Public Health Impacts of Water Fluorides: Current Evidence from a Rapid Systematic Review

Abstract

Despite being established public health practice for >80 y, community water fluoridation continues to attract assertions of harm, and continued scrutiny of the evidence is required to inform policy. A rapid systematic literature review was conducted to examine human nondental health outcomes from fluoride exposure through drinking water. A protocol was developed a priori and registered on the Open Science Framework. Literature searches were conducted in Medline, CINAHL, Web of Science, Embase, PubMed, Campbell Collaboration, Cochrane Library, and Scopus databases. Gray literature and citation searches were also undertaken. Quality assessment was performed using the Mixed Methods Appraisal Tool (MMAT). Meta-analysis was judged not feasible due to the heterogeneous nature of the included studies. A total of 1143 unique records were identified, of which 130 full-text studies were reviewed and 58 were selected for final inclusion. Among these, 37 were cross-sectional studies, 15 were cohort studies, 4 were case-control studies, and 2 were ecological studies. Most studies were judged to be of acceptable quality using MMAT. The most common risk of bias was insufficient control of confounders. Health outcomes studied included blood pressure, neurological outcomes, bone cancers, thyroid function, skeletal outcomes, low birth weight/preterm birth, and metabolic outcomes. In children, some evidence of adverse effects on neurological outcomes and thyroid function was observed. In adults, some evidence was identified of adverse effects on blood pressure, thyroid function, and skeletal structure. In general, these effects occurred at drinking water fluoride concentrations >1.5 mg/L. No evidence of adverse effects was found at concentrations <1.0 mg/L in both children and adults. The nature of study designs and methodological limitations precluded causal inference. No convincing evidence of harm was identified from community water fluoridation at concentrations between 0.7 and 1.0 mg/L, whereas uncertainty remains at higher concentrations. Significant methodological limitations highlight the need for more rigorous future studies. A protocol was developed a priori and registered on the Open Science Framework (Registration DOI: https://doi.org/10.17605/OSF.IO/JH245).