Shift Work And Our Health

The body is synchronized to night and day by a part of the brain known as the circadian clock. A shift-worker confuses their circadian clock by working when their body is programmed to be sleeping. 

The sleep-wake cycle appears to have evolved for humans to be awake during the day and to sleep for approximately eight hours at night. There is a small part of the brain called the ‘circadian clock’, which monitors the amount of light you see, moment by moment. In the evening, when the light starts to wane, your clock notices and prompts a flood of a brain chemical called melatonin, which gives the body the signal to fall asleep. Overnight, melatonin levels remain high. They drop at daybreak and remain low during the day. Circadian rhythms are physical, mental and behavioral changes that follow a roughly 24-hour cycle, responding primarily to light and darkness in an organism’s environment. They are found in most living things, including animals, plants and many tiny microbes. The study of circadian rhythms is called chronobiology.

During the day, other chemicals (neurotransmitters) – such as nor-adrenaline and acetylcholine – increase in the body and keep you awake. This system keeps you synchronized through the day-night cycle. Many other functions of the body – including temperature, digestion, heart rate and blood pressure – fluctuate through the day, tuned by the activity of the circadian clock. 

This changing rate of activity over each 24-hour period is known as the circadian rhythm. A person who works nights, or starts their working day before 6 am, is running counter to their circadian rhythm. This may put them at risk of health problems.

Metabolism at night
An important body function, which follows the circadian rhythm, is the internal body temperature. This temperature increases through the day. It reaches the lower level in the early hours of the morning and reaches the maximum level late in the afternoon. 

The tendency to fall asleep and stay asleep occurs during the decreasing phase of the temperature circadian rhythm (between midnight and 4 am). As the body temperature rises, it is more difficult to stay asleep. This is one of the reasons why night workers who try to fall asleep at 8 am find it very difficult and also find it difficult to remain asleep through the day.

Short-Term Health Effects of Shift Work
The short-term health effects of shift work are clear. Even if you're not a shift worker yourself, you've probably experienced the equivalent effects -- maybe after a transatlantic flight, an all-nighter in college, or a few nights with a wailing newborn. Aside from the obvious fatigue, effects include:
• Gastrointestinal symptoms like upset stomach, nausea, diarrhoea, constipation, and heartburn
• Increased risk of injuries and accidents
• Insomnia
• Decreased quality of life
• General feeling of being unwell

Long-Term Health Effects of Shift Work
The long-term effects of shift work are harder to measure. But researchers have found compelling connections between shift workers and an increased risk of serious health conditions and diseases.
• Cardiovascular disease. For decades, researchers have seen an association between shift work and the risk of heart attacks and heart disease.

One review of the research found that shift work seems to raise the risk of cardiovascular disease by 40%. In general, the risks seem to grow the longer a person continues to work nights. One analysis found that the risk of stroke increased by 5% for every five years a person performed shift work. However, the stroke risks rose only after a person performed shift work for 15 years.
• Diabetes and metabolic syndrome. A number of studies have found that shift work seems to be a risk factor for diabetes. One Japanese study found that shift workers -- specifically, those who worked 16-hour shifts -- had a 50% higher incidence of diabetes than day workers.
Shift work has also been linked with metabolic syndrome, a combination of health problems like high blood pressure, high blood sugar, obesity, and unhealthy cholesterol levels. It's a serious risk factor for diabetes, heart attacks, and stroke. One 2007 study followed more than 700 healthy medical workers over four years. The incidence of metabolic syndrome was more than three times as high in those who worked night shifts.
• Obesity. There are several possible reasons for the link between obesity and shift work. Poor diet and lack of exercise might be part of the problem. Hormone balance seems to be important too. The hormone leptin plays a key role in regulating our appetite; it helps make us feel full. Since shift work seems to lower the levels of leptin, it could be that night workers just feel hungrier -- and thus eat more -- than day workers.
• Depression and Mood Disorders. Some studies have found that shift workers are more likely to suffer from symptoms of depression and other mood disorders. The social isolation of shift work surely takes a psychological toll. Shift work might also affect brain chemistry directly. One 2007 study found that when compared to day workers, night workers had significantly lower levels of serotonin, a brain chemical that plays a key role in mood.
• Serious Gastrointestinal Problems. For more than 50 years, researchers have noticed that shift work seems to increase the risk of peptic ulcers. It also seems to raise the risk of general GI symptoms (like nausea, diarrhoea, and constipation) and possibly some types of functional bowel disease (like irritable bowel syndrome.) One 2008 study found evidence linking shift work with chronic heartburn or GERD.
• Problems with Fertility and Pregnancy. Research has shown that shift work can affect a woman's reproductive system. One study looked at flight attendants, who typically work in shifts. The results showed that flight attendants who worked during pregnancy were twice as likely to have a miscarriage as flight attendants who did not. Shift work also seems to be associated with an increase the risk of complications during delivery, premature and low-weight babies, fertility problems, endometriosis, irregular periods, and painful periods.
• Cancer. There is some strong evidence -- from both human and animal studies -- that shift work poses an increased risk of cancer. A 2007, a subcommittee of the World Health Organization went as far as to state that shift work is "probably carcinogenic."

Two analyses of data from different studies found that night work increased the risk of breast cancer by 50%. Working shifts on airplanes, like pilots and flight attendants do, increased the risk by 70%. There's evidence that shift work might increase the risk of colorectal and prostate cancer as well.

So far, evidence suggests that the cancer risks go up only after many years of shift work -- perhaps as many as 20 years.

If you work shifts, there are some things you can do.
• Eat well and exercise. Since many of the risks of shift work are tied to obesity and metabolic syndrome, step up your efforts to prevent them. Exercising regularly, eating well, and keeping a healthy weight could make a difference.
• Get enough sleep. Sleep deprivation has its own health risks, and studies suggest that shift workers sleep less effectively than day workers. Part of the problem is that even brief exposure to light during the day naturally wakes up your body, making it hard to sleep.
• Change your schedule. While moving to daytime shift might not be possible, making changes to how you work at night could help, too. For instance, some experts think that working stable rather than rotating shifts might be healthier.

Rotating shifts
The best rotating shift pattern is still undecided. For the most people, rotating forward through day, afternoon and night shift is better than backwards (night, afternoon then day). The frequency of rotation is also controversial. Some people advocate prolonged rotation, such as two to three weeks. Others advocate short rotations of two to three days. Both have advantages and disadvantages. 

It takes about 10 days for the body to adjust to night shift work. However, it is common for night shift workers to revert to daytime routines for a day or two during days off, which tends to make the circadian rhythm unstable.

The amount of hours (8-hour versus 12-hour shifts) is also controversial. It can be said that 12-hour shifts stretch the body’s tolerance as far as possible. It’s very important that no overtime should be allowed during a rotation of 12-hour shifts. Another risk to sleep is when a worker on seven 12-hour shifts a fortnight uses their free time for another, almost full-time job.

A proportion of shift-workers may have marked daytime sleepiness, called Shift Work Sleep Disorder. 

Prevention

DESIGN OF WORK SCHEDULE
Most of the work on minimising the deleterious effects of shift work has concentrated on the three 8 hour shift rotation. As the night shift seems to cause a disproportionate amount of the problems of shift work, night work should be reduced as much as possible, perhaps by increasing the number of crews involved. Rapid rotation of shifts (a change every few days) is preferable to slow rotation as this schedule produces less interference with circadian rhythm. Clockwise rotation (morning, afternoon, night) is preferable to counter clockwise rotation as quick changeovers—for example, the morning and the night shift in the same 24 hour period—are avoided and this rotation allows longer rest periods between shifts. Finally, a later start for the morning shift which is traditionally 0600 reduces the truncation of the previous sleep period, particularly for REM sleep. 
• On balance, the duration of shift should not be extended to 10 or 12 hours as complaints of fatigue are greater on the long shifts. However, the evidence that this translates into poorer performance and increased accidents is lacking. Many workers favour the longer shifts, not because they are longer but because the breaks between shift weeks are longer often 3–4 days. 
• Finally, there is some evidence that allowing the workers to design their own shift schedules encourages good work performance as they take responsibility for achieving the work output targets. 
• Other factors which can ameliorate shift schedules include workplace improvements in catering, supervision, health care, transportation, and recreational facilities. There is some limited evidence that bright light might be useful on the night shift to offset some of the circadian effects of the day-night changes. 

Conclusions
Work involving long hours or abnormal night-day schedules has been in existence for centuries. There is evidence to suggest that such schedules are here to stay, for one reason or another, for one in five workers. The main physiological consequence of such shift schedules is disruption of circadian rhythm which can have a deleterious effect on performance, sleep patterns, accident rates, mental health, and cardiovascular mortality. Reproductive outcome effects may be linked to disruption of menstrual cycles. Individual issues such as sex, age, and personality are also important. 
Coping with these potentially harmful work schedules involves helping people to cope and by designing workplace environments and shift scheduling schemes that lead to the least disruption to mental, physical, and social wellbeing.