17 December 2014. A meta-analysis on IQ deficits in children exposed to elevated levels of fluoride in drinking water spurred much discussion in the US, mostly in regard to the safety of water fluoridation. The 27 studies reviewed in the study were mainly from China and covered exposures similar to those that occur in areas with fluoridated water and up to 10 times that level. Although children in the high-fluoride areas showed an average IQ 7 points below the controls, the dose-dependence of such deficits is uncertain.
To explore the association further, the team behind the meta-analysis carried out a pilot study in rural Sichuan, China. The results have just been released. The researchers used the best available and feasible approaches to exposure assessment and cognitive testing of 51 children. Their lifetime exposures to fluoride from drinking water covered the full range allowed in the US. Among the findings, children with fluoride-induced mottling of their teeth – even the mildest forms that appears as whitish specks on the enamel – showed lower performance on some neuropsychological tests. This observation runs contrary to popular wisdom that the enamel effects represent a cosmetic problem only and not a sign of toxicity. At least one of five American children has some degree of mottling of their teeth.
The safety of fluoridation for caries prevention is being defended in a recent commentary that claims that the meta-analysis of 27 studies had been “severely criticized”, although this critique is not further explained. As evidence of safety, the authors refer to a New Zealand study that “found that fluoridation is not neurotoxic for either children or adults, and does not have a negative effect on IQ”. This interpretation is rather optimistic, as the statistical confidence limits suggest that a loss of 2-3 IQ points could not be excluded by their findings.
Prevention of caries is an important goal, but that does not justify an exaggeration of fluoridation safety. In the past, scientific evidence on other neurotoxicants, such as lead, mercury, and certain pesticides, has been similarly misconstrued by vested interests. Although the link between mottled teeth and brain toxicity still needs to be further characterized, the existence of uncertainty is no excuse for mottling the debate with hyperbole. Prevention of chemical brain drain should be considered at least as important as protection against caries.