Washington ? 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.