RT Journal Article
SR Electronic
T1 Role of nocturnal light intensity on adaptation to three consecutive night shifts: a counterbalanced crossover study
JF Occupational and Environmental Medicine
JO Occup Environ Med
FD BMJ Publishing Group Ltd
SP 249
OP 255
DO 10.1136/oemed-2019-106049
VO 77
IS 4
A1 Sunde, Erlend
A1 Mrdalj, Jelena
A1 Pedersen, Torhild
A1 Thun, Eirunn
A1 Bjorvatn, Bjørn
A1 Grønli, Janne
A1 Harris, Anette
A1 Waage, Siri
A1 Pallesen, Ståle
YR 2020
UL http://oem.bmj.com/content/77/4/249.abstract
AB Objectives To investigate how a standard ceiling mounted light-emitting diode (LED)-based bright light intervention affected alertness and neurobehavioural performance during three consecutive simulated night shifts, and timing of circadian rhythm after the shifts.Methods Twenty seven participants (20 females, 21.4±2.1 years; mean±SD) worked three consecutive night shifts (23:00–07:00) under a full-spectrum (4000 K) bright light (900 lx) and a standard light (90 lx) condition in a counterbalanced crossover design (separated by 4 weeks). Subjective alertness (Karolinska Sleepiness Scale) and neurobehavioural performance (Psychomotor Vigilance Task and Digit Symbol Substitution Test) were assessed five times during each shift. Salivary dim-light melatonin onset (DLMO) was assessed before and after the shifts. The simulated night shifts were conducted in a laboratory while the participants slept at home.Results Subjective alertness and neurobehavioural performance deteriorated during the night shifts in both light conditions. However, bright light significantly reduced alertness and performance decrements as compared with standard light. For a subset of the participants, DLMO was delayed by a mean of 3:17±0:23 (mean±SEM) hours after three night shifts in bright light and by 2:06±0:15 hours in standard light, indicating that bright light causes larger phase delay.Conclusion Bright light improved performance and alertness during simulated night shifts and improved adaptation to night work. Bright light administered by ceiling mounted LED luminaires has the potential to improve adaptation to night work and reduce the risk of accidents and injuries among night workers.Trial registration number NCT03203538.