Fluoridation not associated with ADHD – a myth put to rest

Fluoridated water is NOT associated with ADHD: Photo by mtl_moe

The myth of community water fluoridation causing attention deficit hyperactivity disorder (ADHD) is just not supported by the data. I show this in a new paper accepted for publication in the British Dental Journal. This should remove any validity for the claims about ADHD by anti-fluoride campaigners.

Mind you, I do not expect them to stop making those claims.

The citation for this new paper is (will be):

Perrott, K. W. (2017). Fluoridation and attention hyperactivity disorder – a critique of Malin and Till. British Dental Journal. In press.

The Background

The fluoridation causes ADHD myth was initially started by the publication of Malin & Till’s paper in 2015:

Malin, A. J., & Till, C. (2015). Exposure to fluoridated water and attention deficit hyperactivity disorder prevalence among children and adolescents in the United States: an ecological association. Environmental Health, 14.

It was quickly taken up and promoted by anti-fluoride campaigners – becoming one of their most cited papers when claiming harmful psychological effects from fluoridation. Part of the reason for its popularity is that it is the only published paper reporting an association between community water fluoridation (CWF) incidence and the prevalence of a psychological deficit. All other reports on this used by anti-fluoride campaigners are based on studies made in high fluoride regions like China where fluorosis is endemic. Those studies are just not relevant to CWF.

While many critics rejected Malin & Till’s conclusions on the simple basis that correlation does not mean causation I decided to look a bit deeper and test their statistical analyses. This was easy because they used published US data for each US state and such data is available for many factors.

I posted my original findings in the article ADHD linked to elevation not fluoridation. This showed that a number of factors were independently associated with ADHD prevalence (eg., home ownership, poverty, educational attainment, personal income, and % of the population older than 65) and these associations were just as significant statistically as the associaiton reported by Malin & Till.

However, multiple regression of possible modifying factors showed no statistically significant of ADHD prevalence with CWF incidence when mean state elevation was includedd.

The importance of elevation was confirmed by Huber et al. (2015):

Huber, R. S., Kim, T.-S., Kim, N., Kuykendall, M. D., Sherwood, S. N., Renshaw, P. F., & Kondo, D. G. (2015). Association Between Altitude and Regional Variation of ADHD in Youth. Journal of Attention Disorders.

Huber et al., (2015) did not include CWF incidence in their analyses. I have done this with the new paper in the British Dental Journal.

Publication problems

I firmly believe that scientific journals, like  Environmental Health which published the Malin & Till paper, have an ethical obligation to accept critiques of papers they publish (subject to peer review of course). Similarly, it is appropriate that any critique of a published paper is made in the journal where it was originally published. Implicit in this arrangement, of course, is that the authors of the original paper get the chance to respond to any critique and that the response be published by the original journal.

Unfortunately, this was not possible for this paper because the Chief Editor of  Environmental Health,  Prof Philippe Grandjeansimply refused to allow this critique to be considered for publication. No question of any peer reviuew. In his rejection he wrote:

“Although our journal does not currently have a time limit for submission of comments on articles published in EH, we are concerned that your response appears a very long time after the publication of the article that you criticize. During that period, new evidence has been published, and you cite some of it. There are additional studies that would also have to be taken into regard in a comprehensive comment, as would usually be the case after two years. In addition, the way the letter is written makes us believe that the letter is part of a controversy, and our journal is certainly not the appropriate forum for a dispute on fluoride policies.”

My response pointed out the reasons for the time gap (problems related to the journals large publication fee), that no other critique of the Malin & Till paper had yet been published and that any perceived polemics in the draft should normally be attended to by reviewers. This was ignored by Grandjean.

While Grandjean’s rejection astounded me – something I thought editors would consider unethical – it was perhaps understandable. Grandjean is directly involved as an author of several papers that activists use to criticise community water fluoridation. Examples are:

Grandjean is part of the research group that has published data on IQ deficits in areas of endemic fluorosis – studies central to the anti-fluoride activist claims that CWF damages IQ.  He has also often appears in news reports supporting research findings that are apparently critical of CWF so has an anti-fluoridation public standing.

In my posts Poor peer-review – a case study and Poor peer review – and its consequences I showed how the peer review of the original Malin & Till paper was one-sided and inadequate. I also provided a diagram (see below) showing the relationship of Grandjean as Chief Editor of the Journal, and the reviewers as proponents of chemical toxicity mechanisms of IQ deficits.

So, I guess a lesson learned. But the unethical nature of Grandjean’s response did surprise me.

I then submitted to paper to the British Dental Journal. It was peer-reviewed, revised and here we are.

The guts of the paper

This basically repeated the contents of my article ADHD linked to elevation not fluoridation. However, I tried to use Malin &Till’s paper as an example of problems in ecological or correlation studies. In particular the inadequate consideration of possible risk-modifying factors. Malin & Till clearly had a bias against CWF which they confirmed by limiting the choice of covariates that might show them wrong. I agree that a geographic factor like altitude may not have been obvious to them but their discussion showed a bias towards chemical toxicity mechanisms – even though other social factors are often considered to be implicated in ADHD prevalence.

Unfortunately, Malin & Till’s paper is not an isolated example. Another obvious example of confirmation bias is that of Peckham et al., (2015). They reported an association of hypothyroidism with fluoridation but did not include the most obvious example of iodine deficiency as a risk-modifying factor in their statistical analysis

Of course, anti-fluoride campaigners latched on to the papers of Peckham et al., (2015) and Malin & Till (2015) to “prove” fluoridation was harmful. I guess such biased use of the scientific literature simply to be expected from political activists.

However,  I also believe the scientific literature contains many other examples where inadequate statistical analyses in ecological studies have been used to argue for associations which may not be real. Such papers are easily adopted by activists who are arguing for or against specific social policies or social attitudes. For example, online articles about religion will sometimes refer to published correlations of religosity with IQ, educational level or scoio-economic status. Commenters simply select the studies which confirm the bias they are arguing for.

These sort of ecological or corellations studies can be useful for developing hypotheses for future study but it is wrong to use them to support an argument and worse as “proof” of an argument.

Take home message

  1. There is no statistically significant association of CWF with ADHD prevalence. Malin & Till’s study was flawed by lack of consideration of other possible risk-modifying factors;
  2. Be very wary of ecological or correlation studies.Correlation is not evidence for causation and many of these sudues iognore other possible important risk-modifying factors.

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7 responses to “Fluoridation not associated with ADHD – a myth put to rest

  1. Congratulations, Ken, on your persisistence in getting this important piece published. Whether he admits it to himself or not, Grandjean’s actions are no different than the censorship of opposing views exhibited by the majority of little antifluoridationist controlled websites, blogs, “journals”, and other online publications. Not only is it is clear demonstration of the lack of confidence they have that their position can survive under proper scrutiny, but, of the fact that like so many failed ideologues throughout history, they fail to understand that such censorship only hurts their own credibility. In Grandjean’s case, it is yet one more giant step in sending his publication to the moot pile, where it belongs.

    Connett circumventing peer-review by publishing his opinions as a book rather than seeking publication in a respected journal…..antifluoridationists providing as their “evidence” links and redirects to filtered and edited nonsense posted on their own websites instead of citing independent sources of credible information as support for their claims…….applying censorship of opposing information rather than attempting to defend their position on its merits…..selective gatekeeping and obvious bias in publications such as Grandjean’s……….

    …..and antifluoridationists just can’t figure out why respected science and healthcare accords them no credibility?

    Steven D. Slott, DDS


  2. Ken, aside from nullifying a causative link between CWF and adhd, does your paper establish a causative link between altitude and adhd?

    I’ve thus far assumed your investigation just did the former.
    If the later shouldn’t a causative mechanism also be established?


  3. No, Richard. And that was not my intention. In fact, the overall message, using this example, is to warn against drawing these sort of conclsuions from ecological or correlational studies.

    To be fair neither Malin & Till or Huber et al argued anything was proven by the associations they revealed. In fact, Huber et al actually suggested alternative mechanisms.

    But Malin & Till’s qualification is really nothing more than the standard required. They were arguing very strongly for a fluoridation cause and the fact they did not adequately consider other possible covariates reveals their bias. Incidentally, their reviewers were also biased as they only suggest an alternative chemical toxicity fact (lead) be considered.

    Such statistically significant associations should only be used to indicate possible hypotheses. And then only if other risk-modifying factors are included. Considering the poor quality of the Malin & Till investigation I do not think they were justified in advancing any hypothesis or claiming the results supported any selected hypothesis.

    But political activists do not give a stuff about that. Unfortunately, it seems, many scientists who publish such poor work don’t appear to give a stuff either. And I would say the same for some scientific journals and their editors – as the example of Grandjean in not even allowing consideration of a critique of a published paper shows.


  4. Thanks, that’s basically what I had earlier assumed.


  5. Pingback: Anti-fluoridation campaigners often use statistical significance to confirm bias – The Science Page

  6. Funnily enough, home ownership, poverty, educational attainment, personal income, and % of the population older than 65 are also related to the amount of fluoride a person consumes. Those in poverty are significantly more likely to drink fluoridated water than those who are not. Those who own homes are significantly less likely to drink fluoridated water as they are able to install whole house filters. Those with education are less likelu to drink fluoridated water as they are aware of the potential risks, whereas the uneducated do not even know their water is being fluoridated. Those with a higher person income are less likely to consume as much fluoride as those with a lower income. And those above 65 are more likely to consume fluoridated water due to convenience depending om a variety of factors. So in an essence you haven’t disproved much.


  7. Noname – are you just making these associations up or do you have any evidence to support these claims? Please provide citations if you do. Failure to do so will tell me they are your inventions.

    But what you do not seem to realise that any associations that exist between fluoridation and these factors just make simple regression analysis of ADHD with fluoridation (that Malin & Till did) so unscientific. These other factors must be included in the statistical analysis – as I did.

    What usually happens is that the statistical analysis reveals that fluoridation is simply acting as a proxy for the other, more fundamental, risk factors. And multiple regression shows that there is no actual relationship of ADHD to fluoridation itself.

    Perhaps you should read my paper linked to the article.


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