H567/03 Section B Option 3 - Czeisler et al. (1982) and shift-work or jetlag

Circadian principles and aim

Czeisler, Moore-Ede and Coleman (1982), Rotating shift work schedules that disrupt sleep are improved by applying circadian principles, investigated whether redesigned industrial shift schedules could improve workers' adaptation. Work schedules can require sleep and alertness at times that conflict with endogenous timing and external light–dark cues.

The authors reasoned that moving shifts later, a phase delay, would usually be easier to accommodate than moving them earlier, a phase advance. Longer intervals between changes might also allow more adjustment before the next rotation. Their historical argument used an approximately 25-hour estimate of the free-running human rhythm. Modern teaching describes human circadian timing as near 24 hours; the historical estimate should not become a universal current fact.

A phase delay shifts the required timing later around the clock, for example day to evening to night. A phase advance shifts it earlier, such as night to evening to day. These labels concern timing, not an increase or reduction in working hours. The study connects biological rhythms with the social organisation of work, rather than assuming workers can freely choose when an industrial process operates.

Workplace sample and original roster

The research took place at Great Salt Lake Minerals and Chemicals Corporation near Ogden, Utah, USA. The initial survey included 85 male rotating-shift workers, aged 19–68, with mean age 31.4, and 68 male non-rotating day or evening workers, aged 19–56, with mean age 27.3. Jobs were comparable. The initial response rate was 84%; the article reports that follow-up questionnaire analysis included rotating workers who completed both surveys, rather than treating every initial respondent as complete outcome data.

For about ten years, the rotating schedule had moved weekly from the midnight shift to evening to day: 00:00–08:00 → 16:00–00:00 → 08:00–16:00. Each step required an eight-hour phase advance around the clock. Workers could therefore be asked to adjust again before fully adapting to the previous timing.

Questionnaires assessed sleep and waking patterns, preferences and complaints, with established job-description and health indices. Company records supplied staff turnover and potash-production outcomes. These measures addressed both experience and organisational consequences. The fixed-shift workers provided useful comparisons but were not a randomly assigned no-treatment equivalent of the rotating workers.

The sample is informative for this male industrial workforce. It gives less direct evidence about women, different chronotypes, caring responsibilities or other occupations. Comparable jobs reduce one difference between groups without removing age differences or making a single plant representative of all shift work.

Intervention and follow-up

Workers and managers received an audiovisual explanation and booklet about circadian adjustment before the revised schedules. The rotating workers then changed to a phase-delay sequence: 08:00–16:00 → 16:00–00:00 → 00:00–08:00. Thirty-three rotated on a weekly delay schedule; 52 rotated once every 21 days. The study therefore compared timing changes within the workforce and two revised rotation intervals, alongside non-rotating groups.

An initial plan for the 21-day group used gradual delays of one or two hours per day over five days. This was abandoned after about a month because it conflicted with family life and shared travel. The adopted arrangement used eight-hour changes every 21 days. Distinguishing the attempted from the adopted procedure prevents attributing the final results to a permanently gradual roster.

Questionnaires were repeated after about three months. Turnover and production were followed over a longer period, including approximately nine months of company outcomes. Some improvement in production persisted into the next harvest after the study team had left.

This was a workplace field intervention with before-and-after evidence, not a fully randomised laboratory experiment. Direction, rotation interval and education formed an intervention package. The contribution of each cannot be cleanly isolated. Following the same workers helps control stable individual differences, but time, expectations and organisational changes can still affect outcomes.

Outcomes and interpretation

Before the change, workers reported sleep problems; 29% of rotating workers reported falling asleep at work at least once in the preceding three months. Most needed several days to adjust, and some reported never adjusting before the next change. These are retrospective reports, not continuous observation of sleep or a laboratory clock measurement.