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

https://doi.org/10.1016/j.ijpsycho.2005.08.005Get rights and content

Abstract

Shift work is related to problems in sleep/wakefulness and social life. The effects of a very rapidly forward rotating shift system on sleep, health and well-being of young (− 45) and elderly (45+) maintenance workers were studied by a controlled intervention study. In the beginning, all the workers had a continuous backward rotating three-shift system. A very quickly forward rotating shift system was developed, avoiding consecutive night shifts and with more free-time between the individual shifts. The effect of the new shift system on sleep/wakefulness and general well-being was studied by questionnaire and field studies including on-site registration of sleep (actigraphy), subjective sleepiness (KSS) and psychomotor performance (PVT). Based on a linear mixed model for repeated measurements, the new shift system increased the main sleep length after the night shift and improved alertness and PVT performance during the night shift among the older workers. Alertness also improved during free-time after the night shift and sleep complaints decreased after all shifts. The workers on the new shift schedule perceived the effects of the new shift system on sleep, alertness, general health, well-being at work, social and family life more positively than the workers in the old shift system. At the end of the study, all subjects voted for the new shift system. It is concluded that although the new shift system increased the operating hours at night, the very rapidly forward rotating shift system had positive effects on the sleep, alertness and well-being of especially the older 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)

  • H. Brown et al.

    Applied Mixed Models in Medicine

    (1999)
  • S. Campbell

    Effects of timed bright-light exposure on shift-work adaptation in middle-aged subjects

    Sleep

    (1995)
  • J. Carrier et al.

    Sleep and morningness–eveningness in the ‘middle’ years of life (20–59 y)

    J. Sleep Res.

    (1997)
  • R.J. Cole et al.

    Automatic sleep/wake identification from wrist activity

    Sleep

    (1992)
  • G. Costa et al.

    Circadian characteristics influencing interindividual differences in tolerance and adjustment to shiftwork

    Ergonomics

    (1989)
  • D.J. Dijk et al.

    Contribution of circadian physiology and sleep homeostasis to age-related changes in human sleep

    Chronobiol. Int.

    (2000)
  • Cited by (0)

    View full text