The 52 IQ studies used by anti-fluoride campaigners

Slide number 30 from Paul Connett presentation prepared for a talk at NZ Parliament buildings in February 2018.

Continuing my critique of the presentation prepared by Paul Connett for his much-publicised meeting at Parliament Building in February. The meeting attracted only three MPs but his presentation is useful as it presents all the arguments anti-fluoride campaigners rely on at the moment.

My previous articles on this presentation are Anti-fluoride activist commits “Death by PowerPoint” and Paul Connett’s misrepresentation of maternal F exposure study debunked.

In this article, I deal with the argument presented in the slide above. it is an argument repeated again and again by activists. Connett has posted a more detailed list of these studies and his description of them in Fluoride & IQ: The 52 Studiesat the Fluoride Action Network website.

Studies in areas of endemic fluorosis

All the 52 studies comment refers to are from regions of endemic fluorosis in countries like India, China, Mexico and Iran where dietary fluoride intake is above the recommended maximum level. People in these areas suffer a range of health problems and studies show cognitive deficits as one of them. However, a quick survey of Google Scholar shows this concern is well down the list (See Endemic fluorosis and its health effects). Only 5% of the Google Scholar hits related to health effects of endemic fluorosis considered IQ effects.

People in high fluoride areas where fluorosis is endemic suffer a range of health problems. Credit: Xiang (2014)

In, most, but not all, cases the major source of fluoride in the diet is drinking water with high fluoride levels (above the WHO recommended 1.5 mg/L). Paul Connett’s logic is simply to extrapolate to low drinking water fluoride concentrations typical of community water fluoridation (CWF). However, we do not see the other health effects like severe dental fluorosis, skeletal fluorosis, etc., where CWF is used.

His logic also ignores the possibility that cognitive deficits may result from other health problems common in areas of endemic fluorosis. Problems such as premature births and low birth weight, skeletal fluorosis or even the psychological effect of unsightly teeth due to severe dental fluorosis.

Comparing “high” fluoride villages with “low” fluoride villages

This approach is simplistic as it simply compares a population suffering fluorosis with another population not. Yes, the underlying problem is the high dietary intake (mainly from drinking water) in the high fluoride villages – but that does not prove fluoride in drinking water is the direct cause of a problem. The examples discussed above, eg., low birth weights or premature births, could be the direct cause.

It is easy to show statistically significant differences of drinking water fluoride and a whole host of fluorosis related diseases between two villages but that, in itself, does not prove that drinking water fluoride is the direct cause. Nor does it justify extrapolating such results to other low concentrations situations typical of CWF.

Paul Connett’s logic ignores the fact that in most of these studies the “low” fluoride villages (which the studies were treating as the control or normal situations where IQ deficits did not occur) had drinking water fluoride concentrations like that used in CWF. It also ignores, or unjustly attempts to dismiss) studies which show no cognitive deficits related to CWF.

A low fluoride concentration study showing an IQ effect

After making a big thing about the large numbers of studies and being challenged by the high fluoride concentrations involved Connett normally goes into a “yes, but” mode and attempts to transfer that credibility of “large numbers” to the very few studies which report effects at low fluoride concentrations.

He usually makes a big thing of the study by Lin et al (1991):

Lin Fa-Fu, Aihaiti, Zhao Hong-Xin, Lin Jin, Jiang Ji-Yong, M. (1991). THE RELATIONSHIP OF A LOW-IODINE AND HIGH- FLUORIDE .ENVIRONMENT TO SUBCLINICAL CRETINISM lN XINJIANG. Iodine Deficiency Disorder Newsletter, 24–25.

Connett claims this study shows a lower IQ when the drinking water F concentration was 0.88 ppm, but the areas suffered from iodine deficiency which is related to cognitive deficits.

The study I reviewed recent by Bashash et al (2017) (see Paul Connett’s misrepresentation of maternal F exposure study debunked) is also on Connett’s list. He doesn’t mention, however, that while an association of child IQ with prenatal maternal urinary fluoride was reported the paper also reported there was no observed association of child IQ with child urinary fluoride concentrations.

Studies not showing an effect

Connett lists 7 studies which showed no effect on IQ. One of these was the well-known Broadbent et al., (2014) study from New Zealand, which he, of course, proceeds to debunk in an irrational and not very truthful manner.

He does not mention the studies from Canada (Barberio et al. 2017 ) and Sweden (Aggeborn & Öhman 2016) which also show no effect of CWF on IQ.

The 6 other studies listed are all Chinese, and not translated. Interesting because Connett’s Fluoride Action Network invested money and time into translating obscure Chinese papers that could support their argument of harm. They obviously did not bother translating those papers which did not confirm their bias.


So, Connett’s 52 studies are rather a waste of time. Based in areas of endemic fluorosis their findings are not transferable to areas where CWF is used. The quality of most papers is low and, usually, the studies are simply a comparison of two villages, one where fluorosis is endemic and the “control” village where it isn’t but drinking water concentrations are like that used in CWF.

Connett simply is not able to properly evaluate, or in some cases even consider, studies which show no effect of fluoride on IQ or were made in areas where CWF exists and no effects are shown.

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One response to “The 52 IQ studies used by anti-fluoride campaigners

  1. Pingback: Anti-fluoridationists rejection of IQ studies in fluoridated area. – The Science Page

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