Safety gets short shrift on long night shift.

Safety gets short shrift on long night shift

New studies of the human "biological clock" and its interactions with the chemistry of sleep deprivation have important implications for night-shift workers--and for anybody depending on their services. The research shows that workers who regularly put in unusually long hours, especially when those hourts stretch through the night and into dawn, are significantly less attentive, think and remember less clearly and have more accidents and near-accidents during working hours than do co-workers on regular day or afternoon/evening shifts.

These findings have direct relevance to the 20 million to 30 million U.S. workers who have nontraditional work schedules--including medical interns and residents - and appear to contradict a recent report in the NEW ENGLAND JOURNAL OF MEDICINE that found no decrease in performance among sleep-deprived medical interns (SN: 10/1/88, p.218).

Charles Czeiler of Brigham and Women's Hospital in Boston studied some of the behavioral effects of innate human biological rhythms by giving a battery of tests to people living in a sealed, "time-free" laboratory. He also interviewed thousand of rotating-shift workers about their work habits. He got an eye-opening view of what happens when you combine the generalized fatigue that comes with daytime sleeping with workforce-enforced wakefulness during the hours when the brain's pacemaker most wants you to go to sleep. "The safety implications for this kind of disruption of the circadian timing system have not really been fully recognized in our society," he said this week in San Francisco at the annual meeting of the American Association for the Advancement of Science.

More than half of the interviewed rotating-shift workers -- including truck drivers and nuclear power plant operators -- reported nodding off or falling asleep at least once a week while at work. Mean alertness ratings of workers on night shifts were about half the value reported by workers on afternoon/evening shifts -- the time whem workers report being most alert.

In a pilot study of 28 medical interns, Czeisler says he was surprised to find that during the past year more than one-quarter of them had fallen asleep while talking on the telephone. Thirty-four percent reported at least one actual or nearmiss automobile accident during the year because of sleepiness--more than triple the percentage they reported in the year before their internship.

Laboratory research suggests that cyclic changes in performance, including a slump typically experienced by workers in the hours before dawn, are programmed by the biological clock -- a small nucleus of nerves embedded deep within the brain. Scientists have found no quick and easy way to eliminate that early-morning slump or otherwise alter the human clock's basic 24-hour rhythm by more than about one hour. So for now, Czeisler says, the way to make shift work safer is to accommodate the body's natural rhythms by allowing sufficient sleep, stabilizing work schedules and -- when shifts must be rotated -- doing so in a clockwise direction from day to evening to night.

But new research by Czeisler, involving scheduled exposures to bright light and darkness, suggests "the human circadian pacemaker is more sensitive to resetting by ... simulated sunlight and darkness than has previously been recognized," he says. He declines to discuss the unpublished work. However, he hints that the use of bright lights may someday serve to reset the human clock in the elderly--whose biological clocks tend to "speed up" with age -- or in physicians and other workers who must toil through the night.