Prenatal Exposure to Fluoride in Public Water and Child Cognition in the US ECHO Cohort, 2006-2019

Prior studies suggest fluoride exposure in drinking water above 1500 μg/L is associated with lower child cognition, but evidence is limited at lower exposure levels and in U.S. populations. We evaluated whether prenatal exposure to fluoride in regulated public drinking water was associated with cognition in a pooled U.S. cohort. We analyzed observational data from the Environmental influences on Child Health Outcomes (ECHO) Cohort, including 2514 children born 2006-2019 across 17 sites in 23 states. Individual prenatal time-weighted average public water fluoride concentrations were estimated by linking census tract-level concentrations to residential addresses across pregnancy. Fluid and crystallized cognition were assessed using NIH Toolbox scores. Generalized estimating equation models estimated adjusted mean differences using restricted cubic spline and linear change-point models. Individual prenatal time-weighted average water fluoride concentrations ranged from < 1.0-1940.0 μg/L (mean = 396.9 μg/L). Cubic spline models showed significant inverse associations for fluid cognition above 1107.0 μg/L. Linear change-point models identified 675 μg/L as the best-fitting change-point for fluid cognition; above this value, fluid scores were 0.67 points lower (95% CI, -0.92, -0.42) per 100 μg/L higher fluoride. These findings indicate that prenatal fluoride exposure in regulated public water is nonlinearly associated with lower fluid cognition scores in U.S. children at concentrations below current WHO and U.S. EPA thresholds.