Night Shift Work Raises Diabetes Risk in Women

A new study has found that women who worked a rotating night shift had an increased risk of diabetes, a result that was not completely explained by an increase in body mass index (BMI).

Researchers at Brigham and Women's Hospital/Harvard School of Medicine (Boston, MD, USA) followed 69,269 women (aged 42-67) participating in the Nurses' Health Study I (NHS I) and 107,915 women (aged 25-42) enrolled in NHS II who were without diabetes, cardiovascular (CV) disease, or cancer at baseline. The participants were asked how long they had worked rotating night shifts--defined as at least three nights per month in addition to days and evenings in that month--at baseline; this information was updated every 2 to 4 years in NHS II. Self-reported type 2 diabetes was confirmed by a validated supplementary questionnaire.

In all, the researchers documented 6,165 (NHS I) and 3,961 (NHS II) incident type 2 diabetes cases during the 18-20 years of follow-up. On analysis, with adjustment for diabetes risk factors, the duration of shift work was monotonically associated with an increased risk of type 2 diabetes in both cohorts. Compared with women who reported no shift work, the pooled hazard ratio (HR) for participants with 1–2, 3–9, 10–19, and over 20 years of shift work were 1.05, 1.20, 1.40, and 1.58, respectively. Further adjustment for updated BMI attenuated the association, and the pooled hazard ratios were 1.03, 1.06, 1.10, and 1.24, respectively. The study was published on December 6, 2011, in PLoS Medicine.

“Rotating night shift work is generally associated with chronic misalignment between the endogenous circadian timing system and the behavior cycles,” explained senior author Frank Hu, MD, PhD, and colleagues of the department of nutrition. “This circadian misalignment has been found to result in adverse metabolic and cardiovascular consequences, including a decrease in leptin, an increase in glucose and insulin, an increase in mean arterial blood pressure, and reduced sleep efficiency.”

“Other factors such as disturbed sociotemporal patterns (resulting from atypical work hours leading to family problems, reduced social support, and stress) and unfavorable changes to biomarkers (e.g., cholesterol and other lipids, plasminogen, blood pressure, and cardiac activity) might also impact the association,” added the researchers.

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Brigham and Women's Hospital/Harvard School of Medicine