Millions of men and women perform shift work, whether they have a night job or rotate shifts during the week. From fire fighters to truck drivers, shift work is part of their career and for many a financial need.
There is strong evidence that shift work is linked to several serious health conditions including cardiovascular disease, digestive disorders and obesity. Observational studies have suggested that shift work may be associated with diabetes but the results have been inconsistent.
Professor Zuxun Lu and colleagues from School of Public Health, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, Hubei, China, examined the association between shift work and diabetes.
Researchers searched through scientific research database; PubMed, Embase, Web of Science and ProQuest Dissertation and Theses to April 2014, for relevant observational studies that evaluated the association between shift work and diabetes.
The researchers had retrieved 12 international studies out of a potential total of 448, involving more than 226,500 participants, 14,600 of whom had diabetes.
The researchers pooled all the study’s results together and found that ever exposure to shift work was associated to a 9% increased risk for developing diabetes.
The subgroup analysis found a stronger association between shift work and diabetes risk for men was higher at 37% compared to women at 9%. The subgroup analysis examined the potential effects that included gender, study design, study location, job, shift schedule, body mass index (BMI), family history of diabetes and physical activity levels.
All shift work schedules with the exception of mixed shifts and evening shifts were associated with a statistically higher risk of DM than normal daytime schedules, and the difference among those shift work schedules was significant
The reasons for these findings are not clear according to the authors but they suggest that men working shift patterns might need to pay more attention to the possible health consequences of their working schedule.
Daytime levels of the male hormone testosterone are controlled by the internal body clock, so it's possible that repeated disruption may affect this, say the authors, pointing to research implicating low male hormone levels in insulin resistance and diabetes.
Most shift patterns, except mixed and evening shifts, were associated with a heightened risk of the disease compared with those working normal office hours.
The results also revealed that people who worked rotating shifts; a work schedule where people move through a cycle of working the day, swing, and night shifts, had the highest risk associated to developing diabetes at 42%.
Rotating shifts make it harder for people to adjust to a regular sleep-wake cycle, and some research has suggested that a lack of sleep, or poor quality sleep, may prompt or worsen insulin resistance, say the authors.
The authors point out that although their study was large, it was observational, so no conclusions can be drawn about direct cause and effect.
Dr. Alasdair Rankin, director of research at charity 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.
"They can do this by taking a type 2 diabetes risk assessment, either online or in their local pharmacy.
According to the World Health Organization (WHO) 347 million people worldwide have diabetes. WHO projects that diabetes will be the 7th leading cause of death in 2030.
This study is published online in Occupational & Environmental Medicine.