Women who work an erratic mixture of day and night shifts have an ‘especially high risk’ of type 2 diabetes, a new study warns.
We already know the disease can be fueled by unhealthy lifestyle factors – smoking, eating fast food, scrimping on veg, and skipping the gym.
But the new Harvard research, a study of 150,000 nurses over 15 years, found a person’s work schedule can hamper the body’s resilience and control over blood sugar levels.
They say the findings, published in the British Medical Journal, show a greater need to be conscious of how shift work – particularly on an irregular schedule – can have serious, damaging impacts on a woman’s health.
The researchers who conducted the new study believe this is the first to look at the combined impact of an unhealthy lifestyle and rotating night shift work on the risk of type 2 diabetes
This is hardly the first study to tie shift work and night shifts to poor health.
Previous research has shown women who work night shifts have a higher risk of anxiety, hypertension, and even breast cancer – as well as type 2 diabetes.
But the researchers who conducted the new study believe this is the first to look at the combined impact of an unhealthy lifestyle and rotating night shift work on the risk of type 2 diabetes.
They combined figures from two long-term health studies in nurses – the Nurses’ Health Study (NHS) and NHS II – which enrolled female American nurses in 1976 and 1989.
They extracted data on 143,410 women without type 2 diabetes, cardiovascular disease, or cancer who had filled out medical, food and lifestyle questionnaires at regular intervals.
Nursing care is required around the clock, which means nursing rotas include a mixture of day, evening and night shifts which can be disruptive to personal routines and biological rhythms.
For the study, working rotating night shift work was defined as working at least three night shifts per month in addition to day and evening shifts that month.
Unhealthy lifestyle was defined using four factors: being overweight or obese – a body mass index of 25 or above; ever having smoked, doing less than 30 minutes per day of moderate to vigorous intensity exercise and having a poor diet – low in fruit, veg, nuts and whole grains, and high in processed meat, trans fats, sugar and salt.
Over 22 to 24 years of follow-up, 10,915 of the 143,410 nurses were diagnosed as having type 2 diabetes.
For every five years of working rotating night shifts the nurses were almost a third (31 per cent) 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 the 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.
Study co-author Dr Zhilei Shan, of Harvard T.H. Chan School of Public Health, said: ‘This risk is higher than simply adding the two individual risks for rotating shifts and for poor lifestyle together, indicating that some kind of interaction of the two risk factors adds further risk.’
The researchers calculated that rotating night shift work accounted for abut 17 per cent of the combined higher risk of type 2 diabetes, unhealthy lifestyle for around 71 per cent, and the remaining 11 per cent was additional risk related to the interaction of the two.
Dr Shan said: ‘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.’
The researchers pointed that all the nurses were female and mostly white, so their findings may not be applicable to men or other ethnic groups.
The research team suggested that the extra risk of type 2 diabetes that occurs when rotating night shift workers follow an unhealthy lifestyle may be the result of disrupted sleep and circadian rhythms affecting hormones, or the balance of bacteria in the gut.
But they emphasized that further studies are needed to confirm and explain their findings.