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Expert Evaluation by Michael Waalkes, Ph.D. <br /> Recent studies and systematic literature reviews have stimulated debate about the potential <br /> neurotoxicity of excessive fluoride exposure, possibly indicating that prenatal or early life may be a <br /> sensitive period for exposure. For example, a recent study (Bashash et al., 20172) looked at pregnant <br /> women and their offspring living in Mexico and found that higher prenatal fluoride exposure apparently <br /> caused slightly lower offspring cognitive function (IQ, etc.). In this study (Bashash et al., 20172) fluoride <br /> intake was appraised in both mothers and children by urinary fluoride output, an indirect measure of <br /> consumption with unknown potential confounding factors including diet. In fact, in this study the levels <br /> of fluoride in the drinking water were never actually measured, and, unlike in the USA, in Mexico they <br /> add fluoride to salt for supplementation. The effect on IQ in this study was limited to higher levels of <br /> fluoride exposure. In addition, there was also significant exposure to mercury and lead in the study <br /> population, which are both potentially neurotoxic metals, and there was a lack of information about <br /> arsenic exposure, a neurotoxic element. The authors themselves could not rule out the impact of <br /> unmeasured variables, including total exposure to established neurotoxic agents, on their findings with <br /> fluoride (Bashash et al., 20172). These confounding factors appear to largely limit the usefulness of this <br /> study and it is difficult to translate these findings at high levels to the levels used to fluorinate drinking <br /> water in the US particularly since drinking water exposure was never actually measured. <br /> Systematic reviews are a type of literature review that uses systematic criteria to collect <br /> previously published scientific research studies, and then critically appraises the selected studies, and <br /> finally synthesizes findings into an overall set of conclusions. One such systematic review looked at <br /> human studies of fluoride exposure from the drinking water and how fluoride exposure might impact <br /> neurodevelopmental status from studies carried out primarily in rural China and mostly published in the <br /> Chinese scientific literature and "not widely disseminated" (Choi et al., 20123). The authors indicate that <br /> 36 <br />