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Shift workers have higher risk of type 2 diabetes

9% higher risk of diabetes in shift workers

Adrian O'Dowd

Friday, 25 July 2014

People who work irregular or unusual hours of work have a noticeably higher risk of developing type 2 diabetes, concludes a study* published online today in the journal Occupational & Environmental Medicine.

This risk is also greatest among men and those working rotating shift patterns, indicated the analysis of available evidence by a team of researchers from China.

Previous research has suggested links between working shifts and a heightened risk of various health problems, including digestive disorders, certain cancers, and heart disease, but it has not been clear if diabetes is another possible consequence.

After looking for relevant studies assessing associations between shift work and diabetes risk from existing scientific research databases, the authors found 12 international studies involving 226,652 participants, 14,595 of whom had diabetes.

They pooled all the results together and calculated that any period of shift work was associated with a 9% increased risk of developing diabetes compared with working normal office hours.

This heightened risk rose to 37% for men, after further analysis to look at the potential effects of gender, study design, study location, job, shift schedule, body mass index, family history of diabetes and physical activity levels.

Rotating shifts, in which people work different parts of the 24-hour cycle on a regular basis, rather than a fixed pattern, were associated with the highest risk of 42%, said the authors.

These rotating shifts make it harder for people to adjust to a regular sleep-wake cycle, they said, and some research has suggested that a lack of sleep, or poor quality sleep, could prompt or worsen insulin resistance.

The researchers from the Huazhong University of Science and Technology in China said the full reasons were unclear but they speculated that the heightened risk might be due to frequent disruption of the internal body clock which could affect daytime levels of the male hormone testosterone.

They pointed to research that implicates low male hormone levels in insulin resistance and diabetes.

Other possible explanations included shift work leading to weight gain and increased appetite – both risk factors for diabetes – and shift work disturbing cholesterol levels and blood pressure.

Men working shift patterns might need to pay more attention to the possible health consequences of their working schedule, said the authors.

They concluded: “Given the increasing prevalence of shift work worldwide and the heavy economic burden of DM [diabetes mellitus], the results of our study provide practical and valuable clues for the prevention of DM and a study of its aetiology.”

Dr Alasdair Rankin, director of research at Diabetes UK, said: “This study combines evidence from previous research to suggest people who do lots of shift work may be at increased risk of type 2 diabetes, especially for men and people who work rotating shifts.

“The exact reasons for this are unclear and the evidence that it is the shift work that is causing an increase to risk of Type 2 diabetes is not conclusive.

“Nonetheless, these findings suggest that shift workers need to be aware of their personal risk of developing type 2 diabetes.”

* Gan Y, et al. Shift work and diabetes mellitus: a meta-analysis of observational studies. Occup Environ Med. July 2014. doi:10.1136/oemed-2014-102150

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