Driving home from night shift may be safer with light therapy

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Exhausted shift workers may be safer driving home at night when they're exposed to bright light before they hit the road, a small study suggests.

To test the effect of light therapy on driving, researchers did a series of three experiments with 19 adults. In two scenarios, participants spent a night being sleep-deprived in a lab and then spent 45 minutes in dim or bright light before a driving test. For a third test, people got a good nights' sleep at home and then went to the lab for 45 minutes of bright light exposure before a driving test.

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After sleep deprivation in the lab, five people exposed to dim light therapy got in car accidents during the driving simulations. None of the people who slept at home crashed, and neither did any of the sleep-deprived people who got bright light therapy before getting behind the wheel, the study found.

"We experience severe sleepiness toward the end of the night shift, and this may overlap with our commute time," said senior study author Dr. Ralph Mistlberger of Simon Fraser University in British Columbia, Canada.

"Sleep deprivation makes this worse of course, and together with the clock, this conspires to impair our ability to sustain attention to task (e.g., driving), and avoid distraction, and react quickly to external stimuli like traffic lights, brake lights in front of you, road signs, etc," Mistlberger added by email.

"Bright light is alerting," Mistlberger said.

Sleepiness is a leading risk factor for automobile accidents because it can make drivers less vigilant, slow reaction times and dull cognitive abilities, researchers note in Sleep Medicine.

Shift workers with chronic sleep deprivation also face an increased risk of accidents. Strategies like drinking coffee or soda, napping before a drive or blasting music or rolling down the windows in the car may help increase alertness behind the wheel, but none of these strategies is fool-proof.

For the current study, researchers wanted to see if bright light might help reduce driving impairments related to sleep deprivation.

They found participants had lower body temperatures after spending a sleep-deprived night in the lab, as well as longer reaction times and increased sleepiness.

Exposure to bright light didn't appear to improve reaction times or sleepiness. But light was associated with better driving.

Beyond its small size, other limitations of the study include the reliance on lab conditions for sleep deprivation and light exposure, which may not match what shift workers would experience on the job, the authors note.

"There is evidence that the use of bright light at the office (or even at home directly prior to beginning the work shift) may be beneficial in preventing sleep deprivation-related motor vehicle collisions," said Russell Griffin, a researcher at the University of Alabama at Birmingham who wasn't involved in the study.

"That said, there is not enough evidence to date to fully suggest the use of bright light therapy to avoid collision," Griffin added by email.

The proven way to avoid the effects of sleepiness on the road is to consistently get enough sleep, said Dr. Flaura Koplin Winston, a researcher at the University of Pennsylvania and the Children's Hospital of Philadelphia who wasn't involved in the study.

"Drowsy driving is perhaps the most under-recognized cause of serious crashes and sadly, the evidence is not there on how to counter it," Winston said by email.

More research is needed on the potential of bright light therapy to make exhausted drivers safer, said Dr. Donald Redelmeier, a researcher at the University of Toronto who wasn't involved in the study.

But there are still things drivers can do now to stay safer on the road.

"Safety strategies while driving can include minimizing distractions, stopping at stop signs, respecting speed limits, yielding right-of-way, buckling a seatbelt, signaling all turns and not driving after drinking alcohol," Redelmeier said.