Canadian studies confirm findings of Broadbent et al (2015) – fluoridation has no effect on child IQ

Readers may remember the scathing reaction of anti-fluoride campaigners to the paper of Broadbent et al (2015). This was the first paper to compare child and adult IQ levels for people living in fluoridated and unfluoridated areas.

The anti-fluoride campaigners were extremely rude in their reaction – accusing the authors of fraud and claiming the paper was “fatally flawed.” Interestingly, several scientists known for their anti-fluoride bias also launched attacks – but more respectably as letters to the editor of the journal. For example, see articles by Osmunson et al (2016),  Grandjean (2015),; and Menkes et al (2014).

And why? Simply because Broadbent et al (2015) showed there was no difference in IQ of people living in fluoridated areas. That the studies from areas of endemic fluorosis used by anti-fluoride activists to argue at CWF were just not relevant (see Child IQ in countries with endemic fluorosis imply fluoridation is safe).

But isn’t it strange? Two more recent papers (Green et al 2019 & Till et al 2020) have effectively repeated the work of Broadbent et al (2015). They found the same result – no difference in IQ of children living in fluoridated and unfluoridated areas. And simply no reaction, no condemnation from anti-fluoride activists or the anti-fluoride scientists.

No condemnation because these anti-fluoride critics promote these papers for other reasons. But this underlines how biased the critics of the Broadbent et al (2015) paper were.

I have completed a detailed analysis of all the 65 studies the Fluoride Action Network (FAN) lists as evidence that community water fluoridation (CWF) is harmful to child IQ. The full analysis is available for download as the document Analysis of FAN’s 65 brain-fluoride studies.

In this article, I discuss the studies in the FAN’s list (see FLUORIDE & IQ: THE 65 STUDIES”) which compare child IQ in areas of “fluoridated” and “unfluoridated” fluoride in Canada. Only two studies – but I include that of Broadbent et al (2015) (which FAN’s list ignores) for completeness. All three studies found no difference in the IQ of children living in fluoridated and unfluoridated areas.

Comparing IQ of children in fluoridated and unfluoridated areas

The table below summarises the results reported by all three studies – Broadbent et al (2015), Green et al (2019), and Till et al (2020).

Table 1: Results from studies comparing IQ of children and adults from fluoridated and fluoridated areas

Data from Green et al (2019) for children whose mothers lived in fluoridated or unfluoridated areas during pregnancy.
Data from Till et al (2020) for children either breastfed of formula-fed as babies while living in fluoridated or unfluoridated areas.

There is absolutely no difference in IQ due to fluoridation. Remember, the standard dedication of the values in the table are about 13 to 16 IQ points.

I have presented all the results from these papers graphically below. FSIQ is the normal IQ measurement. VIQ (Verbal IQ) and PIQ (Performance IQ) are subsets of FSIQ.

The only statistically significant differences between fluoridated and unfluoridated areas were for VIQ of breastfed babies (VIQ higher for fluoridated areas) and PIQ of formula-fed babies (PIQ lower for fluoridated areas).

Anti-fluoride campaigners and (biased scientists like Grandjean) love the Green et al (2019) and Till et al (2020) papers because they reported (very weak) negative relationships of some child cognitive measures with fluoride intake ( I discuss this in separate articles). This is largely a result of the statistical methods used – particularly resorting to several different cognitive measures and measures of fluoride exposure, as well as the separation of results according to gender. Reminds me of the old saying that one can always get the results one requires by torturing the data hard enough.

I will return to the statistical problems of these and similar papers in a separate article.

Misrepresentation by anti-fluoride activists

Anti-fluoride campaigners have latched on to the two Canadian studies – often making claims that simply are not supported. But always ignoring the data shown above.

For example – this propaganda poster from FAN promoting the Green et al (2019) study.

This completely misrepresents the results of the study. No difference was found in the IQs of children from fluoridated and unfluoridated areas. These people completely ignore that result while placing unwarranted faith in the weak relationships reported elsewhere in that paper. (In fact, Green et al (2019) found a weak significant relationship only for boys – the relationships for all children and for girls were not significant. See my articles about this statistical torture).

And this FAN propaganda poster promoting the Till et al (2020) study.

Again – completely wrong. There was no difference in IQ of formula-fed babies in fluoridated and unfluoridated areas (see Table 1 above). Even worse – FAN is misrepresenting the statistical relationships reported in this paper as there’s was no statistically significant relationship between child IQ and fluoride exposure for formula-fed our breastfed babies once the influence of outliers and/or confounders were considered.

Misrepresentation by anti-fluoride scientists

It is understandable, I guess, that the authors of the two Canadian papers make a lot of the poor statistical relationships they reported and ignored the fact that they did not see any effect of fluoridation. Perhaps they can be excused some bias due to professional ambition. But this underlines why sensible readers should always critically and intelligently read the papers in this controversial area. One should never rely on the public relations claims of authors and their institutes. But it is sad to see how scientific basis and ambitions can lead scientists to support the claims of political activists. or worse, to attack honest scientists who do post-publication peer review of the studies (see for example When scientists get political: Lead fluoride-IQ researcher launches emotional attack on her scientific critics).

I am also very critical of scientific supporters of these studies who have their own anti-fluoride motivations. Philippe Grandjean, for example, was one of the authors very critical of the Broadbent et al (2015) paper and ignored completely the fact that the Green et al (2019) and Till et al (2020) papers report exactly the same result – no effect of fluoridation on child IQ. Grandjean often makes public comments supporting the claims of anti-fluoride campaigners like FAN. He also behaved in a scientifically unethical way when he refused to allow my critique of the flawed paper by Malin & Till (2015) to be published in Environmental Health – the journal he acts as the chief editor of (see Fluoridation not associated with ADHD – a myth put to rest).

I am repeating myself but it is a matter of “reader beware.” Readers should not simply rely on the scientific “standing” of authors who are only human and suffer from the same biases as others. They should read these papers for themselves and make up their own mind about what the data actually says.

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4 responses to “Canadian studies confirm findings of Broadbent et al (2015) – fluoridation has no effect on child IQ

  1. Kane Kitchener, a leader of the anti-fluoride activist group Fluoride Free NZ claims “Your comment on the 65 studies go against the expert testimony of the plaintiffs” in the case taken by FAN against the USEPA.

    That is my point about the bias of these anti-fluoride scientists. Phillippe Grandjean, one of the FAN experts, attacked the Broadbent et al (2015) study because it didn’t show any effect of fluoridation in child IQ. Yet he remains completely silent about the Green et al (2019) and Till et al (2020) studies which show exactly the same result because he wants to draw unwarranted conclusions from the shonky statistics used in these studies.

    I should also point out that other experts, without the pro-FAN bias, did point out the fact that the Gree et al (2109) study showed no difference between fluoridated and non-fluoridated areas).

    Of course the FAN “experts” would disagree with my analyses (except they are strangely silent about the way FAN has used most of these studies). Why else would FAN employ them?

    It is up to readers toa actually look at the facts and claims, not relying on the apparent standing of biased “experts” and think things out for themselves. Act scientifically.


  2. Bill Osmunson DDS MPH

    You still have not considered dosage or margin of safety.

    To claim Green and Till papers are comparable to Broadbent (have effectively repeated the work of Broadbent) goes beyond fake science.

    For example, Green et al, Concluded, “A 1-mg higher daily intake of fluoride among pregnant women was associated with a 3.66 lower IQ score (95% CI, −7.16 to −0.14) in boys and girls.”

    Did Broadbent provide individual measurements of fluoride in mother’s urine?

    What was the difference in measured dosage of fluoride between the Broadbent cohorts?

    Dosage, Ken. You fail to consider dosage.

    So long as you refuse to consider dosage, you will have flawed conclusions.

    On another controversial subject, What’s your scientific position on wearing face masks in mitigating the transmission of the virus? As a public health scientist, I recommend and I wear face masks and glasses, and/or face shields. But the science is certainly incomplete, would you agree?

    Could a prospective double blinded randomized controlled trial be done for mitigating the transmission of the virus?


  3. Bill, I never claimed “Green and Till papers are comparable to Broadbent.” In fact, Guth et al specifically considered limitations in both the Green and Broadbent studies and found more limitations for Green than Broadbent.

    However, specifically the Green and Till paper decisively concluded that there was no difference in IQ for children (or children/mother pairs) that lived in fluoridated and unfluoridated areas. Do I really have to reproduce the data from Table 1 – can you not read it yourself?

    table 1

    Are you going to ignore that data for fluoridated and unfluoridated comparisons?

    You are staw clutching to quote a detail from Green (significant relationship for male children) while ignoring that most relationships were not significant and there was absolutely no difference between fluoridated and unfluoridated areas.

    Bill, you are one of the authors who climbed out of your tree because Broadbent’s data did not support your bias. Yet, similar data from both Green and Till (comparing fluoridated and nonfluoridated areas) also do not support your bias – and you remained silent.

    That is just hypocrisy on your part.

    And your organisation (FAN) reproduces a graphic claiming that Till showed a relationship between fluoride levels and IQ of formula-fed children – when that paper specifically points out the relationship they obtained was not statistically significant.

    Here is the relevant quote from their paper:

    “Controlling for fetal exposure by adding MUF to the model resulted in non-significant associations between water fluoride concentration and FSIQ in both the FF (B=−3.58, 95% CI: −7.83, 0.66, p=.098) and BF groups (B=−1.69, 95% CI: −5.66, 2.27, p=.40). Removing two cases with extreme IQ scores from the models resulted in non-significant associations between water fluoride concentration and FSIQ in both groups (Table S3).”

    Such misrepresentation is disgusting. How do you sleep straight in your bed at night?

    As for your attempt to discuss facemask here – please do not raise distraction like that. In New Zealand, this is simply not a problem.

    But you are only here on suffrage as you have not yet apologised for your lies about our attempted online discussion you refused to fulfil – or your claim I am funded by the Russians. I am not going to tolerate these sort of diversions from you.


  4. Bill, it is completely hypocritical of you to say “You still have not considered dosage or margin of safety” when in fact it is your organisation FAN that always avoids that at issue (or more correctly the issue of exposure as “dosage” is not a relevant term here). In fact, iot6 has been me who has referred to this issue – not you or your crowd FAN.

    I pointed out in my last article – Child IQ in countries with endemic fluorosis imply fluoridation is safe – that most of the studies in FAN’s list of 65 related to situations where endemic fluorosis rife because the F exposure is far too high. I also point out that all these studies implicitly assume that the low “dodge”, low exposure areas are safe. That there is no harm from fluoride at concentrations relevant to community water fluoridation. That is also illustrated in my figure summarising these studies.

    So, please Bill, stop blaming others for your complete lack of consideration of this issue of “dosage” – in fact, your complete covering up the fact that you are promoting studies incorrectly to actually avoid the issue of “dosage.”


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