A controlled intervention study on the effects of a very rapidly forward rotating shift system on sleep–wakefulness and well-being among young and elderly shift workers
Introduction
Shift work is related to a higher risk for sleep complaints, gastrointestinal and cardiovascular diseases (Åkerstedt, 2003, Knutsson, 2003) and the prevalence of sleep problems tend to increase with aging (Härmä et al., 1998, Härmä and Ilmarinen, 1999, Moneta et al., 1996, Rosa et al., 1996). The age-related changes in sleep arise mostly from the curtailment of day sleep after the night shifts. In a field study with an actigraph and sleep diary methods, shift workers over 40 years of age slept consistently less than younger shift workers, but morning shift sleep was similar in both age groups (Rosa et al., 1996). In spite of the general age-related deceleration of cognitive performance (e.g. Reid and Dawson, 2001), there is still no convincing evidence on ageing being related to greater sleepiness or poorer performance at work (e.g. Härmä et al., 2002).
The interaction between ageing, sleep and sleepiness in morning and night shifts fits well with the observation that ageing is connected to increased “morningness”, i.e. an advanced circadian rhythm of sleep–wakefulness and activity (Åkerstedt and Torsvall, 1981). Ageing also decreases the amplitude of many circadian rhythms, increases the instability of the human circadian system (Van Gool and Mirmiran, 1986, Van Someren, 2000) and is related to the inability to adjust to consecutive night shifts (Härmä et al., 1994).
In an intervention study among steel workers, a change from a slower backward rotating shift system (three successive shifts) to a more rapidly forward rotating system (two successive shifts) increased sleep length and sleep efficiency and was experienced positively by the older shift workers (Hakola and Härmä, 2001). Since circadian adjustment to night work is dependent on the number of consecutive night shifts (e.g. Härmä, 2000, Koller et al., 1993), it is possible that quickly forward rotating shift schedules would support a faster recovery in shift systems with also morning and evening shifts. Forward rotating shift systems also give more recovery time between the individual spells of the shifts.
Due to the general ageing of the working population, a new way to organize atypical working hours is becoming an important issue. The current study was designed to evaluate the effects of a very rapidly forward rotating shift system, including only a single morning, evening and night shift, on the sleep–wakefulness, well-being and social life of young and older shift workers.
Section snippets
Design
A controlled on-site intervention study was carried out in a line maintenance unit of a large airline company. The effects of the new shift system were studied by questionnaire and field studies among an intervention group and a control group. The measurements took place in both groups 1.5 years before (May–April in 2001) and 6 months after (May–April in 2003) the first installation of a new shift system.
Shift systems
The Line Maintenance Unit of Finnair is responsible for small and medium-sized maintenance
Perceived general effects of the current shift schedule
The change of the shift system was associated with an improved perception of the effects of the shift system on sleep, health, well-being at work, and free-time activities (Fig. 2). This change was also dependent on age as demonstrated by a significant three-way interaction between the group (intervention/control), time (before/after the intervention), and age (45−/45+). The improvement of general health was greater for the younger group (group * time * age: df 4, 406, F = 4.1, p < 0.003), while the
Discussion
The intervention showed that the change from a slower backward rotating shift system (shift changes every 3 shifts) to a quickly forward rotating shift schedule improved the perceived effects of the current shift schedule on sleep and alertness, general well-being and social and family life. Perceived alertness during and after the night shift improved, and sleep complaints decreased on all shifts. The positive changes in objective sleep and psychomotor performance were also significant but
Acknowledgements
The study was supported by an EU-grant QLRT2000-00038 of the “Respect”-program. The authors are grateful for the representatives of the employer, employees, unions and the occupational health specialists of the Finnair Line Maintenance.
References (33)
- et al.
Effects of an afternoon nap on night-time alertness and performance in long-haul drivers
Accid. Anal. Prev.
(2002) - et al.
Time-trend of sleep disorder in relation to night work. A study of sequential 1-year prevalences within the GAZEL cohort
J. Clin. Epidemiol.
(1996) - et al.
Aging and circadian rhythms
Prog. Brain Res.
(1986) Circadian and sleep disturbances in the elderly
Exp. Gerontol.
(2000)- et al.
Chronobiology of aging: temperature, sleep-wake rhythms and entrainment
Neurobiol. Aging
(1982) Shift work and disturbed sleep/wakefulness
Occup. Med.
(2003)- et al.
Subjective and objective sleepiness in the active individual
Int. J. Neurosci.
(1990) - et al.
Shiftwork. Shift-dependent well-being and individual differences
Ergonomics
(1981) - et al.
The standard shiftwork index: a battery of questionnaires for assessing shiftwork related problems
Work Stress
(1995) - Bonnefond, A., Härmä ,M., Hakola, T., Sallinen, M., Kandolin, I., Virkkala, J.I., in press. Interaction of age with...