Abstract
This project investigated a series of shift schedules (14-Days, 14-Nights, 7-Night,7-Days, and 7-Days,7-Nights,) to determine circadian status (using the rhythm of urnary 6-sulphatoxymelatonin), sleep (by actigraphy) and selected metabolic parameters, in the offshore petrochemical industry, which operates a range of schedules with uncertain impact on biological rhythms and health. No circadian adaptation was observed in the 14-Days schedule. All subjects adapted to the 14-Nights schedule by circadian phase delay, and to the night shift of 7-Days,7-Nights by phase advance. On the 7-Nights,7-Days schedule the majority of subjects also adapted to the night shift by delay, but most did not re-adapt back to dayshift. The novel parameter 'Desynchrony Load' (cumulated deviation from ideal circadian timing, in hours) was used as a quantitative indicator of disruption. The 7-Nights,7-Days schedule gave the highest score (61.7h), 14-Nights, 7-days,7-nights and 14-Days gave 31.5, 26.2 and 13.9h respectively. The timing of light exposure in relation to circadian phase was identified as a major influence in adaptation. The 7-Nights,7-Days and 7-Days,7-Nights schedules impacted negatively on sleep, as the night after the swing-shift had the shortest sleep (shortest duration and longest latency). Sleep efficiency was significantly improved after the 7-Nights,7-Days rollover suggesting that returning to normal clock-time was associated with better sleep despite the desynchrony. There was no significant difference in overall macronutrient or energy intake between day and night shifts, despite a temporal redistribution of meal times. Postprandial TAG on night 2 (desynchronised) was raised compared with night 6 (adapted) of night shifts (14-Nights and nights of 7-Nights,7-Days). Similar trends were seen in postprandial cholesterol and insulin, but not in glucose. The improved TAG on night-6 seen in adapting subjects was still seen as a trend in non-adapters, suggesting that metabolic recovery may occur independently of, or faster than, the central circadian clock. In conclusion, the raised postprandial TAG on night-2 is evidence that shiftwork desynchrony may contribute to CVD risk via disturbance to normal metabolic processes. Finally, when night work is essential, the 14-Nights schedule is preferable to the schedules that impose a double desynchronisation.