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Community water fluoridation and intelligence.

Community water fluoridation (CWF) is a costeffective, safe, and environmentally friendly means of reducing dental caries rates and social inequalities. However, CWF has recently been criticized as a cause of IQ deficits among children, despite a lack of evidence to support that claim. This claim was considered pivotal in the recent rejection of CWF by voters in Portland, Oregon, and by local government politicians in Hamilton, New Zealand. It is likely that such claims may continue to be lobbied against CWF worldwide. Since the 1960s, about half of New Zealand’s population has had access to CWF. Nationally, average fluoride intakes remain below the adequate intake level for dental caries protection, and CWF schemes are only 1 (albeit important) source of exposure to fluoride. The New Zealand Ministry of Health supports CWF in policy, but implementation of that policy is decided upon and undertaken by Territorial Local Authorities (local government) mandated to supply water services to people in their areas (and improve the health of their populations). Hamilton city (New Zealand’s fifth-largest metropolitan area) has had CWF since 1966 and has recently become a target for CWF opponents. Despite a binding 2006 referendum that showed 70% support for CWF among voting Hamiltonians, Hamilton’s City Council chose to relitigate CWF and held a tribunal on fluoridation in early 2013. The councilors voted to cease CWF, leading to an outcry from members of the public and health officials. A new referendum was then held (accompanying a local government election), which again showed 70% support for CWF among voting Hamiltonians. The Hamilton City Council elected to await the outcome of a High Court ruling on a challenge to the legality of CWF in another New Zealand city (New Plymouth) before reinstating CWF. Following the release of the ruling in favor of CWF, the Hamilton City Council reversed their previous decision, and voted in February 2014 to reintroduce CWF to Hamilton in April 2014. In the tribunal submissions and hearings, CWF opponents relied heavily on 2 studies as the basis for linking CWF with IQ deficits. The first was a 2006 review article in which fluoride was included in a list of “compounds known to cause neurotoxicity in man”; however, the text of the same article stated that this had been inconclusive. The second study was a 2012 meta-analysis that compiled the findings of studies from China and Iran, which related IQ and naturally occurring fluoride in water and other sources of exposure, but none were in the context of CWF. The meta-analysis conceded that the included studies were of low quality and that potential confounders were not investigated. Furthermore, the fluoride levels in the water sources for the high fluoride and low IQ groups had very high and variable fluoride levels. In a majority of the studies that considered fluoride in water, the reference groups had exposure to water with similar or even greater fluoride levels than those used in CWF programs. Selective readings of the metaanalysis generated enough misinformation that a press release issued by the authors in September 2012 had to emphasize the fact that their research was irrelevant to CWF. The EU Scientific Committee on Health and Environmental Risks has reported on these fluoride---IQ studies and found them to be of simplistic methodological design with no (or at best little) control for confounders such as nutrition, exposure to iodine or lead, or socioeconomic status. A New Zealand review also considered many of the same studies and found them to be of low quality and with a high risk of bias. Despite these problems, several public antiCWF submissions that were made to the Hamilton City Council Fluoridation Tribunal cited these studies; for example, one submission stated “recent research findings show that fluoride can be toxic to children’s brain development”; another stated “The decrease in average IQ results in a significant drop in the number of geniuses in society and an equally disproportionate increase in the number of mentally handicapped people”; yet another stated “fluoride is a known neurotoxin” and suggested a relationship with fictionalWorldWar II “mental numbing” experiments. These statements Objectives. This study aimed to clarify the relationship between community water fluoridation (CWF) and IQ. Methods.We conducted a prospective study of a general population sample of those born in Dunedin, New Zealand, between April 1, 1972, and March 30, 1973 (95.4% retention of cohort after 38 years of prospective follow-up). Residence in a CWF area, use of fluoride dentifrice and intake of 0.5-milligram fluoride tablets were assessed in early life (prior to age 5 years); we assessed IQ repeatedly between ages 7 to 13 years and at age 38 years. Results. No clear differences in IQ because of fluoride exposure were noted. These findings held after adjusting for potential confounding variables, including sex, socioeconomic status, breastfeeding, and birth weight (as well as educational attainment for adult IQ outcomes). Conclusions. These findings do not support the assertion that fluoride in the context of CWF programs is neurotoxic. Associations between very high fluoride exposure and low IQ reported in previous studies may have been affected by confounding, particularly by urban or rural status. (Am J Public Health. 2015;105: 72–76. doi:10.2105/AJPH.2013.301857) RESEARCH AND PRACTICE