Light at night, melatonin levels and nurses working at night

Light at night has been implicated in health risks associated with night-shift work and circadian system disruption, but there are scant data on actual nighttime light exposures experienced by night-shift workers and how they affect melatonin levels. This study analysed salivary melatonin assays and calibrated personal light-exposure measurements obtained from a larger 20-week field study to explore the association between nocturnal melatonin levels and light exposures in 27 nurses working night shifts at four hospitals in southern New York and southern Indiana. Complete time-matched melatonin and light exposure data were available for 20 of the participants, who underwent three 2-week data collection periods (6 weeks total), each separated by six weeks. A mixed-effects model was used to quantify the adjusted association between melatonin levels and light exposures. No significant association was found between the measures after adjusting for age and years working night shifts (β = −6.8, p = 0.26). This study demonstrates that healthcare environments can provide sufficient light for visual tasks without affecting melatonin levels, a marker of the circadian system. Our research also highlights the value of personal light-measurement devices when examining the relationship between exposure to light at night, melatonin levels and the potential for circadian disruption.