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Working night shift puts women at higher risk for diabetes

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ADA 71st Scientific Sessions

SAN DIEGO — Women who work the night shift for a prolonged period of time appear to have a modestly increased risk for developing type 2 diabetes.

Previous studies have shown that working the night shift interrupts circadian rhythms and is associated with obesity, metabolic syndrome and glucose dysregulation, researchers said. This study, however, found that even after adjusting for BMI, the risk for type 2 diabetes was still modestly higher.

Researchers evaluated the association between night shift and diabetes within two large cohorts, the Nurses’ Health Study I and II. They followed more than 69,000 women aged 42 to 67 years from 1988 to 2008 in the Nurses’ Health Study I and more than 107,000 women aged 25 to 42 years from 1989 to 2007 in the Nurses’ Health Study II. Participants were questioned about how long they had worked rotating night shifts, which was defined as working at least three nights per month in addition to days and evenings in that month.

Overall, 6,165 and 3,961 incident type 2 diabetes cases were documented in the Nurses’ Health Study I and II, respectively. The duration of shift work was associated with an increased risk for type 2 diabetes in both cohorts, according to age-adjusted models (P<.001). This association was attenuated when the researchers controlled for other covariates, excluding BMI. Further adjustment for BMI largely attenuated the association, the researchers said.

Compared with women who reported no shift work, the risk for type 2 diabetes based on years working the night shift were as follows:

• More than 20 years of experience: HR=1.20 (95% CI, 1.08-1.34) in Nurses’ Health Study I and HR=1.34 (95% CI, 1.02-1.76) in Nurses’ Health Study II
• 10 to 19 years of experience: HR=1.09 (95% CI, 1.00-1.20) in Nurses’ Health Study I and HR=1.10 (95% CI, 0.98-1.24) in Nurses’ Health Study II
• 3 to 9 years of experience: HR=1.06 (95% CI, 0.99-1.13) in Nurses’ Health Study I and HR=1.05 (95% CI, 0.96-1.13) in Nurses’ Health Study II
• 1 to 2 years of experience: HR=1.00 (95% CI, 0.94-1.07) in Nurses’ Health Study I and HR=1.04 (95% CI, 0.96-1.14) in Nurses’ Health Study II

Every 5-year increase of shift work was associated with an 11% increased risk for diabetes in the Nurses’ Health Study I and 17% in the Nurses’ Health Study II. This estimate was reduced to 5% and 4%, respectively, after the researchers adjusted for BMI.

“Our results suggest that women have a modestly increased risk of type 2 diabetes after extended-period shift work, and this association appears to be largely mediated through BMI,” the researchers concluded.

The study did not look at the effect of night work on men.

For more information:

• Pan A. 0257-OR. Presented at: American Diabetes Association’s 71st Scientific Sessions; June 24-28, 2011; San Diego, Calif.

Disclosure: The researchers report no relevant financial disclosures.

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