Women who work intermittent night shifts and do not follow a healthy lifestyle face an especially high risk of type 2 diabetes, greater than the risk from either factor alone.
It is well known that behaviours such as smoking, a poor diet and little exercise, and being overweight or obese increase the risk of type 2 diabetes. Shift work, especially night shift work, has also been associated with a greater risk of type 2 diabetes.
However, this study in the BMJ is thought to the first study to look at the combined impact.
Researchers combined data from two long-term health studies in nurses – the Nurses’ Health Study (NHS) and NHS II – which enrolled female US nurses in 1976 and 1989.
Over 22-24 years of follow-up, 10,915 of the 143,410 nurses reported having a new diagnosis of type 2 diabetes.
For every five years of working rotating night shifts the nurses were almost a third (31%) more likely to have been diagnosed with type 2 diabetes.
Each unhealthy lifestyle factor – ever being a smoker, being overweight or obese, having a low quality diet or a low level of physical activity – more than doubled (2.3 times) the risk of being diagnosed with type 2 diabetes.
Women who exhibited any of these four unhealthy lifestyle factors and also worked rotating night shifts faced an even higher risk of a diagnosis of type 2 diabetes: for each individual unhealthy lifestyle factor they had a 2.83 times higher risk.
The authors say: ‘Most cases of type 2 diabetes could be prevented by adherence to a healthy lifestyle, and the benefits could be larger in rotating night shift workers.’
Shan Z, et al. BMJ 2018;363:k4641