International fluoride symposium: effects of fluoride on human health and its mechanisms of action – a meeting report

Fluoride prevents dental caries in a dose–response manner, leading some countries to adjust fluoride levels in water or table salt, as well as to promote the widespread use of topical fluoride. Recent studies have found associations between prenatal fluoride exposure levels of < 1.5 mg/L in water and urine and adverse neurodevelopmental outcomes. Although high fluoride levels have been recognized as neurotoxic in the past, a large body of contemporary evidence derived from retrospective analyses of birth cohort studies suggests fluoride may be neurotoxic to children at lower levels, highlighting the need for further, prospective research and multidisciplinary collaborations. The International Fluoride Symposium, held from April 29 to 30, 2024, brought together 20 researchers from the United States, Canada, Mexico, and Spain to discuss the impacts of fluoride on human health and its mechanisms of action. The primary goals of the symposium were to address challenges related to assessing fluoride exposure, share findings from cohort studies, develop a comprehensive research agenda, and foster international research partnerships. Key discussions included the dental caries preventive and toxic effects of fluoride, sources of fluoride exposure, biomarkers, dietary intake assessment methods, and analytical challenges. Presentation of results from cohort studies highlighted research on prenatal fluoride exposure and its association with neurodevelopmental outcomes and presented perspectives for future analyses. The symposium emphasized the need for customized dietary fluoride intake assessment tools, the development of high-throughput analytical methods for fluoride analysis, and research on the combined effects of fluoride with other chemical elements commonly found in the environment and the human diet. Additionally, there was a call for the harmonization of cohort data from diverse populations to address urgent questions about the impact of fluoride on human neurodevelopment and other health outcomes beyond oral health. It was agreed that prospective longitudinal cohort studies intentionally designed to assess fluoride exposure and neurodevelopment are essential, as none of the existing birth cohorts were designed to specifically study fluoride exposure (e.g., selection of biomarkers, collection intervals, diet exposure assessment). Furthermore, broader environmental health cohort studies that incorporate high-quality biomonitoring of waterborne neurotoxicants (such as fluoride, arsenic, lead, mercury), repeated measures of exposure, and inclusion of key covariates (e.g., socio-economic status, diet, iodine) are encouraged. Finally, developing effective communication strategies among scientists and the public was considered crucial for advancing fluoride research and mitigating potential health risks.