Working women, who are subjected to rotating schedules, comprising of three or more night shifts per month are more vulnerable to type 2 diabetes risk compared to women who only work on day or evening shifts, a new study has revealed.
The study led by researchers at Harvard School of Public Health (HSPH), found that extended years of rotating night shift work was associated with weight gain, which causes increased risk of type 2 diabetes.
"Long-term rotating night shift work is an important risk factor for the development of type 2 diabetes and this risk increases with the numbers of years working rotating shifts," said An Pan, research fellow in HSPH's Department of Nutrition and the study's lead author.
The researchers, led by Pan and senior author Frank Hu, professor of nutrition and epidemiology, analyzed data on more than 69,269 U.S. women, ages 42 to 67, in the Nurses' Health Study I, tracked from 1988 to 2008, and 107,915 women, ages 25 to 42, in the Nurses' Health Study II, tracked from 1989 to 2007.
About 60 per cent of the nurses performed more than one year of rotating night shift work at baseline; about 11 per cent in Nurses' Health Study I had more than 10 years of rotating night shift work at baseline, and about 4 per cent in Nurses' Health Study II worked more than 10 years of rotating night shifts at baseline, and this proportion increased during the follow-up.
The researchers found that the longer women worked rotating night shifts, the greater their risk of developing type 2 diabetes.
Those women who worked rotating night shifts for three to nine years faced a 20 per cent increased risk; women who worked nights for 10 to 19 years had a 40 per cent rise in risk; and women who worked night shifts for over 20 years were 58 per cent more at risk. In addition, women who worked rotating night shifts gained more weight and were more likely to become obese during the follow-up.
According to the U.S. Centers for Disease Control and Prevention (CDC), shift work has been shown to disrupt sleeping patterns and other body rhythms, and has been associated with obesity and metabolic syndrome, conditions associated with type 2 diabetes.
"This study raises the awareness of increased obesity and diabetes risk among night shift workers and underscores the importance of improving diet and lifestyle for primary prevention of type 2 diabetes in this high risk group," said Hu.
The findings were published online December 6, 2011 in the open access journal PLoS Medicine.