Shift work, sleep, and sleepiness - differences between shift schedules and systems.

In this narrative review, we examined what level of research evidence is available that shift workers' sleep-wake disturbances can be minimized through ergonomic shift scheduling. We classified the pertinent studies conducted on real shift workers in field conditions by the type of shift system and study design (ie, whether the shift systems were modified or not - "treatment" versus "no treatment"). The results of the observational studies in which no changes to the shift system were made (ie, no treatment) showed that, irrespective of the shift system, night and early-morning shifts and quick returns are associated with short sleep and increases in sleepiness. The same is true for very long shifts (>16 hours) and extremely long weekly working hours (>55 hours). For all categories of shift systems, there was a lack of controlled intervention studies, limiting the possibility to provide solution-focused recommendations for shift scheduling. Most of the controlled intervention studies had been conducted on workers under regular 3-shift systems. These studies suggested that a change from slowly backward-rotating shifts to rapidly forward-rotating shifts is advantageous for alertness and, to some degree, sleep. We also found that a change from an 8- to 12-hour shift system does not necessarily result in impairments in the sleep-wake pattern. The level of research evidence was affected by many of the studies' frequent methodological limitations in measuring sleep and sleepiness. In all, to have reliable and solution-focused recommendations for shift scheduling, methodologically sound controlled intervention studies are required in different categories of shift systems.