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JournalFeed Health – Does Fluoride Cause Neurotoxicity?

Introducing JournalFeed Health!

We are excited to announce JournalFeed Health. For years, JournalFeed has been searching the medical literature, selecting and concisely summarizing the most important academic journal articles, and sending them to health professionals around the world. Our focus has largely been to serve emergency physicians and clinicians, who need to have a broad knowledge base. We now also cover Internal Medicine, Primary Care, and Pediatrics. JournalFeed has physician authors from various backgrounds. All our physician authors actively practice medicine. When we are not writing for JournalFeed, we are at work in emergency departments, clinics, hospitals, and doing research. In addition to patient care, we are passionate about understanding how the current literature impacts our own practice and about sharing this with our colleagues to improve the health and save the lives of more patients.

But we sense a need in the community. People are hungry for information they can trust. We want to bring clear, factual information on current health-related issues to our community, employing the same behind-the-scenes academic rigor we use deliver to vital, practice-changing information to healthcare professionals. We want to be a steady, reliable, objective source of information that is easy to understand, interesting, and (dare we say!) entertaining to read.

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Thanks for reading our inaugural post!

Clay

Clay Smith, MD
Founder, Editor-in-Chief | JournalFeed

Written by Clay Smith

Spoon Feed

(The Spoon Feed is how we quickly summarize the entire post – it’s the bottom line up front.)

There is convincing evidence that fluoride helps prevent tooth decay. In many parts of the world, a small amount is added to the water supply. This appears to have a small public health benefit in reducing tooth decay, especially among children. But using topical fluoride (such as toothpaste with fluoride) may be just as effective. In some parts of the world with naturally occurring high fluoride in water, excessive fluoride intake is associated with lower intelligence quotient (IQ) scores in children. However, the amount of fluoride used for community water fluoridation does not appear to have a negative impact on childhood cognitive development.

Let’s brush up on fluoride

Fluorine is an element that exists in nature as a negative ion called fluoride, which is usually abbreviated F or F-.  Fluoride is used to prevent dental caries, or tooth decay.  For over 80 years, fluoride has been used in topical form (i.e. toothpaste, rinses, varnishes) and has been added to public drinking water in areas across the world, affecting 400-500 million people. Usually, fluoridated drinking water has 0.7 to 1.2mg per liter of water. Fluoridated water has been celebrated as a public health success1.

The case for fluoride

Tooth decay is a significant problem. Up to 1 in 3 children 2 to 5 years old, suffer the negative effects of pain, tooth loss, altered cosmetic appearance, poor weight gain, lower quality of life, poor school performance, and ongoing dental problems into adulthood2. There is evidence from public health research from around the world that fluoride is associated with reduced risk of tooth decay2–5. In addition, a recent study from Israel found that since water fluoridation was stopped in 2014, there has been an associated increase in dental procedures in children6.  On the other hand, a rigorous 2024 Cochrane review of 157 studies since 1975, a time after which most household toothpastes contained fluoride, found only slight improvement in tooth decay in children exposed to community water fluoridation, and the improvement was not statistically significant7. They concluded that since most people use topical fluoride when they brush their teeth, that there is little impact of community water fluoridation on reducing dental caries. So, the evidence that fluoride works to reduce tooth decay is compelling, but it seems that topical fluoride (toothbrushing with a fluoride toothpaste) may have the biggest impact.  Community water fluoridation likely has some impact, but it seems to be very minor in the current era of fluoride-containing toothpaste.

Fluoride controversies…Col-Gate, as it were…

There are three major concerns about potential harms from fluoride use.

  • First, too much fluoride may lower IQ.  Concerns have been raised as to the safety of fluoride exposure on neurological development, listing fluoride alongside lead, mercury, arsenic, and other known neurotoxins8. Fluoride can cross the blood-brain barrier, and it is known that very high doses can cause acute neurotoxicity (i.e. seizures, muscle contraction) in animal studies and in human overdose cases9.  Several studies, largely based in China, have reported concerns about the long-term effects of fluoride on childhood IQ10.
  • Some recent studies have raised concern that excessive fluoride may increase fracture risk in adults, although a meta-analysis of 14 studies, with tens of millions of patients, did not find an association with increased risk of hip fracture in people exposed to fluoridated water11.
  • In addition to the potential adverse impact on IQ, excessive fluoride is known to cause fluorosis, a mottling and discoloration of tooth enamel12,13. While fluorosis is a real problem, our focus will be on the potential for adverse cognitive effects of fluoride on children.

Does fluoride in water lower IQ?

In China, some areas have naturally-occurring high levels of fluoride in water, and some do not, allowing for comparison between populations. Multiple population-based studies were grouped together in a large systematic review and meta-analysis in 2012.  The conclusion was that children in areas with high fluoride concentration in the water had an association with almost a half-point lower IQ score than those with low fluoride concentration: IQ score decreased 0.45. There was wide variation among studies as to what was considered high (range: 0.8mg/L to 11.5mg/L) vs low (range: 0.34mg/L to 2.35mg/L), and there was some overlap between the groups10. For reference, the maximum concentration allowed by the U.S. Environmental Protection Agency (EPA) is 2.0 mg/L and most drinking water contains, on average, 0.7mg/L4. So, this meta-analysis found an association of excessive fluoride intake with lower IQ in children.

Subsequent recent systematic reviews and meta-analyses have come to similar conclusions. A 2017 review looked more carefully at a possible dose-response relationship – namely, whether a higher dose of fluoride was associated with a lower IQ. As the fluoride in water rose from 1-2mg/L, 2-3mg/L, 3-4mg/L, and 4-5mg/L (mg/L can also be written as parts per million, ppm), there was a steady increase in the difference in IQ scores of high-dose compared to low-dose groups.  That is, there was an association with lower IQ in the children exposed to higher doses of fluoride. The overall, combined effect of higher dose fluoride compared to lower dose was, again, a half-point lower average IQ score: -0.529, similar to the 2012 study above10.

A small but rigorously conducted, prospective study from Canada found an association with higher fluoride intake during pregnancy and lower full scale IQ score in children14. This association was only seen in boys, and there was no effect on girls’ IQ scores.  Also, fluoride exposure was disproportionately associated with a lower Performance IQ sub-score but not the Verbal IQ sub-score of the IQ test.  These inconsistencies raise some questions about potential confounding (more on confounding below). Interestingly, women who drank more fluoridated water had slight educational and social advantages compared to women who drank less water with fluoride, which would be expected to give this group a statistical advantage – but it did not. In short, greater maternal fluoride consumption was associated with an almost 4-point decrease in IQ score. Keep in mind, this was a single study and, though it raises concern, we usually maintain healthy skepticism until we see multiple studies which confirm the findings. That is why most of the articles covered in this post are meta-analyses – groupings of multiple similar studies into an amalgam (pun intended).

A quick word about confounding – when reading observational studies, such as the ones we are covering in this post, we must consider whether results may be confounded. In other words, could there be an unmeasured exposure that is related to the same outcome (lower IQ in this instance) which makes it appear that fluoride is the cause, when it is not? For example, areas of China with higher fluoride contamination tend to be more rural and lower income, which raises concern about confounders that could impact childhood IQ, such as low birth weight, educational opportunities, socioeconomic status, other environmental toxic exposures, or other potential confounders15.

The two studies from China focused on water sources with high levels of fluoride in water from naturally occurring sources. However, in the U.S. and many other countries, fluoride is usually not a natural contaminant but is purposefully added to public water supplies to prevent tooth decay, as was the case in the Canadian study. A third meta-analysis examined populations in which there was community fluoridation of water sources.  All eight included studies did not have fluoride in water from natural sources, and all had maximum concentrations of added fluoride <1.5mg/L.  When these studies were combined, there was no difference in children who had relatively higher fluoride exposure vs lower. In fact, the average IQ score was slightly higher in the high-fluoride group: IQ score increase 0.07 (95%CI -0.02 to 0.17; P = 0.14)16. This increase was not statistically significant and was also not large enough to make any meaningful difference in intelligence. Another important note is that there was no heterogeneity in the data (I2 = 0)16.  This means these eight studies were very similar, and the differences seen in the results are likely due to random chance, not differences in study design, population, or methods.  In short, low heterogeneity makes the findings of this meta-analysis more reliable and increases our confidence in the results. So, community water fluoridation does not appear to have an association with IQ scores in children.

“Filling” you in on next steps for fluoride…

What if you have fluoride contamination?

For those who live in areas with fluoride contamination of the water supply, it is important to take measures, such as use of reverse osmosis filters, to reduce the amount of fluoride exposure, especially among children.  The evidence for very high fluoride exposure adversely impacting childhood IQ is concerning.

What about community water fluoridation?

For the ~500 million people who receive fluoridated water from a municipal supply, the best available evidence suggests that there is no concern for any adverse impact on childhood cognitive development. Kids that drink fluoridated water appear to have an IQ equal to peers who have lower fluoride exposure. The Canadian study14 calls for pregnant women to consider drinking less fluoridated water, which seems reasonable until we have more studies to replicate and confirm the impact of maternal fluoride exposure. Regarding public health policy on water fluoridation, it is best for both sides to approach this with intellectual humility. There are reasonable arguments on both sides of this issue. Our goal is not so much to settle this debate as to be a safe place to learn more and make informed decisions for yourself and your family.

What’s in your water?

The CDC has a tool called My Water’s Fluoride that allows you to look up the level of fluoridation in areas across the U.S. But often the best source is to contact your local water utility directly, as not all U.S. data are reported in the CDC tool.

What if my family does not have fluoridated water?

If you live in an area where you do not have a municipal water source, such as a home with a well, it’s a good idea to have your water tested by a reputable company to ensure there is not too much fluoride.  There may be little added benefit to oral fluoride supplementation for children who do not have a fluoridated water supply if they use fluoride-containing toothpaste and have regular follow up with a dentist.  However, talk to your pediatrician and dentist to make an individualized plan for your family.

Brush, brush, brush!

There is very good quality evidence that toothbrushing with topical fluoride is helpful in reducing dental caries5.  In this review, a fluoride concentration in toothpaste of 1000-1500 ppm seemed to be ideal for most adults. However, children appear to be different.  There is some low-quality evidence that toothbrushing with a fluoride-containing toothpaste in children under 12 months of age may be associated with increased risk of tooth fluorosis (a mottling of the tooth color). This is likely due to swallowing of the toothpaste by younger children. To be safe, it is reasonable to use a toothpaste with fluoride concentration under 1000 ppm in children under age 6 and to use a toothpaste without fluoride or very low fluoride toothpaste in children under 12 months of age12.

How much fluoride is in my toothpaste?

For reference, here is a picture of my random toothpaste.

It has 0.15% weight/volume fluoride ion, which translates to 1500ppm.

Here is the math: 0.15 gram/100mL = 150mg/0.1L = 1500mg/L. 1mg/L is the same as 1 part per million (ppm). So, 0.15%w/v = 1500ppm.

An ounce of prevention…

Dental caries occurs as tooth bacteria metabolize carbohydrates (sugars) and produce weak acids which can, over time, weaken tooth enamel. In addition to toothbrushing, reducing sugary foods and candies is an important first step in children. Avoid “bottle propping” – that is, keeping a bottle in a child’s crib, as this can increase risk for not only tooth decay but excessive calorie intake17. Even with the best care at home and fluoride in water for many people, dental caries may still occur. So, regular follow up with a dentist is important in children and adults.

Wrap Up

For most people who use toothpaste with fluoride, there may be little added benefit from community water fluoridation. However, water fluoridation is weakly associated with reduced risk of tooth decay and does not appear to negatively impact IQ. Topical fluoride from toothbrushing also reduces dental caries, but it may be best to use lower-fluoride toothpaste in children 1-6 years old and consider a toothpaste without fluoride in children under 1 year to avoid tooth fluorosis.

Works Cited

  1. Achievements in Public Health, 1900-1999: Fluoridation of Drinking Water to Prevent Dental Caries [Internet]. Available from: https://www.cdc.gov/mmwr/preview/mmwrhtml/mm4841a1.htm
  2. Davidson KW, Barry MJ, Mangione CM, Cabana M, Caughey AB, Davis EM, Donahue KE, Doubeni CA, Kubik M, Li L, Ogedegbe G, Pbert L, Silverstein M, Stevermer J, Tseng CW, Wong JB. Screening and Interventions to Prevent Dental Caries in Children Younger Than 5 Years: US Preventive Services Task Force Recommendation Statement. JAMA [Internet]. American Medical Association; 2021 Dec 7;326(21):2172–2178. Available from: https://jamanetwork.com/journals/jama/fullarticle/2786823 PMID: 34874412
  3. CDC Scientific Statement on Community Water Fluoridation | Fluoridation | CDC [Internet]. Available from: https://www.cdc.gov/fluoridation/about/statement-on-the-evidence-supporting-the-safety-and-effectiveness-of-community-water-fluoridation.html
  4. Boehmer TJ, Lesaja S, Espinoza L, Ladva CN. Community Water Fluoridation Levels To Promote Effectiveness and Safety in Oral Health — United States, 2016–2021. MMWR Morb Mortal Wkly Rep. 2023;72(22):593–596. PMID: 37261997
  5. Walsh T, Worthington H V., Glenny AM, Marinho VCC, Jeroncic A. Fluoride toothpastes of different concentrations for preventing dental caries. Cochrane Database of Systematic Reviews. 2019;2019(3). PMID: 30829399
  6. Nezihovski SS, Findler M, Chackartchi T, Mann J, Haim D, Tobias G. The effect of cessation of drinking water fluoridation on dental restorations and crowns in children aged 3–5 years in Israel – a retrospective study. Isr J Health Policy Res [Internet]. BioMed Central Ltd; 2024 Dec 1;13(1):1–8. Available from: https://link.springer.com/articles/10.1186/s13584-024-00637-5 PMID: 39304948
  7. Iheozor-Ejiofor Z, Walsh T, Lewis SR, Riley P, Boyers D, Clarkson JE, Worthington H V, Glenny AM, O’Malley L. Water fluoridation for the prevention of dental caries. Cochrane Database of Systematic Reviews [Internet]. John Wiley & Sons, Ltd; 2024 Oct 4;2024(10). Available from: https://www.cochranelibrary.com/cdsr/doi/10.1002/14651858.CD010856.pub3/full
  8. Grandjean P, Landrigan PJ. Neurobehavioural effects of developmental toxicity. Lancet Neurol [Internet]. Elsevier; 2014 Mar 1;13(3):330–338. Available from: http://www.thelancet.com/article/S1474442213702783/fulltext PMID: 24556010
  9. Duan 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. PMID: 29220711
  10. Choi AL, Sun G, Zhang Y, Grandjean P. Developmental Fluoride Neurotoxicity: A Systematic Review and Meta-Analysis. Environ Health Perspect [Internet]. 2012 Oct;120(10):1362. Available from: https://pmc.ncbi.nlm.nih.gov/articles/PMC3491930/ PMID: 22820538
  11. Yin XH, Huang GL, Lin DR, Wan CC, Wang YD, Song JK, Xu P. Exposure to fluoride in drinking water and hip fracture risk: A meta-analysis of observational studies. PLoS One. 2015;10(5):1–14. PMID: 26020536
  12. Wong MCM, Zhang R, Luo BW, Glenny AM, Worthington H V., Lo ECM. Topical fluoride as a cause of dental fluorosis in children. Cochrane Database of Systematic Reviews. 2024;2024(6). PMID: 38899538
  13. Mohd Nor NA, Chadwick BL, Farnell DJJ, Chestnutt IG. The impact of stopping or reducing the level of fluoride in public water supplies on dental fluorosis: A systematic review. Rev Environ Health. 2020;35(4):419–426. PMID: 32598322
  14. Green R, Lanphear B, Hornung R, Flora D, Martinez-Mier EA, Neufeld R, Ayotte P, Muckle G, Till C. Association between Maternal Fluoride Exposure during Pregnancy and IQ Scores in Offspring in Canada. JAMA Pediatr. American Medical Association; 2019 Oct 1;173(10):940–948. PMID: 31424532
  15. Guth S, Hüser S, Roth A, Degen G, Diel P, Edlund K, Eisenbrand G, Engel KH, Epe B, Grune T, Heinz V, Henle T, Humpf HU, Jäger H, Joost HG, Kulling SE, Lampen A, Mally A, Marchan R, Marko D, Mühle E, Nitsche MA, Röhrdanz E, Stadler R, van Thriel C, Vieths S, Vogel RF, Wascher E, Watzl C, Nöthlings U, Hengstler JG. Toxicity of fluoride: critical evaluation of evidence for human developmental neurotoxicity in epidemiological studies, animal experiments and in vitro analyses. Archives of Toxicology. Springer; 2020. p. 1375–1415. PMID: 32382957
  16. Kumar J V., Moss ME, Liu H, Fisher-Owens S. Association between low fluoride exposure and children’s intelligence: a meta-analysis relevant to community water fluoridation. Public Health. 2023;219:73–84. PMID: 37120936
  17. Cheng H, Chen R, Milosevic M, Rossiter C, Arora A, Denney-Wilson E. Interventions targeting bottle and formula feeding in the prevention and treatment of early childhood caries, overweight and obesity: An integrative review. International Journal of Environmental Research and Public Health. MDPI; 2021. PMID: 34886023

About the Author

Clay Smith, MD is an emergency physician, husband, and dad of seven kids. He works at Vanderbilt University Medical Center and has been there for the past 25 years, serving patients in the adult and pediatric emergency departments. He is Associate Professor of Emergency Medicine, Internal Medicine, and Pediatrics, is board certified in these three specialties, and is the founder of JournalFeed.

The views and opinions expressed here are not necessarily those of Vanderbilt University Medical Center, and they may not be used for advertising or product endorsement purposes.

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