Artificial water fluoridation for dental health improvement: a review and meta-analysis of the evidence and implications of a possible association between water fluoride and IQ

BackgroundGlobally, dental caries affects 60-90% of schoolchildren. Although artificial water fluoridation improves dental health and reduces dental health inequalities, there is concern that excessive fluoride exposure may lower cognition. We systematically reviewed and meta-analysed the association between water fluoride and intelligence quotient (IQ). MethodsA literature search of Medline and Web of Science and random-effects meta-analysis comparing mean IQ of children living in low/normal or higher water fluoride areas was investigated. Followed by exploration of possible dose effects among sub-groups, living in moderate (<1.5 ppm) high (1.5-3.0 ppm) or extremely high (>3ppm) water fluoride areas. ResultsTwenty-three observational studies (n=9539 children) were included. Overall, the higher water fluoride group had a lower mean IQ compared with the low water fluoride group (standardised mean difference (95% confidence interval): -0.43 (-0.63 to -0.24) p<0.0001, I2=94.2% p<0.0001). Sub-group analysis showed no association between water fluoride and mean IQ in studies of moderate fluoride concentrations (moderate: 0.04 (-0.08 to 0.15) p=0.53, I2=0.0% p=0.68). Mean IQ was lower in the higher water fluoride groups (high: - 0.52 (-0.92 to -0.12) p=0.01, I2=96.2% p<0.00001, extremely high: -0.60 (-0.87 to -0.33), p<0.0001, I2=84.6% p<0.0001). ConclusionsAt moderate levels (<1.5 ppm) there was no statistical or clinically meaningful association between water fluoride and IQ. This suggests that populations living in these areas could benefit from artificial water fluoridation without experiencing neurotoxicity. An association between lower mean IQ and high water fluoride observed suggests a need to prioritise removal of excess fluoride from drinking water in these regions. Key Message (3-5 bullet points in complete sentence)At low concentrations of water fluoride (<1.5 ppm) there was no detectable association between water fluoride and intelligence quotient (IQ); At high levels of water fluoride concentrations (>1.5 ppm) there was an inverse association between increasing fluoride concentration and decreasing mean IQ; In countries in which fluoridation of water is considered but kept within safe concentrations, the available evidence suggests that fluoridation has demonstrable benefits on public dental health without any clinically significant effect on IQ. In countries with excessive groundwater fluoride concentrations there is an imperative to promote water de-fluoridation schemes to protect the public from skeletal and dental fluorosis and from possible neurotoxicity.