New Review Sheds Doubt on the Safety of Fluoride
The monograph evaluates the existing literature on fluoride exposure and its potential neurodevelopmental and cognitive effects in humans. While limited evidence exists regarding adult cognition, the review finds a moderate correlation between higher fluoride exposure and reduced IQ levels in children, underscoring the need for further research to clarify these associations.
Fluoride is widely recognized for its benefits to dental and oral health, yet concerns have emerged regarding its potential neurodevelopmental effects, particularly in children. A 2006 evaluation by the National Research Council highlighted possible links between high levels of naturally occurring fluoride in drinking water and adverse neurological outcomes, prompting calls for further investigation. Following this, numerous studies — especially prospective cohort studies from North America — have explored the cognitive and neurobehavioral impacts of prenatal fluoride exposure.
The objective of the National Toxicology Program’s (NTP) Monograph on the State of Science Concerning Fluoride Exposure and Neurodevelopment and Cognition was to assess the quality and extent of evidence linking fluoride exposure to neurodevelopmental and cognitive effects in humans. Employing the standardized Oral Health Assessment Tool systematic review protocol, the researchers examined human studies, experimental animal data, and mechanistic literature while excluding discussions on the oral health benefits of fluoride.
The review revealed a lack of clarity from both animal studies and human mechanistic research regarding the cognitive effects of fluoride. Although the literature on adult cognition was sparse — with only two high-quality studies available — the research concerning children was more robust. The review identified 72 studies focusing on fluoride’s association with children’s IQ, of which 19 were high-quality. Remarkably, 18 of these high-quality studies demonstrated that as fluoride exposure increases, IQ tends to decrease and vice versa. Furthermore, among 53 low-quality studies, 46 indicated similar associations.
Despite the substantial body of evidence linking fluoride exposure to lower IQ in children, findings on other neurodevelopmental outcomes were inconsistent, reflecting heterogeneity in study designs and measures. The review indicates that existing animal studies do not offer significant insights into the relationship between fluoride exposure and IQ. Additionally, human mechanistic studies lacked the necessary homogeneity and quantity to establish biological plausibility.
Overall, the review concludes that higher fluoride exposure — particularly concentrations exceeding the World Health Organization’s guideline of 1.5 mg/L — is consistently associated with decreased IQ in children. However, due to the variability in other cognitive effects, confidence in these findings remains low. The authors emphasize the need for further research to better understand the implications of fluoride exposure on children’s cognitive development and the potential benefits of lower fluoride exposure.
In response to the release of the monograph, the American Dental Hygienists’ Association (ADHA) emphasized its support of community water fluoridation as a safe and effective means of reducing dental caries throughout the lifespan and emphasizes the importance of understanding the context of the studies referenced.
The ADHA’s statement noted that the United States Public Health Service recommends a fluoride concentration of 0.7 mg/L in drinking water, which has been shown to safely reduce tooth decay by 25% in both children and adults. Importantly, the studies highlighted in the NTP’s report were conducted outside of the US and focused on fluoride concentrations exceeding 1.5 mg/L, far above the levels recommended for US water fluoridation. These studies, based primarily on epidemiology data from non-US countries, should be interpreted with caution when considering fluoride levels typically found in US public water supplies.
