Overtime work and its effects on sleep, sleepiness, cortisol and blood pressure in an experimental field study.
OBJECTIVE
Previous studies of long workhours and their effects on stress, sleep, and health show inconclusive results. This inconclusiveness may be partly due to methodological problems such as the use of between-group designs or comparisons before and after reorganizations. In addition, stress is usually a confounder. A within-person design was used to examine the effects of working 8- or 12-hour shifts in the absence of additional stress.


METHODS
In an experimental field study, 16 white-collar workers [9 women, mean age 45.9 (SD 15) years] undertook one workweek with normal workhours (8 hours) and 1 week of overtime with 4 extra hours of regular worktasks (12 hours). The participants wore actigraphs, rated sleepiness (Karolinska Sleepiness Scale) and stress throughout the day, and rated workload and how exhausted they felt. Saliva samples were collected on Mondays and Thursdays for cortisol analysis. On these days, ambulatory heart rate and blood pressure were also measured for 24 hours.


RESULTS
Overtime was associated with higher levels of exhaustion. Sleepiness showed a significant interaction between conditions, with higher levels at the end of the workweek featuring overtime. Total sleep time was shorter in the overtime week. There were no significant differences between ratings of stress and workload. Cortisol showed a circadian variation but no main effect of condition.


CONCLUSIONS
One week of overtime work with a moderate workload produced no main effects on physiological stress markers. Nevertheless, sleep was negatively affected, with shorter sleeps during overtime work and greater problems with fatigue and sleepiness.
Dahlgren
Anna
A
National Institute for Psychosocial Medicine, PO Box 230, S-171 77 Stockholm, Sweden. anna.dahlgren@ipm.ki.se
Kecklund
Göran
G
Akerstedt
Torbjörn
T
D000328:Adult; D000368:Aged; D000704:Analysis of Variance; D015415:Biomarkers / Q000097:blood / Q000378:metabolism; D001794:Blood Pressure / Q000502:physiology*; D005260:Female; D006339:Heart Rate / Q000502:physiology; D006801:Humans; D006854:Hydrocortisone / Q000097:blood; D008297:Male; D008875:Middle Aged; D012890:Sleep; D012894:Sleep Stages / Q000502:physiology*; D014851:Wakefulness / Q000502:physiology*; D014940:Work Schedule Tolerance / Q000502:physiology*
D015415:Biomarkers; D006854:Hydrocortisone