The Health Risks of Shift Work
How Does Shift Work Affect Us? continued...
But Scheer and other experts believe a significant part of the problem with shift work is physiological. On a fundamental level, being awake at odd or irregular hours fights with our biological rhythms. Shift work disrupts the circadian rhythm -- our internal body clock that is keyed to natural daylight and darkness.
Because circadian rhythm affects how the body functions, disrupting it can throw everything out of whack -- including our cardiovascular system, metabolism, digestion, immune system, and hormonal balance. That appears to have serious consequences.
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:
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, diarrhea, 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.