Reviews of developmental fluoride neurotoxicity by Grandjean and Guth et al.

Abstract

An updated review by Philippe Grandjean, published in Environmental Health on December 19, 2019, of developmental fluoride neurotoxicity concluded that recent epidemiological results support the notion that elevated fluoride intake during early development can result in IQ deficits that may be considerable. He noted that the recognition of neurotoxic risks is necessary when determining the safety of fluoride contaminated drinking water and fluoride uses for preventive dentistry purposes. In contrast, another review by Guth et al., published online in Archives of Toxicology on May 8, 2020, concluded that fluoride was not a human developmental neurotoxicant at the current exposure levels in Europe where there is a mean fluoride intake in adults of 5–14 ug/kg bw/day in areas with a low drinking water fluoride level and of 30–40 ug/kg bw/day in areas with a high drinking water fluoride level. This editorial explores the
reasons for the different conclusions being reached and finds that Guth et al. reached their conclusion by not considering the well-designed 2017 prospective cohort study by Basash et al. in sufficient detail to recognize that intrauterine exposure to fluoride is more important than exposure at 6–12 years in causing developmental fluoride neurotoxicity and by not considering the calculations made of the threshold for the drinking water fluoride level for the development of fluoride-induced neurotoxicity of approximately 0.2 mg/L, calculated by Hirzy et al. in 2016 and Grandjean in 2019. A drinking water fluoride level of 0.2 mg/L would result in a fluoride intake of 0.248 mg day or 3.5 ug/kg bw/day in a 70 kg adult with a water intake of 1.24 L/day which is less than the mean adult European intakes of 5–14 and 30–40 ug/kg bw/day in areas with low and high drinking water fluoride levels, respectively. The conclusions that can be drawn from the studies by Basash et al, Hirzy et al., and Grandjean, together with the prospective studies by Valdez Jiménez et al. and Green et al., are that intrauterine exposure to fluoride is more important than exposure during childhood at age 6–12 years in causing developmental fluoride neurotoxicity and that the threshold level for drinking water fluoride for the development of this effect is approximately 0.2 mg/L. A further 2019 study by Till et al. indicates that the developing brain may also be adversely affected by exposure to drinking water with approximately 0.6 mg/L of fluoride during infancy. Accordingly, exposure of pregnant women and infants to community water fluoridation, with water with 0.7 mg/L of fluoride, the level recommended in the USA for community water fluoridation, or with 0.6–0.8 mg/L the level recommended in the Republic of Ireland, or to the current exposure levels in Europe, where there is a mean fluoride intake in adults of 5–14 ug/kg bw/day in areas with a low drinking water fluoride level and of 30–40 ug/kg bw/day in areas with a high drinking water fluoride level, is
unsafe, will lead to a fluoride intake that exceeds the threshold for developmental fluoride neurotoxicity of 0.2 mg/L or 3.5 ug/kg bw/day, and will result in the occurrence of developmental fluoride neurotoxicity. For these reasons, rather than accepting the reassurance of Guth et al., the editorial concurs with Grandjean’s conclusion.