Study finds shift workers can improve alertness, implement sleep schedule

Shift workers have options that can help them increase alertness and ensure safety while still implementing an adequate sleep schedule on days off, according to a recent study.

Irregular and extended shift employees are particularly at risk of health and safety problems because of night shifts. Night schedules disrupt human biological functions as well as traditional social structures. Shift workers also typically get less sleep and poorer-quality sleep than their day-only coworkers. This builds up and creates a chronic cycle of fatigue, which can supersede a worker's training, skills and experience, and create an environment that's more conducive to workplace accidents.

However, according to researchers at Rush University Medical Center, shift workers can combat these risks. In a study published in the December issue of the journal SLEEP, researchers found that the use of light exposure therapy, dark sunglasses, and a strict sleep schedule can help night-shift workers create a "compromise circadian phase position," which may result in increased performance and alertness during night shifts while still allowing adequate nighttime sleep on days off.

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"The major finding of this study was that complete physiological adaptation to a night shift and day sleep schedule does not appear necessary in order to improve night-shift alertness and lengthen daytime sleep," said Mark Smith, lead author of the study and postdoctoral fellow in the Biological Rhythms Research Laboratory at Rush University Medical Center. "Instead, we found that partial physiological adaptation using scheduled exposure to light and darkness is sufficient to bring night-shift performance back to daytime levels."

Twenty-four subjects were included in the study. The individuals underwent seven simulated night shifts from 11 p.m. to 7 a.m. with two days off. Experimental subjects slept in dark bedrooms at scheduled times: 8:30 a.m. to 3:30 p.m. after the first two night shifts; from 8:30 a.m. to 1:30 p.m. after the third night shift; from 3 a.m. to 12 p.m. on the two weekend days off; and again from 8:30 a.m. to 3:30 p.m. after the final four night shifts. They also were exposed to five, 15-minute, intermittent bright light pulses each night shift; wore dark sunglasses when outside; and received outdoor afternoon light exposure. Control subjects remained in normal room light during night shifts, wore lightly tinted sunglasses when outside, and had unrestricted sleep and outdoor light exposure.

Subjects in the experimental group achieved a dim light melatonin onset time of 4:30 a.m., which was close to the target compromise phase position and significantly later than the control group's DLMO time of 12:30 a.m. The body temperature minimum, an estimate for the sleepiest circadian time, occurs about seven hours after the DLMO. The goal was to delay the sleepiest circadian time so that it fell within the sleep episodes after night shifts and on days off, but to keep it from delaying too far beyond the scheduled sleep episodes on days off.

The data suggested that in addition to adopting the recommended sleep pattern and wearing sunglasses, night-shift workers who used bright light exposure therapy were able to alter their circadian rhythm in order to improve performance during night-shift work, continue daytime interaction with peers, and have the ability to sleep at night on days off.

January 22, 2009

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