Systematic Review: Fluoride Exposure and Children’s IQ Scores

Fluoride, a naturally occurring mineral, is commonly added to public drinking water systems in many countries, including the United States, to prevent tooth decay. While the benefits of fluoride for dental health are well-documented, concerns have been raised about its potential impact on neurodevelopment, particularly in children. A recent systematic review and meta-analysis published in JAMA Pediatrics on January 6, 2025, explores the association between fluoride exposure and children’s IQ scores. The study, conducted by Kyla W. Taylor, PhD, and colleagues, synthesizes evidence from 74 studies across multiple countries to provide a comprehensive assessment of this issue.

Study Overview

The research team conducted a systematic review and meta-analysis of epidemiological studies investigating the relationship between prenatal or postnatal fluoride exposure and children’s IQ scores. The study aimed to address the question: Is fluoride exposure associated with children’s IQ scores? The findings, based on data from 74 cross-sectional and prospective cohort studies, revealed significant inverse associations between fluoride exposure and children’s IQ scores.

Key Findings

Inverse Associations Between Fluoride Exposure and IQ

The analysis found that higher fluoride exposure, whether measured in drinking water or urine, was associated with lower IQ scores in children. The study reported a pooled standardized mean difference (SMD) of −0.45 (95% CI, −0.57 to −0.33; P < .001) for fluoride exposure measured in drinking water, dental fluorosis, or other exposure metrics. Similarly, for fluoride measured in urine, the SMD was −0.15 (95% CI, −0.23 to −0.07; P < .001).

Dose-Response Relationship

A dose-response relationship was observed, with higher fluoride concentrations correlating with greater reductions in IQ scores. For example, in studies reporting fluoride levels in drinking water, the association remained inverse when exposure was restricted to less than 4 mg/L and less than 2 mg/L. However, the association was null at concentrations below 1.5 mg/L. Notably, in low risk-of-bias studies, the inverse association persisted even at fluoride levels below 1.5 mg/L.

Individual-Level Exposure Data

The analysis of 13 studies with individual-level exposure measures found that a 1-mg/L increase in urinary fluoride was associated with a 1.63-point decrease in IQ scores (95% CI, −2.33 to −0.93; P < .001). Among low risk-of-bias studies, the decrease was 1.14 points (95% CI, –1.68 to –0.61; P < .001).

Study Methodology

The research team conducted a rigorous systematic review, searching databases such as BIOSIS, Embase, PsycInfo, PubMed, Scopus, Web of Science, CNKI, and Wanfang for studies published through October 2023. Studies were included if they reported children’s IQ scores, fluoride exposure, and effect sizes. Data extraction and synthesis were performed using the Health Assessment Workplace Collaborative system, and study quality was evaluated using the OHAT risk-of-bias tool.

The analysis included 74 studies, with 64 cross-sectional and 10 cohort studies. Most studies were conducted in China (n = 45), with additional studies from Canada, Denmark, India, Iran, Mexico, New Zealand, Pakistan, Spain, and Taiwan. Of these, 52 studies were rated as high risk of bias, while 22 were rated as low risk.

Contextualizing Fluoride Exposure

Fluoride exposure primarily comes from drinking water, food, and beverages. In the United States, the Centers for Disease Control and Prevention (CDC) estimates that water and processed beverages provide approximately 75% of a person’s fluoride intake. The US Public Health Service recommends a fluoride concentration of 0.7 mg/L in community water systems, while the US Environmental Protection Agency (EPA) sets enforceable and nonenforceable standards at 4.0 mg/L and 2.0 mg/L, respectively. The World Health Organization (WHO) recommends a guideline of 1.5 mg/L.

Implications for Public Health

The findings of this meta-analysis may inform future risk-benefit assessments of fluoride use in children’s oral health. While fluoride is effective in preventing dental caries, the study highlights the need for careful consideration of exposure levels, particularly in regions with naturally high fluoride concentrations in water. As the authors note, “This comprehensive meta-analysis may inform future risk-benefit assessments of the use of fluoride in children’s oral health.”

Conclusion

This systematic review and meta-analysis provide robust evidence of an inverse association between fluoride exposure and children’s IQ scores. The study underscores the importance of further research to clarify the dose-response relationship, particularly at lower fluoride concentrations, and to guide public health policies aimed at balancing the benefits of fluoride for dental health with potential risks to neurodevelopment.

For more details, the full study can be accessed at JAMA Pediatrics: doi:10.1001/jamapediatrics.2024.5542.