Working night shifts may raise risk of diabetes: Study

By Dr. Ananya Mandal, MDDec 8 2011

About 26% percent of the American workforce, including health-care workers and sanitation staff, need to work night shifts. Earlier research has shown that regular night shifts may disrupt the circadian rhythm, raising the risk of heart disease, obesity, ulcers and even depression.

In a new study in the journal PLoS Medicine, scientists also find that rotating night-shift work can increase the risk of developing Type 2 diabetes. Dr. Frank Hu, a professor of nutrition and epidemiology at Harvard School of Public Health explains that the schedule mismatch can interfere with the body's ability to use insulin properly to break down sugars in the blood.

In the study involving nearly 177,000 middle-aged women enrolled in two Nurses' Health Studies, women who worked rotating night shifts for 1 to 2 years increased their risk of developing diabetes by 5% over a 20-year follow-up period, compared with women who didn't get assigned these shifts. Women who kept up night work for 10 to 19 years increased their risk by 40%. Working on and off at night for more than 20 years boosted the risk of diabetes by 60%.

“The increased risk is not huge, but it's substantial and can have important public health implications given that almost one-fifth of the workforce is on some kind of rotating night shift,” says Dr. Hu

The study adds that body weight is part of the problem, since excess weight is a risk factor for diabetes. People who work at night may snack more when they should be sleeping. Since bodies are metabolically more inactive after sun down, these extra calories are less likely to get burned off efficiently, and more likely to be stored as fat.

Additionally not getting enough sleep raises levels of the appetite-stimulating hormone ghrelin and suppresses the appetite-curbing hormone leptin. “The bottom line is there are probably multiple mechanisms through which disrupted sleep patterns or long term rotating night shift work can influence the risk of Type 2 diabetes,” says Hu. Shift workers tend to sleep less, smoke more, and eat less healthy diets than other people, Hu says. “The overall risk associated with rotating shift work is probably due to the combination of biological factors resulting from disruption of circadian rhythms and…behavioral risk factors,” he says.

What intrigued Hu and his team the most was the cumulative effect that night work had on diabetes risk. The longer people worked irregular hours at night, the higher their risk of developing the disease. “It's something people should keep in mind,” he says. “If they minimize or reduce the time they work on night shifts, they may be able to attenuate their risk.”

The study was the largest to date to explore the link between shift work and diabetes, but the authors stress that more research will be needed to confirm the results, especially in other populations. The study included only female nurses and the vast majority was white, so the findings don't necessarily apply to men or other ethnic groups, they say.