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Study links shift work to risk for Type 2 diabetes

Researchers cite many possible reasons for the effect, including hormonal changes

July 31, 2014
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nighttimeShift workers, especially men, may be at higher risk for type 2 diabetes compared to people not on such schedules, a new study suggests.

Also at special risk are shift workers who don't work on a set schedule, with shifts moving around at various times of the day.

"Not surprising"

The findings are "not at all surprising," said one expert, Dr. Alan Manevitz, a clinical psychiatrist at Lenox Hill Hospital in New York City.

"Physicians have long known that working shifts disrupts many key body chemicals, creating a ripple effect that can lead to ailments such as gastrointestinal disorders, cardiovascular disease and even cancer," he said. "Now type 2 diabetes can be added to this considerable list."

In the new review, researchers analyzed data from 12 international studies involving more than 226,500 people.

The study, led by Zuxun Lu of Huazhong University of Science and Technology in Wuhan, China, took several factors into account, such as workers' shift schedules, their body mass index (BMI, a calculation of height and weight), family history of diabetes and their level of physical activity.

The gender factor

Although the findings weren't able to show a direct cause-and-effect relationship, the researchers found that any amount of shift work was linked to a 9 percent greater risk for developing diabetes. Gender also played a role -- for men engaged in shift work, the risk jumped to 37 percent.

Although the reason why men are at greater risk than women isn't clear, the researchers believe that testosterone levels may play a role. Prior studies have pointed to an association between low testosterone levels and insulin resistance and diabetes, the researchers noted.

Daytime levels of this male hormone are regulated by the internal body clock, Lu's team explained.

Those whose shifts moved around through different periods of the day were especially likely to develop type 2 diabetes than those who worked normal "office hours." The study found rotating shift work to be linked to a 42 percent greater risk for diabetes.

Possible reasons for the link

According to Lu's team, erratic working schedules make it more difficult for the body to establish a sleep-wake cycle, and poor sleep may worsen insulin resistance, a precursor to diabetes.

Previous studies have also linked shift work to weight gain and obesity, a big risk factor for type 2 diabetes. And the researchers note that shift work can also affect cholesterol levels and blood pressure.

Another expert said other factors may be at play as well.

"Growth hormone, known to elevate blood glucose when present in excess, peaks at 1 a.m.," noted Dr. Gerald Bernstein, director of the Diabetes Management Program at Friedman Diabetes Institute at the Beth Israel Medical Center in New York City. "Shift work also often makes it more difficult to schedule regular meals and exercise."

For people who work those shifts...

Still, Bernstein said that "even with a strong risk for diabetes I would not discourage someone from taking a job that is based on shifts."

Instead, he said "it would be better to screen shift workers regularly for pre-diabetes and intervene to slow the progression to full-blown diabetes."

Manevitz agreed. "Those who must do shift work would be wise to consult their doctor, who can monitor cholesterol levels, blood pressure and insulin levels to detect if blood sugar levels are creeping up dangerously," he said. "Doctors may also be able to prescribe sleep aids to help shift workers get the proper amount of sleep, even if that sleep comes during odd hours."

The study was published recently in Occupational & Environmental Medicine.

SOURCE: Alan Manevitz, M.D., clinical psychiatrist, Lenox Hill Hospital, New York City; Gerald Bernstein, M.D., director, Diabetes Management Program, Friedman Diabetes Institute, Beth Israel Medical Center, New York City; Occupational & Environmental Medicine, news release, July 24, 2014

Source: HealthDay, A service of the U.S. National Library of Medicine, National Institutes of Health

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