(AP) -- Reports of sleeping air traffic controllers highlight a long-known and often ignored hazard: Workers on night shifts can have trouble concentrating and even staying awake.
"Government officials haven't recognized that people routinely fall asleep at night when they're doing shift work," said Dr. Charles Czeisler, chief of sleep medicine at Brigham and Women's Hospital in Boston.
Czeisler said studies show that 30 percent to 50 percent of night-shift workers report falling asleep at least once a week while on the job.
So the notion that this has happened only a few times among the thousands of controllers "is preposterous," he said in a telephone interview.
In a sign of growing awareness of the problem, the Federal Aviation Administration said Saturday it was changing air traffic controllers' work schedules most likely to cause fatigue. The announcement comes after the agency disclosed another incident in which a controller fell asleep while on duty early Saturday morning at a busy Miami regional facility. According to a preliminary review, there was no impact to flight operations, the FAA said.
Czeisler said the potential danger isn't limited to air traffic controllers, but can apply to truck and bus drivers, airline pilots and those in the maritime industry. Who else? Factory workers, police, firefighters, emergency workers, nurses and doctors, cooks, hotel employees, people in the media and others on night or changing shifts.
"We live in a very sleep-deprived society where many people are burning the candle at both ends," Czeisler said. He said that a half-century ago, just 2 percent of people slept six hours or less per night; today it's 28 percent.
Dr. William Fishbein, a neuroscientist at the City University of New York, said that when people work odd shifts "it mucks up their biological rhythms."
Hormones are synchronized with the wake-sleep cycle. When people change shifts, the brain never knows when it's supposed to be asleep, so this affects how people function.
People who change shifts every few days are going to have all kinds of problems related to memory and learning, Fishbein said. This kind of schedule especially affects what he called relational memories, which involve the ability to understand how one thing is related to another.
In addition to drowsiness and inability to concentrate, people working night shifts are more subject to chronic intestinal and heart diseases and have been shown to have a higher incidence of some forms of cancer. The World Health Organization has classified shift work as a probable carcinogen.
"We have 500 cable channels, we take work home with us on our Blackberrys and computers, both work and entertainment options are available 24 hours a day seven days a week and there is much more and brighter light exposure in our homes in evenings, which affects hormones involved in sleep, Czeisler said.
"And we are still trying to get up with the chickens because our work hours are starting earlier and earlier," he said.
Today, controllers are at the center of the firestorm, with recent reports that several planes couldn't contact airport towers for assistance in landing. Members of Congress are responding to a worried public, controllers have been suspended and the head of the government's air traffic control system has resigned.
President Barack Obama told ABC News that controllers must stay alert and do their jobs.
One old solution back in the news is allowing night workers to nap.
"There should be sanctioned on-shift napping. That's the way to handle night shift work," said Gregory Belenky, a sleep expert at Washington State University in Spokane.
A NASA study suggested that pilots on long-distance flights would perform much better if given a chance to take a scheduled nap, as long the rest was planned and the both pilots didn't sleep at the same time.
"But even though that's been known for decades, it's never been allowed because we prefer to pretend that these things are not happening," instead of managing the problem, Czeisler said. "We have a bury-our-head-in-the-sand attitude."
Controllers are often scheduled for a week of midnight shifts followed by a week of morning shifts and then a week on swing shifts. This pattern, sleep scientists say, interrupts the body's natural sleep cycles.
Many of the Federal Aviation Administration's 15,700 controllers work schedules that allow no realistic opportunity for rest. Their record for errors on the job has grown sharply over the past several years.
FAA rules prohibit sleeping on the job, even during breaks. Employees who violate them can be fired. But controllers told The Associated Press that napping at night where one controller works two jobs while the other sleeps, and then they swap, is an open secret within the agency.
Czeisler also is urging screening of truck drivers for sleep apnea, a breathing problem they can be prone to because many are obese. He estimates that as many as 250,000 people in the U.S. doze off while driving every day, mostly in the daytime.
Studies have shown that a sleep-deprived driver is as impaired as someone with enough alcohol in his blood to be considered a drunken driver.
Even a drunk has some reflexes. "If you fall asleep, your performance is much worse," he said.
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Brigham and Women's Hospital's Division of Sleep Medicine: http://tinyurl.com/3sll8q7
National Sleep Foundation: http://www.sleepfoundation.org/