Over the past year, many important papers on fluoride toxicity were published in the peer-reviewed scientific literature. To give an indication of this recent research, the Fluoride Action Network (FAN) has selected the “Top 10” scientific developments of the year, from 2006 through to the early weeks of 2007.

1) National Research Council: EPA’s fluoride standards are unsafe

The National Research Council’s long-awaited review of fluoride, released in March of 2006, was a watershed moment in the fluoride debate. The 500 page review, which took 12 scientists over three years to produce, describes in great detail why EPA’s purportedly “safe” drinking water standard (4 ppm) needs to be reduced in order to protect human health (1). The report documents myriad potential hazards from fluoride exposure, including damage to the bones, brain, and various glands of the endocrine system. According to Dr. Bob Carton, a former risk-assessment scientist at EPA, this report “should be the centerpiece of every discussion on fluoridation. It changes everything.” 

2) Harvard Study: Fluoridation associated with bone cancer in boys

In the wake of media scrutiny and an NIH ethics investigation, the first paper from Harvard University’s ongoing study of fluoride and bone cancer was finally published (2). The paper — published 14 years after the study began — reported that boys exposed to fluoridated water had a significantly higher rate of an often fatal form of bone cancer called osteosarcoma. According to the study, the boys with the highest rate of osteosarcoma were those that were exposed to fluoridated water during the ages of 6 to 8, although other years of life were also associated with increased risk – including the first year of life.  These findings, which are consistent with a 1990 government study that reported the same form of bone cancer in fluoride-treated rats, have resulted in a similar degree of controversy. For example, in 1992, the top toxicologist in EPA’s Office of Drinking Water was fired after publicly expressing concern that the government was downplaying the study’s findings, while, in 2005, the principal investigator of the Harvard study (a dental professor with ties to Colgate) sparked a public outcry after it was revealed he had withheld the study’s findings from federal authorities while claiming it showed no relationship between fluoridation and bone cancer. Together, the government and Harvard studies reveal a disturbing pattern: when it comes to fluoride and cancer, politics can become a malignant force.

3) Too much fluoride can damage the developing brain

In March, the National Research Council broke important ground by dedicating an entire chapter of its report to the growing body of evidence indicating that fluoride can damage the brain. According to the NRC, “it is apparent that fluorides have the ability to interfere with the functions of the brain and the body by direct and indirect means.” However, since we’ve already selected the NRC report as our #1 pick, our #3 pick goes to two recent papers that add further support to the NRC’s conclusions on fluoride’s potential to damage the brain.

The first paper was a review, published in the esteemed medical journal The Lancet, examining the various chemicals in today’s world that may damage a child’s developing brain (3A). The review classified fluoride, along with the rocket fuel additive perchlorate, as an “emerging neurotoxic substance” due to studies linking it to brain damage in animals and lower IQs in children.

The Lancet’s review was officially published on December 16, 2006, less than a month before an environmental health journal in the US published a new study demonstrating — once again — that high fluoride exposure can reduce children’s IQ (3B). The study, published in Environmental Health Perspectives, reports that groups of children exposed to 8 ppm fluoride in water have lower average IQ’s, less children attaining high IQ, and more children affected by low IQ. While 8 ppm is higher than the fluoride level added to water in fluoridation programs (0.7-1.2 ppm), previous studies from China indicate that fluoride may affect IQ at lower levels (Xiang 2003), including as low as 0.9 ppm among children with iodine-deficiencies (Lin Fa Fu 1991).

Together, the publication of the Lancet review & the Environmental Health Perspectives study suggest that the mainstream medical literature is finally beginning to recognize this critically important, but previously ignored, issue.

4) Infant fluoride exposure linked to permanent tooth discoloration

The upper front two teeth are the most visible teeth when a person smiles. If a baby is exposed to fluoride during the first year of their life, these two teeth are at risk of being permanently discolored – according to a new study from the University of Iowa (4). And the risk is not just for “baby teeth”, but for permanent teeth as well.

According to the study, exposure to fluoride during the child’s first year of life can cause a tooth defect, known as dental fluorosis, that won’t become apparent until the teeth erupt 7 or 8 years later. Dental fluorosis can result in white and/or brown staining of the teeth and sometimes corrosion of the enamel – effects which will last the child’s entire life if cosmetic treatment cannot be afforded.

The Iowa researchers’ findings may help explain why the American Dental Association later warned, on November 9th, that infants should not receive fluoridated water. The ADA’s warning did not, however, go far enough. According to the Iowa study, the risk of developing fluorosis on the permanent teeth is greatest for those children exposed to fluoride for each of their first four years of life. The take home message: To avoid fluorosis on the permanent front two teeth, keep fluoride away from children until they are at least 5 years old.

5) Kidney patients at risk of chronic fluoride poisoning

It’s not just infants that should avoid fluoridated water. New research provides yet further reason why people with kidney disease – particularly advanced kidney disease – should be advised to avoid fluoride as well.

Because kidney patients have a reduced ability to clear fluoride from their body, they have long been recognized to be at heightened risk of fluoride poisoning. In 2006, new research helped to further highlight this risk.  Research from India confirmed that fluoride can cause a painful bone disease in kidney patients (5A), while research from Poland indicated that the health risks may extend well beyond the bones (5B). According to the Polish researchers, the heightened body burden of fluoride that kidney patients face (as measured by high levels of fluoride in their blood) may increase the rate of cell damage (oxidative stress) throughout the body – making them more vulnerable to a host of illnesses.

So, should people with kidney disease be concerned about drinking fluoridated water? According to two new reviews, the answer is yes (5C,D). According to one review, “Individuals with kidney disease have decreased ability to excrete fluoride in urine and are at risk of developing fluorosis even at normal recommended limit of 0.7 to 1.2 mg/l” (5C).

It’s time, therefore, for dental and medical organizations to start warning kidney patients to avoid water with added fluoride. As noted by Dr. Kathleen Thiessen, a scientist who helped author the National Research Council’s review on fluoride: “People with kidney disease should be very concerned about drinking fluoridated water because it does put them at a higher risk for a number of problems.”

6) Cornell scientist diagnoses fluoride poisoning in horses drinking fluoridated water

When fluoride is added to drinking water, it’s not just humans who will consume it. Millions of dogs, cats, and other animals will consume it as well. As we await the publication of a national study investigating the relationship between fluoridated water and bone cancer in dogs, a study published in 2006 provides compelling evidence that some animals may indeed be silent victims of the national water fluoridation program (6A,B).

For years, Cathy Justus’ horses in Pagosa Springs, Colorado, were experiencing symptoms that, no matter what medical treatment she tried, would not go away. The symptoms included colic (i.e. gastrointestinal pain), arthritis-like stiffness of the bones, and skin allergies. Cathy brought her horses to multiple veterinarians in the area, but none were able to find a cure for the horses’ problems — that is, until she met Dr. Lennart Krook, a retired veterinary researcher from Cornell University. Upon examining the horses, Dr Krook quickly discovered that Cathy’s horses had dental fluorosis – a fluoride-induced condition that created large brown stains and pits on the horses’ teeth. (None of the previous veterinarians Cathy went to had ever bothered to examine the horses’ teeth, and had therefore missed this important warning sign.)

Following the discovery of dental fluorosis, Dr. Krook conducted microscopic analyses of some of the deceased horses’ bones, and found changes in the bone structure that were consistent with skeletal fluorosis. While the horses’ bone fluoride levels (between 600 and 900 ppm) were well below the levels typically associated with skeletal fluorosis (in cattle), Dr. Krook concluded that the horses were, in fact, suffering from “chronic fluoride intoxication.”

Although some have questioned Dr. Krook’s diagnosis (based on the low fluoride levels in the horses’ bones), the owner of the horses swears by it. After her town council voted (in March 2005) to end its water fluoridation program, the symptoms that had plagued Cathy’s horses for nearly 20 years, began to subside – and have not returned since. Coincidence? According to Cathy Justus, the proof is in the pudding.

So, how many other horses are being affected in a similar manner? Dr Krook and Cathy think this is a question horse owners would do well to consider. We agree.

7) Fluoride exposure linked to kidney damage in children

The kidney has long been recognized as a potential target of fluoride toxicity. This is because, as noted by the National Research Council, “Human kidneys… concentrate fluoride as much as 50-fold from plasma to urine. Portions of the renal system may therefore be at higher risk of fluoride toxicity than most soft tissues.”

It was of great interest, therefore, to read the results of a new study investigating the relationship between water fluoride exposure and kidney damage in children (7). According to the study: “our results suggest that drinking water fluoride levels over 2.0 mg/L (ppm) can cause damage to liver and kidney function in children.”

The authors reached this conclusion after studying a group of 210 children living in areas of China with varying levels of fluoride in water (from 0.61 to 5.69 ppm). Among this group, the children drinking water with more than 2 ppm fluoride – particularly those with dental fluorosis – were found to have increased levels of NAG and y-GT in their urine, both of which are markers of kidney damage. The children’s urine also contain increased levels of lactic dehydrogenase – a possible indicator of liver damage.

While definitive conclusions can not be drawn from this single study, it’s findings are consistent with previous animal studies which reported kidney damage from fluoride exposure at levels as low as 1 ppm in rats, and 5 ppm in monkeys. Taken together, the studies suggest that minimizing fluoride intake could well have a positive effect on kidney health.

8 ) Water fluoridation linked to higher blood lead levels in children from old homes

Can water fluoridation increase the levels of lead circulating in a child’s blood? This is the question that has been asked ever since Dartmouth scientist, Dr Roger Masters, and chemical engineer, Myron Coplan, published studies in 1999 and 2000 reporting that exposure to fluoridated water was associated with increased blood lead levels in children surveyed from Massachusetts and New York State. According to Masters and Coplan, this association was not observed for all fluoride chemicals, but only those water supplies treated with “silicofluorides” (e.g. fluorosilicic acid and sodium silicofluoride).

Prompted by Masters’ & Coplan’s research, a team of scientists from the University of Maryland and Centers for Disease Control (CDC) examined the blood lead levels of children from a recent national survey to assess if there is any association with water fluoridation (8). In January 2006, the authors published the results of their study in Environmental Health Perspectives. While their findings do not neatly agree with Master’s and Coplan’s earlier studies, they also do not rule out a relationship between fluoridation and blood lead. Indeed, the authors report that water fluoridation is associated with significantly higher blood lead levels among children living in houses built prior to 1946. This is quite a striking finding as there is no shortage of houses built prior to 1946!

Thus, while the study may add a few important nuances to Masters’ & Coplan’s research, it is consistent with the theory that water fluoridation can increase the level of lead in children’s blood. Considering that lead exposure during childhood can result in permanent learning and behavioral disorders, this paper easily deserves recognition as one of the top 10 most important papers on fluoride of the past year.

9) Dental fluorosis linked to tooth decay & psychological stress

One of the myths that has long been perpetuated about fluoride is that dental fluorosis – no matter how severe – is simply a “cosmetic effect.” Based, however, on the research of the past year, it appears this myth is finally on its way out. In March, the National Research Council kicked things off by stating that severe dental fluorosis (marked by extensive staining and pitting of enamel) is an adverse health effect due to its ability to make teeth weaker and prone to decay.

NRC’s conclusion was further reinforced by a study published in December in the journal Community Dental Health (9A). The study, a national survey of children’s teeth in Puerto Rico, found that both severe fluorosis and moderate fluorosis are associated with increased tooth decay and/or restorations.

The physical damage that fluorosis may cause to teeth is not, however, the only concern. Another concern, as detailed over 20 years ago by the National Institute of Mental Health (NIMH), is the psychological impact that dental fluorosis may have on a child. The NIMH’s warning gained renewed support this past year from a study published in Community Dentistry & Oral Epidemiology (9B). According to the study, children with severe dental fluorosis are more likely to be perceived by their peers as less intelligent, less attractive, less social, less happy, less careful, less hygienic, and less reliable – characteristics which could have major effects on a child’s self-esteem. (The latest surveys of dental fluorosis in the US indicate that about 1% of American children now have severe fluorosis, while about 1-3% have moderate fluorosis.)

 Water fluoridation & the “Precautionary Principle”

Based on the studies from 2006 and early 2007, it is clear that fluoride exposure – at relatively low levels – can harm human health. It has the potential to cause bone cancer, damage the brain, damage the kidney, damage the thyroid, damage the bones (particularly in kidney patients), increase the uptake of lead, and damage the teeth. However, in order to fully prove and understand the nature of these risks (including the range of doses that can cause the effects, and how these doses vary based on environmental, genetic, and dietary factors) more research would need to be conducted. Is it ethical, however, to continue exposing entire populations to fluoride in their water or salt (often against people’s will), while additional long-term studies are carried out to clarify the risks?

That is the crux of the question posed by an insightful analysis published in the March 2006 issue of the Journal of Evidence Based Dental Practice. The analysis, written by Joel Tickner and Melissa Coffin, examines the water fluoridation controversy in the context of the “precautionary principle.” The precautionary principle has become a core guiding principle of environmental health regulations in Europe and reflects the position that:

“if there is uncertainty, yet credible scientific evidence or concern of threats to health, precautionary measures should be taken. In other words, preventive action should be taken on early warnings even though the nature and magnitude of the risk are not fully understood.”

As noted by Tickner & Coffin “The need for precaution arises because the costs of inaction in the face of uncertainty can be high, and paid at the expense of sound public health.”

In determining whether the precautionary principle should be applied to fluoridation, the authors note that:

  • there are other ways of delivering fluoride besides the water supply;
  • fluoride does not need to be swallowed to prevent tooth decay;
  • tooth decay has dropped at the same rate in countries with, and without, water fluoridation;
  • people are now receiving fluoride from many other sources besides the water supply;
  • studies indicate fluoride’s potential to cause a range of adverse, systemic effects;
  • since fluoridation affects so many people, “one might accept a lower level of proof before taking preventive actions.”

While the authors never state their personal opinion on water fluoridation, the issues and questions they’ve raised certainly help to put the debate about fluoridation on the right track.


1) National Research Council. (2006). Fluoride in Drinking Water: A Scientific Review of EPA’s Standards. National Academies Press, Washington D.C. (Reviewed in: Fluoride 2006; 39(3):163-172.)

2) Bassin EB, Wypij D, Davis RB, Mittleman MA. (2006). Age-specific fluoride exposure in drinking water and osteosarcoma (United States). Cancer Causes and Control 17: 421-8.

3A) Grandjean P, Landrigan P. (2006). Developmental neurotoxicity of industrial chemicals. The Lancet 368: 2167-2178

3B) Wang SX, et al. (2007). Water arsenic and fluoride exposure and children’s intelligence quotient and growth in Shanyin County, Shanxi, China. Environmental Health Perspectives [Epub Jan 9].

4) Hong L, Levy SM, et al. (2006). Timing of fluoride intake in relation to development of fluorosis on maxillary central incisors.Community Dentistry and Oral Epidemiology 34:299-309.

5A) Harinarayan CV, et al. (2006). Fluorotoxic metabolic bone disease: an osteo-renal syndrome caused by excess fluoride ingestion in the tropics. Bone 39: 907-14.

5B) Bober J, et al. (2006). Fluoride aggravation of oxidative stress in patients with chronic renal failure. Fluoride 39:302-309. [See paper]

5C) Bansal R, Tiwari SC. (2006). Back pain in chronic renal failure. Nephrology Dialysis Transplantation 21:2331-2332.

5D) Ayoob S, Gupta AK. (2006). Fluoride in Drinking Water: A Review on the Status and Stress Effects. Critical Reviews in Environmental Science and Technology 36:433–487

6A) Krook LP, Justus CJ. (2006). Fluoride poisoning of horses from artificially fluoridated drinking water. Fluoride 39:3-10. [See paper]

6B) Justus CJ, Krook LP. (2006). Allergy in horses from artificially fluoridated water. Fluoride 39:89-94. [See paper]

7) Xiong X, et al. (2007). Dose-effect relationship between drinking water fluoride levels and damage to liver and kidney functions in children. Environmental Research 103:112-116. (Reviewed in: American Academy of Pediatrics (AAP) Grand Rounds; 2007; 17:7).

8 ) Macek M, et al. (2006). Blood lead concentrations in children and method of water fluoridation in the United States, 1988-1994.Environmental Health Perspectives  114:130-134.

9A) Elias-Boneta AR, et al. (2006). Relationship between dental caries experience (DMFS) and dental fluorosis in 12-year-old Puerto Ricans. Community Dental Health 23:244-50.

9B) Williams DM, et al. (2006). Attitudes to fluorosis and dental caries by a response latency method. Community Dentistry and Oral Epidemiology 34:153-9.

10) Tickner J, Coffin M. (2006). What does the precautionary principle mean for evidence-based dentistry? Journal of Evidence Based Dental Practice 6:6-15.

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