Associations of urinary heavy metals and their mixture with sleep quality during pregnancy: A prospective study

The high prevalence of pregnant women's poor sleep quality is a prominent public health concern. The relationships between heavy metal exposure and sleep quality are unclear and seldom examined in pregnant women. This study aimed to investigate the longitudinal associations of women's exposure to four heavy metals and their mixture during the first trimester with sleep quality during pregnancy.

We included 268 pregnant women from Jinan, Shandong, China, in this prospective study. Concentrations of four heavy metals, nickel (Ni), manganese (Mn), uranium (U), and vanadium (V), were measured in the spot urine samples collected during the first trimester. The sleep quality of participants was evaluated with the Pittsburgh Sleep Quality Index during the first and third trimesters.

Generalized additive mixed models and Bayesian kernel machine regression (BKMR) models consistently showed a nonlinear association between U and sleep quality during pregnancy. In quantile g‑computation models, U received the largest weight in the negative direction, and V received the largest weight in the positive direction for the association with sleep quality. Moreover, BKMR results indicated the interaction between U and V on sleep quality. When all heavy metals were fixed at their 75th percentiles compared to their 50th percentiles, the overall mixture effect on sleep quality was significantly negative.

Early pregnancy U exposure was non-linearly related to women's sleep quality over gestation, with a generally negative association between them across the main exposure range, whereas V exposure was positively associated with sleep quality. Our findings suggest a potential interaction between V and U, and a negative association between the overall metal mixture and sleep quality. Further studies are needed to confirm these exploratory findings.