"The children in high fluoride areas had significantly lower IQ than those who lived in low fluoride areas," write Choi et al.
Further, the EPA says fluoride is a chemical "with substantial evidence of developmental neurotoxicity."
Fluoride (fluosilicic acid) is added to US water supplies at approximately 1 part per million attempting to reduce tooth decay.
Water was the only fluoride source in the studies reviewed and was based on high water fluoride levels. However, they point out research by Ding (2011) suggested that low water fluoride levels had significant negative associations with children's intelligence.