Fluoride and children’s brain development — what do doctors critical of fluoridation say?

Aim of the study: Many uncertainties still surround the possible harmful effect of fluoride exposure on cognitive neurodevelopment in children.

Results: A weaker and substantially linear decrease of -2.15 (95% CI -4.48; 0.18) IQ points with increasing urinary fluoride emerged above 0.28 mg/L (approximately reflecting a water fluoride content of 0.7 mg/L). The inverse association between fluoride exposure and IQ was particularly strong in the studies at high risk of bias, while no adverse effect emerged in the only study judged at low risk of bias. Overall, most studies suggested an adverse effect of fluoride exposure on children's IQ, starting at low levels of exposure. However, a major role of residual confounding could not be ruled out, thus indicating the need of additional prospective studies at low risk of bias to conclusively assess the relation between fluoride exposure and cognitive neurodevelopment.

Aim of the study: Background and objectives: Attention deficit hyperactivity disorder (ADHD) is a childhood-onset neurodevelopmental disorder characterized by two dimensions: inattentiveness and hyperactivity/impulsivity. ADHD may be the result of complex interactions between genetic, biological and environmental factors possibly including fluoride exposure.

Results: Three studies reported a positive association with ADHD risk, all assessing exposure through fluoride levels. By using urinary fluoride, conversely, a positive correlation with inattention, internalizing symptoms, cognitive and psychosomatic problems was found in three studies, but no relation was found in the other one. Conclusions: The present review suggests that early exposure to fluoride may have neurotoxic effects on neurodevelopment affecting behavioral, cognitive and psychosomatic symptoms related to ADHD diagnosis. However, due to the heterogeneity of the studies included, current evidence does not allow to conclusively confirm that fluoride exposure is specifically linked to ADHD development.

Aim of the study: We recently completed a comprehensive systematic review of the literature on fluoride exposure and neurodevelopment and cognition, resulting in two publications. The 2024 National Toxicology Program Monograph concluded-with moderate confidence-that higher fluoride exposure is associated with lower IQ in children.

Results: These publications have received considerable public and media attention, prompted healthy scientific discourse, and have been cited by public health decision‑makers. Many scientific comments were carefully considered and resolved during development and peer review, which contributed to the rigor of the final documents. However, some recurrent critiques continue to be raised. This viewpoint provides a high‑level summary of these key critiques and corresponding responses to help the public, media, and the scientific community better understand the strength and implications of the scientific evidence on fluoride exposures and neurodevelopment and cognition.

Aim of the study: Foods and beverages provide a source of fluoride exposure in Mexico. While high fluoride concentrations are neurotoxic, recent research suggests that exposures within the optimal range may also pose a risk to the developing brain.

Results: However, child sex modified the association between maternal fluoride intake and cognitive outcome (p interaction term = 0.06). A 0.5 mg/day increase in overall dietary fluoride intake was associated with a 3.50-point lower cognitive outcome in 24-month old boys (95 % CI: -6.58, -0.42); there was no statistical association with girls (β = 0.07, 95 % CI: -2.37, 2.51), nor on the cognitive outcome at 12-months of age. Averaging across the 12- and 24-month cognitive outcomes using mixed-effects models revealed a similar association: a 0.5 mg/day increase in overall dietary fluoride intake was associated with a 3.46-point lower cognitive outcome in boys (95 % CI: -6.23, -0.70). These findings suggest that the development of nonverbal abilities in males may be more vulnerable to prenatal fluoride exposure than language or motor abilities, even at levels within the recommended intake range.

Aim of the study: Prenatal exposure to fluoride has been associated with adverse neurodevelopmental outcomes. However, the neuropsychological profile of fluoride's developmental neurotoxicity at low levels and the stability of this relationship across childhood has not been characterized.

Results: The mean/median MUFCRE concentration was 0.90/0.83 mg/L (SD = 0.39; IQR, 0.64-1.11 mg/L). A 0.5 mg/L increase in MUFCRE predicted an average 2.12-point decrease in GCI/FSIQ (95% CI: -3.49, -0.75) and 2.63-point decrease in PIQ (95% CI: -3.87, -1.40). MUFCRE was marginally associated with VIQ across time (B = -1.29, 95% CI: -2.60, 0.01). No interactions between MUFCRE and child sex or MUFCRE and time were observed. The negative association between prenatal fluoride exposure and longitudinal IQ was driven by decrements in non-verbal intelligence (i.e. PIQ), suggesting that visual-spatial and perceptual reasoning abilities may be more impacted by prenatal fluoride exposure as compared to verbal abilities.

Aim of the study: In animal studies, the combination of in utero fluoride exposure and low iodine has greater negative effects on offspring learning and memory than either alone, but this has not been studied in children. We evaluated whether the maternal urinary iodine concentration (MUIC) modifies the association between maternal urinary fluoride (MUF) and boys' and girls' intelligence.

Results: The MUICCRE by MUFCRE interaction was significant for boys (p = 0.042), but not girls (p = 0.190). For boys whose mothers had low iodine, a 0.5 mg/g increase in MUFCRE was associated with a 4.65-point lower FSIQ score (95% CI: -7.67, -1.62). For boys whose mothers had adequate iodine, a 0.5 mg/g increase in MUFCRE was associated with a 2.95-point lower FSIQ score (95% CI: -4.77, -1.13). These results suggest adequate iodine intake during pregnancy may minimize fluoride's neurotoxicity in boys.

Aim of the study: Prenatal fluoride exposure, at United States (US) population relevant levels, has been associated with poorer child neurodevelopmental outcomes; however, no US study has examined whether these associations manifest in infancy. This study investigated associations between prenatal fluoride exposure and infants' neurodevelopment in Los Angeles, California.

Results: Among 346 mother-child pairs, the median (IQR) MUFSG was 0.79 (0.54-1.07) mg/L. Higher MUFSG was associated with worse gross motor performance (IRR = 1.22, 95% CI: 1.03-1.45, p = 0.02). No significant associations were observed between MUFSG and fine motor: IRR = 1.15 (95% CI: 0.96-1.39), problem solving: IRR = 1.15 (95% CI: 0.90-1.48), personal-social: IRR = 1.04 (95% CI: 0.83-1.31), or communication: IRR = 0.90 (95% CI: 0.71-1.14) scores. Third trimester fluoride exposure may increase risk of developmental neurotoxicity manifesting in infancy. Additional studies are needed to further explore this association across other US-based regions and the nation.