Measurements of Light at Night (LAN) for a Sample of Female School Teachers

Abstract

Epidemiological studies have shown an association between rotating shiftwork and breast cancer (BC) risk. Recently, light at night (LAN) measured by satellite photometry and by self-reports of bedroom brightness has been shown to be associated with BC risk, irrespective of shiftwork history. Importance has been placed on these associations because retinal light exposures at night can suppress the hormone melatonin and/or disrupt circadian entrainment to the local 24-h light-dark cycle. The present study examined whether it was valid to use satellite photometry and self-reports of brightness to characterize light, as it might stimulate the circadian system and thereby affect BC incidence. Calibrated photometric measurements were made at the bedroom windows and in the bedrooms of a sample of female school teachers, who worked regular dayshifts and lived in a variety of satellite-measured sky brightness categories. The light levels at both locations were usually very low and were independent of the amount of satellite-measured light. Calibrated photometric measurements were also obtained at the corneas of these female school teachers together with calibrated accelerometer measurements for seven consecutive days and evenings. Based upon these personal light exposure and activity measurements, the female teachers who participated in this study did not have disrupted light-dark cycles like those associated with rotating shiftworkers who do exhibit a higher risk for BC. Rather, this sample of female school teachers had 24-h light-dark and activity-rest patterns very much like those experienced by dayshift nurses examined in an earlier study who are not at an elevated risk of BC. No relationship was found between the amount of satellite-measured light levels and the 24-h light-dark patterns these women experienced. It was concluded from the present study that satellite photometry is unrelated to personal light exposures as they might affect melatonin suppression and/or circadian disruption. More generally, photometric devices calibrated in terms of the operational characteristics of the human circadian system must be used to meaningfully link LAN and BC incidence. (Authors correspondence: E-mail: [email protected])

Keywords:

• Breast cancer
• Circadian light
• Circadian light levels
• Light pollution
• Melatonin

ACKNOWLEDGMENTS

Assistance in this research was provided by Lighting Research Center colleagues: Andrew Bierman, Mary Cimo, Brian Donlan, Basar Erdener, Daniel Frering, Dennis Guyon, Robert Hamner, Terry Klein, Natalia Lesniak, Anna Lok, Lenda Lyman, Ines Martinovic, Nicholas Meyer, Howard Ohlhous, Aaron M. Smith, Rachel Taranta, and Bonnie Westlake. This work was supported in part by CDC Grant R01 OH008171 to Dr. Eva Schernhammer at Harvard Public Health, by the Trans-NIH Genes, Environment and Health Initiative Grant U01 DA023822 to Dr. Mark Rea at the Lighting Research Center, and by the National Electrical Manufacturers Association. The authors wish to thank Karen Sikora of Rensselaer Polytechnic Institute for assistance in publicizing the study with teachers. Finally, thanks to the principals, administrators, and teachers who participated in this research.

Declaration of Interest: The Lighting Research Center is a multidisciplinary university education and research facility funded by industry, government, foundations, and philanthropic donations. The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.