Early Childhood Exposures to Fluorides and Cognitive Neurodevelopment: A Population-Based Longitudinal Study

Abstract

It is important to maintain confidence in the risk and benefit balance of major caries-preventive programs using fluoride. The ongoing debate about potential effects of early-life exposures to fluoride on cognitive neurodevelopment requires high-quality scientific evidence. This study aimed to investigate the potential effects of fluoride exposure on cognitive neurodevelopment assessed with the Wechsler Adult Intelligence Scale 4th edition (WAIS-IV) in an Australian population-based sample. The sample was selected from the National Child Oral Health Study (NCOHS) 2012-2014. NCOHS collected data on socioeconomic factors, oral health behaviors, and residential history to estimate percentage lifetime exposure to fluoridated water during the first 5 y of life (%LEFW). NCOHS children were also examined by trained and calibrated examiners to assess dental fluorosis (a reliable and valid individual biomarker of total fluoride intake during early childhood). The sample was followed up in 2022-2023 to collect data on cognitive neurodevelopment (intelligence quotient [IQ]) using the WAIS-IV, which was administered by trained and calibrated qualified psychologists. Multivariable regression models were generated to investigate associations between the 2 exposure measurements (%LEFW and dental fluorosis) with full-scale IQ (FSIQ) scores, controlling for important confounding effects. Hypotheses of noninferiority were also tested, contrasting different levels of exposure to fluoride. Some 357 participants aged 16 to 26 y completed the WAIS-IV, with a mean FSIQ score of 109.2 (95% confidence interval [CI]: 107.8-110.5). The estimates of the multivariable regression models demonstrated slightly higher FSIQ scores among the exposed than the nonexposed. The adjusted β of 100%LEFW versus 0%LEFW was 1.07 (95% CI: -2.86, 5.01) and of having dental fluorosis versus no fluorosis was 0.28 (95% CI: -3.00, 3.57). The hypothesis of noninferiority tests found that FSIQ scores of those exposed and nonexposed to fluoride were equivalent. The study provided consistent evidence that early childhood exposure to fluoride does not have effects on cognitive neurodevelopment.

Keywords: child development; fluoride use; intelligence quotient; population programs; risk assessment; water fluoridation.

Figure 1.

Equivalence test of IQ scores by percentage lifetime exposure to fluoridated water and by presence of dental fluorosis.