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November 19, 2019
National Toxicology Program
c/o National Academy of Sciences
500 Fifth Street NW
Keck WS625
Washington, DC 20001
Re: Draft Monograph on the Systematic Review of Fluoride Exposure and Neurodevelopmental and Cognitive Health Effects
To Whom It May Concern:
On behalf of our 163,000 dentist members, we are pleased to comment on the National Toxicology Program’s Draft Monograph on the Systematic Review of Fluoride Exposure and Neurodevelopmental and Cognitive Health Effects.
At appropriate concentrations, doses and frequency of use in drinking water and dental products, fluoride has proven to reduce the prevalence and severity of tooth decay, a disease with potentially serious consequences. Tooth decay is the most common chronic disease of childhood which also affects the majority of adults. The Centers for Disease Control and Prevention (CDC) hailed community water fluoridation as one of ten great public health achievements of the 20th century.1-2
For the last 75 years, people have raised well-meaning questions about the safety and effectiveness of fluoride exposure, including whether fluoride is somehow associated with neurological development. So, in 1977, the ADA established its National Fluoridation Advisory Committee (NFAC), a standing panel of experts who are able to provide ongoing advice about the safety and effectiveness of fluoride.
Enclosed you will find NFAC’s observations and comments about the draft monograph and a roster of current members. Our panel of experts concluded that the available literature is insufficient to establish causation between fluoride exposure as experienced in the United States and neurocognitive development. It found that the literature generally is either lacking, unreliable, inconclusive, conflicting or subject to widespread interpretation.
We are also enclosing copy of Fluoridation Facts—the ADA’s premier informational resource on community water fluoridation. Fluoridation Facts provides answers to frequently asked questions about fluoride and community water fluoridation. Our goal is to provide clear answers—supported by numerous of credible scientific articles—to help policy makers and the public navigate through the many myths and misperceptions about fluoride.
The 2018 edition of Fluoridation Facts contains evidence-based answers to the question of whether there is a relationship between consumption of optimally fluoridated water and lowered intelligence quotients or behavioral disorders in children. The evidence from systematic reviews and individual studies does not support claims of a causal relationship.
Given the state of the literature, we ask that you revisit the monograph’s draft hazard rating that fluoride is “presumed to be a cognitive neurodevelopmental hazard to humans.” It is also critical to the public’s health that you include some type of modifier to distinguish the health benefits of optimally fluoridated drinking water, currently recommended at 0.7 parts per million (ppm), from the higher level exposures the monograph addresses (above 1.5 ppm).
Whatever final form the monograph takes, we appreciate the opportunity to comment. If you have any questions, please contact Mr. Robert J. Burns at 202-789-5176 or burnsr@ada.org.
Sincerely,
Chad P. Gehani, D.D.S.
President
Kathleen T. O’Loughlin, D.M.D., M.P.H.
Executive Director
CPG:KTO:rjb
Enclosures (3)
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1 Centers for Disease Control and Prevention. Ten Great Public Health Achievements — United States, 1900-1999. MMWR 1999; 48 (12): 241-243.
2 Vivek H. Murthy, Surgeon General’s Perspectives: Community Water Fluoridation—One of CDC’s 10 Great Public Health Achievements of the 20th Century, Public Health Rep 2015; 130(4): 296-298.
ADA American Dental Association
National Fluoridation Advisory Committee
Scientific/Technical Comments
on the
National Toxicology Program Draft Monograph on the
Systematic Review of Fluoride Exposure and Neurodevelopmental and
Cognitive Health Effects
November 19, 2019
The American Dental Association’s National Fluoridation Advisory Committee is pleased to offer the following scientific/technical comments on the National Toxicology Program’s Draft Monograph on the Systematic Review of Fluoride Exposure and Neurodevelopmental and Cognitive Health Effects.
On November 6, 2019, the Overview of the Systematic Review shared that the NTP found a “moderate level of evidence that high fluoride exposure is associated with decreased IQ and other cognitive effects in children”.
However, we believe that the hazard rating of fluoride as “presumed to be a cognitive neurodevelopmental hazard to humans” is not supported by the systematic review of fluoride exposure.
We offer these comments and summarize our concerns in the following paragraphs:
- 1. The literature review did not take into account the lack of support for a neurobehavioral effect of fluoride from animal studies conducted in the U.S.The NTP animal study concluded that “At these exposure levels, we observed no exposure-related differences in motor, sensory, or learning and memory performance on running wheel, open-field activity, light/ dark place preference, elevated plus maze, pre-pulse startle inhibition, passive avoidance, hot-plate latency, Morris water maze acquisition, probe test, reversal learning, and Y-maze… No evidence of neuronal death or glial activation was observed in the hippocampus at 20 ppm F? .” (McPherson et al., 2018, p. 781)1.“ Whitford et al. also concluded that “Chronic ingestion of fluoride at levels up to 230 times more than that experienced by humans whose main source of fluoride is fluoridated water had no significant effect on appetitive-based learning (Whitford, et al, 2009).2” It is worth noting these two US studies are not in agreement with many of the animal studies conducted in China and India, thus raising questions about the validity of those other studies.
- 2. No meta-analysis was conducted to determine a summary effect size. It appears that the determination that the IQ effect size was large is based on subjective assessment and does not take into account measurement error.Figure D 7 in the review shows 53 beta estimates. Of these 23 are listed as significant (red) and the remaining 30 are not. None of these estimates accounted for the cluster sample design used (the samples were drawn from cities, schools or prenatal clinics). Accounting for cluster design effect may result in larger standard errors, thus reducing the p-value (statistical significance) associated with the results.
- 3. The characterization that effect sizes observed were of relatively large magnitude is not consistent with the data that show small effect sizes.
IQ assessment in young children is subjective and influenced by multiple factors. Thus, small IQ score differences such as 1.5 points or even 4.5 points are not likely to be readily detectable due to measurement challenges between noise and signal nor have implications for normal children’s activities. The review states that the IQ effect is relatively large and thus classifies fluoride as a “presumed” neurotoxin. There are differing views whether the IQ differences are large, and the Canadian Agency for Drugs and Technologies in Health (CADTH) have called the reported IQ effects as small3. Therefore, the panel should re-assess the clinical significance of the IQ studies.
- 4. The NTP report’s assertion that “There is a low expectation that new studies would change the hazard conclusion” is not adequately justified considering that there are no prospective epidemiological studies that were designed to assess the neurobehavioral effects of fluoride.
A reanalysis of the Canadian and Mexican studies that takes into account the cluster sampling design may not show an effect. Furthermore, a recent study conducted by Santa-Marina, et al., 2019, in Spain showed, “At the age of 4-5 years, an increase of 1 mg/l in the level of fluoride in urine during pregnancy (mean level of 1st and 3rd trimesters) was related to a higher score on the perceptual-manipulative scale of 4.44 (0.13, 0.75) points.4” If additional consideration and peer review of this study’s results are forthcoming, this certainly would contradict this assertion from the NTP draft report.
With the concerns about the validity, reliability, and generalizability of the research used, we ask the team to reconsider how they classify Fluoride’s Hazard Conclusion. With the research community of experts raising questions about the evidence used, the correlation between fluoride exposure in drinking water as publicly available in the United States and neurocognitive development is still unknown.
Also, very importantly, even if the NTP report’s classification does not change, an extremely important element that is missing from the conclusion is a modifier to distinguish the difference between a high level of fluoride exposure and any exposure. Without replicated study findings showing strong correlations between fluoride exposures near 0.7 ppm (which is much less than 1.5 ppm, and a relatively rare level in the US) and neurodevelopment, the results are misleading to the public.
The ADA is truly gratified when, in the interest of the public’s health and welfare, communities provide optimally fluoridated water to their residents. The current classification is misleading to the public, could scare them unnecessarily, and could ultimately decrease the oral health status of individuals and communities.
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1 McPherson CA, Zhang G, Gilliam R, et al. An Evaluation of Neurotoxicity Following Fluoride Exposure from Gestational Through Adult Ages in Long-Evans Hooded Rats. Neurotox Res. 2018;34(4):781–798. doi:10.1007/s12640-018-9870-x
2 Whitford, G, Whitford, J, Hobbs, S. Appetitive-based learning in rats: Lack of effect of chronic exposure to fluoride. Neurotoxicology and Teratology. 2009; 31(4):210-215. https://doi.org/10.1016/j.ntt.2009.02.003
3 Canadian Agency for Drugs and Technology in Health. Community Water Fluoridation: A Review of Neurological and Cognitive Effects. Ottawa: CADTH; 2019 Oct. (CADTH rapid response report: summary with critical appraisal). ISSN: 1922-8147 (online) Available at
https://cadth.ca/sites/default/files/pdf/htis/2019/RC1198%20Community%20Water%20Fluoridation%20Exposure%20Final.pdf
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