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
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
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.