Objectives Night workers often experience high levels of sleepiness due to misalignment of the sleep-wake cycle from the circadian pacemaker, in addition to acute and chronic sleep loss. Exposure to light, in particular short wavelength light, can improve alertness and neurobehavioural performance. This randomised controlled trial examined the efficacy of blue-enriched polychromatic light to improve alertness and neurobehavioural performance in night workers.
Design Participants were 71 night shift workers (42 males; 32.8±10.5 years) who worked at least 6 hours between 22:00 and 08:00 hours. Sleep-wake logs and wrist actigraphy were collected for 1–3 weeks, followed by 48-hour urine collection to measure the circadian 6-sulphatoxymelatonin (aMT6s) rhythm. On the night following at least two consecutive night shifts, workers attended a simulated night shift in the laboratory which included subjective and objective assessments of sleepiness and performance. Workers were randomly assigned for exposure to one of two treatment conditions from 23:00 hours to 07:00 hours: blue-enriched white light (17 000 K, 89 lux; n=36) or standard white light (4000 K, 84 lux; n=35).
Results Subjective and objective sleepiness increased during the night shift in both light conditions (p<0.05, ηp 2=0.06–0.31), but no significant effects of light condition were observed. The 17 000 K light, however, did improve subjective sleepiness relative to the 4000 K condition when light exposure coincided with the time of the aMT6s peak (p<0.05, d=0.41–0.60).
Conclusion This study suggests that, while blue-enriched light has potential to improve subjective sleepiness in night shift workers, further research is needed in the selection of light properties to maximise the benefits.
Trial registration number The Australian New Zealand Clinical Trials Registry ACTRN12610000097044 (https://www.anzctr.org.au/Trial/Registration/TrialReview.aspx?id=320845&isReview=true).
- shift work
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Contributors Conceived and designed the experiments: TLS, SFt, CLN, MM, RRG, SFe, DJK, DO, SWL, SMWR. Performed the experiments: TLS, SFt, DO. Analysed the data: TLS, SFt, CLN, MM. Wrote the paper: TLS, SFt, CLN, MM, RRG, SFe, DJK, DO, SWL, SMWR. Contributors. Study preparation, participant recruitment and data cleaning: JM, AM, SW, MC, SB. Statistical expertise: WX. Radioimmunoassays: MS.
Funding This research was supported by National Health and Medical Research Council (NHMRC) project grant (# 545871) and was endorsed by the Australasian Sleep Trials Network (NHMRC Enabling Grant # 343020).
Competing interests TLS reports that her institution has received equipment donations or other support from Philips Lighting, Philips Respironics, Optalert and Compumedics. She serves as a Project Leader in the Cooperative Research Centre for Alertness, Safety and Productivity. SFt serves as a Project Leader in the Cooperative Research Centre for Alertness, Safety and Productivity. RRG serves as a Program Leader in the Cooperative Research Centre for Alertness, Safety and Productivity which provides equipment and other in-kind support for research from Philips. In the past 5 years, SWL has received consulting fees from Blackrock, Carbon Limiting Technologies (on behalf of PhotonStar LED), Cowen & Co, Endurant Capital Management, Far West Capital Management, Fidelity, Frankel Group, Impax Laboratories, Kearney Venture Partners, Lazard Capital Markets, Naturebright, New Horizon Capital, Perceptive Advisors, Polar Capital, ResearchWorks, Serrado Capital, Thomas Jefferson University and Wyvern Funds; has current consulting contracts with Akili Interactive, Delos Living LLC, Environmental Light Sciences LLC, Focal Point LLC, Headwaters, Hintsa Performance AG, OpTerra Energy Services, Pegasus Capital Advisors LP, PlanLED, Wyle Integrated Science and Engineering; has received unrestricted equipment gifts from Bioilluminations LLC, Bionetics Corporation and Philips Lighting; a fellowship gift from Optalert; advance author payment and royalties from Oxford University Press; payment for editing a textbook section from Elsevier; honoraria from the National Sleep Foundation and for an article in the Wall Street Journal; honoraria plus travel, accommodation or meals for invited seminars, conference presentations or teaching from Brookline Adult Education, Brown University, Estee Lauder, Harvard University (CME), MediCom Worldwide (CME); travel, accommodation and/or meals only (no honoraria) for invited seminars, conference presentations or teaching from the 8th International Conference on Managing Fatigue, 14th Annual Tennessee Perfusion Conference, American Society for Photobiology, Cantifix, Connecticut Business & Industry Association Health and Safety Conference, Emergency Services Steering Committee, FASEB, Harvard University, Hintsa Performance AG, Illuminating Engineering Society, Lightfair, Massachusetts General Hospital, Midwest Lighting Institute, New England College of Occupational and Environmental Medicine, Ontario Association of Fire Chiefs, Rio Tinto, UMass Memorial, University of Manchester, University of Texas Medical Branch and Woolcock Institute of Medical Research; ongoing investigator-initiated research grants from Biological Illuminations LLC and Respironics; completed service agreements with Rio Tinto Iron Ore and Vanda Pharmaceuticals; three completed sponsor-initiated clinical research contracts with Vanda Pharmaceuticals; and one completed investigator-initiated research grant from Vanda Pharmaceuticals. SWL also holds a process patent for the use of short-wavelength light for resetting the human circadian pacemaker and improving alertness and performance which is assigned to the Brigham and Women’s Hospital per hospital policy and has received revenue from a patent on the use of short-wavelength light, which is assigned to the University of Surrey. SWL has also served as a paid expert witness on behalf of eight public bodies and one union for arbitration and cases related to sleep, circadian rhythms and work hours. SWL also serves as a Program Leader in the Cooperative Research Centre for Alertness, Safety and Productivity. SMWR reports that he has served as a consultant through his institution to Vanda Pharmaceuticals, Philips Respironics, EdanSafe, The Australian Workers’ Union, National Transport Commission and Transport Accident Commission and has through his institution received research grants and/or unrestricted educational grants from Vanda Pharmaceuticals, Takeda Pharmaceuticals North America, Philips Lighting, Philips Respironics, Cephalon and ResMed Foundation and reimbursements for conference travel expenses from Vanda Pharmaceuticals. His institution has received equipment donations or other support from Optalert, Compumedics and Tyco Healthcare. He has also served as an expert witness and/or consultant to shift work organisations. SMWR also serves as a Program Leader in the Cooperative Research Centre for Alertness, Safety and Productivity.
Patient consent Obtained.
Ethics approval Human Research Ethics Committees of Monash University, University of Sydney and University of South Australia.
Provenance and peer review Not commissioned; externally peer reviewed.
Correction notice This paper has been amended since it was published Online First. Owing to a scripting error, some of the publisher names in the references were replaced with ’BMJ Publishing Group'. This only affected the full text version, not the PDF. We have since corrected these errors and the correct publishers have been inserted into the references.