The Facts About Fluoride & Human Intelligence

Michael Connett, Esq, Fluoride Action Network
Waking Times

In the initial version of this article, we estimated that “over 200,000″ Americans drink water with 1.8 to 2.0 ppm. Based on data from the National Research Council, however, it appears that a more accurate estimate is “about 600,000.” We have changed our estimate accordingly.

In July, a team of Harvard and Chinese scientists published a study that warned of fluoride’s potential to reduce human intelligence.  The researchers issued their warning after reviewing dozens of studies from the past two decades that have linked elevated fluoride exposure to reduced IQ in children. Although the National Research Council issued a similar warning in 2006, advocates of fluoridation continue to push ahead with plans to fluoridate yet more water supplies in what is already the most fluoridated nation on Earth: the United States.Fluoridation advocates — including both scientists and city officials — are seriously misrepresenting, and in some cases making outright false statements, about the Harvard team’s study. To help remedy this situation, the Fluoride Action Network (FAN) is releasing the results of its six-month investigation into fluoride’s effects on the brain, and thyroid gland. In the course of this investigation, FAN has located, obtained, and — in many cases — translated dozens of studies on all facets of fluoride’s neurotoxicity, including studies detailing fluoride’s effects on the thyroid gland. In total, FAN has identified 34 studies which detected an association between fluoride and reduced IQ in human populations. FAN has also identified dozens of other studies which correlate fluoride exposure with impaired learning and memory, altered neurobehavioral function, fetal brain damage, and altered thyroid hormone levels.

Legislators who continue to mandate the addition of fluoride to public water without fully apprising themselves of this research are doing a profound disservice to the health and welfare of their constituents.

The Harvard Study

A research team led by scientists at the Harvard School of Public Health (HSPH) sparked national headlines in July when they reported that the vast majority of research that has been conducted on fluoride and human intelligence has found significant reductions in childhood IQ. Twenty-six of the twenty-seven studies that fit the Harvard team’s criteria found a relationship between fluoride and reduced IQ, with 20 of the studies finding a statistically significant effect.

  • Although some of the IQ studies have used simple designs, the Harvard team concluded that study deficiencies were unlikely to explain why 26 of the 27 studies found associations between fluoride and reduced IQ. The Harvard team thus concluded that fluoride’s effect on children’s developing brain should be a “high research priority” in countries like the U.S. where, despite mass fluoridation programs, no studies have yet been conducted to investigate the issue.

    Protecting Public Policy Instead of Public Health

    Despite the Harvard team’s findings, U.S. fluoridation proponents have continued their “full speed ahead” approach of forcing every individual, including toddlers and children, to ingest fluoride through public tap water and all of the processed foods and beverages made with it. Rather than pausing to consider that current fluoride exposures (from all sources, including fluoridated water, fluoridated dental products, pesticides, tea, and processed beverages) might be permanently damaging the brain of some children in the United States, particularly those children with nutrient deficiencies (e.g., iodine) and the 3.6% of children who now have moderate/severe fluorosis, proponents have concluded (based on assumptions, not data) that fluoride cannot be causing reduced IQ in the United States.

    False & Misleading Claims

    The quick dismissal by fluoride advocates of the Harvard team’s findings is rooted, in part, on demonstrably false and misleading claims. Two of the most common claims are that (1) the size of the IQ reduction from fluoride is “meaningless,” and  (2) the fluoride levels were too high to be relevant to U.S. populations. Both of these claims will now be addressed:

    The Size of the IQ Reduction

    Dr. Myron Allukian, a longtime fluoridation proponent, has stated that the Harvard team found only “a half point difference in IQ” between the children from high-fluoride and low-fluoride areas. According to Allukian, “a half point difference in IQ is meaningless. That’s like saying, we measured all the people in New York and Chicago and in New York they were a half millimeter taller.” Several other fluoridation “experts” made similar statements at a September 6th hearing before the city council of Portland, Oregon.

    The problem with Allukian’s claim is that it is completely false — a fact that can be readily verified by actually reading the Harvard study. The Harvard team found that high-fluoride exposure was associated with a 0.45 reduction in the “standardized mean difference” (SMD) in intelligence. Dr. Allukian and other fluoridation proponents have mistakenly interpreted this to mean that a half-point reduction in SMD equates to a half-point reduction in IQ. This, however, is NOT the case. As the Harvard team has recently confirmed, a reduction of 0.45 SMD is “approximately equivalent to seven IQ points for commonly used IQ scores.”

    If Allukian and other fluoridation “experts” had read the Harvard study and understood the SMD concept, they would have known this. Instead, it appears they relied on second-hand accounts of the Harvard study, including an HSPH press release. After FAN Researcher Chris Neurath brought the error to HSPH’s attention, a correction was made. The “experts” however continue to repeat the error as if it were true. It goes without saying that experts and policy officials should not be basing public statements about the Harvard team’s findings without having read the study themselves. The lack of diligence by these “experts” and public officials on an issue involving permanent potential damage to some children’s brains is as breathtaking as it is appalling.

    The Relevance of the IQ Studies to Fluoridated Populations

    Another misleading claim made by fluoridation proponents is that the fluoride levels in the IQ studies were far higher than the fluoride levels to which children are exposed in the United States. Fluoridation proponents have reached this conclusion by (a) focusing on the highest water fluoride level (11.5 mg/L) studied in 1 of the 27 studies, and then (b) insinuating that this high level is representative of all of the studies. The Pew Children’s Dental Campaign (which now promotes fluoridation schemes across the U.S.) initiated this line of reasoning within days of the Harvard study’s release. According to the Pew campaign:

    “In many cases, the high-fluoride areas were significantly higher than the levels used to fluoridate public water systems in the U.S.  In fact, the high-fluoride areas in these foreign countries reached levels as high as 11.5 mg/L, which is more than 10 times higher than the optimal level used in the U.S.”

    Other fluoridation proponents, including Sam Adams, the Mayor of Portland, Oregon, have since repeated Pew’s claim. What these proponents have failed to acknowledge is that only ONE of the studies that the Harvard team reviewed had fluoride levels as high as 11.5 mg/l.  By contrast, the majority of the studies that the Harvard team reviewed investigated fluoride levels that are still considered “safe” in the United States.  Of the twenty studies that investigated the effect of fluoride intake from water, twelve examined communities with a fluoride content less than 4 mg/l. This is a level that is still considered “safe” by the U.S. EPA. Every one of these twelve studies found reduced IQ in the “high-fluoride” community when compared to a low-fluoride community. Of these twelve studies:

    • Seven studies found reduced IQs among children drinking water with fluoride levels between 2.1 mg/l and 4 mg/l — levels that 1.4 million Americans drink everyday.(Poureslami 2011; Seraj 2006; Hong 2001; Wang 2001; Lu 2000; Yang 1994; An 1992)
    • Four studies found effects at levels between 1.8 mg/l and 2.0 mg/l — levels thatabout 600,000 Americans drink everyday. (Xiang 2004; Yao 1997; Yao 1996; Xu 1994)
    • One study (sponsored by UNICEF) found reduced IQ at just 0.88 mg/l – a level within the “optimal” range of fluoride that is added to the drinking water of over 200 million Americans(Lin 1991)

    Far from being irrelevant to U.S. exposures, these fluoride levels are actually being consumed on a regular basis by  millions of Americans. Further, the fluoride levels that have been detected in the children’s urine in five of these studies (1.5 to 3 mg/l) were found to be exceeded by many adults living in fluoridated populations in England. (Mansfield 1999) While there is a striking absence of urinary fluoride data among both children and adults in the United States, the high exposure to fluoride toothpasteamong young children is almost certain to produce urine fluoride levels that match the levels documented in the Chinese children.

    Another population at clear risk from fluoride are children born to women who drink large amounts of low-quality teas. Research from China has repeatedly found that high fluoride exposure during pregnancy can damage the brain of the fetus in ways that can permanently reduce the intelligence of the child. (Yu 1996; Dong 1993; Du 1992; Han 1989) Damage to fetal brain has been found in women with urinary fluoride levels of just 4.3 ppm. (Yu 1996). Notably, this is a level of fluoride that heavy tea drinkers in the U.S. and England are known to exceed. (Izuora 2011; Whyte 2005; Mansfield 1999). The neurological impact of heavy-tea consumption during pregnancy has never been studied.

    The “Margin of Safety” Problem

    Fluoridation proponents’ dismissal of the IQ studies has also been based on a failure to address the “margin of safety” problem. The concept of a margin of safety is a deeply rooted cornerstone in all modern risk assessments; yet fluoridation proponents act as if they don’t even know the concept exists. As demonstrated here, this failure to address the margin of safety issue is a critically important omission.

    In conventional risk assessment, the U.S. EPA uses a default margin of safety often. Translated, this means EPA seeks to limit exposure to chemicals to levels that are ten times less than the levels that cause adverse effects. With fluoride and IQ, however, the levels of fluoride (in water and urine) that have repeatedly been linked to IQ reductions are — at most — just two or three times more than tens of millions of American children now receive on a daily basis. From a risk assessment perspective, this is an extremely unnerving situation, one almost certain to cause neurological harm in an untold number of children. The situation is particularly unnerving, and particularly serious, for those children who have a heightened vulnerability to fluoride’s neurological toxicity.

    While there are occasions where the EPA will accept a margin of safety lower than ten, it only does so when there is clear data demonstrating that the default margin of safety is unnecessary. This exception does not apply to fluoride and IQ because a safe level of fluoride exposure for the neurological health of all children has not yet been demonstrated.

    Vulnerable Children Are Being Disregarded and Ignored

    Human studies have repeatedly found that some children are at a much greater risk of suffering neurological damage from fluoride than others. A UNICEF-funded study, for example, found that children with iodine deficiencies suffered reductions in IQ at fluoride levels of just 0.88 mg/L. (Lin 1991) Other research — both animal and human — has repeatedly confirmed that children with iodine deficiency suffer greater neurological disorders when exposed to elevated fluoride than they do from the iodine deficiency itself. This is a striking fact when considering that, according to the CDC, the rate of iodine deficiency in the U.S. has increased significantly in the past three decades, and now affects up to 12% of the population.

    Since U.S. Health Authorities Aren’t Doing Their Job, FAN Will Do It for Them

    It has become obvious in recent weeks that U.S. health authorities are more interested in convincing communities to fluoridate their water than honestly communicating the facts about fluoride and intelligence. Because of their systemic, ongoing failure to honestly address this serious public health issue, FAN has expended a significant amount of time and money searching for, accessing, and translating all studies on fluoride and intelligence, whether they be in English, Chinese, or other languages.

    In total, FAN has identified 40 studies that have investigated fluoride’s impact on human intelligence, as well as 16 studies that — in carefully controlled laboratory conditions — have examined fluoride’s impact on the learning and memory capacity of animals. As we document here, 34 of the 40 human studies have detected reductions in IQ from fluoride exposure, while 15 of the 16 animal studies have found fluoride exposure impairs the ability to learn and remember.

    To facilitate public understanding of this research, FAN is making all of its translations publicly available, including the studies that did not find a relationship between fluoride and reduced IQ. FAN’s summary of this research, as well as links to full-text copies of the studies, can be accessed at the following links:

    Other Evidence that Fluoride Damages the Brain

    As part of FAN’s unprecedentedly comprehensive review, dozens of additional studies that address fluoride’s broader effects on the brain and thyroid gland have also been reviewed and summarized. This includes studies investigating:


    At FAN, we believe that better information produces better results. For decades, proponents of water fluoridation have decided that it is better to convince communities to fluoridate water than inform the public about the true state of knowledge about fluoride’s toxicity, including the breathtaking uncertainties and reasonably looming hazards. As the public learns the deeply disturbing details that have been systematically omitted by fluoridation proponents we have no doubt that fluoridation of water will end. The fate of those who helped perpetuate this ill-conceived program is less clear.


    • An J, et al. (1992). The effects of high fluoride on the level of intelligence of primary and secondary students. Chinese Journal of Control of Endemic Diseases 7(2):93-94. [See study]
    • Choi AL, et al. (2012). Developmental Fluoride Neurotoxicity: A Systematic Review and Meta-Analysis. Environmental Health Perspectives 2012 Jul 20. [Epub ahead of print] [See study]
    • Dong Z, et al. (1993). Determination of the contents of amino-acid and monoamine neurotransmitters in fetal brains from a fluorosis-endemic area.Journal of Guiyang Medical College 18(4):241-45. [See study]
    • Du L. (1992). The effect of fluorine on the developing human brain. Chinese Journal of Pathology 21(4):218-20. [See study]
    • Han H, et al. (1989). Effects of fluorine on the human fetus. Chinese Journal of Control of Endemic Diseases 4:136-138. [See study]
    • Hong F, et al. (2001). Research on the effects of fluoride on child intellectual development under different environments. Chinese Primary Health Care 15(3):56-57 (republished in Fluoride 2008; 41(2):156–60). [See study]
    • Izuora K, et al. (2011). Skeletal fluorosis from brewed tea. Journal of Clinical Endocrinology & Metabolism 96(8):2318-24.
    • Lin F, et al (1991). The relationship of a low-iodine and high-fluoride environment to subclinical cretinism in Xinjiang. Endemic Disease Bulletin 6(2):62-67 (republished inIodine Deficiency Disorder Newsletter Vol. 7(3):24-25).  [See study]
    • Lu Y, et al (2000). Effect of high-fluoride water on intelligence of children. Fluoride 33:74-78. [See study]
    • Mansfield P. (1999). The distribution of urinary fluoride concentration in the U.K.Fluoride 32(1):27-32. [See study]
    • Poureslami HR, et al. (2011). Intelligence quotient of 7 to 9 year-old children from an area with high fluoride in drinking water. Journal of Dentistry and Oral Hygiene 3(4):61-64.
    • Seraj B, et al. (2006). [Effect of high fluoride concentration in drinking water on children’s intelligence]. [Study in Persian] Journal of Dental Medicine 19(2):80-86. [See abstract]
    • Wang X, et al. (2001). Effects of high iodine and high fluorine on children’s intelligence and thyroid function. Chinese Journal of Endemiology 20(4):288-90. [See study]
    • Whyte MP, et al. (2005). Skeletal fluorosis and instant tea. American Journal of Medicine 118:78-82.
    • Xiang Q, et al. (2003a). Effect of fluoride in drinking water on children’s intelligence. Fluoride 36: 84-94. [See study]
    • Xiang Q, et al. (2003b). Blood lead of children in Wamiao-Xinhuai intelligence study. Fluoride 36: 198-199. [See study]
    • Xu Y, et al. (1994). The effect of fluorine on the level of intelligence in children. Endemic Diseases Bulletin 9(2):83-84. [See study]
    • Yang Y, et al. (1994). The effects of high levels of fluoride and iodine on intellectual ability and the metabolism of fluoride and iodine. Chinese Journal of Epidemiology 15(4):296-98 (republished in Fluoride 2008; 41:336-339). [See study]
    • Yao Y, et al. (1997). Comparative assessment of the physical and mental development of children in endemic fluorosis area with water improvement and without water improvement. Literature and Information on Preventive Medicine 3(1):42-43. [See study]
    • Yao Y, et al. (1996). Analysis on TSH and intelligence level of children with dental Fluorosis in a high fluoride area. Literature and Information on Preventive Medicine 2(1):26-27. [See study]
    • Yu Y, et al. (1996). Neurotransmitter and receptor changes in the brains of fetuses from areas of endemic fluorosis. Chinese Journal of Endemiology 15:257-259. [See study]

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