Anti-fluoride IQ claims are false

Anti-fluoridation campaigners’ claims that community water fluoridation reduces IQ are simply false. That is the conclusion of  Alex Kasprak – and he says why in his new article (see Fact Check -Fluor-IQ).

These days anti-fluoridation activists use this claim as their main argument – and they often cite scientific articles to back it up. But, Kasprak says, this claim  is based on “either willful or negligent misreading of actual science.” The claim that  studies have “linked” fluoride to reduced intelligence “is a textbook-ready case of bait-and-switch:”

” the topic has surreptitiously been shifted from the act of water fluoridation as a public health measure to the broader concept of fluoride toxicity in children. Many otherwise benign chemicals can also be harmful in high concentrations. Thiocyanate, a chemical found in kale, may kill you at high doses, for example.”

Scale and context

Kasprak critiques the way anti-fluoride campaigners so often use and cite the Choi et al., (2012) study. This was a meta-analysis of 27 mostly poor quality Chinese studies from areas of endemic fluorosis where drinking water fluoride levels are much higher than that used in community water fluoridation.

Citing neuroscientist Steven Novella Kasprak points out:

“There was a lot of variability across the studies, but generally the high fluoride groups were in the 2-10 mg/L range, while the reference low fluoride groups were in the 0.5-1.0 mg/L range […]”

In other words – fluoridated water in the US has the same level of fluoride as the control or low fluoride groups in the China studies reviewed in the recent article, and the negative association with IQ was only found where fluoride levels were much higher – generally above EPA limits.

Note: The optimum level of fluoridated water in the US is 0.7 mg/L.

Anti-fluoride campaigners sometimes concentrate on those studies in the meta-review which did focus on concentrations close to that considered optimum. But:

“Of those eight studies, half of them co-investigated fluoride and iodine together (Lin et al 1991, Xu et al 1994, Yang et al 1994, Hong et al 2001) making it hard or in some cases impossible to separate out the combined effects, and two of those four studies reached conclusions that are counter to the hypothesis that fluoridation levels alone are the main driver of a lower IQ.”


“Two of those eight studies use a control group with fluoride values that are literally the same or higher than the target range of fluoridation efforts in the United States (Xu et al 1994, Hong et al 2001), seemingly ceding the point that those levels do not affect children’s IQ.”

So, as far as scale is concerned, Kasprak concludes:

“Collectively, this demonstrates that most of the IQ variance presented in the Harvard study still stems from exposures to extremely high levels of fluoride that would already be considered dangerous in the US, and those studies finding effects on a smaller scale are not sufficient to demonstrate the effects those groups opposed to fluoridation claim they demonstrate.”

As far as context is concerned none of these 27 studies were relevant to community water fluoridation:

“Literally none of the studies involved tested populations of individuals exposed to drinking water that was artificially supplemented with fluoride as a public health measure. Instead, all of the studies come from China or Iran, both of which have areas of naturally occurring (endemic) high fluoride pockets of groundwater.

That means that studies utilized in its analysis are wholly irrelevant to the question that advocates claim they are answering. This is significant, as the use of these very specific studies introduces a veritable Homerian epic of confounding details, some of which came up in our analysis of the eight low-level fluoride studies discussed above. Among the most pressing of these are a lack of information on other confounding variables and the quality of the studies they utilized. These issues are noted by the authors of the Harvard study themselves”

The authors of the Choi et al (2012) meta-review also:

“explicitly state that the results cannot be used to estimate the possible limits of fluoride exposure with respect to developmental damage, due to lack of data – ‘Our review cannot be used to derive an exposure limit, because the actual exposures of the individual children are not known.'”

Other mechanisms

Kasprek disagrees with the unsubstantiated claim of Choi et al., (2012) that other neurotoxicants are unlikely to be present in the groundwater of the studied areas. Rightly so because all those studies suffer from insufficient consideration of confounding factors. As Choi et al., (2012) said: “Most reports were fairly brief and complete information on covariates was not available.” 

In fact, statistical analysis of the data in one of the better papers the anti-fluoride campaigners rely on shows that fluoride can explain only about 3% of the measured variance in IQ. It is extremely likely that inclusion of sensible confounders in the statistical analysis would have shown any relationship of IQ with fluoride is not statistically signficant (see Connett misrepresents the fluoride and IQ data yet again).

Kasprek briefly considered arsenic as a possible confounder but with subjects like cognitive ability or IQ there are many other physical and social factors that could be imnportant.contaminants. Parental income and education as well as the psychological consequences of deformities resulting from dental and skeletal fluorosis. I discussed this last aspect in my peer-reviewed article Perrott (2015), Severe dental fluorosis and cognitive deficits and my post- Severe dental fluorosis the real cause of IQ deficits?

Fallacy of publication journal

I think Kasprek’s argument about the journal used for publishing some of these papers is fallacious:”

“Finally, four of these eight papers (Yang et al 1994, Lu et al 2000, Hong et al 2001, Xiang et al 2003a) are either published (or republished) in the allegedly peer-reviewed journal Fluoride, a publication of the “International Society for Fluoride Research Inc.” — an anti-fluoridation group whose editor-in-chief is a psychiatrist in private practice, with no academic background on the topic of fluoride toxicity.”

I am very much opposed to using the place of publication as an argument against the scientific veracity of a paper. True, Fluoride is a very poor quality journal. True, is has an ant-fluoride agenda. And true, it shows no evidence of proper peer review. However, it is disingenuous to use these facts to argue against the scientific content of these papers. Critique of the papers should rest on an analysis of their scientific content – not the place of publication.

This lazy approach is doubly worse because it carries the implication that if these papers had been published in a reputable journal with good peer review then that would be sufficient to guarantee the veracity of the science. It is not.

On the fluoride issue, there are plenty of examples of papers involving poor science that are published in reputable journals. I have discussed some of these in my articles – for example ADHD linked to elevation not fluoridationAnti-fluoride hypothyroidism paper slammed yet againPoor peer review – and its consequencesDoes community water fluoridation reduce diabetes prevalence?, The Harvard study and the Lancet paperControversial IQ study hammered in The Lancet and Repeating bad science on fluoride.

The lazy judgmentalism based on place of publication, and not content, is particularly relevant at the moment with the public concern about “false news” and efforts to introduce mechanisms of “fact checking.” Some people are advocating reliance on websites like – yet this site can be blatantly biased on political matters. And its bias can rest on the lazy approach of condemning a news article by its place of publication.

[A recent example was a article which cast aspersions on an independent journalist, Eva Bartlett, because – “She is also a contributor at RT, a news site funded by the Russian government.” OK, you may not see how lazy that argument is but try replacing the words RT and Russian by “Al Jazeera” and Qatar” or “BBC” and “British.” And, I also think describing the fact that Bartlett had been interviewed by an RT reporter, and participated in a debate aired by RT, as being a “contributor” shows a bias]

The good science

Despite delving into the details of the poor quality papers the anti-fluoride IQ argument relies on Kasprak is quite right to stress:

“This should not function as a distraction from the larger point that studying naturally occurring pockets of high fluoride and the assessing the risks of supplementing public drinking water in an effort to have it reach a concentration of 0.7 mg/L are two completely different beasts.”

So, my other criticism of Kasprak’s article is that he could have said more about the studies which are relevant to community water fluoridation.  He does briefly refer to the New Zealand study of Broadbent et al (2014) in a quote from  Ireland’s Health Research Board:

“There was only one study carried out in a non-endemic or CWF [community water fluoridation] area that examined fluoride and IQ. This was a prospective cohort study (whose design is appropriate to infer causality) in New Zealand. The study concluded that there was no evidence of a detrimental effect on IQ as a result of exposure to CWF.”

However, he missed the 2016 study of  Aggeborn & Öhman (perhaps it was too recent for him) which I discussed in my article Large Swedish study finds no effect of fluoride on IQ. The results of this study were so precise and the sample numbers used are so large it should be seriously considered by anyone looking at this issue.


Kasprak’s article is useful in exposing the false claim of activists that fluoride lowers IQ – especially when used in arguments against community water fluoridation. But he could have said more – and he could have avoided the fallacious argument based on place of publication which is so easily reversed to support poor quality science in reputable journals.

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5 responses to “Anti-fluoride IQ claims are false

  1. Good piece, Ken. Your point about not judging the science based on the publication in which it appears is a good one. I’m as guilty as anyone about dismissing literature simply because it is published in “Fluoride”.

    Steven D. Slott, DDS


  2. James Jacobs, DDS

    The “Clinical Toxicology of Commercial Products, 5th addition” (1984) gives lead a toxicity rating of 3-4 (3=moderately toxic,4=very toxic) and the EPA has set 0.015 ppm as the maximum safe level for lead in drinking water (with a goal of 0.0 ppm), while the toxicity rating for sodium fluoride is 4, and yet the safe level is currently set at 4.0 ppm (250 times as much as lead).

    Clinical toxicology of commercial products
    1984, 5th ed, Baltimore: Williams & Wilkins
    by Robert E Gosselin; Roger P Smith; Harold C Hodge

    Dr. Gosselin retired from Dartmouth Medical School in Hanover, N.H., where he was the founding chairman of the Department of Pharmacology and Toxicology. Together with Dartmouth colleague Dr. Roger P. Smith and a small group from Rochester, he published Clinical Toxicology of Commercial Products, which for decades was the primary reference work for emergency rooms across the country. He played a founding role in the poison control center movement.


  3. James, what point are you making and how does it relate to this post which is about the false claim that community water fluoridation lowers IQ?


  4. Steven Slott

    So, James, you are saying that lead and fluoride have exactly the same effect on the human body? If not, then your toxicity comparison is meaningless.

    The EPA sets its MCL for drinking water contaminants based on the level at which adverse effects are known to occur for each substance, not on comparitive toxicity ratings of commercial products.

    Steven D. Slott, DDS


  5. James Jacobs, read a little closer in Dr. Gosselin’s Clinical Toxicology and you will discover other substances that have a toxicological rating between lead and arsenic: Table salt and caffeine.

    If you are truly a dentist, then, you should understand that “The dose makes the poison”.


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