The Effects of Water Fluoridation on Cognitive Function: The Story Continues

On August 19, 2019 a paper published in JAMA Pediatrics1Green R, Lanphear B, Hornung R, et al. Association between maternal fluoride exposure during pregnancy and IQ scores in offspring in Canada. JAMA Pediatr 2019 Aug 2019: e191729. reported an epidemiologic study from Canada that examined the relationship of pregnant women’s exposure to water fluoridation during pregnancy to the intelligent quotient (IQ) of their children. A reduction in IQ scores was observed with increased exposure to fluoride.

This study was noteworthy because the participants resided in communities in which the concentration of fluoride in water was at the level recommended by the United States Public Health Service (0.7 mg of fluoride per liter of water).

The records of 601 mother-child pairs (fluoride intake of the pregnant women and IQ scores of their children when they were between 3 and 4 years of age) were available for study. Fluoride intake during pregnancy was estimated based on the fluoride concentration in the urine (measured 3 times during the pregnancy from 512 women). The data analysis revealed that for each 1 mg increase in the fluoride concentration in urine, there was a 4.5-point decrease in the IQ of male children. A similar decrease was not seen in female children. Further, fluoride intake by the mothers (based on data from a questionnaire completed twice during pregnancy from 400 women) would reflect exposure of parents and children, who are presumably drinking from the same water source as their mothers. Here, for each 1 mg increase in fluoride, the child’s IQ decreased by 3.7 points, and this was seen for both male and female children.

The authors noted the uniqueness of the findings is the reduction in IQ of children living in an area where the water was fluoridated at the currently established optimal level. The general finding of neurotoxic effects of fluoride in the water is in agreement with other recent studies that have reported reduced neurological function in children exposed to water fluoridation, including reduced memory and learning2Choi AL, Zhang Y, Sun G, et al. Association of lifetime exposure to fluoride and cognitive functions in Chinese children: a pilot study. Neurotoxicol Teratol 2015;47:96-101., IQ3Das K, Mondal NK. Dental fluorosis and urinary fluoride concentration as a reflection of fluoride exposure and its impact on IQ level and BMI of children of Laxmisagar, Simlapal Block of Bankura District, W.B., India. Environ Monit Assess 2016;188:218.,4Aravind A, Dhanya RS, Narayan A, Sam G, Adarsh VJ, Kiran M. Effect of fluoridated water on intelligence in 10-12-year-old school children. J Int Soc Prev Community Dent 2016;6:S237-S242., cognitive development5Valdez Jimenez L, Lopez Guzman OD, Cervantes Flores M, et al. In utero exposure to fluoride and cognitive development delay in infants. Neurotoxicology 2017;59:65-70., and a higher prevalence of attention deficit/hyperactivity disorder6Bashash M, Marchand M, Hu H, et al. Prenatal fluoride exposure and attention deficit hyperactivity disorder (ADHD) symptoms in children at 6-12years of age in Mexico City. Environ Int 2018;121:658-666.. A meta-analysis of the association of water fluoridation and children’s intelligence concluded that “greater exposure to high levels of fluoride in water was significantly associated with reduced levels of intelligence in children”7Duan Q, Jiao J, Chen X, Wang X. Association between water fluoride and the level of children’s intelligence: a dose-response meta-analysis. Public Health 2018;154:87-97.. Other adverse systemic effects of exposure to fluoride in drinking water have been examined8Follin-Arbelet B, Moum B. Fluoride: a risk factor for inflammatory bowel disease? Scand J Gastroenterol 2016;51:1019-1024.,9Chaitanya N, Karunakar P, Allam NSJ, Priya MH, Alekhya B, Nauseen S. A systematic analysis on possibility of water fluoridation causing hypothyroidism. Indian J Dent Res 2018;29:358-363., but these associations have not been well defined.

This newly published paper was expected to be controversial, and two commentaries were published in the same issue of JAMA Pediatrics to accompany the research report. The first10Christakis DA. Decision to publish study on maternal fluoride exposure during pregnancy. JAMA Pediatr 2019. 3120. was a brief note from the editor stating that the Journal decided to publish the article though it was recognized that the findings will be contentious. However, the editor supported the soundness of the research and the manuscript was scrutinized very carefully before being published. Further, the Journal’s commitment is to improve the health of children and therefore sound evidence needed to be brought forward. He also acknowledged that no one study will ultimately determine the final answer.

A thoughtful and balanced editorial also accompanied the published article11Bellinger DC. Is fluoride potentially neurotoxic? JAMA Pediatr 2019. 1728.. In that editorial, several important points were noted.

  1. Water fluoridation for prevention of dental caries is considered one of the top 10 public health measures of the 20th century12Centers for Disease Control and Prevention. Ten great public health achievements–United States, 1900-1999. MMWR Morb Mortal Wkly Rep 1999;48:241-243..
  2. There has always been a vocal minority who have objected to fluoridation of the public water supply because it represents a “compulsory medication administered indiscriminately to water consumers without their consent.”11Bellinger DC. Is fluoride potentially neurotoxic? JAMA Pediatr 2019. 1728.. Other objections include an increased occurrence of both dental and skeletal fluorosis.
  3. The quality of earlier publications that examined the relationship of fluoride exposure to cognition have generally been poor, and not all studies report an inverse relationship.
  4. The authors of the JAMA Pediatrics publication1Green R, Lanphear B, Hornung R, et al. Association between maternal fluoride exposure during pregnancy and IQ scores in offspring in Canada. JAMA Pediatr 2019 Aug 2019: e191729. recognized that their research findings would receive scrutiny, but their research methodology and statistical analysis were thorough, and their findings robust.
  5. Considering those findings, “fluoride as a neurodevelopmental toxicant must now be given serious consideration”11Bellinger DC. Is fluoride potentially neurotoxic? JAMA Pediatr 2019. 1728..
  6. The need for additional research is critical. Many questions remain, which include the generalizability of the new findings, what other aspects of cognitive function are affected, and what is the critical period of exposure of the fetus? Of importance, it is emphasized that this research and subsequent discussion of the findings must be focused on the reliability of the data.

With the publication of the JAMA Pediatrics paper, the American Dental Association issued a news release13American Dental Association. ADA Statement on Study in JAMA Pediatrics. Accessed on August 19, 2019. which stated that water fluoridation is the most effective public health approach to preventing caries. It continued, echoing themes raised in the editorial. These include the importance of examining all available data, the existing evidence attesting to the safety of water fluoridation and the need to continuously evaluate new research findings.

The report by Green et al1Green R, Lanphear B, Hornung R, et al. Association between maternal fluoride exposure during pregnancy and IQ scores in offspring in Canada. JAMA Pediatr 2019 Aug 2019: e191729. is sure to re-ignite the debate about the benefits/risks of water fluoridation, a debate that is often rancorous and contentious. It is important to empathize that other means of delivering fluoride, specifically in different topical forms, have proven to be very successful in preventing dental caries, i.e. in toothpaste14Wright JT, Hanson N, Ristic H, Whall CW, Estrich CG, Zentz RR. Fluoride toothpaste efficacy and safety in children younger than 6 years: a systematic review. J Am Dent Assoc 2014;145:182-189., in mouthrinses15Shahid M. Regular supervised fluoride mouthrinse use by children and adolescents associated with caries reduction. Evid Based Dent 2017;18:11-12. and as a varnish16Marinho VC, Worthington HV, Walsh T, Clarkson JE. Fluoride varnishes for preventing dental caries in children and adolescents. Cochrane Database Syst Rev 2013:CD002279.. Under proper conditions, these approaches to delivering topical fluoride are associated with a very small risk of systemic fluoride ingestion.

Oral health care providers need to be aware of the latest information on this topic. When asked about this research, providers should be familiar with the themes mentioned in the original article as well as the accompanying editorial and ADA statement. These points include the long history of successful use of water fluoridation to prevent dental caries, that a 1 mg change in the fluoride concentration in drinking water (the relative change referenced above) represents a very large difference when considering the optimal concentration of fluoride in drinking water, as well as other confounding factors that may in part explain the findings (i.e. differences in the IQ of the mothers).

The story certainly continues.


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