Working night shifts puts women at greater risk of type 2 diabetes

Women who work night shifts and have unhealthy lifestyle habits face an especially high risk of developing type 2 diabetes, research finds.

Carried out by US, Chinese and Austrian researchers, the study, which is published in the British Medical Journal, looks at data gathered from two long-term US health studies in nurses; the Nurses’ Health Study (NHS) and NHS II, which started in 1976 and 1989 respectively.

Researchers extracted data on 143,410 women without type 2 diabetes, cardiovascular disease, or cancer, who had completed medical, diet and lifestyle questionnaires at regular intervals.

Nurses were selected due to their changing rotas which include a combination of day, evening and night shifts, which can be disruptive to personal routines and biological rhythms.

For this study, working rotating night shifts was defined as having at least three night shifts per month in addition to regular day and evening shifts.

Similarly, unhealthy lifestyle was defined using four factors: being overweight or obese, ever having smoked, doing less than 30 minutes of exercise per day and have a poor diet, which is low in fruit, veg, nuts and whole grains, and high in processed meat, trans fats, sugar and salt.

Over 22-24 years of follow-up, the study found that 10,915 of the 143,410 nurses reported having a diagnosis of type 2 diabetes.

For every five years of working night shifts it discovered that the nurses were almost a third (31 per cent) more likely to have been diagnosed with the condition.

Similarly, those who were considered to have an unhealthy lifestyle more than doubled (2.3 times) the risk of being diagnosed with type 2 diabetes.

The study also looked into women who exhibited any of the four unhealthy lifestyle factors in conjunction with working night shifts and found that they faced an even higher risk.

For each individual unhealthy lifestyle factor, women who worked irregular hours increased their risk of type 2 diabetes by 2.83 times.

In total, the researchers calculated that rotating night shift work accounted for approximately 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.

“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,” they conclude.

The authors believe that this is the first study to look at the combined impact of an unhealthy lifestyle and night shift work on the risk of type 2 diabetes but admit that because all the nurses were female and mostly white, their findings may not be applicable to men or other racial and ethnic groups.

Diabetes.co.uk – a community website that provides support to people across the world – says that it’s all too easy for people not to be aware of the risks that stem from shift work.

“When circadian rhythms are disrupted through shift work, short-term effects can include insomnia, while long-term effects may include obesity, type 2 diabetes and high blood pressure,” the website says.

“If you work shifts, there are some lifestyle changes worth making to improve your health. Three key areas to maximise your health during shift work are: Diet - meal planning and snacking, physical activity and sleep."