FLUORIDE, IQ, EMOTION, AND CHILDREN'S SCHOOL PERFORMANCE

In a study, in the current issue of Fluoride, on the relationship between drinking water F levels and the schooling performance of 775 primary school pupils, 315 boys and 460 girls, aged 6-14 years, in 27 schools, in 16 rural areas remote from industrial pollution by heavy metal neurotoxicants in Khartoum state, Sudan, with a similar socioeconomic status, Mustafa et al. found an inverse relationship between the F level in the drinking water, range 0.01-2.07 mg/L, and the schooling performance. Another 2018 study by Yu et al. of 2,886 children, aged 7 to 13 years, from endemic and non-endemic fluorosis areas in Tianjin, China, found that for a drinking water F range of 0.20-1.40 mg/L there was significantly decreased probability of developing excellent intelligence (IQ >= 130, OR=0.60, 95% CI: 0.47 to 0.77). For the drinking water F range of 1.60-2.50 mg/L, every 0.5 mg/L increment in the urinary F level was associated with a decrease of 2.67 in the IQ score (95% CI: -4.67 to -0.68). In an earlier 2013 study, Liu et al. reported that developmental exposure to F induces cognitive deficits and anxiety-depression-like behaviors in mice. Although Mustafa et al. and Yu et al. found an significant inverse association between the drinking water F levels and IQ in children aged 6-14 years and 7-13 years, respectively, the findings of Bashash et al. and Thomas et al. indicate that it was the F exposure experienced by their mothers during pregnancy that was the major cause of the F-induced neurotoxicity rather than the levels of F that the children were exposed to at ages 6-14 years. Bearing in mind the work by Liu et al. showing that F exposure during development in mice can affect both cognition and emotion, and the literature on emotion and school performance, it is possible that the reduced school performance found by Mustafa et al. was the result of F-induced changes in emotional regulation as well as F-induced impairment in IQ. The safe daily dose of F for pregnant women to prevent in utero foetal neurotoxicity, has been calculated, using the standard LOAEL/NOAEL method, to be 0.04 mg F/day, which corresponds to an oral reference value for longer-term (up to 10% of an average life span) exposure (RfV(LO)) of approximately 0.0006 mg/kg bw/day. Obtaining safe drinking water is challenging in many countries but it should be easier to achieve in countries that deliberately add F to the water with the goal of reducing dental caries, although in practice "seeing the light" on the need to reduce public exposure to a toxin after its toxicity has been identified is, for various reasons, often a slow process (tardive photopsia).