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Health effects of shift work and extended hours of work
  1. J M Harrington
  1. Professor J M Harrington Institute of Occupational Health, University of Birmingham, Birmingham B15 2TT, UKj.m.harrington{at}

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“Normal” hours of work are generally taken to mean a working day with hours left for recreation and rest. Rest is a night time activity, work a daytime activity. This review is concerned with those who work other schedules either on shifts or with extended hours which transcend the day-night work-sleep pattern.

Such abnormal” working hours are not a modern phenomenon. Ramazzini (1633–1714) noted that bakers, innkeepers, and soldiers worked such hours. The advent of the industrial revolution led to many people working long hours until legislation was introduced to curtail the worst vicissitudes of the new factory based economy.


Today, about one in five workers in Europe are employed on shift work involving night work and over one in 20 work extended hours . Shift systems involve periods of 6–12 hours work at a time with the shift crews alternating on two, three, or four shifts in any 24 hour period. The traditional three shifts start at 0600, 1400, and 2200 hours but there are many variations on this. Some workers only work on the two day shifts, some only nights, while others rotate through all three shifts with variable degrees of speed of rotation and direction of rotation. Extended hours of work is generally accepted to mean working more than 48 hours a week. This can occur on either day work or shift work due to either a high number of hours worked per day or a higher number of days worked per week.

Box 1: Summary of EC Working Time Directive

  • No more than 48 hours a week averaged over a 17 week period

  • A minimum daily rest period of 11 consecutive hours

  • A minimum weekly rest period of 24 or 48 consecutive hours averaged over 14 days

  • A minimum of 20 minutes rest in any work …

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