More nails in the coffin of the anti-fluoridation myths around IQ and hypothyroidism


Large Canadian study finds no effect of fluoridation on thyroid health

A new Canadian study shows no relationship of cognitive deficits or diagnosis of hypothyroidism with fluoride in drinking water. This work is important because it counters the claims made by anti-fluoride campaigners. While the campaigners cite scientific studies to support their claims, those studies are usually very weak, or irrelevant because they involve areas of endemic fluorosis where drinking water fluoride concentrations are much higher than in situations where community water fluoridation (CWF) is used.

The study is reported in:

Barberio, A. M. (2016). A Canadian Population-based Study of the Relationship between Fluoride Exposure and Indicators of Cognitive and Thyroid Functioning; Implications for Community Water Fluoridation. MSc Thesis, University of Calgary

This new study is important as it has the advantages of using a large representative sample of the Canadian population, with extensive data validation and quality control measures. It also uses individual-level estimates of fluoride exposure on the one hand, and thyroid health and cognitive problems on the other.

Fluoride exposure was measured both by concentration in tap water for selected households and concentration in urine samples from individuals.

Thyroid health

The Canadian study found:

“Fluoride exposure (from urine and tap water) was not associated with impaired thyroid functioning, as measured by self-reported diagnosis of a thyroid condition or abnormal TSH level.”

This contradicts the conclusions from the population-level study of Peckham et al., (2015) which reported that fluoridation was correlated with the prevalence of hypothyroidism. That study is quoted extensively by anti-fluoridation activists but has been roundly criticised because it did not include the influence of confounders – particularly iodine which is known to influence thyroid health.

Barberio (2016) also suggests that the different recommended fluoride concentrations used for CWF in Canada and the UK, and the fact that the Peckham et al (2015) study did not involve individual measures, could also be factors in the different findings.

Cognitive functioning

The Canadian study reported:

“Fluoride exposure (from urine and tap water) was not associated with self-reported diagnosis of a learning disability.”

Barberio (2016) did also investigate a more detailed diagnosis for cognitive problems and found:

“Higher urinary fluoride was associated with having ‘some’ compared to ‘no’ cognitive problems . . . . however, this association:

  • Was weak;

  • Was not dose-response in nature; and

  • Disappeared when the sample was constrained to those for whom we could discern fluoride exposure from drinking water.”

I guess anti-fluoride activists might latch on to this last point regarding urinary fluoride but, at least as far as tap water fluoride is concerned, there was no relationship with learning difficulties.


So – yet another large-scale study contradicts anti-fluoridationist claims. It shows that CWF has no influence on cognitive problems or thyroid health.

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3 responses to “More nails in the coffin of the anti-fluoridation myths around IQ and hypothyroidism

  1. Great piece, Ken!

    If Connett and his followers want to exploit this last point as being some sort of support for their position, fine, they will then have to accept the finding of no adverse effect on the thyroid. The Fluegge diabetes study which the antis all jumped on initially because, as usual, they only read the study title, was a somewhat similar two-edged sword, with the edge supporting fluoridation far sharper than the dull edge which seemed not to do so. While the study title proclaimed a link berween fluoride and diabetes, a brief read of the study revealed the finding that communities utilizing HFA to fluoridate, had less incidence of diabetes. Once the antis were educated on this point, their mention of this study disappeared like a wisp of smoke in a windstorm. The only ones who still attempt to use it are one or two of the most unscrupulous antis who plaster verbatim dishonest nonsense all over the internet.

    It also reminds me of a Canadian bottled water dealer who is a regular online commenter. He constantly disparages Health Canada because of its support for fluoridation. He foolishlishly went so far recently to proudly proclaim that he does not follow the recommendations of Health Canada, an astounding statement in view of the fact that he sells water that is ingested by the Canadian public. So, anyway, when it has been pointed out to him that the level of the known neurotoxin BPA in the plastic bottles in which he sells his water, is deemed to be safe because Health Canada has verified this, he is in a quandry……of which I have most certainly not allowed him out. Either HC is incompetent as he has repeatedly proclaimed, in which case his BPA levels have no validation, or HC is competent, in which case he must accept their validation of fluoridation along with the validation of his BPA levels.

    The blatant hypocrisy of antis is frequently exposed with their highly selective cherry-picking of opinions, studies, and quotes plucked from the scientific literature.

    Steven D. Slott, DDS


  2. I hope the author publishes the findings.


  3. That is the intention, Linda. In fact the thesis includes two draft papers for submission. One on cognitive effects and one on thyroid health.


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