BACKGROUND AND AIM: People of all ages are exposed to fluoride from a variety of sources including dental products, drinking water, food, beverages and pharmaceuticals. In some developed countries, fluoride is added to municipal water systems to prevent tooth decay. The National Toxicology Program (NTP) conducted a systematic review of the human, experimental animal, and mechanistic literature to evaluate the extent and quality of the evidence about whether fluoride exposure is associated with neurodevelopmental and cognitive effects.
METHODS: A systematic review protocol was developed and utilized following the Office of Health Assessment and Translation (OHAT) approach for conducting literature-based health assessments.
RESULTS: The literature search and screening process identified 159 published human studies, 339 published experimental animal studies, and 60 in vitro/mechanistic studies. While the animal data provide some evidence of effects of fluoride on neurodevelopment, the human evidence base is large, directly addresses cognitive neurodevelopmental effects, and is most informative concerning the effects of fluoride on cognitive neurodevelopment in children.
CONCLUSIONS: The human body of evidence provides a consistent and convincing pattern of findings that higher fluoride exposure (e.g., >1.5 mg/L in drinking water) is associated with lower measures of cognitive neurodevelopment, primarily in measures of children’s IQ. When focusing on findings from studies with fluoride exposures in ranges typically found in drinking water in the United States (0.7 mg/L for optimally fluoridated community water systems), effects on cognitive neurodevelopment of children are inconsistent, and therefore unclear. The evidence for effects of fluoride exposures on cognition in adults is also limited. The evidence from animal studies is difficult to directly relate to the observed cognitive effects in humans, and the mechanisms underlying fluoride-associated cognitive neurodevelopmental effects are not well characterized.
Keywords: Fluoride, systematic review, children’s IQ
Authors affiliation: National Institute of Environmental Health Sciences.