Safety l Fluoridation Facts 59 35. Does the ingestion of optimally fluoridated water adversely affect the thyroid gland or its function? Answer. The best available scientific evidence indicates optimally fluoridated water does not have an adverse effect on the thyroid gland or its function. Fact. A number of systematic reviews completed in the last ten years have looked at a possible association between exposure to fluoride and thyroid function. In 2017, the Australian National Health and Medical Research Council’s systematic review Information Paper — Water Fluoridation: Dental and Other Human Health Outcomes10 concluded, “There is no reliable evidence of an association between water fluoridation and current Australian levels and thyroid function.” (Current recommendations for fluoride levels in drinking water in Australia are a range of 0.6 to 1.1 mg/L depending on climate.)10 A scientific evaluation of fluoridating agents of drinking water was done by the Scientific Committee on Health and Environmental Risks (SCHER) as requested by the European Commission (EC). The EC is the European Union’s (EU) executive body with responsibility to manage EU policy. The final report, Critical review of any new evidence on the hazard profile, health effects, and human exposure to fluoride and the fluoridating agents of drinking water, was released in 2011. It stated that “A systematic evaluation of the human studies does not suggest a potential thyroid effect at realistic exposures to fluoride.”20 In 2015, the U.S. Public Health Service Recommendation for Fluoride Concentration in Drinking Water for the Prevention of Dental Caries16 was released. It referred to the 2006 National Research Council’s report, Fluoride in Drinking Water — A Scientific Review of the EPA’s Standards,9 stating: The 2006 NRC review considered a potential association between fluoride exposure (2-4 mg/L) and changes in the thyroid, parathyroid, and pineal glands in experimental animals and humans. The report noted that available studies of the effects of fluoride exposure on endocrine function have limitations. For example, many studies did not measure actual hormone concentrations, and several studies did not report nutritional status or other factors likely to confound findings. The NRC called for better measurement of exposure to fluoride in epidemiological studies and for further research “to characterize the direct and indirect mechanisms of fluoride’s action on the endocrine system and factors that determine the response, if any, in a given individual.”9 On March 22, 2006, during the press webcast127 for the release of the 2006 National Research Council (NRC) Report,9 John Doull, M.D., Ph.D., Professor Emeritus of Pharmacology and Toxicology, University of Kansas Medical Center, Kansas City and Chair of the NRC Committee was asked about the conclusions reached on fluoride and the endocrine system (which includes the thyroid). Dr. Doull replied: The Endocrine Chapter (of the NRC Report) is a relatively new chapter. It has not been extensively reviewed previously and our feeling was that we needed to provide a baseline of all the adverse effects and a lot of the systems that hadn’t really been looked at very closely. We have a chapter for example on the central nervous system which has not been reviewed in detail previously. We went through all those effects in the endocrine chapter, the thyroid effect, the parathyroid effect, calcitonin to see whether there were sufficient evidence for us to include any of those effects as specific adverse effects at 4 mg/L and the conclusion of our Committee was that those were all things we needed to worry about. Those were all things that we made recommendations for additional research. But, none of them reached the level where we considered them to be signs of adverse effects at the 4 mg/L level. (Emphasis added.)127 A population-based Canadian study128 was released in 2017 that examined the association between fluoride exposure and thyroid conditions. Data for the analysis came from Cycles 2 (2009-2011) and 3 (2012-2013) of Statistics Canada’s Canadian Health Measures Survey (CHMS). The CHMS’ target population is all Canadian residents between the ages of 3 and 79 living in all ten Canadian provinces. It collects health information by an individual in-home interview followed by a clinical exam conducted in a mobile clinic. The researchers’ reported findings suggest that, at the population level in Canada, fluoride exposure does not contribute to impaired thyroid functioning during a time when multiple sources of fluoride exposure, including community water