It is estimated that 10% of people who work nights and rotating shifts experience shift work sleep disorder (SWSD). This isn't just people complaining about their jobs; it is considered a legitimate disorder and public health experts and occupational health authorities take it seriously.
Also called shift work disorder, the condition most often affects those who work the overnight and early morning (before 7 AM) shifts. Like other circadian rhythm disorders, the symptoms are a slow-burning multi-threat:
Primary circadian disorders are genetic and/or physiological. Behavioral circadian disorders are caused by people attempting to stay up past their bedtimes. Or in the case of shift work disorder, by working when they should be asleep and sleeping when they should be awake.
In the United States, about 20 to 25 percent of the population that works does some sort of shift work. Surveys show that 60 to 70 percent of shift workers occasionally complain of problem sleepiness on the job, or insomnia at home. These complaints are not all due to shift work sleep disorder. Many who work the day shift have the same complaints. It is true that the doctor must make a judgement call when assigning a diagnosis of shift work disorder, but judgement calls are often needed when treating sleep disorders.
The particulars of the work schedule matter a lot. Working evenings (such as a retailer or restaurant) doesn’t normally cause many problems if the employee is off by midnight. Bar workers often work later than that. The worst is in people who truly have to work overnight and are at work when the Sun comes up the next morning. The length of the shift matters, too, as long shifts add tiredness to the circadian disruption the body experiences.
Some plants and factories employ rotating shifts. An employee might be asked to work one week during the day, followed by a week on "swing shift" (to about midnight), followed by a week on "graveyard shift" (overnight). This schedule is especially rough on a portion of the population whose bodies don’t shift fast enough so they get used to the current week’s schedule. Many people say they prefer a permanent graveyard shift to the rotating shift schedule.
The circadian rhythms naturally prepare people for sleep during nighttime and waking during the day. When you try to adopt a different sleep schedule, your physiology doesn’t fully shift the body’s response in body temperature and melatonin and cortisol levels in the bloodstream. (Cortisol is a steroid hormone produced by the adrenal glands and important in stress control. See also our page on sleep and stress.) Most bodily functions have at least some circadian rhythm, so the confusion created by working at the wrong time for the body can have detrimental effects over the long run.
Additionally, social custom promotes sleep during the night more than during the day. Phone calls, ambient noisiness in a household or neighborhood, and other people can make it hard to sleep during the day.
Even in workers who seem to adapt to their work schedule with ease, the subtle physiological mistimings can put stress on the body, the brain, work productivity, and workers’ relationships.
In April 2012 the CDC's Morbidity and Mortality Weekly Report (MMWR) examined the topic of insufficient sleep and industrial safety. See their report at Short Sleep Duration Among Workers
"The sleep of a laborer is sweet" - Ecclesiastes 5:12
The shift in sleep patterns produces a general stress on the body, and consequent increased risk of disease. The incidence of gastrointestinal symptoms increases. Work productivity is also lower. On-the-job accidents are higher when adjusting for the fact that there are fewer people in the workplace. One survey found that 20% of shift workers reported an accident or near miss driving home from work in the previous year.
SWSD results in lower scores on quality of life surveys and in more reports of feelings of ill health.
Long term downsides associated with SWSD include increased risks for
The connection to cancer is more tenuous. Some studies have suggested shift work increases the risk of breast cancer, although a recent epidemiological study at Ohio State University found no connection between cancer and shift work. On the other hand, a World Health Organization study group in 2007 found "shift-work that involves circadian disruption is probably carcinogenic to humans".
This conclusion was reached from observation of large numbers of people. Nobody knows exactly why this should be true, but there is speculation that the biochemical signals that tell the cells to divide are off. Because malignant cells divide quickly, this may promote the growth of tiny tumors into real cancers.
Psychiatrists generally discourage those from bipolar disorder from taking jobs that require circadian shifts for fear that it might provoke an outbreak of symptoms.
The effect of shift work on pregnant women has received a lot of attention from industrial hygienists. Night work also increases the chances of the baby being of low birth rate according to a couple of studies: http://www.ncbi.nlm.nih.gov/pubmed/15295380 Both of these epidemiological analyses were from studies in the 20th Century. Better prenatal care may have changed the risk. The UK’s Royal College of Physicians published a study which found: "there was evidence that shift work is not associated with a high risk of adverse pregnancy outcome."
Either with their doctor's cooperation or without, many shift workers use medications to manage this disorder. These include both sleep aids (hypnotics), melatonin, and stimulants (especially caffeine.) The prescription stimulant modafnil is approved by the FDA for SWSD. Melatonin may be able to shift the body’s circadian rhythm to accommodate the work schedule, although it is difficult to get the timing and dosage right for this to be effective. Stimulants help people overcome sleepiness caused by the shift.
Keeping healthy in other ways – the regular preventative behavior of eating right and exercising – can somewhat mitigate the risks SWSD brings. A conscious and concerted effort to sleep when the schedule and body permits can help reduce lost sleep. Getting a ride to and from work can help, too, as it lowers the risk of drowsy driving.
Many find they function better when they take a nap just before reporting for a night shift. This may go against the schedule many night workers adopt – that of going to bed immediately after getting home from work and then staying up until the next shift. Adding a nap of an hour or so before going back to work helps many stay alert and performing well on the job. Prophylactic naps have been shown to help pilots before they embark on transmeridian flights. (Like the passengers the pilots are susceptible to jet lag.)
"Early to bed, and early to rise,
makes a man healthy, wealthy, and wise." -- Benjamin Franklin, 1758