It is midnight on a Friday night at the Sainsbury's in Chiswick, west London. The car park is dead and the shop is not much livelier. The number of customers barely outweighs the number of staff, who are pottering about between storerooms, aisles and checkout points. Somewhere in the grocery section, sandwiched between the bananas and the peaches, is Andrew, busying himself stacking grapefruits. He is one of the night shift workers on the supermarket's new 24-hour opening slot. He's been here three hours and has another seven to go.
"It has its moments," he says (and he gets paid more than he would for day work, of course). "I try and get into the swing of it but it's still tough on my days off. When I get home in the morning I usually sleep until midday. I manage to catch about four or five hours a night." Beneath glaring white lights, I ask whether he's noticed any changes in himself since he's been doing the night shift. He says he still feels tired all the time, even though he has been doing nights for almost four years now.
Four years of feeling tired... As Britain goes headlong down the 24-7, open-all-hours road, experts are becoming increasingly concerned by the number of people working unsocial hours - whether very early or very late. Last week a new exhibition, Rhythms of Life, opened at the Natural History Museum. The message there is that we are meant to sleep at night - from about 10.30pm onwards, for about six to eight hours - and anything else can be harmful.
"We have an internal clock that is hard-wired into our brains and tells us that we're just not supposed to be awake at night," says Mike Rosekind, whose American company, Alertness Solutions, advises businesses on the risks of tinkering with our natural timetabling. "Every 24 hours we are programmed to be hungry at certain points, alert at certain points and sleepy at certain points. Critical to the clock is that we're awake in the day and asleep at night."
Our internal clock, says Rosekind, is kept in sync by the natural cycles of light and dark. "People always say to me, 'Won't my body adjust?' Well, it could do, but as soon as someone leaves work to drive home they get that trigger of light that says it's time to be awake."
Sleep researcher Barbara Stone, at the centre for human sciences in Farnborough, Hampshire, says: "It's very rare someone can totally turn around their 24-hour clock and get a good day of sleep. Studies on night nurses show that as soon as they have time off they quickly go back to being diurnal."
Research suggests that cheating this basic programming can seriously damage your health. Long-term shift-working can cause cardiac problems and a greater incidence of depression, although researchers admit that both effects could be caused by the fact that the workers' unsocial hours have left their family and social life in tatters.
Studies on a variety of animals indicate that being kept awake at night may lower life expectancy. "The long shifts can also affect people's immunity to illnesses and damage nutritional intake," says Stone. "It seems people who work night shifts also have more problems with ulcers, though that may be to do with the wrong sort of diet since night workers tend to snack on things like chips."
That rings true for Tarq, a barman who used to work the all-night shifts. "I just felt really unhealthy all the time. Because of my hours I'd be having dinner really early and another snack in the middle of the night. And when I woke up I just didn't know whether to eat breakfast or lunch or what. And the weird hours also meant it was virtually impossible to keep the proper exercise routine which I was used to, so I just ended up feeling really greasy and horrible," he says.
"What you're hit with," says Rosekind, "is a kind of double whammy. As well as disrupting the clock, a person is lucky if they can get more than 5 or 6 hours sleep during the day. So all the time they are night-working, they are building up a sleep debt that makes them twice as vulnerable to mental and physical problems."
Laura used to work through the night to prepare for a morning television show. She describes the experience of doing regular night shifts - and these were pretty much from dusk until dawn - as nothing short of awful. "I just couldn't sleep during the day and was getting colds and coughs and chest infections when I had basically never got ill before," she says. "Only now that I've stopped doing it do I realise that it can really impact on you and that it could cause long-term sleep and energy problems and really make people depressed. I think if you've got a vaguely sensitive constitution it's a really tough thing to do."
Professor Neil Douglas, chairman of the British Sleep Foundation, argues that while the physical impact may be severe, the real strain of night shifts is on our mental capabilities. "People who work nights are jeopardising their decision-making, their planning - and they are more likely to have accidents, simply because they are too sleepy. Just coming home from work is a high-risk activity since car accidents are much, much more common for night shift workers than day shift workers." The evidence is cast in both statistics and history. The highest number of errors and accidents on the road is between 3am and 5am - our body's most naturally sleepy time - and disruption of the body clock has also been implicated as one of the root causes of the Chernobyl and Challenger disasters.
"This is the downside to the invention of the light bulb," says Douglas. "Before it existed people got their eight hours sleep in total darkness. Now people can stay up all night, but it's all to the detriment of their performance and to their health."
But surely there must be simple of ways of tricking your body into thinking everything's all right? Going for a run when you get home, say, or having a quick nap during the night? "Nothing helps," says Laura. "It's just wrong and you can't fool your body into thinking it's right. There do seem to be a handful of people, largely men, who seem to adapt well to nights and are happy to do them for years, seeing their family in the mornings, but they are a tiny minority.
"You'll hear advice about breaking up your sleep - snatching four hours here and four hours there - but it's basically rubbish. The bottom line is that we should be tucked up in bed at night, and anything else will start to feel like torture after a while. And it takes a long time to get over - it can be months before you feel you've really recovered from a long run of nights."
If you do have be awake at night, the best thing to do is avoid the triggers that tell you you are supposed to be awake
• Try and leave work before it gets light. If it has already started getting light, wear dark glasses to help you "miss" the morning signal.
• Have your home environment as light-proof as possible. Use black out curtains or put cardboard up by the windows.
• Keep the environment around you as quiet as possible. Unplug the phone, put up "Do Not Disturb" signs. A masking background noise, such as a tape playing the sound of the ocean, can also help block out daytime noises.
• Create sleeping habits. A regular ritual before bed will help tell your body it's time to sleep.
• Avoid snacking and maintain a diet of three healthy meals when awake.
• Schedule time with family and friends. Make sure they know when is a good time and when is a bad time to disturb you.
For more information visit www.alertness-solutions.com
