Exposure to Bright Light and Darkness to Treat Physiologic Maladaptation to Night Work

May 3, 1990The New England journal of medicine

Using bright light and darkness to help the body adjust to night work

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Abstract

Bright light exposure at night (7000 to 12,000 lux) shifted the temperature nadir in subjects to a significantly later time of 14:53 +/- 0:32 hours.

A lack of circadian adaptation was observed in control subjects, with the temperature nadir occurring at 3:31 +/- 0:56 hours during ordinary light.
Treatment with bright light at night and darkness during the day resulted in a successful adaptation of the circadian system after four days.
Concomitant shifts were noted in the 24-hour patterns of plasma cortisol concentration and urinary excretion rate during the treatment.
Subjective assessments indicated improved alertness and cognitive performance in the treatment group during night-shift hours.
Maladaptation to nighttime work may lead to declines in alertness, performance, and quality of daytime sleep, which could be mitigated by the treatment regimen.

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Working at night results in a misalignment between the sleep-wake cycle and the output of the hypothalamic pacemaker that regulates the circadian rhythms of certain physiologic and behavioral variables. We evaluated whether such physiologic maladaptation to nighttime work could be prevented effectively by a treatment regimen of exposure to bright light during the night and darkness during the day. We assessed the functioning of the circadian pacemaker in five control and five treatment studies in order to assess the extent of adaptation in eight normal young men to a week of night work. In the control studies, on the sixth consecutive night of sedentary work in ordinary light (approximately 150 lux), the mean (+/- SEM) nadir of the endogenous temperature cycle continued to occur during the night (at 3:31 +/- 0:56 hours), indicating a lack of circadian adaptation to the nighttime work schedule. In contrast, the subjects in the treatment studies were exposed to bright light (7000 to 12,000 lux) at night and to nearly complete darkness during the day, and the temperature nadir shifted after four days of treatment to a significantly later, midafternoon hour (14:53 +/- 0:32; P less than 0.0001), indicating a successful circadian adaptation to daytime sleep and nighttime work. There were concomitant shifts in the 24-hour patterns of plasma cortisol concentration, urinary excretion rate, subjective assessment of alertness, and cognitive performance in the treatment studies. These shifts resulted in a significant improvement in both alertness and cognitive performance in the treatment group during the night-shift hours. We conclude that maladaptation of the human circadian system to night work, with its associated decline in alertness, performance, and quality of daytime sleep, can be treated effectively with scheduled exposure to bright light at night and darkness during the day.

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Exposure to Bright Light and Darkness to Treat Physiologic Maladaptation to Night Work

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