New Study Sheds Light on Working Nights

Exposure to Light, Use of Sunglasses May Help Weary Night-Shift Workers Stay Alert

Medically Reviewed by Louise Chang, MD on December 05, 2008

Dec. 5, 2008 -- Night-shift workers of the world, wake up.

A new study offers tips that might make you more alert on the job and help you sleep better when you're off.

Researchers at Rush University Medical Center found that participants who worked a simulated night shift and who were exposed during the wee hours to bright lights for five 15-minute periods became more alert, not immediately but later.

But it wasn't just the lights that helped them, says Charmane Eastman, PhD, one of the researchers.

People in the "experimental" group -- those exposed to the bright lights -- also were given dark sunglasses to wear on their way home and went straight to bed at 8:30 a.m.

Those in the experimental group slept in dark bedrooms between 8:30 a.m. and 3:30 p.m. after the first two night shifts, 8:30 a.m. to 1:30 p.m. after the third night shift, and from 3 a.m. to noon on two weekend days off.

People in a control group who also worked simulated night shifts weren't exposed to bright lights, were given dim but not dark sunglasses, and were allowed unrestricted sleep and all the exposure they wanted to outdoor light.

All 24 participants worked from 11 p.m. to 7 a.m. with two days off.

Eastman and colleague Mark Smith, a postdoctoral fellow, conducted the study to try to make the participants' body clocks more normal. And they found the bright lights, the dark sunglasses, and enforced sleeping times helped the night workers become more alert and feel less abnormal.

The findings suggest that real shift workers could "set up light boxes where they work or in the break room" and eventually will feel better and sharper, Eastman tells WebMD.

"The sunglasses also are important," she says. "They cut out a lot of blue light, that light in the morning is what keeps real shift workers from adjusting. You go outside, that light tells your body clock it's morning. So the real night shift worker never adjusts. We're tricking the body clock to think night is day and day is night."

Those in the experimental group were told to go to bed at 3 a.m. on their days off, partially resetting their body clocks so that they could sleep and feel somewhat normal in the evening.

Night shift workers also should sleep in "very dark" rooms, even if they think they can get enough shut-eye with light filtering in through windows, she tells WebMD.

Those in the study's experimental group had black plastic placed over windows.

The researchers also measured chemicals in saliva to determine their success in "resetting the body clock" by taking the steps they did with those in the experimental group.

"If you're on the night shift, unplug your phone, put signs on the door not to ring the bell, don't drink a lot of coffee at the end of the shift," she says. "Alcohol in general helps people fall asleep, but it wears off and makes them wake up. Waking up early is the biggest problem."

She says one important finding is that night shift workers (she and Smith defined night shift as 11 p.m. to 7 a.m., which many describe as the "graveyard" shift) should wake up late on their off days, but no earlier than noon.

The scientists conclude that the workers in the experimental group were able to improve performance on computerized tasks over time, while the control group was not.

The study, published in Sleep, says the light therapy, sunglasses, and strict sleep schedules helped 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 off days.

"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," Smith says. "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."

Show Sources


News release, American Academy of Sleep Medicine.

News release, Rush University Medical Center.

Eastman, C. Sleep, December 2008; vol 31: pp 1639-1645.

Charmane Eastman, PhD, Rush University Medical Center, Chicago.

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