People who work shifts are more likely to develop type 2 diabetes, according to a large international study, with men and those working rotating shift patterns at particular risk.
Compared to those with normal hours, employees who work any period of shift work are 9% more likely to have the condition, according to the pooled analysis of 12 studies.
Researchers found that the heightened risk rose to 37% for men when variables such as the potential effects of gender, body mass index and family history of diabetes were taken into consideration.
Most shift patterns, except mixed and evening shifts, were associated with a heightened risk of the disease, according to the paper published in the journal Occupational and Environmental Medicine.
However, 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 heightened risk: 42%.
Previous research has suggested links between working shifts and an increased risk of various health problems, including digestive disorders, certain cancers and cardiovascular disease. But whether diabetes can be added to the list has not been clear.
"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,” the researchers said.
While the exact reason for the increased risk not known – and the authors point out that their study is observational and therefore conclusions cannot made about direct cause and effect – previous research has suggested a lack of sleep, or poor quality sleep, may prompt or worsen insulin resistance. Rotating shifts make it harder for people to adjust to a regular sleep-wake cycle.
The authors also point out that daytime levels of the male hormone testosterone are controlled by the internal body clock, so it’s possible that repeated disruption may affect this, pointing to research implicating low male hormone levels in insulin resistance and diabetes.
The authors trawled through scientific research databases, looking for relevant observational studies assessing associations between shift work and diabetes risk. They retrieved 12 international studies out of a potential total of 448, involving more than 226,500 participants, 14,600 of whom had diabetes.
Dr Alasdair Rankin, director of research for Diabetes UK, said: “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.
“They can do this by taking a type 2 diabetes risk assessment, either online or in their local pharmacy. The best way to reduce your risk of type 2 is to maintain a healthy weight through regular physical activity and by eating a healthy balanced diet.”
An estimated 380m people are predicted to have type 2 diabetes by 2025, and the researchers suggest that any potentially variable factors could be of considerable public health importance.
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