Rotating night shift work, gestational diabetes and risk of type 2 diabetes among US nurses

We sought to evaluate whether rotating night shift work increases the risk of type 2 diabetes, particularly among women with a history of gestational diabetes mellitus (GDM).

We included 50 122 Nurses' Health Study II participants who were parous at baseline in 1989 or at any time during follow-up through 2019. Using multivariable-adjusted Cox proportional hazards models, we estimated the HRs and 95% CIs for the associations between cumulative years of rotating night shift work and incident type 2 diabetes, overall, and by history of GDM.

Compared with participants who never engaged in rotating night shift work, we observed a graded increase in the risk of type 2 diabetes with cumulative years of rotating night shift work: HR (95% CI) 1.14 (1.04 to 1.24) for <5 years, 1.32 (1.17 to 1.49) for 5-10 years and 1.32 (1.16 to 1.50) for >10 years (p-linear trend <0.001). Stratifying by history of GDM, we observed a similar pattern of associations 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 rotating night shifts: HR (95% CI) 4.76 (3.90 to 5.81).

Cumulative years of rotating night shift work were 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 subgroup for type 2 diabetes.