KEY POINTS:
Anyone who does shift work knows it can be brutal and even if you think you're getting used to it, researchers say you're not.
"Physiologically, people don't fully adapt to night work. Your body doesn't make you into a night-active person just because you're on the night shift," says Professor Philippa Gander, director of Massey's Sleep/Wake Research Centre.
Shift workers suffer from cardiovascular disease, suppressed immune systems and digestive problems, such as gastric ulcers, more than other workers.
Gander says the digestive issues are due to the body's inability to digest food efficiently at night and the shift workers' poor diet. (She suggests not having a heavy meal during the night shift.)
But these workers also suffer socially. The lack of normal sleep causes fatigue and irritability that might also take their toll on relationships.
"With shift work, it's not only the effects on sleep but the increasing conflict between work demands and the other things that you want to do in your life."
New Zealand Data shows fluctuating sleep cycles makes people more prone to accidents.
"People who work rotating shifts are about twice as likely to report having a workplace injury."
But more and more businesses are moving to 24-hour operations.
Managers who just dream up rosters without carefully considering workers' circadian rhythms might be causing them undue stress and physical harm.
Gander says many managers are often not fully aware of the hours workers put in on shifts until payroll and rostering data are tracked over time.
"Often managers get quite a surprise to see what's actually being worked when they think they've put in place good principles for doing this right, but in fact it doesn't work like that."
Whether it's people swapping shifts or shifts running late, rosters can end up being quite fluid.
Gander recommends an open dialogue between workers and management to make sure things are kept in check.
"When you're looking across a roster you have to look at how much sleep people are losing day by day and how that is building up. The effects of restricted sleep accumulate."
Also, the more you displace sleep from its preferred time, the less good quality sleep people are able to get.
"Sleep goes back to normal after two nights of unrestricted sleep but we're not sure how long it takes for their daytime performance to get back to normal."
Sometimes a weekend is not enough. In laboratory experiments people were given five nights of unrestricted recovery sleep but were still unable to restore their performance.
The reason likely lies with our circadian rhythm. Gander says our body clock only allows us certain windows for sleep.
"There's a period of time just before your normal bedtime at night when you can't go to sleep. We call it the evening wake maintenance zone."
This can make it hard to fall asleep when you've got an early start even if you're sleep deprived.
"Just because you know you've got a start at 4am tomorrow, you can't go to bed at 7pm tonight and fall asleep," she says.
In a normal sleep pattern, Gander says we go to sleep five hours before our body temperature hits its minimum and wake three hours after.
The body sticks with this pattern even if we're working the overnight shift.
Night workers generally find they have a hard time sleeping for very long when they get off work in the morning.
"Your body temperature is starting to rise and it's very hard to sleep beyond about lunchtime for most people. You're only allowed to sleep basically up to about six hours after your body temperature minimum," she says.
The solution is for night workers to go straight to bed after work in the morning.
Gander recommends no shopping, no exercise - just get to bed as quickly as you can before your body clock clicks back into wake-mode.
Since overnight workers will have a hard time sleeping eight straight hours, Gander says a split-sleep, with a nap just before work in the evening, works well.
Just keep the bedroom dark and quiet and switch the phones off.
The brain is measuring light levels even when your eyes are shut.
"The body clock is sensitive to light. It has its own input pathways from the retina so that even some people who are blind still have light input to their body clocks."
But even if we can't cheat the circadian rhythm, we have to find a way to deal with shift work.
Whether it's the overnight security guard or the foreman who must keep the plant running 24/7, workers will have to endure having their sleep displaced - and Gander says medication is not a solution.
"It's not a reasonable expectation that somebody will manage their entire working life on pills," she says, adding that the only solution at present is improved communication between shift workers and managers.
"There isn't a unique solution or a best roster," says Gander. "What you need is a process for all parties to be in an ongoing dialogue about what's working and what's not and how to improve it."
