The association between artificial light at night and gestational diabetes mellitus: A prospective cohort study from China

Background: Emerging evidence suggests that exposure to outdoor artificial light at night (ALAN) may be associated with diabetes. However, limited research explores the relationship between outdoor ALAN and gestational diabetes mellitus (GDM).

Methods: We utilized data from a multilevel infant and early life cohort study conducted in Sichuan Province, China, between February 2018 and April 2021. A total of 9,120 participants were included in the final analysis. Outdoor ALAN exposure at participants' residential locations was estimated using time-varying satellite data, focusing on persistent night-time illumination at a scale of approximately 500x500m. The information about GDM was obtained from medical records. After adjusting for potential confounders, multivariable logistic regression models and restricted cubic splines were employed to estimate the association between ALAN exposure during pregnancy and GDM.

Results: Among the total recruitments, 1,484 (16.27%) women were diagnosed with GDM. Compared to women without GDM, those with GDM had a significantly higher mean outdoor ALAN exposure during pregnancy (18.98 nW/cm²/sr¹ vs 24.28 nW/cm²/sr¹, P < 0.001). Results from multivariable logistic models showed that higher outdoor ALAN exposure during pregnancy could increase the risk of GDM (OR (95% CI) _{1st+2nd trimesters ALAN} = 1.253 (1.157-1.356)). Meanwhile, results from the restricted cubic spline further indicated a non-linear association between outdoor ALAN exposure during pregnancy and GDM. Generally, with the radiance of the first two trimesters of ALAN increasing to about 17.9 nW/cm²/sr¹, outdoor ALAN exposure became a risk factor for GDM. However, when the radiance of ALAN reached about 40.7 nW/cm²/sr¹, the continued increasing OR estimation (OR (95% CI) = 1.489 (1.223-1.814)) of outdoor ALAN changed to steady.

Conclusion: Our findings suggested that high levels of outdoor ALAN exposure during pregnancy can be associated with an increased risk of GDM, and a non-linear relationship pattern might exist. These findings substantially augment existing evidence, positing outdoor ALAN as an emergent, modifiable risk factor for GDM.