Shift work linked to greater diabetes risk

By Shereen Lehman

NEW YORK (Reuters Health) - People who work night shifts, or constantly changing shifts are more likely to develop type 2 diabetes compared to non-shift workers, suggests a new meta-analysis.

The risk was highest for men and people who worked rotating shifts, but the reasons for those differences remain unclear, researchers say.

"Shift work is very common in modern society," the study's senior author Zuxun Lu told Reuters Health in an email.

"Over the past decades, a few epidemiological studies have assessed the association between shift work and the risk of diabetes mellitus with the inconsistent results," said Lu, a researcher at Tongji Medical College, Huazhong University of Science and Technology in Wuhan, China.

As reported online July 16th in Occupational and Environmental Medicine, Lu and colleagues pooled data from 12 previous studies that looked at the association between shift work and chances of developing diabetes. The studies, published between 1982 and 2013, involved 226,652 participants, including 14,595 with diabetes.

Six of the studies were conducted in Japan, with two each from the U.S. and Sweden and one each from Belgium and China.

The risk of diabetes was increased by 9% overall for shift workers, compared to people who had never been exposed to shift work.

Male shift workers had a 28% greater risk of developing diabetes than their female counterparts. And people who worked rotating shifts had a 42% greater risk of diabetes compared to non-shift workers.

It's not known how long the participants in those studies had been shift workers, which limits the authors' ability to interpret their results.

The new analysis doesn't prove that shift work causes diabetes or explain how it might do so, they acknowledge.

"More prospective cohort studies with long follow-up periods are warranted to replicate our findings and reveal the underlying biological mechanism," Lu said.

He speculated that shift work may interfere with eating and sleeping patterns and disrupt circadian rhythms.

"Some studies have shown that insufficient sleep and poor sleep quality may develop and exacerbate insulin resistance," Lu said.

In addition, previous studies show that shift work is associated with weight gain, increase in appetite and body fat, which are major risk factors for diabetes Lu and his coauthors write.

"The overall literature in this subject right now has been fairly convincing that there is in fact an association between a misalignment of circadian rhythm and risk for diabetes," Dr. Peter Butler told Reuters Health.

Butler directs the Larry L. Hillblom Islet Research Center at the David Geffen School of Medicine at the University of California, Los Angeles.

Butler, who was not involved in the study, said he wasn't surprised that the authors found rotating shifts tended to have more of an effect. "If your circadian rhythms aren't synchronized, it's not at all surprising that bad things would happen."

But, Butler said, it's not a problem for most people and that most people on night shifts don't get diabetes.

"Probably about 20% of us are vulnerable for diabetes, and what I think probably happens is the people who get diabetes in relation to shift work are the ones who were vulnerable to getting diabetes anyway," he said.

SOURCE: http://bit.ly/1s4yYnh

Occup Environ Med 2014.

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