Graveyard shifts or nigh shifts might raise scary visions, from ulcers and depression to heart disease and cancer. Still it is possible to manipulate one's circadian rhythm to suit odd working hours.
Reacting to some recent studies on the adverse impact of working in night shifts, Dr. Louis Ptacek, a University of California neurologist studying genes and sleep behaviours, said, ""It's not surprising....We evolved on a planet that is rotating every 24 hours. Our internal clock is more than just when we sleep and wake. It's related to cell division and it regulates our immune systems. When we battle our internal clock, that has complications."
Most researchers - and night-shift employees - agree that a fatigue factor undoubtedly goes along with working the graveyard shift. It's more difficult to get a good night's, or rather day's, sleep, and it can be a challenge to force the mind and body to be at their best in the middle of the night.
Roughly 15 million people, or 15 percent of American workers, regularly work a shift that's outside the typical daytime schedule, according to the U.S. Department of Labor. Studies have shown that between 10 and 20 percent of shift workers have trouble with insomnia when they're trying to sleep and feeling sleepy on the job when they're trying to stay awake.
That leads to the obvious connection between sleepiness and the risk of accident - either on the job or driving to and from work. People who are sleep-deprived can succumb to "microsleeps," where they fall asleep for just a few seconds and don't even realize it, said Dr. Clete Kushida, director of the Stanford University Center for Human Sleep Research.
"Probably the most obvious problems with (night) shift work are cognitive functions, so people have difficulty focusing. They might have problems with irritability and mood fluctuations," Kushida said. "And then there is excessive sleepiness, which can lead to motor vehicle accidents and industrial accidents."
But then not everyone agrees that shift work is much of a health concern, points out Erin Allday, writing in San Francisco Chronicle.
"The data here is not extremely firm," said Dr. Allan Pont, vice president of medical affairs at California Pacific Medical Center, who ran the hospital's residency training program for 20 years. Pont, who has worked many night shifts himself, said he's skeptical of the idea that many health problems are related to work schedule.
"Obviously it's difficult when people change from a day shift to a night shift," he said. "There are those who can adapt to it and those who don't. Those who adapt probably do just fine, and the others quit."
The focus of much research on shift work disorder is on the circadian rhythm - the body's internal clock that keeps everyone on roughly a 24-hour schedule. It's possible, doctors say, for people to alter their circadian rhythm so that they are perfectly healthy and comfortable working a night shift regularly.
The problem is that humans are accustomed - both by societal pressures and centuries of evolution - to sleeping at night and being active during the day. Very few people want to live on a permanent schedule that has them sleeping away the daylight hours. Instead, most people who work a regular night shift end up throwing their clock off every weekend when they try to adjust to the rest of society.
"If you can get the person to stay on the schedule seven days a week, they're usually OK. But who wants to live their life at night on their days off? What about their vacations?" noted Dr. Sunil Rama, medical director of the Kaiser sleep laboratory.
"A reasonable percentage of Americans work a night shift, and a majority of them have health issues related to it," he said.
"It's been linked to arteriosclerosis, headaches, insomnia, excessive sleepiness. You ask anyone who's worked nights, and they're usually a wreck the next day."
But a woman said that after 30 years of off-and-on graveyard duty she had adjusted pretty well to her overnight shifts. The key to staying healthy, she said, was to prioritize.
She typically gets off a night shift at around 6:30 a.m. and drives home wearing dark glasses - bright light generally stimulates the body to stay awake despite the exhaustion.
At home, she takes care of any potential disturbances - she feeds the cats, turns off the phone, closes dark blinds in her bedroom. Sometimes she'll have a small snack, but usually it's just some tea.
She usually sleeps until about 3 p.m., then has breakfast. She'll get some light exercise like yoga - she saves the active workouts for days she doesn't work. Lunch is at 9 p.m., dinner at 3 a.m.
"You have to really be aware of your health - am I eating well, am I sleeping enough, am I exercising?" Toms said. "It just takes planning. You have to realize this is your lifestyle and be ready for it."
-- Those who work five nights a week should stick close to the same schedule on days off.
-- Try to go to bed as soon as possible after getting off work.
-- Set up a bedtime routine - something to signal to the body that it's time to sleep. That could mean making a cup of tea or taking a hot bath or shower.
-- Wear dark sunglasses when leaving work in the morning.
-- Use window coverings that block out all light. Sleeping masks also can help.
-- Get rid of noisy distractions.
-- Make time for exercise.