Personal light-at-night exposures and components of variability in two common shift work industries: uses and implications for future research

• Published in: Scandinavian Journal of Work, Environment ＆ Health Vol. 44; no. 1; pp. 80 - 87
• Main Authors: Hall, Amy L, Davies, Hugh W, Koehoorn, Mieke
• Format: Journal Article
• Language: English
• Published: Finland Scandinavian Journal of Work, Environment ＆ Health 01-01-2018; NOROSH Nordic Association of Occupational Safety and health; Scandinavian Journal of Work, Environment & Health; Nordic Association of Occupational Safety and Health (NOROSH)
• Subjects: Biomarkers; Biomedical Research; British Columbia; Cancer; circadian disruption; Circadian Rhythm - physiology; Emergency medical services; Emergency services; Epidemiology; Error analysis; Error detection; Exposure; exposure assessment; exposure metric; Female; Guards; Health care; Health risk assessment; Health risks; Humans; Laboratories; lan; Light; light at night; light exposure; light-at-night exposure; Male; Medical personnel; Melatonin; Models, Statistical; Night shifts; night work; Occupational exposure; Occupational Exposure - adverse effects; Occupational health; Occupations; Photoperiod; Physiology; Research methodology; Research methods; Security; Shift work; Shift Work Schedule - adverse effects; shift worker; Variability; Variance analysis; Work Schedule Tolerance - physiology; Workers; Working conditions; Workplaces; British Columbia Canada; Canada; exposure metric; night work; shift worker; LAN; light exposure; exposure assessment; circadian disruption
• ISSN: 0355-3140; 1795-990X
• DOI: 10.5271/sjweh.3673

Objectives Shift workers' increased risk of various adverse health outcomes has been linked to light-at-night (LAN) exposure, but few studies have measured LAN exposure in workplaces. To inform future research methods, this study aimed to (i) measure shift workers' exposures to LAN across industries, occupations, and work environments and (ii) assess components of variance across different exposure groupings and metrics. Methods Between October 2015 and March 2016, 152 personal full-shift measurements were collected from 102 night shift workers in emergency services (paramedics, dispatchers) and healthcare (nurses, care aides, security guards, unit clerks, and laboratory, pharmacy, and respiratory therapy staff) industries in the province of British Columbia, Canada. Descriptive and variance component analyses were conducted for the 23:00–05:00 period to characterize exposures using multiple metrics of potential biological relevance (median lux, 90th percentile lux, sum of minutes ≥30 lux, and sum of minutes ≥100 lux). Results Average exposure levels were highest in the healthcare industry. By occupation, laboratory workers and care aides displayed the highest and emergency dispatch officers displayed the lowest levels for all LAN exposure metrics. Between-group variance was large relative to within-group variance for all exposure groupings and metrics, and increased as grouping specificity increased (moving from industry to occupation). Conclusions Results from this study suggest that high-level grouping schemes may provide a simple yet effective way of characterizing individual LAN exposures in epidemiological studies of shift work. Ongoing measurement of LAN exposures and assessment of exposure variability is needed in future studies of shift workers as a means to increase sampling efficiency, reduce measurement error, and maximize researchers' ability to detect relationships where they exist.