From Our 2010 Archives

Your Job's Start Time Affects Fatigue Level

Study Shows People Who Begin Work Between 8 p.m. and Midnight Have the Most Fatigue

By Katrina Woznicki
WebMD Health News

Reviewed By Laura J. Martin, MD

June 8, 2010 -- The time at which you report to work may have a significant impact on the hours and the quality of sleep you get, as well as on-the-job fatigue, according to new research presented at an annual sleep conference.

Reporting for duty between 9 a.m. and 2 p.m. was not a problem when it came to getting optimal sleep, but researchers from Washington State University in Spokane found that reporting to work between the hours of 8 p.m. and midnight created the most problems for sleep duration and fatigue.

Not surprisingly, maximum fatigue occurred when work shifts began at 11 p.m. and minimum fatigue occurred when the work day started at 9 a.m. There was also a decrease in predicted fatigue for shifts starting after midnight as compared with before midnight.

The research team used mathematical modeling and hypothetical work schedules to predict the effects of starting work and when sleep occurred during a 24-hour period, and also factored in on-the-job fatigue during a nine-hour work period over six days. The model did not allow for sleeping on the job or for sleeping one hour before or after the shift at work.

The findings were presented at the American Academy of Sleep Medicine and the Sleep Research Society conference, the 24th annual meeting of the Associated Professional Sleep Societies, in San Antonio.

Before Midnight vs. After Midnight

The results suggest the time you are required to show up for work may be as important as how many hours you spend on the shift.The researchers said employers may want to consider work schedules that maximize sleep and on-the-job alertness, which, in turn, could help maximize job performance and productivity.

"Our most interesting finding was that shifts beginning between 8 p.m. and midnight yielded consistently poorer predicted performance and less than adequate predicted total sleep per 24 hours," says study researcher author Angela Bowen, a research assistant at the Sleep and Performance Research Center at Washington State University Spokane. "Shifts of equal duration differ in how fatiguing they are depending on the time of day when they are scheduled. The same limitation on the number of duty hours may be either overly restrictive if during the day or too liberal if during the night."

The researchers say that work shifts that begin after midnight allow workers to sleep right until their duty, so they were able to come to work somewhat well-rested. But this was not the case for workers who had to report to their jobs between 8 p.m. and midnight. Researchers said this may be because workers are not able to get restorative sleep prior to going to work because the shift is too early in their own biological clock, or circadian rhythm.

Other studies have shown how nighttime work disrupts natural circadian rhythms and may increase the risk of stress, metabolic disorders, gastrointestinal conditions, such as irritable bowel syndrome, and even cardiovascular disease. For example, a study published last year in the American Journal of Epidemiology reported that individuals who worked night shifts had a 4% increased risk of ischemic stroke for every five years spent working nights.

SOURCES: News release, American Academy of Sleep Medicine.

24th annual meeting of the Associated Professional Sleep Societies, San Antonio.

National Sleep Foundation web site: "Shift Work and Sleep."

Brown American Journal of Epidemiology, June 1, 2009; vol 169: pp 1370-1377.

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