Women night shiftworkers ‘at greater risk of diabetes’

Women who work a rotating schedule that includes three or more night shifts per month, in addition to day and evening working hours in that month, may have an increased risk of developing type 2 diabetes when compared with women who only worked days or evenings, according to a new study led by researchers at Harvard School of Public Health.

Women who work a rotating schedule that includes three or more night shifts per month, in addition to day and evening working hours in that month, may have an increased risk of developing type 2 diabetes when compared with women who only worked days or evenings, according to a new study led by researchers at Harvard School of Public Health.

In addition, the researchers found that extended years of rotating night shift work was associated with weight gain, which may contribute to the increased risk of type 2 diabetes.

Previous studies have focused on the association between shift work and risk of cancer and cardiovascular disease. The new study is the largest study so far to look at the link between shift work and type 2 diabetes and the first large study to follow women.

“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 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% increased risk; women who worked nights for 10 to 19 years had a 40% rise in risk; and women who worked night shifts for over 20 years were 58% 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.

After taking into account body weight in the analyses, the increased risk of type 2 diabetes for women who worked rotating night shifts was reduced but remained statistically significant. For example, women who worked rotating night shifts for more than 20 years had 24% increased risk. These findings indicate that the relationship between night shift work and type 2 diabetes is partly explained by increased weight, say the researchers.

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