Fluoride Action Network


A birth cohort of 1265 children born in Christchurch in 1977 was studied longitudinally including assessment measures of cognitive ability at ages 8 and 9 years using the Wechsler Intelligence Scale for Children (WISC-R). It was possible to study the association between intelligence and fluoride exposure as approximately half of the sample resided in Waimairi County, fluoridated with 1 ppm of fluoride, while the other half resided in non-fluoridated Christchurch with 0.1 ppm. The children were grouped according to the duration of fluoridation exposure to age 7 years with the groups being exposed for 0, 1-3, 4-6 and 7 years. The mean IQs (WISC-R) at 8 years for these groups were 100.0, 99.04, 99.40 and 100.5 (p>0.30). The values at 9 years were 99.9, 99.3, 98.7 and 101.2 (p>0.70). It was evident that there was no trend for IQ to decline with increasing exposure to fluoridated water. In fact those who lived for 7 years in an area with fluoridated water had the highest mean IQ scores, although this difference was not statistically significant. The results can be seen as being consistent with other studies. In the study by Zhao et al on Chinese children intelligence was impaired with drinking water with 4.12 ppm of fluoride but not with 0.91 ppm. In the rat study by Mullenix et al neurotoxicity was present with plasma fluoride levels of 0.059-0.640 ppm which were seen to be similar to those found in humans of 0.076- 0.25 ppm drinking water with 5-10 ppm of fluoride. Thus a threshold effect for fluoride toxicity may be present with demonstrable effects being present with water containing 4-10 ppm but not 1 ppm of fluoride. However, recent work by Varner, Isaacson et al suggests that fluoride may have the potential to cause neurotoxicity at a level of 1 ppm if present with trivalent aluminium ions at a concentration of 0.5 ppm