An update on community water fluoridation, part 2: Fluoride exposure and children's intelligence (IQ) scores—relevance of systematic reviews and meta-analyses to community water fluoridation

Abstract

Background: The authors provide an overview of the literature on the association between fluoride (F) exposure related to community water fluoridation (CWF) and children's intelligence (IQ). It also critically evaluates the limitations of the evidence base. Types of Studies Reviewed: This review is grounded in assessments from 4 government reports and supplemented by means of 3 independent reports and 7 other meta-analyses and systematic reviews. Collectively, these resources offer an overview of the literature on the relationship between F exposure and IQ. In addition, a meta-analysis of the association between urinary F and IQ is reanalyzed for its relevance to CWF. Results: The authors found there is no association between F concentrations relevant to CWF and IQ scores. Although researchers reported an association in endemic areas (ie, with F levels exceeding 1.5 mg/L), the design and conduct of these studies have numerous methodological weaknesses, including a limited number of high-quality studies; weak study designs; inadequate attention to accurately measuring F exposure, confounding variables, and outcomes; and the use of inappropriate statistical procedures. There is no established biological mechanism to explain F's effect on IQ. These limitations raise questions about the findings and preclude discussion of causal relationships. Furthermore, differences in water intake among countries should be considered when making cross-national comparisons. Conclusions and Practical Implications: The evidence does not support a causal link between F in drinking water and children's IQ. Dental and public health care practitioners should use this evidence to inform, educate, and empower patients and the public about the safety and benefits of CWF.