Associations of pre- and postnatal levels of three heavy metals with visual impairment in 3-year-old children.

Visual impairment is an important public health issue affecting young children. Environmental heavy metals, such as lead (Pb), mercury (Hg), and cadmium (Cd), are neurotoxicants that may disrupt visual development, yet evidence of their impact remains limited. We aimed to investigate the associations between pre- and postnatal blood concentrations of Pb, Hg, and Cd and the risk of visual impairment in children at age three, considering exposure timing, sex differences, and behavioral factors. We analyzed data from 599 children enrolled in the Korean Children's Environmental Health Study, a prospective cohort initially comprising 5458 children. Maternal blood metal concentrations were measured during early (<20 weeks) and late pregnancy (>30 weeks), while child blood levels were measured at 24 and 36 months. Visual impairment was defined as visual acuity (VA) below 0.5 (Snellen ≤20/40) on Jin's vision chart at age three. Logistic regression and generalized estimating equations were used to estimate associations, adjusting for confounders. Higher maternal blood Cd concentrations during early pregnancy were significantly associated with increased risk of unilateral visual impairment in offspring (OR = 2.49; 95 % CI: 2.01-3.10 per 1 μg/L). Associations were stronger among girls and children with higher screen time and lower outdoor activity. No significant differences were observed for Pb or Hg, or across other exposure time points. Our findings suggest maternal exposure to Cd during early pregnancy may adversely affect visual development in preschool children, particularly in girls and children with sedentary behaviors. Prenatal biomonitoring and targeted behavioral interventions are warranted to mitigate these risks.