Reference: JAMA Pediatr 2025 Jan 6 early online
Practice Point: The reported association between fluoride in water and lower IQ doesn’t apply at the levels recommended by American dental and medical organizations.
EBM Pearl: Consistent findings in multiple subgroup analyses, especially separate analysis including only studies with the lowest risk of bias, offers reassurance that results of a systematic review of observational studies are trustworthy.
Balancing risks and benefits makes up a lot of what we do in clinical medicine. But this equation works best when, if not requires that, we have a full and accurate representation of the risks and benefits. In the case of water fluoridation, it’s possible that the discussion of risks and benefits has not been fully informed or updated with new information.
Water fluoridation was first introduced in the United States in the 1950s as a public health intervention to decrease dental caries. Currently, about 70% of United States communities have fluoridation, with some communities choosing to ban it for a wide variety of stated reasons. The argument in the 1950s was that fluoridation led to a 60% reduction in dental caries. Over time, however, later studies found smaller and smaller benefits. Is this another example of the old adage “use new drugs quickly while they still work”? Well, it’s complicated. Since the 1950s, fluoride toothpastes, dental sealants, and pediatrician-applied fluoride during well-child checks for preschoolers have all become commonplace. This was reflected in a 2024 Cochrane review of water fluoridation that found an absolute decrease in dental caries on average of about 2 teeth per child in studies published before 1975 and ¼ tooth per child in studies published more recently. It’s important to note that the children most likely to benefit from water fluoridation are those without access to other modalities for proper oral health, and so there may be a health equity component to water fluoridation that should be kept in mind.
So, if the benefit of water fluoridation is smaller than it used to be, what about the risks? Dental fluorosis is a well-known problem and is directly related to exposure to too much fluoride. At water fluoridation levels of 0.7 PPM, which is the current recommended level in the United States, aesthetically significant fluorosis is estimated at about 10%. That hasn’t changed. Ok, fine. Of greater concern, however, is data from a recent systematic review that reported an inverse relationship between fluoride exposure and children’s IQ levels. This systematic review published in JAMA Pediatrics evaluated 59 observational studies; 45 were conducted in China, and 47 were considered to be at high risk of bias. In a subgroup analysis that evaluated fluoride specifically in drinking water, a dose-dependent association between fluoride exposure and lower IQ scores in children was found, but only when studies of fluoride concentrations above 1.5 PPM were included. When the analysis included only studies with < 1.5 PPM, there was no association with lower IQ scores.
There are many limitations of this study, but two noteworthy pitfalls are 1) most of the studies were deemed to have a high risk of bias (with concern for bias above and beyond that which is inherent to observational studies) and 2) there was evidence of publication bias, suggesting there may have been studies finding no association that were never published. Also, extraneous sources of topical fluoride, such as those provided at well-child and dental visits as well as fluoride sources in diet may confound the ability to draw strong conclusions from risks associated with water fluoridation and its impact on dental caries.
This systematic review made for exciting headlines, but the bottom line seems to be that while water fluoride levels below 1.5 PPM do not pose a risk to IQ, there may be some risk at higher concentrations. In the United States in particular, water fluoridation seems to still be a low-risk intervention. However, the benefit to dental health is also much smaller than once thought. All taken, it seems that perhaps a recalibration of the scales is in order when discussing the risks and benefits of water fluoridation at both the patient- and population-health levels.
For more information, see the topic Dental Caries in DynaMed.
DynaMed EBM Focus Editorial Team
This EBM Focus was written by Alan Ehrlich, MD, FAAFP, Executive Editor at DynaMed and Associate Professor in Family Medicine at the University of Massachusetts Medical School. Edited by Katharine DeGeorge, MD, MS, Senior Deputy Editor at DynaMed and Associate Professor of Family Medicine at the University of Virginia; Dan Randall, MD, MPH, FACP, Senior Deputy Editor at DynaMed; McKenzie Ferguson, PharmD, BCPS, Senior Clinical Writer at DynaMed; Rich Lamkin, MPH, MPAS, PA-C, Clinical Writer at DynaMed; Matthew Lavoie, BA, Senior Medical Copyeditor at DynaMed; Hannah Ekeh, MA, Senior Associate Editor II at DynaMed; and Jennifer Wallace, BA, Senior Associate Editor at DynaMed.