Abstract Body: Aims/hypothesis: Delayed and non-circadian sleep are emerging risk factors for poor cardiometabolic health. We sought to evaluate whether rotating night shift work in female nurses is related to risk of type 2 diabetes, particularly among high-risk women with a history of gestational diabetes (GDM).

Methods: The Nurses’ Health Study II is an ongoing longitudinal cohort of 116,429 female nurses enrolled in 1989. Participants self-reported their history of rotating night shift work at baseline and updated recent night shift work (months with ≥3 night shifts) every 2-4 years thereafter. We included participants who were parous at baseline or at any time during follow-up from 1991 through 2019. Using multivariable-adjusted Cox proportional hazards models, we estimated the hazard ratios (HRs) and 95% confidence intervals (CIs) for the associations between cumulative years of rotating night shift work and incident type 2 diabetes, overall, and by history of GDM.

Results: Among 50,122 participants (mean age 37 years in 1991), 36% did not work rotating night shifts, 48% worked <5 years of rotating night shifts, 11% worked 5-10 years, and 5% worked >10 years at baseline. A total of 2,548 participants had a history of GDM and there were 2,814 cases of incident type 2 diabetes. In the overall population, compared with participants who never engaged in night shift work, we observed a graded increase in the risk of type 2 diabetes with cumulative night shift work: HR(95%CI)= 1.14(1.04, 1.24) for <5 years, 1.32(1.17, 1.49) for 5-10 years, and 1.32(1.16, 1.50) for >10 years (p-linear trend <0.001). Stratifying by history of GDM, we observed a similar pattern of associations between cumulative years of night shift work and risk of type 2 diabetes among participants without a history of GDM, but not among those with a history of GDM (p-interaction=0.02). History of GDM was strongly associated with risk of incident type 2 diabetes in all women, including those who never worked night shifts: HR(95%CI)=4.76(3.90, 5.81).

Conclusions/interpretation: Cumulative years of rotating night shift work was modestly associated with a higher risk of type 2 diabetes, overall, and among nurses without a history of GDM. Rotating night shift work was not associated with risk of type 2 diabetes among individuals with a history of GDM, an exceptionally high-risk sub-group for type 2 diabetes.