Shift-working has been implicated in reduced quality of life, and with increased morbidity and mortality rates in shift-workers. These are exacerbated by the longer time spent working shifts, the rapidity with which those shifts rotate, and the more antisocial the hours worked (e.g. night-shifts). Increased stress hormones (especially cortisol) are implicated in this increased morbidity and mortality and are most certainly driven by inadequate amounts of sleep and continually adjusting and readjusting the circadian rhythm.
A consistent routine is an essential part of a healthy sleep (and wake) pattern. With a consistent routine, the circadian rhythms of sleep / wakefulness (alertness) and body temperature become synchronised, or entrained to each other. Concurrent dips in body temperature and alertness culminate in a strong signal for the induction of sleep (in the late evening), and concurrent rises in body temperature and alertness culminate in a strong signal to wake (in the morning). Rotating shift patterns disrupt the synchrony between these two rhythms, making sleep less easy to induce and to maintain. Thus, people living with frequently rotating shift patterns are continually disrupting the synchrony of their circadian rhythms and their sleep often suffers as a result.
The consequences of this are manifold. Long-term there are clearly established negative health consequences (Costa, 1996), but in the short- and medium-terms there are feelings of fatigue, and so impaired performance, which leads to mental health problems (Lac & Chamoux, 2004), decreased productivity and an increased rate of work-related accidents (Rajaratnam & Arendt, 2001).
