Further Updates on Water Fluoridation (2024)
Summary
Water fluoridation is an effective public health measure that reduces the burden of dental caries. However, fluoridation has been, and remains, a controversial issue in the United States and other developed countries. Essays were posted on the COHN in 2019 and 2020 that addressed the question of potential adverse effects of water fluoridation, specifically cognitive status. The first reported the findings from a study relating in utero exposure to water fluoridation to the intelligence quotient (IQ) of 3–4-year-old children. Though the level of fluoride in the public water supply was at the concentration recommended by the U.S. Public Health Service (0.7 mg/liter), maternal fluoride exposure via the public water system was associated with lower IQ scores in their children at 3-4 years of age. The second essay was a broader examination of this association, focusing on two longer term studies (from New Zealand and Sweden) which did not find any association between pregnant women drinking fluoridated water and cognitive impairment of their children.
Four recent developments illustrate the continuing debate. First, the U.S. National Toxicology Program released the final version of a comprehensive review of the published literature, stating that higher concentrations of fluoride in drinking water (i.e. 1.5 mg/L) pose a risk for lower IQ scores in children. Second, a ruling in a court case in northern California found that fluoride in drinking water posed a threat to health and ordered the U.S. Environmental Protection Agency to review the data. Third, a Cochrane Library review compared the reduction in the caries rates attributable to water fluoridation over time. The authors found a smaller reduction in the caries rate in more recent studies. This change was suggested to be the result of exposure to fluoride from non-water sources, mainly oral hygiene products that contain fluoride. This would lead to questioning the need for water fluoridation in developed countries where other sources of fluoride are available. Lastly, concern about the safety of exposure to fluoride in the water system was raised in the lead-up to the 2024 U.S. presidential election, which may result in this soon becoming a national issue. It is imperative that oral health care providers remain current regarding future developments on this important subject.
Water fluoridation is recognized as one of the top ten public health measures of the 20th century1Gooch, B.F. Community Water fluoridation – One of the 10 Greatest Public Health Achievements of the 20th Century. Preventing Chronic Disease Dialogue. Centers for Disease Control and Prevention; 2015, April 13. Available from: https://blogs.cdc.gov/pcd/2015/04/23/community-water-fluoridation. Accessed November 3, 2024.. Nevertheless, water fluoridation has always been the subject of some controversy. It is a public health measure that adds an active agent to the public water supply and removes the decision to participate in this public health initiative away from the individual if they use that water supply. Further, published data about the potential deleterious effects of fluoride exposure have raised concern about the safety of water fluoridation.
Previous essays on the water fluoridation controversy
In 2019 and 2020, two essays were posted on the Colgate Oral Health Network (COHN) that addressed the issue of the safety of water fluoridation. The first of these2Lamster, I. (2019, September 19). The effects of water fluoridation on cognitive function: The story continues. Colgate Oral Health Network. Available from: https://www.colgateoralhealthnetwork.com/article/the-effects-of-water-fluoridation-on-cognitive-function-the-story-continues/. reviewed a paper published in JAMA Pediatrics3Green R, Lanphear B, Hornung R, Flora D, Martinez-Mier EA, Neufeld R, et al. Association between maternal fluoride exposure during pregnancy and IQ Scores in offspring in Canada. JAMA Pediatr. 2019;173(10):940-8. that reported the results of an epidemiologic study from Canada that found reduced intelligence quotient (IQ) scores of young children born to women who drank fluoridated water during pregnancy. The second was a more in-depth look at studies that examined the relationship of water fluoridation and fluoride intake to intelligence and cognition4Lamster, I., and Foley, M. (2020, May 26). Water fluoridation and cognitive function: A closer look at the evidence. Colgate Oral Health Network. https://www.ohasa.colgateoralhealthnetwork.com/article/water-fluoridation-and-cognitive-function-a-closer-look-at-the-evidence/.. These essays are summarized below.
2019 essay
In the JAMA Pediatrics report, fluoride intake during pregnancy was estimated based on fluoride levels in expectant mothers’ urine, measured three times during pregnancy. The IQ scores of the children of these mothers were assessed at 3-4 years of age. Of note, the concentration of fluoride in the water supply that participants were exposed to was 0.7 mg per liter of water (0.7 mg/L), which is the concentration recommended by the United States Public Health Service. The findings were that for each 1 mg increase in the fluoride levels in urine, there was a 4.5-point decrease in the IQ of male children (a similar decrease was not seen in female children). In addition, based on a questionnaire that sought to determine total fluoride intake by mothers and children, for every 1 mg increase in fluoride intake, both male and female children had a 3.7-point decrease in IQ.3Green R, Lanphear B, Hornung R, Flora D, Martinez-Mier EA, Neufeld R, et al. Association between maternal fluoride exposure during pregnancy and IQ Scores in offspring in Canada. JAMA Pediatr. 2019;173(10):940-8.
These findings were noted to agree with other studies demonstrating reduced neurologic function related to the consumption of fluoridated water.
Given the controversial nature of the described findings, an editorial accompanied the publication of this article5Christakis DA. Decision to Publish Study on Maternal Fluoride Exposure During Pregnancy. JAMA Pediatr. 2019;173(10):948.. Key points were:
- Historically, water fluoridation has had a beneficial impact on caries prevalence and therefore a positive impact on oral health.
- Previous research studies examining the relationship of water fluoridation to cognition have not always been of the highest quality, and not all previous reports agree that consumption of fluoridated water was associated with cognitive impairment.
- The data analysis in the JAMA Pediatrics study was thorough, and the editors stated that “fluoride as a neurodevelopmental toxicant must now be given serious consideration.”
- Many questions remain, i.e., is there a critical time of exposure for the fetus? To address these unanswered questions, additional research was required.
2020 Essay
This essay was published to more broadly examine the water fluoridation-cognitive function relationship4Lamster, I., and Foley, M. (2020, May 26). Water fluoridation and cognitive function: A closer look at the evidence. Colgate Oral Health Network. https://www.ohasa.colgateoralhealthnetwork.com/article/water-fluoridation-and-cognitive-function-a-closer-look-at-the-evidence/..
At the time this essay as published, the National Toxicology Program (NTP, a part of the National Institute of Environmental Health Sciences, which is a component of the U.S. National Institutes of Health) issued a draft report examining the published reports on the relationship of fluoride exposure and cognitive function6NTP. 2019. Draft NTP Monograph on the systematic review of fluoride exposure and neurodevelopmental and cognitive health effects. Office of Health Assessment and Translation, Division of the NTP National Institute of Environmental Health Services, National Institute of Health, U.S. Department of Health and Human Services.. The conclusion was that fluoride is a “…neurodevelopmental hazard to humans”. However, an additional complication was introduced when the National Academy of Sciences, Engineering and Medicine (NASEM) examined the draft NTP report and could not support the draft report’s conclusions (i.e., the evidence did not support the conclusion that at the proper concentration water fluoridation is neurotoxic7Review of the draft NTP Monograph: Systematic review of fluoride exposure and neurodevelopmental and cognitive health effects. The National Academics Collection: reports funded by the National Institutes of Health. Washington (DC) 2020..
Why did the NASEM question the preliminary report of NTP? There are several reasons:
- The studies selected for review may have been biased, as they were selected by the Fluoride Action Network, an anti-fluoridation group.
- Information about the risk of bias was not included.
- Studies differed in methodology, yet other studies with similar methodology were not included (i.e. measurement of fluoride exposure, how neurodevelopment was determined).
- The cited studies did not always consider confounders, which are other variables that could have influenced the outcome.
- There was no meta-analysis, which would have combined the effects of different studies and thereby strengthened the findings. A meta-analysis requires careful consideration of inclusion criteria, which increases the validity of the conclusions.
- Some studies that were included had poor methodology.
In this second essay, a longitudinal study from New Zealand was reviewed in detail. This report was part of a larger cohort study based in Dunedin, New Zealand, which has followed a birth cohort from 1972-1973. Here, fluoride exposure at age 5 was evaluated in relationship to IQ at 7 to 12 years of age, and again at 38 years of age8Broadbent JM, Thomson WM, Ramrakha S, Moffitt TE, Zeng J, Foster Page LA, et al. Community Water Fluoridation and Intelligence: Prospective Study in New Zealand. Am J Public Health. 2015;105(1):72-6..
Age-appropriate intelligence tests were administered, and adjustment was made for potential confounders. In sum, no differences were observed in the measures of intelligence when comparing individuals who drank fluoridated water, who used fluoride-containing toothpaste or ingested fluoride tablets, and those that did not ingest fluoride. The authors of this study also thoroughly discussed the strengths and weaknesses of their study.
A national study from Sweden, with a defined and thorough methodology, also did not find differences in cognitive function, comparing those exposed and not exposed to fluoride9Aggeborn, C. and Öhman, M. (2017). The Effects of Fluoride in the Drinking Water. [Working paper series no. 20]. Institute For Evaluation of Labour, Market and Education Policy (Sweden). .. Further, those who ingested fluoride had a higher income and better employment history than those who did not. This was attributed to better oral health providing an advantage when seeking employment.
This essay reached 4 general conclusions:
- There is clear evidence of the benefits of water fluoridation on oral health.
- At high concentrations, fluoride is toxic. At the current recommended concentration for water fluoridation (0.7 mg/L), water fluoridation is safe and has important oral health benefits.
- The potential adverse effects of water fluoridation compared to the established dental and general health benefits requires a thorough review. Care must be taken to identify and compare only data from well-conducted, unbiased studies.
- The current recommended concentration of fluoride in water is 0.7 mg/L. This needs to be adhered to, monitored, and adjusted if new data so indicates.
The concluding sentence of the 2019 essay is, “The story certainly continues.” That is as true today as it was then. The recent contributions to this controversy include the release of the final NTP monograph, a court ruling and a publication from the Cochrane Library.
New developments
In August 2024, the NTP released its final report, which was a systematic review, concerning the relationship of exposure to fluoride and cognitive development10National Toxicology Program (NTP). 2024. NTP monograph on the state of the science concerning fluoride exposure and neurodevelopment and cognition: a systematic review. Research Triangle Park, NC: National Toxicology Program. NTP Monograph 08. https://doi.org/10.22427/NTP-MGRAPH-8.. This state of the science monograph considered comments from the NASEM, other experts in the field, as well as from other health agencies within the federal government. The final report was modified based on this feedback.
Key conclusions were:
- “…higher levels of fluoride exposure, such as drinking water containing more than 1.5 milligrams of fluoride per liter, are associated with low IQ in children.”
- “The NTP report was designed to evaluate total fluoride exposure from all sources and was not designed to evaluate the health effects of fluoridated drinking water alone.”
- “…there were insufficient data to determine if the fluoride level of 0.7 mg/L currently recommended for U.S. community water supplies has a negative effect on children’s IQ.”
- “The NTP found no evidence that fluoride exposure had adverse effects on adult cognition.”
The report also noted that many chemicals, drugs and other substances have been shown to be of benefit at lower concentrations but are toxic at higher concentrations. The document called for additional research, and did not include any assessment of the health benefits of exposure to fluoride. In addition, none of the reviewed studies provided any clarity regarding the mechanism or mechanisms that account for an adverse effect of fluoride on cognition. This report included studies from the United States and several other countries.
In September 2024, a case was heard in the U.S. District Court for Northern California to determine if water fluoridation is harmful11Food & Water Watching, Inc., et al, v. United States Environmental Protection Agency, et. al. United States District Court Northern District of California. Case No. 17-cv-02162-FMC. Document 465, Filled 09/24/24. 80 pages.. The plaintiff in this case is the nonprofit organization Food & Water Watch, which is based in Washington, D.C. This organization is not strictly focused on water fluoridation, but rather has a broad environmental agenda that includes government action on water contaminants (i.e., limits on “forever chemicals”), pollution related to large scale farming, and fracking.
The action of the court did not ban fluoride in water but agreed with the plaintiff’s claims that even at the concentration recommended for the U.S. of 0.7 mg/L represented a risk to certain individuals. The recommendation was for the U.S. Environmental Protection Agency (EPA) to develop a response.
The American Dental Association responded to this ruling in late September, reiterating the oral health benefits of water fluoridation, noting both its inclusion as one of the top ten public health measures of the 20th century, and that the American Academy of Pediatrics recommends total intake of fluoride at age-appropriate amounts12AAP, ADA stand by fluoride recommendations following court ruling. California Oral Health Technical Assistance Center. 2024, September 26. CDHP Office of Oral Health. https://oralhealthsupport.ucsf.edu/news/aap-ada-stand-fluoride-recommendations-following-court-ruling. Accessed November 6, 2024..
In October 2024, a publication from the Cochrane Library titled “Water fluoridation for the prevention for the prevention of dental caries” added another perspective to this discussion. The purpose of the review was to assess the impact of water fluoridation on the prevalence of dental caries, and how this may have changes over the past 50 years. This review also examined the relationship of water fluoridation to the occurrence of dental fluorosis14Kounang, N., Hassan, C. & McPhillips, D. (2024, November 4). RFK Jr. says fluoride is ‘an industrial waste’ linked to cancer, diseases and disorders. Here’s what the science says. Health. CNN. https://www.cnn.com/2024/11/03/health/rfk-jr-fluoride-science/index.html. Accessed November 6, 2024..
As to the effect of water fluoridation on the prevalence of dental caries, the data published before and after 1975 (when water fluoridation became widely available) differ in the magnitude of the reduction in dental caries. For more recent studies, the reduction in caries was determined to be 0.24 using the decayed, missing, and filled index (DMFT). Expressed differently, 1 in 4 individuals will have a 1 DMFT lower score when drinking fluoridated water. This is a small benefit. In contrast, the difference in the prevalence of caries in studies published prior to 1975 was much greater in favor of the use of fluoridated water.
They also determined that water fluoridation “may slightly increase that number of children who have no tooth decay in either their baby teeth or permanent teeth. However, these results also include the possibility that little or no difference in tooth decay.” Lastly, they determined that 12% of individuals who live in areas with fluoridated water at a concentration of 0.7mg/L will have dental fluorosis, which represents an esthetic concern.
In sum, this newly released Cochrane review suggests that in industrialized countries, given the availability of fluoride-containing oral hygiene products (i.e., fluoride-containing toothpaste and mouthrinses), fluoride exposure that does not include water fluoridation is sufficient to result in a clinically significant reduction in dental caries.
These three new additions to the water fluoridation debate will increase the attention paid to the long-term future of water fluoridation.
First, the NTP monograph yet again identifies water fluoridation, even at the currently recommended concentration of fluoride, as a health risk. The outcome of the case in California supports the claim that water fluoridation at the recommended concentration may be unsafe and tasks the EPA with examining this question. Finally, the Cochrane Library review questions the need for water fluoridation in developed countries, as other sources of fluoride in the daily routine of children account for a decrease in the prevalence of dental caries.
In response to the NTP monograph, and the ruling in Northern California which cited that report, the ADA and AAP issued a statement supporting the importance of water fluoridation as a public health measure. That statement emphasized the long history of reports detailing the efficacy of caries prevention, and its particularly beneficial effects for low-income communities and racial minorities. This statement also noted the NTP’s focus on the higher fluoride concentration of 1.5 mg/liter (versus the current recommendation in the U.S. of 0.7 mg/L), the complexity of assessing IQ, and the concerns raised by the NASEM regarding the NTP report.
The findings and conclusions in the recent Cochrane review raise questions and concerns:
- Is it practical to suggest that the benefits of water fluoridation can be replaced by fluoride exposure associated with standard oral hygiene practices?
- The argument that the beneficial effects of water fluoridation on caries prevalence can be replaced by standard oral hygiene practices, including topical fluoride application (toothpaste, mouth rinse), will used by those opposed to water fluoridation.
- Water fluoridation represents a true public health approach to disease (dental caries) prevention. If a person lives in a fluoridated community and uses the public water supply, that person will realize the benefit. If water fluoridation is discontinued, caries prevention relies on individual use of fluoride-containing oral hygiene products. That situation will introduce a variable that likely will depend on economic considerations and health literacy to determine who will and who will not realize a reduction in dental caries. How will that situation be managed?
- If exposure to non-water sources of fluoride provides a significant preventive effect, this benefit is dependent upon the use of fluoride-containing oral hygiene products. This may be a valid argument in developed countries but not in underdeveloped countries where such products are either not available or too costly. This concern becomes an even more important issue, when considering that as underdeveloped countries see greater availability of carbohydrate-rich foods and snacks, the risk of caries development will increase.
In conclusion, the status of water fluoridation and prevention of dental caries in children is entering yet another period of uncertainty. In the U.S., three federal agencies have or will be involved in the risk-benefit determination, and alternate community preventive strategies need to be considered.
Water Fluoridation as a National Debate
As reported on CNN (November 4, 2024)14Kounang, N., Hassan, C. & McPhillips, D. (2024, November 4). RFK Jr. says fluoride is ‘an industrial waste’ linked to cancer, diseases and disorders. Here’s what the science says. Health. CNN. https://www.cnn.com/2024/11/03/health/rfk-jr-fluoride-science/index.html. Accessed November 6, 2024., and subsequently reported by other media outlets15Brumfiel, G. and Simmons-Duffin, S. (2024, November 4). No more fluoride in the water? RFK Jr. wants that and Trump says it ‘sounds OK’. Shots: Health News from NPR. NPR. Available from: https://www.npr.org/sections/shots-health-news/2024/11/04/nx-s1-5178706/fluoride-drinking-water-rfk-jr-trump-conspiracy. Accessed November 10, 2024., this debate has become a national political issue. Robert F. Kennedy Jr., who at the time of this writing has been proposed as Secretary of Health and Human Services in the new Republican administration, has said that fluoride is “…an industrial waste associated with arthritis, bone fractures, bone cancer, IQ loss, neurodevelopmental disorders and thyroid disease” and should not be in the water supply. If Kennedy is approved as Secretary, this issue will assume national prominence.
So, the debate about water fluoridation, which was first introduced in the U.S. in 1945, does not just continue, but may soon become a national public health issue. It is important that all oral health care providers be familiar with the latest developments and continue to follow this question, which has been a cornerstone of preventive dentistry in the United States for 80 years.
References
- 1.Gooch, B.F. Community Water fluoridation – One of the 10 Greatest Public Health Achievements of the 20th Century. Preventing Chronic Disease Dialogue. Centers for Disease Control and Prevention; 2015, April 13. Available from: https://blogs.cdc.gov/pcd/2015/04/23/community-water-fluoridation. Accessed November 3, 2024.
- 2.Lamster, I. (2019, September 19). The effects of water fluoridation on cognitive function: The story continues. Colgate Oral Health Network. Available from: https://www.colgateoralhealthnetwork.com/article/the-effects-of-water-fluoridation-on-cognitive-function-the-story-continues/.
- 3.Green R, Lanphear B, Hornung R, Flora D, Martinez-Mier EA, Neufeld R, et al. Association between maternal fluoride exposure during pregnancy and IQ Scores in offspring in Canada. JAMA Pediatr. 2019;173(10):940-8.
- 4.Lamster, I., and Foley, M. (2020, May 26). Water fluoridation and cognitive function: A closer look at the evidence. Colgate Oral Health Network. https://www.ohasa.colgateoralhealthnetwork.com/article/water-fluoridation-and-cognitive-function-a-closer-look-at-the-evidence/.
- 5.Christakis DA. Decision to Publish Study on Maternal Fluoride Exposure During Pregnancy. JAMA Pediatr. 2019;173(10):948.
- 6.NTP. 2019. Draft NTP Monograph on the systematic review of fluoride exposure and neurodevelopmental and cognitive health effects. Office of Health Assessment and Translation, Division of the NTP National Institute of Environmental Health Services, National Institute of Health, U.S. Department of Health and Human Services.
- 7.Review of the draft NTP Monograph: Systematic review of fluoride exposure and neurodevelopmental and cognitive health effects. The National Academics Collection: reports funded by the National Institutes of Health. Washington (DC) 2020.
- 8.Broadbent JM, Thomson WM, Ramrakha S, Moffitt TE, Zeng J, Foster Page LA, et al. Community Water Fluoridation and Intelligence: Prospective Study in New Zealand. Am J Public Health. 2015;105(1):72-6.
- 9.Aggeborn, C. and Öhman, M. (2017). The Effects of Fluoride in the Drinking Water. [Working paper series no. 20]. Institute For Evaluation of Labour, Market and Education Policy (Sweden). .
- 10.National Toxicology Program (NTP). 2024. NTP monograph on the state of the science concerning fluoride exposure and neurodevelopment and cognition: a systematic review. Research Triangle Park, NC: National Toxicology Program. NTP Monograph 08. https://doi.org/10.22427/NTP-MGRAPH-8.
- 11.Food & Water Watching, Inc., et al, v. United States Environmental Protection Agency, et. al. United States District Court Northern District of California. Case No. 17-cv-02162-FMC. Document 465, Filled 09/24/24. 80 pages.
- 12.AAP, ADA stand by fluoride recommendations following court ruling. California Oral Health Technical Assistance Center. 2024, September 26. CDHP Office of Oral Health. https://oralhealthsupport.ucsf.edu/news/aap-ada-stand-fluoride-recommendations-following-court-ruling. Accessed November 6, 2024.
- 14.Kounang, N., Hassan, C. & McPhillips, D. (2024, November 4). RFK Jr. says fluoride is ‘an industrial waste’ linked to cancer, diseases and disorders. Here’s what the science says. Health. CNN. https://www.cnn.com/2024/11/03/health/rfk-jr-fluoride-science/index.html. Accessed November 6, 2024.
- 15.Brumfiel, G. and Simmons-Duffin, S. (2024, November 4). No more fluoride in the water? RFK Jr. wants that and Trump says it ‘sounds OK’. Shots: Health News from NPR. NPR. Available from: https://www.npr.org/sections/shots-health-news/2024/11/04/nx-s1-5178706/fluoride-drinking-water-rfk-jr-trump-conspiracy. Accessed November 10, 2024.