The Health Risks of Shift Work

Medically Reviewed by Brunilda Nazario, MD on March 25, 2010
9 min read

In the U.S., about 8.6 million people perform shift work, whether they have a night job or rotate shifts during the week. For many, it's a rite of passage in their careers; for others, it's a financial necessity. But there's a growing sense that shift work could be taking a serious toll on their health.

"There is strong evidence that shift work is related to a number of serious health conditions, like cardiovascular disease, diabetes, and obesity," says Frank Scheer PhD, a neuroscientist at Harvard Medical School and Brigham and Women's Hospital in Boston. "These differences we're seeing can't just be explained by lifestyle or socioeconomic status."

Shift work is also linked to stomach problems and ulcers, depression, and an increased risk of accidents or injury.

According to the National Sleep Foundation, a shift worker is not just someone who works nights, but anyone who works outside a steady 9 to 5 schedule.

The millions of shift workers in the U.S. include police officers, firefighters, nurses, doctors, pilots, waitresses, truck drivers, and many more professionals. Even a personal trainer who works out at the gym with clients in the early mornings and evenings is a shift worker.

As shift work has become more widespread in the U.S., the health risks have become a focus both for researchers and for the businesses that employ shift workers. How serious are those dangers -- and can they be reduced? Unfortunately, we don't have all the answers yet.

Experts say that shift work could have a serious impact on our health in at least two ways. Some of it may have to do with the lifestyle that shift work encourages. The rest has to do with our biology.

In terms of lifestyle, working odd hours leads to some obvious problems. People who do shift work tend to have sleep disturbances and sleep loss. They might feel isolated, since their jobs cut them off from their friends and families. They might find it harder to exercise regularly, and may be prone to eat junk food out of a handy vending machine, says Scheer.

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.

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:

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.

Some of the serious risks associated with shift work seem to develop gradually over decades, but others develop more quickly.

Scheer led a small laboratory experiment to test the effects of disrupting the circadian rhythm. To simulate the effects of shift work, Scheer had 10 healthy adults adopt a constantly changing schedule of eating and sleeping. After just 10 days, he found that they all had lower leptin levels (which would increase appetite), higher blood pressure, and worse sleep.

Most disturbing, three of the adults showed higher than normal blood sugar levels -- high enough to qualify as prediabetic.

"The changes were very rapid," says Scheer. "It didn't take years for disruption to the circadian rhythm to have medical effects."

Scheer cautions that the implications of the study, which was published in the Proceedings of the National Academy of Sciences in 2009, are limited. A small laboratory experiment can't fully reflect what's happening to actual shift workers. It's also possible that some of these health effects might improve as people get used to shift work. On the other hand, it's also possible that these effects would just worsen over time. For now, we don't know.

The apparent risks of shift work might seem alarming. What are you supposed to do if you work nights -- or if you have a child in nursing school or training to be a firefighter? How concerned should you be?

It's important to keep the risks in perspective. Even if performing shift work is a risk factor for some diseases, it's only one of many -- just like not getting enough sleep or eating too many sweets. If you're in good health to begin with, the overall risks to any given person performing shift work remain low.

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.

    Scheer recommends that shift workers make an extra effort to practice good sleep hygiene when they're getting ready for bed. Make sure to block out the light in your bedroom with room darkening shades or with a sleep mask. Some people drive home from a night shift wearing sunglasses to reduce their exposure to morning light.

  • 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.

    Many industries are also experimenting with different approaches to shift work -- like shorter shifts and scheduled nap times.

  • See your doctor. Your doctor might suggest medicine either to help you stay awake during shifts or to help you sleep when you get into bed. Also, if you're concerned about the health effects of shift work, your doctor should monitor your health more closely. That's especially true if you already have any health problems.

    "People who perform shift work need closer monitoring," Scheer tells WebMD. "That way their doctors can tell them if they're not coping well medically."

    If your health is obviously suffering -- if you're gaining weight and your blood sugar is rising -- it could be an obvious sign that you need to consider a new line of work. If your doctor doesn't see any problems, you could perform your shift work with more confidence.

As researchers learn more about the connections between shift work and health, they'll be able to give clearer advice about the dangers and how to reduce them. For now, Scheer urges caution.

"I don't think people need to be so alarmed by these studies that they rush out and quit their jobs," says Scheer. "They should just be alert to the possible risks."