Elsevier

Science of The Total Environment

Volumes 607–608, 31 December 2017, Pages 1073-1084
Science of The Total Environment

Review
Health consequences of electric lighting practices in the modern world: A report on the National Toxicology Program's workshop on shift work at night, artificial light at night, and circadian disruption

https://doi.org/10.1016/j.scitotenv.2017.07.056Get rights and content

Highlights

  • Patterns of light exposure during day and night have direct effects on circadian biology and health.

  • Modern electric lighting practices also enable 24/7 activities and may lead to circadian disruption.

  • Work at night is a complex exposure scenario, including, but not limited to, light at night.

  • Some light and work at night are essential to society, making identification of interventions challenging.

  • Better measures of exposure and early disease may help identify interventions to protect public health.

Abstract

The invention of electric light has facilitated a society in which people work, sleep, eat, and play at all hours of the 24-hour day. Although electric light clearly has benefited humankind, exposures to electric light, especially light at night (LAN), may disrupt sleep and biological processes controlled by endogenous circadian clocks, potentially resulting in adverse health outcomes. Many of the studies evaluating adverse health effects have been conducted among night- and rotating-shift workers, because this scenario gives rise to significant exposure to LAN. Because of the complexity of this topic, the National Toxicology Program convened an expert panel at a public workshop entitled “Shift Work at Night, Artificial Light at Night, and Circadian Disruption” to obtain input on conducting literature-based health hazard assessments and to identify data gaps and research needs. The Panel suggested describing light both as a direct effector of endogenous circadian clocks and rhythms and as an enabler of additional activities or behaviors that may lead to circadian disruption, such as night-shift work and atypical and inconsistent sleep-wake patterns that can lead to social jet lag. Future studies should more comprehensively characterize and measure the relevant light-related exposures and link these exposures to both time-independent biomarkers of circadian disruption and biomarkers of adverse health outcomes. This information should lead to improvements in human epidemiological and animal or in vitro models, more rigorous health hazard assessments, and intervention strategies to minimize the occurrence of adverse health outcomes due to these exposures.

Introduction

The widespread adoption of electric light, only about 130 years ago, has facilitated a 24-hour/7-day society in which people work, sleep, eat, play, and expect goods and services at any time during the day or night. In this situation, people are exposed to electric light through lifestyle choices (e.g., use of electronic devices at night), the locations of their residences (e.g., urban light pollution), and employment during the night shift or as a shift worker (i.e., a worker whose schedule switches among morning, day, evening, and night). The United Nations proclaimed 2015 the International Year of Light and Light-Based Technologies in recognition of how light “has revolutionized medicine, opened up international communication via the Internet, and continues to be central to linking cultural, economic, and political aspects of the global economy” (http://www.light2015.org/Home/About.html). Although electric light has clearly benefited humankind, exposures to ill-timed, unnatural electric light, such as light at night (LAN) or differences in the quantity and spectrum of electric light from that provided by daylight exposures, may disrupt sleep and biological processes controlled by endogenous circadian clocks, potentially resulting in adverse health outcomes.

Because of these potential health concerns, LAN was nominated to the National Toxicology Program (NTP) to be the subject of literature-based health-hazard assessments on cancer and non-cancer outcomes. The NTP's Office of the Report on Carcinogens (ORoC) is assessing cancer outcomes for potential listing in the RoC, a U.S. congressionally mandated, science-based document that identifies cancer hazards. The Office of Health Assessment and Translation (OHAT) was asked to consider evaluating non-cancer (e.g., cardiovascular, metabolic, reproductive, gastrointestinal, immunological, neurological, and psychiatric) outcomes. Both ORoC and OHAT evaluations typically integrate evidence from human, experimental animal, and mechanistic studies. One of the rationales for nominating LAN to the RoC was the International Agency for Research on Cancer (IARC) working group 2007 conclusion that “shift work involving circadian disruption is probably carcinogenic to humans” (IARC, 2010). Therefore, the NTP defined the nomination to include circadian disruption and shift work at night, in addition to LAN. Those nominating this topic emphasized that they were interested in a broader scope than shift work, because of concerns about effects from exposure to LAN in the sleeping area (from indoor and outdoor lights) and outfitting of institutions with light sources rich in short-wavelength content, such as some types of light-emitting diodes, and based on the opinion that carcinogenic effects observed among shift workers were potentially due to LAN.

Because of the complexity and breadth of the topic, the NTP convened a public workshop and webcast entitled “Shift Work at Night, Artificial Light at Night, and Circadian Disruption” on March 10–11, 2016, to help obtain input on the approach for the NTP literature-analysis activities and to identify data gaps and research needs in the field. (The Panel suggested changing the terminology used by the NTP to describe the exposure to light from “artificial light at night” [ALAN] to “electric lighting practices.”)

This workshop report captures the major discussion points of the Panel. The first part introduces the concepts of electric light as effector and enabler and of shift work as a complex exposure scenario, and it provides background information on circadian disruption and links to potential adverse health effects. The second part discusses key issues related to advancing the science, which will help inform NTP literature-based evaluations and identify data gaps and research needs. This section is followed by a brief discussion of interventions to protect public health. Finally, post-workshop activities and meeting outcomes are discussed. It is important to note that the workshop did not require expert consensus and is not intended to provide formal recommendations or guidelines.

Section snippets

Methods: workshop format

To meet the workshop goals, a cross-disciplinary workshop panel was selected by the NTP with experts in (1) the key exposures, such as light, shift work, and sleep, (2) health outcomes, such as cancer and reproductive, neurological, and behavioral outcomes, and (3) other pertinent disciplines, such as circadian biology, exposure assessment, epidemiology, clinical research, toxicology, and mechanisms of disease.

The workshop was organized into six sessions, which reflected a progression of

Light as effector and enabler

One of the key suggestions from the Panel was to describe light both as a direct effector on circadian rhythms and as an enabler of additional activities that may lead to circadian disruption, including night-shift work and other atypical and inconsistent sleep-wake patterns that can lead to social jet lag. It is important to note that the NTP workshop focused on effects of light and shift work on the circadian domain of the biological time structure. Circadian disruption was defined by the

Conclusions

An important outcome of the workshop was to increase the visibility of these pervasive and often unavoidable exposures and their associations with potential adverse health effects. Same-day attendees, either in person or via the webinar, exceeded 150 people from diverse organizations, including government, industry, academia, and non-profits, along with other concerned citizens. Videos of the workshop and summary materials remain available on the NTP website (//ntp.niehs.nih.gov/go/workshop_ALAN

Funding

This research did not receive any specific grants from funding agencies in the public, commercial, or not-for-profit sectors.

Disclaimer

The findings and conclusions in this manuscript are those of the author(s) and do not necessarily represent the views of the National Toxicology Program or the National Institute for Occupational Safety and Health.

Acknowledgments

The authors would like to acknowledge Dr. Gloria Jahnke, Dr. Katie Pelch, Dr. Kyla Taylor, Ms. Whitney Mitchell, and Ms. Courtney Skuce for their support at the workshop or for preparation of background materials for the workshop.

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