either dueto OSA and/or LM. Based on these results, we suggest that besides regu-larly checking the health status of shift workers, it is important to encou-rage healthy habits, such as physical exercise, healthy eating, and sleephygiene, to attenuate the consequences of working night-time shifts. Inaccord with the sleep task force (World Association of Sleep Medicine,2006), the association among OSA and LM can be explained as a conse-quence of respiratory events; this suggests that the OSA must be treatedfirst before the LM can be recognized and treated.

The absence of a control group (of day workers) to compare the find-ings on shift workers is a limitation of the current study. Furthermore, thefull evaluation of sleep disorders requires a more exhaustive clinical evalu-ation that cannot be achieved by a single overnight PSG study alone. Eventhough the cross-sectional study design cannot determine a causal relation-ship between some reported aspects found in the questionnaire and thePSG, due to the strong association between sleep disorders and the inci-dence of fatigue and sleepiness, the evaluation of the sleep patterns andcomplaints of shift workers is essential and should be considered one ofthe basic strategies of industry to prevent accidents.

ACKNOWLEDGMENTS

This work was supported by the Associacao Fundo de Incentivo aPsicofarmacologia (AFIP); CEPID/SONO (grant 98/14303-3), Fundacaode Amparo a Pesquisa do Estado de Sao Paulo-FAPESP (grant: 05/57525-1), and Multidisciplinary Center of Research in Somnolence andAccidents (CEMSA). The authors thank Dr. Jim Waterhouse for his excel-lent suggestions.

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