Fluoride: friend or foe? Exploring the effect of fluoride exposure on children's IQ scores.

Abstract

A commentary on: Taylor KW, Eftim SE, Sibrizzi CA, Blain RB, Magnuson K, Hartman PA, Rooney AA, Bucher JR. Fluoride Exposure and Children's IQ Scores: A Systematic Review and Meta-Analysis. JAMA Pediatr 2025; 179: 282-292.

Data sources: A literature search without language restrictions was undertaken in October 2023 using the following databases: BIOSIS, Embase, PsycINFO, PubMed, Scopus, Web of Science, CNKI, and Wanfang.

Study selection: Two independent reviewers screened studies based on the title and abstract. Studies were included if the exposure was fluoride and the outcome was a quantitative measure of children's intelligence. In studies with multiple fluoride exposure levels, the highest was considered the exposure and the lowest the reference. Exclusion criteria included case reports, articles without original data, and conference abstracts. Full text articles were then screened. Translation assistance was obtained for non-English studies.

Data extraction and synthesis: Data was extracted by one extractor and verified by a second. Risk-of-bias was evaluated by two independent trained assessors using the National Toxicology Programme's OHAT approach. Three meta-analyses were conducted: mean-effects, dose-response mean-effects, and regression slopes. Subgroup and sensitivity analyses were undertaken, including subgroup analyses without high risk-of-bias studies.

Results: 74 studies were included, of which 59 reported mean IQ scores for group-level exposures and 19 reported regression slopes for individual-level exposures. Children exposed to higher levels of fluoride had statistically significantly lower IQs than those exposed to lower levels (standardised mean difference (SMD), -0.45; 95%CI, -0.57 to -0.33; P < 0.001). A dose-response association was also reported, with lower IQ scores reported with increasing fluoride exposure with a SMD of -0.15 (95%CI, -0.20 to -0.11; P < 0.001) for water fluoride levels and -0.15 (95%CI, -0.23 to -0.07; P < 0.001) for urinary fluoride levels. Fluoride exposure concentrations of <4 mg/L, <2 mg/L, and <1.5 mg/L were analysed. For water fluoride <1.5 mg/L, the association was not statistically significant. In the regression slopes meta-analysis, a 1 mg/L increase in urinary fluoride was associated with a decrease in IQ score of 1.63 points (95%CI, -2.33 to -0.93; P < 0.001); the effect size was smaller when analysis was limited to low risk-of-bias studies (decrease of 1.14 points (95%CI, -1.68 to -0.61; P < 0.001)).

Conclusions: An inverse association was found between fluoride exposure and children's IQ scores, including an inverse dose-response association. This association was less certain at water fluoride concentrations <1.5 mg/L.