Scheduled evening sleep and enhanced lighting improve adaptation to night shift work in older adults

Abstract

Objectives We tested whether a sleep and circadian-based treatment shown to improve circadian adaptation to night shifts and attenuate negative effects on alertness, performance, and sleep in young adults would also be effective in older adults. Methods We assessed subjective alertness, sustained attention (psychomotor vigilance task, PVT), sleep duration (actigraphy), and circadian timing (salivary dim-light melatonin onset, DLMO) in eighteen older adults (57.2±3.8 y; mean±SD) in a simulated shift work protocol. Four day shifts were followed by three night shifts in the laboratory. Participants slept at home and were randomized to either the Treatment Group (scheduled evening sleep and enhanced lighting during the latter half of night shifts), or Control Group (ad lib sleep and typical lighting during night shifts). Results Compared to day shifts, alertness and sustained attention declined on the first night shift in both groups, and was worse in the latter half of the night shifts. Alertness and attention improved on nights 2 and 3 for the Treatment Group but remained lower for the Control Group. Sleep duration in the Treatment Group remained similar to baseline (6–7 h) following night shifts, but was shorter (3–5 h) following night shifts in the Control Group. Treatment Group circadian timing advanced by 169.3±16.1 min (mean±SEM) but did not shift (−9.7±9.9 min) in the Control Group. Conclusions The combined treatment of scheduled evening sleep and enhanced lighting increased sleep duration and partially aligned circadian phase with sleep and work timing, resulting in improved night shift alertness and performance.

Role of nocturnal light intensity on adaptation to three consecutive night shifts: a counterbalanced crossover study

“…The reduced sleepiness with bright compared with standard light is in line with previous reports on the alerting effect of bright light 23 26 29. Similar to a former study,25 the effect of bright light was not evident during the first shift, but on nights 2 and 3 alertness deficits were smaller with bright compared with standard light. As we did not put requirements on participants’ sleep after shifts, differences in sleep-wake timing may have affected the initial differences in subjective alertness on night 2.…”

“…The deterioration of performance as assessed with the PVT was evident in both a general slowing of RTs and an increase in number of attentional lapses during night shifts, in line with previous studies 7 8 11. However, participants had fewer attentional lapses and faster RTs in bright than in standard light, similar to previous reports,22 25 28 and these effects were evident already during the first shift. Overall, we did not find that PVT performance improved with consecutive shifts, contrary to some previous studies 19 25.…”

“…However, participants had fewer attentional lapses and faster RTs in bright than in standard light, similar to previous reports,22 25 28 and these effects were evident already during the first shift. Overall, we did not find that PVT performance improved with consecutive shifts, contrary to some previous studies 19 25. A greater increase in attentional lapses during the first shift than on subsequent shifts has been reported to indicate more pronounced cognitive deficits due to greater sleep pressure on the first shift 11 19.…”

“…In the present study, we did not set requirements on participants’ sleep timing after night shifts and light exposure during the time off shifts, as seen in several previous studies 19 22–24. With more control of such parameters, for example, by adding scheduled sleep after shifts,24 25 it is likely that the effects of bright light could have been greater. In addition, individual differences in non-visual responses to light may have affected the results,29 32 as we did not provide an individually adapted light intervention.…”

“…The performance impairments associated with night work can be attributed to circadian misalignment and/or build-up of homeostatic sleep pressure due to prolonged wakefulness 18–21. Consequently, interventions aiming to improve alertness and performance during night work can be based on circadian principles, such as timing of light exposure and sleep 22–27. In addition, light can have acute alerting effects, especially at night when the internal biological timing of alertness is at its trough and sleep pressure is elevated 26 28 29.…”