Night and rotating shift work leads to a mismatch between the timing of circadian rhythms and the timing of the work/sleep schedule. This in turn leads to sleepiness during nighttime work, with greater risk for performance errors and accidents. In addition, daytime sleep is disrupted and shortened, which exacerbates the performance problems on the subsequent night shifts. Problems with night shift adaption are reported to be greater in older workers than in younger workers, and this is hypothesized to be due to their greater inability to sleep during the day. We have shown previously that in young adults, bright light during the night shift can improve circadian adaptation to a night-work, day-sleep schedule, leading to increased alertness at night and longer daytime sleep. Subsequent studies in young adults found that a light treatment could be effective with light of moderate intensity for only half of the work shift. Furthermore, we have shown that in young adults, scheduling sleep before (rather than after) the night shift, when combined with enhanced lighting on the night shift, can improve alertness and vigilance to nearly day shift levels after only one night. However, such studies have not yet been performed in older adults, and we will therefore test that enhanced lighting and scheduled sleep regimen in a group of older adults. In addition to comparing the on-shift alertness, vigilance and performance of older adults in the treatment group to a group of control participants, we will also test each component separately (enhanced lighting only;scheduled evening sleep only) in order to determine how much each contributes to the combined treatment effect. The number of Americans who work during the night has continued to increase as more aspects of our society have moved to round-the-clock operations and the number older workers who work at night is estimated by the US Department of Labor to be as high as 3 million. Thus, countermeasures for older night shift workers have the potential to benefit many individuals. Given our increasing understanding of how inadequate sleep contributes not only to issues of performance and safety, but to risk for cardiovascular disease, obesity and metabolic syndrome, and inflammatory responses, a night treatment regimen could also have future implications for improving the health of older people who must work at night.

Public Health Relevance

As we have moved toward a 24-hour society, more and more workers are required to do their jobs at night. At the same time, our society is rapidly aging. These two trends have resulted in more older night and rotating shift workers, estimated at nearly 3 million in 2001 [US Department of Labor, 2002] and increasing since then. While the same factors that negatively impact the health, safety and productivity of younger shift workers also affect older workers, there are many reports that working at night impacts older workers to a greater extent due to their decreased ability to sleep during the day. Our proposed study will test in older workers a light treatment regimen that has been successful in adapting young workers to a night-work, day-sleep schedule. Information from this study will be an important step in developing shift work treatments for the nearly 3 million older Americans who work night or rotating shift schedules.

National Institute of Health (NIH)
National Institute on Aging (NIA)
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Biobehavioral Mechanisms of Emotion, Stress and Health Study Section (MESH)
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Mackiewicz, Miroslaw
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Brigham and Women's Hospital
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