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 attempt to stay up past their bedtimes. This happens pretty often among people who like to burn the candle at both ends; it can be fun to stay up late on weekends, etc. After a few days with a shifted sleep time, people get used to their new time. However, getting used to the new pattern only happens to some extent. If the natural circadian rhythm clashes with the imposed cycle of the shift work, problems can develop over the long run.
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 complain of problem sleepiness on the job, or insomnia at home. 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 as fast as others. 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. Even working nights 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.)
Additionally, social custom promotes sleep during the night more than during the day. Phone calls, general noisiness in a household or neighborhood, and other people can make it hard to sleep during the day. If the sleep disturbances caused by working an odd shift is severe enough, the person may be designated as having shift work sleep disorder.
In April 2012 the CDC's Morbidity and Mortality Weekly Report (MMWR) examined the topic of insufficient sleep and industrial safety - Short Sleep Duration Among Workers
"The sleep of a laborer is sweet" - Ecclesiastes 5:12
One effect of the shift in sleep patterns is a general stress on the body, and consequent increased risk of disease. 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.
The disruption of the sleep cycle from shift work influences the physiological functions of the body. 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. It has long been known that shift work is associated with an increase in heart attack risk. There are also some suggestions that there is a connection association between metabolic syndrome and shift work. A study released in 2012 found shift work increases the risk for diabetes and obesity.
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 accordning to a couple studies: http://www.ncbi.nlm.nih.gov/pubmed/2617256 and 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.
Napping before a night shift has been proven an easy and effective way to maintain performance on the job. This can be especially valuable for people who have to drive cars on the job, such as police officers.
"Early to bed, and early to rise,
makes a man healthy, wealthy, and wise." -- Benjamin Franklin, 1758