Distribution of rest days in 12 hour shift systems: impacts on health, wellbeing, and on shift alertness

Objectives-To investigate of the effects of distribution of rest days in 12 hour shift systems. Although several studies have examined the effects of compressing work schedules by comparing 8 and 12 hour shift systems, there is little published research examining the various forms of 12 hour shift s ystem. Methods-An abridged version of the standard shiftwork index which included retrospective alertness ratings was completed by a large sample of industri al shiftworkers. The respondents worked 12 hour shift systems that either d id or did not incorporate breaks of >24 hours between the blocks of day and night shifts. For the purposes of the analysis, each of these two groups w ere further subdivided into those who started their morning shifts at 0600 and those who started at 0700. Results-Systems which incorporated rest days between the day and night shif ts were associated with slightly higher levels of on shift alertness, sligh tly lower levels of chronic fatigue, along with longer sleep durations when working night shifts and between rest days. Early changeovers were associa ted with shorter night sleeps between successive day shifts, but longer and less disturbed day sleeps between night shifts. These effects of changeove r time were broadly in agreement with previous research findings. Conclusions-The distribution of rest days in 12 hour shift systems had only limited effects on the outcome measures, although the few modest differenc es that were found favoured systems which incorporated rest days between th e day and night shifts. It is conceded that the design of the study may hav e obscured some subtle differences between the shift systems. Nevertheless, it is concluded that the impact of distribution of rest days seems to be m inor relative to previously found effects of other features of shift system s-for example, shift duration.