Night work, light exposure and melatonin on work days and days off

Abstract

We aimed to examine the effects of night work on salivary melatonin concentration during and subsequent to night work and the mediating role of light. We included 254 day workers and 87 night workers who were followed during 322 work days and 301 days off work. Each day was defined as the 24 hour period starting from the beginning of a night shift or from waking in the mornings with day work and days off. Light levels were recorded and synchronized with diary information (start and end of sleep and work). On average, participants provided four saliva samples per day, and these were analyzed for melatonin concentration by liquid chromatography tandem mass spectrometry (LC-MS/MS). Differences between day and night workers on work days and days off were assessed with multilevel regression models with melatonin concentration as the primary outcome. All models were stratified or adjusted by time of day. For light exposure, we estimated the total, direct and indirect effects of night work on melatonin concentrations obtaining 95% confidence intervals through bootstrapping. On work days, night workers showed 15% lower salivary melatonin concentrations compared with day workers (-15.0%; 95% CI: -31.4%; 5.2%). During the night, light exposure mediated a melatonin suppression of approximately 6% (-5.9%, 95% CI: -10.2%; -1.5%). No mediating effect of light was seen during the day time. On days off, we observed no difference in melatonin concentrations between day and night workers. These findings are in accordance with a transient and partly light-mediated effect of night work on melatonin production.

How to schedule night shift work in order to reduce health and safety risks

“…Night shift workers are exposed to light-at-night, which has earlier been proposed as one of the exposures linked with breast cancer through suppression of melatonin (10). Light-at-night is associated with lower levels of melatonin in both experimental (11)(12)(13) and observational studies of night shift workers compared with day workers (14,15). Animal studies show that alterations in the light-dark schedule suppress melatonin (3).…”

Indoor, outdoor, and night work and blood concentrations of vitamin D and parathyroid hormone

“…2011-41-6850) and the Central Denmark Region Committee on Health Research Ethics (M-20110214) approved the study. Further details of the study design are presented elsewhere (46).…”

Melatonin profiles during the third trimester of pregnancy and health status in the offspring among day and night workers: A case series

“…Additionally, there is strong evidence that melatonin levels differ between day and night shift workers (Daugaard et al, 2017; Liang Zhu et al, 2004) and differ between work days and days off (Daugaard et al, 2017) However, according to Dumont and colleagues these differences could be related to total melatonin production, and not necessarily related to a reduction of melatonin excretion at work (during night work) (Dumont et al, 2012).…”