Abstract
In 1999 the Centers for Disease Control and Prevention declared that fluoridation of drinking water was one of the “ten great public health achievements in the United States” due to the effectiveness of fluoride in preventing dental caries as an inexpensive population-based approach1. Fluoridation benefits everyone in the community, regardless of income, education, or access to dental care. Fluoride (F) naturally occurs in some water supplies, and when optimized to a standard level ensures a uniform level of protection across all social groups. Currently in the United States (U.S.), 73 percent of community water supplies are adjusted to 0.7 mg/liter parts per million (ppm)2. Many leading health and medical organizations, including the U.S. Centers for Disease Control and Prevention (CDC), World Health Organization (WHO), American Dental Association (ADA), American Medical Association (AMA), and the American Academy of Pediatric Dentistry (AAPD), support community water fluoridation based on decades of research showing its safety and efficacy in preventing tooth decay.
Efficacy
The initial and most cited study of the efficacy of community water fluoridation was conducted between 1944 and 1955 in the New York towns of Newburg and Kingston. Newburgh was the test city where fluoride was added to the water supply, while Kingston served as the control city without fluoridation. Children in Newburgh had an approximate 50 percent reduction in dental caries compared to those in Kingston3. This dramatic finding supported the adoption of water fluoridation programs in many communities across the U.S. and globally. However, the study has also been subject to debates about methodological issues regarding randomization, using only one examiner, and absence of examiner or population blinding. Another influential paper on the efficacy of water fluoridation was a U.S. survey of 39,206 children conducted in 1986-87 that reported an 18 percent lower decayed, missing, filled permanent tooth surfaces (DMFS) in children having a life-long exposure to water fluoridation4. The difference in percentage caries reduction between the 1956 and the 1990 report often has been ascribed to a ‘halo effect’ due to food and beverages produced in communities having water fluoridation.
Two Cochrane systematic reviews have evaluated global data of fluoride studies since 1975. The 2015 review found a mean caries reduction of 1.8 decayed, missing, filled primary teeth (dmft) (a 35 percent decrease) in primary teeth and a mean caries reduction of 1.7 decayed, missing, filled permanent teeth (DMFT) (a 26 percent decrease) on permanent teeth5. The follow up 2024 report found two studies having mean caries reduction of 0.24 dmft among children with a low burden of disease6. Such a reduction would calculate to one child experiencing a reduction in caries for every five children receiving community water fluoridation. In contrast to epidemiological studies, a 2006 Medicaid claims data study of children in New York State showed that the number of restorative, endodontic and extraction procedures was 33 percent greater in low fluoridated
communities7.
Risks
Over the years, water fluoridation has been under attack from the far left to the far right with little objectivity and evidence base. Water fluoridation has been reported to be a communist plot to poison Americans, a rat poison, and cause of various medical conditions (e.g., Alzheimer’s, arthritis, kidney disorders, osteosarcoma, Down syndrome, autism, bone fractures, AIDS, early puberty, neurotoxicity, and soft teeth).
There is data on two putative risks associated with water fluoridation that can be analyzed. Oral health providers are well aware of the risk of fluorosis. The probability of dental fluorosis of esthetic concern is estimated to be 12 percent with children consuming water with fluoride levels of 0.7 mg/liter (ppm); and 59 percent at a level of four ppm6.
Another concern is the possible effect of fluoride on intelligence quotient (IQ). Presently, there is no known biological basis for a neurologic risk of fluoride. There are studies of endemic fluorosis (mean 3.7 ppm) in rural areas of China, Iran and India that associate elevated levels of fluoride in the water with decreased IQ. Because of the rural locations of these reports, such results may have confounding factors (e.g., comorbidities, pollutants, heavy metal contaminants) and risks of bias that may affect findings. There is an often-cited Canadian study that examined the association between maternal fluoride exposure during pregnancy and IQ8. The findings showed a difference in IQ in children exposed to high levels of fluoride; however, there was no difference found with the majority of subjects that resided in communities of 0.9 ppm vs. 0.3 ppm F.
A recent systematic review by the National Toxicology Program found that the data were too heterogenous and limited to make any determination on biological plausibility of fluoride affecting neurodevelopment. The report, however, identified studies suggesting that fluoride levels in drinking water exceeding twice the optimal amount of 0.7 ppm were associated with lower IQ9. Additionally, a meta-analysis of eight studies of fluoride exposure of levels below 1.5 ppm has provided consistent evidence of the lack of an adverse effect on neurodevelopment10. As with any medication or food, elevated levels of consumption have a potential for adverse effects.
Implications
Although the collective research regarding fluoride’s efficacy in reducing dental caries is well established, water fluoridation remains a polarizing issue, with vocal opposition from certain segments of the population, particularly over concerns about health risks and ethics. Critics argue that by fluoridating water, goverments are mandating medical treatment without individual consent, violating personal autonomy. Rational discussions with patients should center on the evidence of benefits as well as putative risks of fluoride in community water supplies. Health providers need to share the evidence, be considerate of patient concerns, and respect their preferences. At the community health level, providers should combat misinformation and advocate for evidence-based preventive practices.
Sincerely,
Norman Tinanoff, DDS, MS1
Vineet Dhar, BDS, MDS, PhD2
Erica M. Caffrey, DDS3
1 Professor Emeritus, 2 Clinical Professor and Chair, 3 Assistant Professor,
Department of Orthodontics and Pediatric Dentistry
University of Maryland School of Dentistry Baltimore, Md., USA.
References
1. Centers for Disease Control and Prevention. Ten great public health achievements—United States, 1900-1999.
MMWR Morb Mortal Wkly Rep 1999;48(12):241-3.
2. Hung M, Mohajeri A, Chiang J, et al. Community water fluoridation in focus: A comprehensive look at fluoridation levels across America. Int J Environ Res Public Health 2023;20(23):7100. Available at: “https://doi.org/10.3390/ijerph20237100“. Accessed November 21, 2024.
3. Ast DB, Smith DJ, Wachs B, Cantwell KT. Newburgh-Kingston caries-fluorine study. XIV. Combined clinical
and roentgenographic dental findings after ten years of fluoride experience. J Am Dent Assoc 1956;52(3):314-25.
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5. Iheozor-Ejiofor Z, Worthington HV, Walsh T, et al. Water fluoridation for the prevention of dental caries. Cochrane Database Syst Rev 2015;2015(6):CD010856. Available at: “https:/ doi.org/10.1002/14651858.CD010856.pub2“. Accessed November 21, 2024.
6. Iheozor-Ejiofor Z, Walsh T, Lewis SR, et al. Water fluoridation for the prevention of dental caries. Cochrane
Database Syst Rev 2024;10(10):CD010856. Available at: “https://doi.org/10.1002/14651858.CD010856.pub3“.
Accessed November 21, 2024.
7. Kumar J, Adekugbe O, Melnik TA. Geographic variation in Medicaid claims for dental procedures in New York
State: Role of fluoridation under contemporary conditions. Public Health Rep 2010;125(5):647-54.
8. Green R, Lanphear B, Hornung R, et al. Association between maternal fluoride exposure during pregnancy and IQ scores in offspring in Canada. JAMA Pediatr 2019; 173(10):940-8. Available at: “https://doi.org/10.1001/jama pediatrics.2019.1729“. Accessed November 21, 2024.
9. National Toxicology Program. NTP monograph on the state of the science concerning fluoride exposure and
neurodevelopment and cognition: A systematic review. NTP Monogr 2024;(8):NTP-MGRAPH-8. Available at:
“https://www.ncbi.nlm.nih.gov/books/NBK606081/“. Accessed November 21, 2024.
10. Kumar JV, Moss ME, Liu H, Fisher-Owens S. Association between fluoride exposure and children’s intelligence: A meta-analysis relevant to community water fluoridation. Public Health 2023;219:73-84.