Measuring Light at Night and Melatonin Levels in Shift Workers: A Review of the Literature.

Shift work, especially that involving rotating and night shifts, is associated with an increased risk of diseases, including cancer. Attempts to explain the association between shift work and cancer in particular have focused on the processes of melatonin production and suppression. One hypothesis postulates that exposure to light at night (LAN) suppresses melatonin, whose production is known to slow the development of cancerous cells, while another proposes that circadian disruption associated with shift work, and not just LAN, increases health risks. This review focuses on six studies that employed quantitative measurement of LAN and melatonin levels to assess cancer risks in shift workers. These studies were identified via searching the PubMed database for peer-reviewed, English-language articles examining the links between shift work, LAN, and disease using the terms light at night, circadian disruption, health, risk, cancer, shift work, or rotating shift. While the results indicate a growing consensus on the relationship between disease risks (particularly cancer) and circadian disruption associated with shift work, the establishment of a direct link between LAN and disease has been impeded by contradictory studies and a lack of consistent, quantitative methods for measuring LAN in the research to date. Better protocols for assessing personal LAN exposure are required, particularly those employing calibrated devices that measure and sample exposure to workplace light conditions, to accurately assess LAN's effects on the circadian system and disease. Other methodologies, such as measuring circadian disruption and melatonin levels in the field, may also help to resolve discrepancies in the findings.

The impact of daytime light exposures on sleep and mood in office workers.

BACKGROUND: By affecting the internal timing mechanisms of the brain, light regulates human physiology and behavior, perhaps most notably the sleep-wake cycle. Humans spend over 90% of their waking hours indoors, yet light in the built environment is not designed to affect circadian rhythms. OBJECTIVE: Using a device calibrated to measure light that is effective for the circadian system (circadian-effective light), collect personal light exposures in office workers and relate them to their sleep and mood. SETTING: The research was conducted in 5 buildings managed by the US General Services Administration. PARTICIPANTS: This study recruited 109 participants (69 females), of whom 81 (54 females) participated in both winter and summer. MEASUREMENTS: Self-reported measures of mood and sleep, and objective measures of circadian-effective light and activity rhythms were collected for 7 consecutive days. RESULTS: Compared to office workers receiving low levels of circadian-effective light in the morning, receiving high levels in the morning is associated with reduced sleep onset latency (especially in winter), increased phasor magnitudes (a measure of circadian entrainment), and increased sleep quality. High levels of circadian-effective light during the entire day are also associated with increased phasor magnitudes, reduced depression, and increased sleep quality. CONCLUSIONS: The present study is the first to measure personal light exposures in office workers using a calibrated device that measures circadian-effective light and relate those light measures to mood, stress, and sleep. The study's results underscore the importance of daytime light exposures for sleep health.

Understanding Rotating Shift Workers' Health Risks.

Until we know more, it is recommended that lighting in health care facilities should be designed to minimize acute melatonin suppression in night shift workers.

Tailored Lighting Intervention for Persons with Dementia and Caregivers Living at Home.

OBJECTIVES: Light therapy has shown promise as a nonpharmacological treatment to help regulate abnormal sleep-wake patterns and associated behavioral issues prevalent among individuals diagnosed with Alzheimer's disease and related dementia (ADRD). The present study investigated the effectiveness of a lighting intervention designed to increase circadian stimulation during the day using light sources that have high short-wavelength content and high light output. METHODS: Thirty-five persons with ADRD and 34 caregivers completed the 11-week study. During week 1, subjective questionnaires were administered to the study participants. During week 2, baseline data were collected using Daysimeters and actigraphs. Researchers installed the lighting during week 3, followed by 4 weeks of the tailored lighting intervention. During the last week of the lighting intervention, Daysimeter, actigraph and questionnaire data were again collected. Three weeks after the lighting intervention was removed, a third data collection (post-intervention assessment) was performed. RESULTS: The lighting intervention significantly increased circadian entrainment, as measured by phasor magnitude and sleep efficiency, as measured by actigraphy data, and significantly reduced symptoms of depression in the participants with ADRD. The caregivers also exhibited an increase in circadian entrainment during the lighting intervention; a seasonal effect of greater sleep efficiency and longer sleep duration was also found for caregivers. CONCLUSIONS: An ambient lighting intervention designed to increase daytime circadian stimulation can be used to increase sleep efficiency in persons with ADRD and their caregivers, and may also be effective for other populations such as healthy older adults with sleep problems, adolescents, and veterans with traumatic brain injury.

Bright ideas. Some rules of thumb for interior lighting design and selection.

Interior lighting design and selection can be a demanding assignment for a health facilities manager or department head. It requires a balance between conflicting needs, such as providing good task lighting for a nursing station while also shielding luminaires that are visible from patients' rooms to avoid glare.