Australian study of fluoridation neurotoxicity: Streetlight Effect Fallacy

Researchers looked in the wrong place. Couldn’t find IQ loss that other studies found.

Mutt & Jeff by Bud Fisher, June 3, 1942.

In a classic Mutt & Jeff comic a drunk is crawling around on the ground under a streetlight, looking for his dropped coin.  A cop asks, “Did you drop it here?” and the drunk replies “No, but the light is better here!” 

Insensitive And Unreliable Measures Of Neurotoxicity

A just-published Australian study claims to have found no link between fluoridation and harm to children’s developing brains but didn’t use any IQ tests [Do 2022].  Instead, it used parent questionnaires of child behaviors which have been found to be relatively insensitive to detecting harm from fluoride and other neurotoxic chemicals. 

The study’s lead author, dentist Dr. Loc Do of Queensland University, Australia, used two parent questionnaires to see if he could detect the same neurotoxic effects in Australian children that numerous other studies have found in Canada, Mexico, China, and elsewhere.  But those studies all used standard IQ-type tests.  Do’s study instead used a Strengths and Difficulties Questionnaire (SDQ), which is not a measure of intelligence or cognitive ability but is “a 25-item brief behavioral screening tool that measures children’s behaviors, emotions, and relationships.”  For example, it asks parents whether their child can be described as “Kind”, “Lies”, “Bullied”, “Shares”, “Unhappy”, “Helps”, “Clingy”, and other items having little relationship to IQ [Ribeiro Santiago 2021]. 

Furthermore, one of the two psychologist co-authors with Do published a different paper just last year that recommended against using the SDQ in Australian children because of poor validity.  Her paper concluded: “In summary, the presence of a weak and unstable structure … and poor stability … prevents us from recommending the caregiver-informant SDQ for children … in Australia.” [Ribeiro Santiago 2021]. Why did Do choose an outcome measure that his own co-author recommended against using?  What’s more, in the only previous fluoride neurotoxicity study that used the SDQ questionnaire to try to assess ADHD symptoms, the SDQ hyperactivity subscale found only small or non-significant associations with fluoride while actual diagnosis of ADHD was strongly associated with water fluoride concentration and fluoridation status. Reported ADHD diagnoses were almost 300% greater amongst adolescents in fluoridated areas compared to non-fluoridated areas of Canada [Riddell 2019]. 

The other parental questionnaire Do used, the Behavior Rating Inventory of Executive Function (BRIEF), is equally problematic for trying to detect neurotoxicity.  It has never been used to assess fluoride neurotoxicity.   Furthermore, in the only study where BRIEF was compared to typical IQ-type tests to assess neurotoxicity of a chemical, BRIEF couldn’t detect any harm [Wright 2006].  In the same study, however, standard IQ-type tests were able to detect neurotoxicity. 

Like the drunk and the Streetlight Effect Fallacy, Do seems to have ignored the obvious “place” to look for fluoride’s neurotoxicity, which is with its effect on IQ and cognition.  Over 70 studies have used IQ-type tests and almost all have found adverse effects, including at the same doses as occur from fluoridated water in Australia [FAN webpage list]. Do’s study is an extreme outlier.  Over two dozen of the studies finding an effect were rated high quality by the US National Toxicology Program [Neurath 2022].  Instead of looking where he had the best chance of finding an effect, Do chose questionnaires that asked parents about child behaviors like “kindness” and “clinginess”. 

Having found no effect using insensitive measures, Do makes the bold claim: “This finding shows that consuming water with fluoride at levels used for public supplies in Australia is safe and it supports continuing and expanding fluoridation programs.”  This ignores the large number and higher quality studies showing fluoridation is not safe. 

Was Study Designed To Find No Effect?

The choice of insensitive outcome measures raises the question of whether the Do study was designed to not find an effect.  Furthermore, the original grant of almost $1 million was for a study that would assess fluoride’s effect on “intellectual development” but it appears to have abandoned this original purpose. 

Other Weaknesses: Ecological, Didn’t Account For All Fluoride Sources, Inadequate Control Of Confounders

Do’s study summary for his grant claimed his study would provide “high quality evidence” on fluoridation and intellectual development.  However, it has additional important shortcomings compared to recent studies that found adverse neurotoxic effects.  Do’s study, instead of using an individual-level measure of fluoride exposure, used a group-level measure (also called an ecological measure), and only tried to account for fluoride from fluoridated water, rather than all sources.  This is an important weakness compared to the best studies, which either used the biomarker of urine fluoride concentration which reflects fluoride exposure from all sources, or used combined estimates of fluoride intake from drinking water and tea [Goodman 2022Cantoral 2021Farmus 2021Wang 2021Yu 2021Zhao 2021Till 2020Wang 2019Green 2019Riddell 2019Bashash 2018Bashash 2017Valdez-Jimenez 2017]. Tea has been found to be the second largest source of fluoride exposure after fluoridated water, even in a country with much lower tea consumption than Australia [Helte 2021].  The inability to account for all sources of fluoride exposure in the Do study likely further reduced the study’s ability to detect an effect of fluoride. 

Another weakness of the Do study is its lack of control for potentially important confounders, which other recent studies did control for, including: lead, mercury, arsenic, PFOA, parent IQ, HOME score, gestational age, birth weight, parity, marriage status, smoking, alcohol use of mother, and Body Mass Index (BMI). 

Cites Food & Pharma Industry Front-Group’s Bogus Review

More evidence of the author’s bias is found in the Do paper introduction that cites a very biased German review that concludes fluoride has no association with neurotoxicity [Guth 2020].  This is a favorite review of fluoridation defenders.  But the authors of that review are closely associated with a front-group for food and pharmaceutical interests that has a history of claiming chemical food additives, genetically modified foods, and even endocrine disrupting chemicals are no problem [USRightToKnow 2022CorporateEuropeObservatory 2012TestBioTech 2012]. We’ll have more on those authors and their links with industry in a future bulletin. 

Do’s Advocacy For Fluoridation Reveals Bias

Finally, the choice to publish Do’s paper in the fluoridation-friendly Journal of Dental Research (JDR) instead of a journal specializing in neurotoxicity or environmental health, is further evidence the Do study is biased to avoid finding an adverse effect that might threaten fluoridation.  JDR is sponsored by the International Association for Dental Research (IADR), which has had a long-standing official position supporting fluoridation and claiming it is “safe and effective”.  In fact, the latest update of the IADR Position Statement on fluoridation was written by Dr. Do and has outdated and misleading information about adverse effects [IADR 2021]. 

The Streetlight Effect Fallacy may explain how this Australian study failed to find harm to the brain from fluoridation, but another proverb summarizes what appears to be the attitude of the researchers, and of all fluoridation defenders who are trying to deny the strong scientific evidence that fluoride harms brains: See no evil, hear no evil, speak no evil… about fluoridation.