Defense Technical Information Center Compilation Part Notice

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1 UNCLASSIFIED Defense Technical Information Center Compilation Part Notice ADPO10463 TITLE: Individual Differences in Reactions to Irregular Work Hours DISTRIBUTION: Approved for public release, distribution unlimited This paper is part of the following report: TITLE: Individual Differences in the Adaptability to Irregular Rest-Work Rhythms/Status of the Use of Drugs in Sleep-Wakefulness Management [les Differences entre individus concernant les facultes d' adaptation aux rythmes irreguliers activite-repos/le point sur l'utilisation des medicaments pour la gestion des periodes veille-sommeil] To order the complete compilation report, use: ADA The component part is provided here to allow users access to individually authored sections f proceedings, annals, symposia, ect. However, the component should be considered within he context of the overall compilation report and not as a stand-alone technical report. UNCLASSIFIED hfollowing comonent part numbers A 0compilation cnprie the ADP thru. ADP report-

2 K2-1 INDIVIDUAL DIFFERENCES IN REACTIONS TO IRREGULAR WORK HOURS Torbjorn AKERSTEDT IPM/Karolinska Institute Box , Stockholm, Sweden Fax: Phone: torbjorn.akerstedt@ipm.ki. Introduction successful, however, and there might be alternatives. First, lets look at a Irregular work hours cause disturbed sleep, methodological problem and then discuss reduced alertness and an increased risk of the traditional factors. errors and accidents (Akerstedt, 1998). The reasons are mainly the circadian system Most of the studies in this area have been which increases metabolism during daytime carried out with cross-sectional approaches. and reduces it during night time, thus laying Thus, it is very easy to fall prey to circular the foundation for effective performance reasoning. For example if one asks shift during daytime, but also causing poor sleep works if they have any problems displacing during that period (Akerstedt, 1995). During sleep and then asks them what their sleep is the night time the circadian nadir instead like on different shifts, it would be very promotes sleep and causes reduced alertness surprising indeed if one did not find that and performance in the night working sleep flexibility is a good "predictor" of individual. The night time effects are also sleep disturbances and other problems in strongly enhanced by the increased time shift workers. We run the same risk with awake preceding the night work period. neuroticism (it my easily be a consequence of shift work rather than the reverse). However, the effects of irregular work hours clearly differ between individuals - some will Traditional factors of doubtful value have major problems whereas others may thrive on it (Harmdi, 1993). Clearly, there is Neuroticism a practical and theoretical interest in trying to understand which individual factors may be One of the most well researched factors is of importance in this respect. The present neuroticism. A number of studies have paper will look at some of those factors. shown consistent high relations with problems in shift work (Parkes, 1994; Iskra- Before starting, however, it should be Golec et. al., 1995; Taylor et. al., 1997) On pointed out that authors have taken very the other hand, one of the few prospective different attitudes to the dependent variable, studies show no such relation (Kaliterna et. Thus, outright disease, attitude to work al., 1995). Obviously, one may suspect that hours, fatigue, sleep disturbance, accidents neuroticism may be a consequence of shift and performance failure have been used. This work, rather than the reverse (Bohle and has probably contributed to some of the Tilley, 1989). This is the prevailing opinion confusion in the area. The variables that have among researchers in this area. received most attention over the years are age, gender, experience, diurnal type, sleep Sleep flexibility flexibility, circadian amplitude, and Rigidity of sleep patterns, i.e. feeling unable neuroticism. None of them have proved very to move sleep to other times of day than the Paper presented at the RTO HFM Workshop on "Individual Differences in the Adaptability to Irregular Rest-Work Rhythms/Status of the Use of Drugs in Sleep-Wakefulness Management", held in Venice, Italy, 3-4 June 1999, and published in RTO MP-31.

3 K2-2 conventional night hours (Folkard et. al., Traditional factors of possible value 1979; Costa et. al., 1989), is another dimension that has been used to predict Age adjustment to shift work in general although little data seem available on its application to Thus, one might expect age to have a alertness patterns specifically. Wynn et al negative influences on sleepiness. This is not (1986), however found that rigidity predicted necessarily always the case, however, rather general fatigue and sleep difficulties in the reverse. Several studies suggest that older nurses changing to an alternating day/night individuals suffer less from night shift work period. However, two prospective sleepiness than young (Fri5berg et. al., 1972; studies have failed to find any predictive Bonnet and Rosa, 1987; Monk et. al., 1992). power. (Vidacek et. al., 1987; Kaliterna et. It seems, however, that several night shifts in al., 1995). The results indicate that sleep a row raises sleepiness more in older workers flexibility is not a factor in tclrance of shift (Hrmdi, 1995). work. With respect to disturbed sleep, there is Circadian amplitude usually seen an increase with. increasing age and experience (Foret et. al., 1981; Akerstedt Several studies have tested the hypothesis and Torsvall, 1981a; Parkes, 1994). In EEG that the circadian amplitude (usually of the studies we have found trends towards more body temperature rhythm) should be related superficial sleep in middle-aged shift to difficulties in shift work (Reinberg et. al., workers (Torsvall et. al., 1981). On the other 1978; Reinberg et. al., 1984). The rational hand older individuals usually have less has been that a large amplitude should be problems in relation to early morning work. more difficult to adjust to phase shifts of We have not, however, found any relation work and sleep.however, this does not between age and sleepiness, except for the appear to be the case, most of the amplitude fact that accident rates on the road seem to be differences between individuals seem to be lower at night in older individuals. effects of masking by shift work (Minors and Waterhouse, 1983; Vidacek et. al., 1987). Experience of night work Gender The two previous studies (Foret et. al., 1981; Akerstedt and Torsvall, 198 la) also indicated Studies of males and females seem to that experience was negatively related to suggest that women should have slightly general wellbeing over a number of years. more problems in shift work, particularly Koller et al (1983) found that reduced health with respect to fatigue and injuries (Novak appeared earlier in shift workers than in day et. al., 1990; Dirkx, 1991, Oginska, 1993 workers. Dahlgren (1981) found no effects of #2525). And women seem to a slightly larger three years of night work on the rhythm of need for sleep (Wever, 1979). On the other rated activation across night shifts. Neither hand, studies which control for responsibility did Wynn (1986) over a temporary 10-week for small children find no differences period of weekly alternation between night (Estryn-Behar et. al., 1978, Beermann, 1995 and day work in a group of nurses. Dumont #3401; Estryn-Behar et. al., 1990). And (1987) found that the amount of sleep/wake indeed, lab studies of night work show no and related disturbances in present-day differences between men and women workers were positively related to their (Hakola et. al., 1996). The conclusion seems previous experience of night work. to be that there is no difference in shift work Guilleminault et al (1982) found an tolerance between men and women if social overrepresentation of former shift workers responsibility is controlled for. with different clinical sleep/wake disturbances appearing at a sleep clinic.

4 Neither Folkard et al (1978) nor Knauth et al pathology such as that associated with, for (1981) observed any such "long-term" example, sleep apnea (Lavie, 1981) adjustment. Van Loon (1963) did claim that one of his three subjects increased his speed Some alternative possibilities of adjustment and Dahlgren (1981) did find that after 3 years of rotating shiftwork the As indicated above there are available very flattening occurred earlier in the week. It is few experimental or prospective studies that not clear, however, whether this was due to a may shed light on the inter-individual permanent adjustment, i.e. one that included differences in tolerance of night work. days off. The data cited, together with the However, we have conducted several studies increased subjective nightshift difficulties that may be of some interest in this context. which have been found to be associated with increasing age and experience (Foret et. al., Individual differences in tolerance in rapidly 1981; Torsvall et. al., 1981; Akerstedt and rotating shift work Torsvall, 1981a) do not speak strongly for experience as a major factor in adjustment. One approach to inter-individual differences The issue, however, can only be answered in tolerance may be to compare tolerants and definitely through a longitudinal study. non-tolerants on a number of trait and state variables. We used this approach in a 400 In relation to shift work there is some rapidly rotating shift workers at a paper mill indication that morningness is associated (Akerstedt, unpublished data). The schedule with poor adjustment to shift work involved a Night shift (2200h-0600h) - 8 (Aanonsen, 1964; Folkard et. al., 1979; hours off - an Afternoon shift (1400h-2200h) Akerstedt and Torsvall, 1981b). Breithaupt - 8 hours off - a Morning shift (0600h- (1978) and Hdirmdi (1995) failed to find such 1400h) - 56 hours off (i.e. 2 normal night a relation and prospective studies (Kalitema sleeps). Then the cycle repeated again six et. al., 1993; Vidacek et. al., 1993; Kaliterna more times, after which followed a week off. et. al., 1995) found no predictive power. Frequently it is found that morningness and From the total population was selected a age are highly correlated and that the any group of 60 subjects who scored 1 or 2 (very "effects" of diurnal type may rather be negative + negative) and 4 or 5 (positive + effects of age. An additional observation is very positive) on the scale describing their that there is a selection into shift work of attitude to their work hours. Half the subjects evening types (Knutsson and Akerstedt, in each group were women. The four 1992). We also found in an early study that resulting groups were also followed with three-shift workers who were transferred to actigraphy, sleep diaries and daily alertness day work (for organizational/economical logs during triad 1, 3 and 5. The results were reasons) change their diurnal type strongly analyzed using a two-factor ANOVA with towards morningness (Torsvall and gender and attitude as factors. Akerstedt, 1980). The results showed that among the factors Physical condition that did not differentiate between the attitude Possibly, also the physical condition of the groups or showed an interaction, were age, individual might be of importance to night BMI (significant effect for gender), marriage shift sleepiness. Thus Hirme et al (1986) had status, number of children, or diurnal type. three-shift workers improve their physical However the non-tolerants reported fitness through a training program. This significantly more sleepiness, less "sufficient greatly reduced rated overall fatigue as well sleep", less feeling well restide, a higher as increased two-hourly ratings of alertness need for sleep (8.31±.31h vs 7.15±.21 for on the night shift. Another factor that will men and 8.83±.47 vs 8.23±.31h for women) - exacerbate night work sleepiness is sleep note that women reported a significantly K2-3

5 K2-4 higher need for sleep. In addition, became "Sufficient sleep" (R2=.33, beta=testosterone levels were lower in non-.58). When this variable was removed age tolerants (9.4±.9 vs 13.5±.1 nmol/l), (low) became the significant predictor whereas prolactine and cortisol did not differ. (R=.17, beta=.41), and when age was Three more variables became highly removed, both diurnal type (evening) and significant and were the ones entering the need for sleep (high) became significant final step of the stepwise multiple regression (R=.17, beta=.42 and R2=.17, beta=-.41). analysis (in which all previous variables TST, Sleep efficiency, Sleep quality, Ease of were tested) against attitude. This were Mean rising, Number of small children, etc Sleepiness during the afternoon shift remained outside of the regression. The (R2=.37, beta=-.62), Sufficient time for results suggest, again, that sleep and family (R2=.17, beta=.57) and Sleep quality alertness are key factors, but here it also before the night shift (R2=.09, beta=.48). seems that some of role of sleep and Note that the sleepiness on the afternoon alertness is related to age, diurnal type, and shift would be high if sleep after the night need for sleep. Note that the group studied shift was unsuccessful. The results clearly were day workers who had to rise from sleep suggest that the important factor behind the around 6 a.m. This may have brought in attitude were related to sleep and sleepiness diurnal type and age. in relation to the displaced work hours, and to the social consequences. Conclusion Differences in tolerance of long shifts This limited review suggests that some traditional factors like, personality and In another study we tried to find what was circadian amplitude seem to have little to do related to tolerance of a schedule which with tolerance of shift work. Neither does required seven 12h shifts ( h) gender, at least not if social responsibility is followed by a week off (Akerstedt, controlled for. Age on the other hand seems unpublished data) Here we selected one of more interest and also diurnal type, but the extreme group (12 workers) who reported no two seem closely related. fatigue during the working week and another who reported fatigue, although rather However, the major determinants of shift moderate. Both groups were strongly in work tolerance probably have more to do favor of their schedule because of the week with states or rather ways of coping with off. The same measurements were used as in irregular work hours. Thus, the way an the previous study. individual organizes his behavior to promote sleep may be of importance, as may be the The results showed that the fatigued group need for sleep. This may be related to reported lower sleep quality and shorter sleep commitment to night work, avoiding light (5.4±.2 vs 6.0±.2h), longer time awake, after night work, etc. One should probably higher sleepiness during the working week. give priority to teaching sleep/wake During the recovery week they slept longer optimization, rather than trying to find (8.9±.3 vs 7.9.3). They were also more individuals with particular traits. One gets morning oriented and younger. the feeling that the highly tolerant single night shift worker would be older, have a When these variables were tried in a stepwise low need for sleep, have a high sleep quality, multiple regression analysis against fatigue it be in good physical shape, and plan sleep was found that the only significant predictor strategically (using naps). If several night became "Well rested" (R2=.34, beta=-.58). shifts occur in sequence, younger individuals To study the dynamics this variable was may have an advantage. removed and the new significant predictor

6 K2-5 References Aanonsen, A. eds. Shift work and health. Estryn-Behar, M. Gadbois, C. and Vaichere, Universitetsforlaget, Oslo, E. Effets du travail de nuit en equipes fixes sur une population fdminine. Bohle, P. and Tilley, A. J. The impact of Re sua une enqu letdan le s ec nigh wok onpsyholoica wel beng.rfsultats d'une enqu~te dans le secteur night work on psychological well being. hospitalier. Arch Mal Prof 1978,39:531- Ergonomics 1989,32: Bonnet, M. H. and Rosa, R. R. Sleep and Folkard, S. Monk, T. H. and Lobban, M. C. performance in young adults and older Short and long term adjustment of normals and insomniacs during acute circadian rhythms in "permanent" night sleep loss. Biol Psychol 1987,25: nurses. Ergonomics 1978,21: Breithaupt, H. Hildebrandt, G. D~ihr, D. Folkard, S. Monk, T. H. and Lobban, M. C. Josch, R. Sieber, U. and Werner, M. Towards a predictive test of adjustment to Tolerance to shift of sleep, as related to shift work. Ergonomics 1979,22: the individual's circadian phase position. Ergonomics 1978,21: Foret, J. Bensimon, B. Benoit, 0. and Vieux, N. Quality of sleep as a function of age Cost, G F. Lieore asaetti G.andand shift work. In: A. Reinberg, N. Vieux, Gaffuri, B. Circadian characteristics P. Andlauer, (Eds). Night and shift work: influencing inter-individual differences in biolal and soas t Pergm toleanc andadjstmet t shit wrk.biological and social aspects. Pergamon tolerance and adjustment to shift work. Pes xod Ergoomic 199, Press, Oxford, 1981: Ergonomics 1989,32: Dahlgren, K. Long-term adjustment of Fr6berg, Shift J. work. E. Karlsson, A study C. of G. catecholamine and Levi, L. circadian rhythms to a rotating shiftwork excretion, self-ratings and attitudes. schedule. Scand J Work Environ Health Strdia Labo r atis 1972,11: ,: Studia Laboris Salutis 1972,11: ,7: Dirkx, J. Recent research on night work for Guilleminault, ad Mls C. Czeisler,. Crain S. Coleman, ryhr. women: a review. In: W. Singleton, J. disturbances and sleep disorders in shift Dirkx, (Eds). Ergonomics, Health andditracsndlepiodrsnshf Dre P ds). ergonomies, Healthe aindti. workers. In: P.A. Buser, W.A. Cobb, T. Safety. Perspectives for the Nineties. Leuven University Press, Leuven, Okuma, (Eds). Kyoto Symposia (EEG 1991: Supl no. 36). Elsevier, Amsterdam, 1982: Dumont, M. Montpaisir, J. and Infant- Hakola, T. Hdrmd, M. and Laitinen, J. T. Rivard, C. Past experience of nightwork Circadian adjustment of men and women and present quality of life. Sleep Res to night work. Scand J Work Environ 1987,16:40. Health 1996,22: Estryn-Behar, M. Gadbois, C. Peigne, E. Hirmd, M. Individual differences in Masson, A. and Le Gall, V. Impact of tolerance to shiftwork: a review. nightshift on male and female hospital Ergonomics 1993,36: staff. 9th International Symposium on Night and Shift Work: Shiftwork; health, Hdirmdi, M. Sleepiness and shiftwork: sleep and performance, Verona, 1989, individual differences. J Sleep Res 1995, (suppl 2):57-61.

7 K2-6 Hirmni, M. I. Ilmarinen, J. Knauth, P. Monk, T. H. Buysse, D. J. Reynolds, C. F. Rutenfranz, J. and Hdnninen, 0. The Jarret, D. B. and Kupfer, D. j. Rhythm vs effect of physical fitness intervention on homeostatic influences on mood, adaptation to shiftwork. In: M. Haider, M. activation, and performance in young and Koller, R. Cervinka, (Eds). Night and old men. Journal of Gerontology shift work: longterm effects and their 1992,47: prevention. Peter Lang, Frankfurt am Novak, R. D. Smolensky, M. H. Gairchild, Main, 1986: E. J. and Reves, R. R. Shiftwork and Iskra-Golec, I. Marek, T. and Noworol, C. industrial injuries at a chemical plant in Interactive effect of individual factors on southeast Texas. Chronobiol Int nurses' health and sleep. Work and Stress 1990,7: ,9: Parkes, K. R. Sleep patterns, shiftwork, and Kaliterna, L. Vidacek, S. Prizmic, Z. and individual differences: a comparison of Radosevic-Vidacek. Is tolerance to onshore and offshore control-room shiftwork predictable from individual operators. Ergonomics 1994,37: difference measures? Work and Stress Reinberg, A. Andlauer, P. De Prins, J. 1995,9: Malbec, W. Vieux, N. and Bourdeleau, P. Kaliterna, L. Vidacek, S. Radosevic- Desynchronisation of the oral temperature Vidacek, B. and Prizmic, Z. The circadian rhythm and intolerance to shift reliability and stability of various work. Nature 1984,308: individual differences and tolerance to Reinberg, A. Vieux, N. Ghata, J. Chaumont, shift work measures. Ergonomics A. J. and Laporte, A. Circadian rhythm 1993,9: amplitude and individual ability to adjust Knauth, P. and Rutenfranz, J. Duration of to shift work. Ergonomics 1978,21:1978. sleep related to the type of shift work. In: Taylor, E. Folkard, S. and Shapiro, D. A. A. Reinberg, N. Vieux, P. Andlauer, Shiftwork advantages as predictors of (Eds). Night and Shift Work: Biological health. International Journal of and Social Aspects. Pergamon Press, Occupational and Environmental Health Oxford, 1981: 1997,3: Knutsson, A. and Akerstedt, T. The healthy- Torsvall, L. and Akerstedt, T. A diurnal type worker effect: self-selection among scale. Scand J Work Environ Health Swedish shift workers. Work and Stress 1980,6: ,6: Torsvall, L. Akerstedt, T. and Gillberg, M. Koller, M. Health risks related to shift work. Age, sleep and irregular work hours: a 1983,5t Avfield study with EEG recording, 1983,53: catecholamine excretion, and self-ratings. Lavie, P. Sleep habits and sleep disturbances Scand J Work Environ Health in industry workers in Israel: main 1981,7: findings and some characteristics of Van Loon, J. H. Diurnal body temperature workers complaining of excessive curves in shift workers. Ergonomics daytime sleepiness. Sleep 1981,4: ,6: Minors, D. S. and Waterhouse, J. M. Masking effects during night work. Chronobiologia 1983,10:142.

8 K2-7 Vidacek, S. Kalitema, L. and Radosevic- Vidacek, B. Predictive validity of individual difference measures for health problems in shiftworkers: preliminary results. In: A. Oginski, J. Pokorski, J. Rutenfranz, (Eds). Shiftwork research '87. Contemporary advances in shiftwork research. Medical Academy, Krakow, 1987: Vidacek, S. Radosevic-Vidacek, B. Kalitema, L. and Prizmic, Z. Individual differences in circadian rhythm parameters and short-term tolerance to shiftwork: a follow-up study. Ergonomics 1993,36: Wever, R. eds. The circadian system of man: Results of experiments under temporal isolation. Springer-Verlag, New York, Wynn, R. F. Ryan, G. M. and Cullen, I. H. Adjustment to shiftwork and its prediction. In: M. Haider, M. Koller, R. Cervinka, (Eds). Night and shiftwork: longterm effects an their prevention. Peter Lang, Frankfurt am Main, 1986: Akerstedt, T. Work hours, sleepiness and the underlying mechanism. J Sleep Res 1995,4 (suppl 2): Akerstedt, T. Shift work and disturbed sleep/wakefulness. Sleep Medicine Reviews 1998,2:1-2. Akerstedt, T. and Torsvall, L. Age, sleep, and adjustment to shift work. In: W. Koella, (Eds). Sleep Karger, Basel, 198 1a: Akerstedt, T. and Torsvall, L. Shiftwork. Shift-dependent wellbeing and individual differences. Ergonomics 198 lb,24:

Comparison of eight and 12 hour shifts: impacts

Comparison of eight and 12 hour shifts: impacts Occupational and Environmental Medicine 1996;53:767-772 MRC Body Rhythms and Shiftwork Centre, Department of Psychology, University of Wales Swansea P Tucker S Folkard Shiftwork Research Team, MRCIESRC