Prenatal fluoride exposure, offspring visual acuity and autonomic nervous system function in 6-month-old infants

Abstract

BackgroundPrenatal fluoride exposure can have adverse effects on children’s development; however, associations with visual and cardiac autonomic nervous system functioning are unknown. We examined associations between prenatal fluoride exposure and visual acuity and heart rate variability (HRV) in 6-month-old infants. MethodsWe used data from Canadian mother-infant pairs participating in the Maternal-Infant Research on Environmental Chemicals (MIREC) cohort. We estimated prenatal fluoride exposure using: i) fluoride concentration in drinking water (mg/L), ii) maternal urinary fluoride adjusted for specific gravity (MUFSG; mg/L) and averaged across pregnancy, and iii) maternal fluoride intake (µg/kg/day) from consumption of water, tea, and coffee, adjusted for maternal body weight (kg). We used multivariable linear regression to examine associations between each measure of fluoride exposure and Teller Acuity Card visual acuity scores (n = 435) and assessed HRV (n = 400) using two measures: root mean square of successive differences (RMSSD) and the standard deviation of N-N intervals (SDNN) measured at 6-months of age. ResultsMedian (IQR) values for water fluoride, MUFSG, and daily fluoride intake were 0.20 (IQR: 0.13–0.56) mg/L; 0.44 (0.28–0.70) mg/L and 4.82 (2.58–10.83) µg/kg/day, respectively. After adjustment for confounding variables, water fluoride concentration was associated with poorer infant visual acuity (B = -1.51; 95 % CI: −2.14,-0.88) and HRV as indicated by lower RMSSD (B = -1.60; 95 % CI: −2.74,-0.46) but not SDNN. Maternal fluoride intake was also associated with poorer visual acuity (B = -0.82; 95 % CI: −1.35,-0.29) and lower RMSSD (B = -1.22; 95 % CI: −2.15,-0.30). No significant associations were observed between MUFSG and visual acuity or HRV. ConclusionFluoride in drinking water was associated with reduced visual acuity and alterations in cardiac autonomic function in infancy, adding to the growing body of evidence suggesting fluoride's developmental neurotoxicity.