• Spring Hatfield, RDH

The Bad Science in the Study Linking Low IQ Scores and Fluoride Exposure During Pregnancy

On August 19, 2019 I was cooking dinner when I received an alert on my phone. It was from a news outlet; the story was titled "New study raises questions about how fluoride affects children’s development". My first reaction was a heavy sigh and the thought "here we go again". I feel like dentistry has just gotten over the Root Cause hurdle and here we are faced with another hurdle. I am sure other professions have the same level of scrutiny and I certainly don't want to sound like a complainer, but good grief our industry has fought x-rays cause cancer, you don't need to floss, root canals cause cancer, dentists are over diagnosing and over treating and now fluoride is reducing IQ in our children. It is just exhausting. I decided to review this study and see how credible it was.

Just as I finished reading it, I took a break to give my brain a rest scrolling through my Facebook feed I see in one of my hygiene groups a post that states "Watching Inconvenient Tooth. We need to stop water fluoridation NOW!" Great, I just can't avoid it and now some of my colleagues are being influenced by a documentary on YouTube. This documentary has been available on YouTube since 2012. By some miracle I have avoided seeing or hearing about it until now. I decided to watch it and see what compelling evidence was presented that caused educated dental professionals to question the safety of water fluoridation. About 20 seconds into the documentary Paul Connett’s face appeared on my screen, I immediately stopped watching. You may be wondering why I’m going off on a tangent about this documentary, that I didn’t even watch, but I think it is important for everyone to know who Paul Connett is, this will be valid as I go through and point out the shortcomings of the study previously mentioned.

Paul Connett is an activist and prominent critic of water fluoridation. He is well known in science circles for his use of pseudoscience. He is the executive director of Fluoride Action Network (FAN). He has a PhD in chemistry from Dartmouth College. He has a history of involvement in political activism, and he is currently also the director of the American Environmental Health Studies Project. In November 2016 he along with several other organizations filed a citizen petition with the EPA to stop community water fluoridation. You can read the petition here. For the time being I’m going to move on from Paul Connett, I’ll come back to him later and hopefully you will understand why I wanted to make sure you were familiar with him.

The article titled “Association Between Maternal Fluoride Exposure During Pregnancy and IQ Scores in Offspring in Canada” published in JAMA Pediatrics has been the focus of many news stories since it was published. The first thing that caught my eye, before I really read the study was in the results portion of the abstract. It states “A 1mg higher daily intake of fluoride among pregnant women was associated with a 3.66 lower IQ score in boys and girls.” There are two things about these results that are concerning first, we have had community water fluoridation for the past 70 years.[1] If this assessment were true (I’m going to use my immediate family as an example here) we are looking at minimum 2 generations of offspring with lower IQ’s. That would mean my children would have an IQ that is 7.32 points lower than their grandparents. Yet if this were true the statistics wouldn’t show an upward trend in intelligence. Which leads me to the second thing that makes these results seem a little off and that is the Flynn Effect. The Flynn Effect refers to the steady rise in IQ scores over time. James Flynn an intelligence researcher in New Zealand conducted a longitudinal study from 1932 to 1978 to observe IQ levels through the years. He discovered a consistent increase of 0.3 points per year or 3 points per decade. His study was supported when it was replicated. During this study the years 1972 to 2006 were observed for falling or increasing IQ levels, this study confirmed a 0.31 increase in IQ per year which was consistent with Flynn’s earlier findings.[2] So, which is it? Are our children smarter than their grandparents or not?

To dig even deeper into the lower IQ reported, one must consider the margin of error. The margin of error associated with IQ tests are generally a 5-point margin of error, which falls in line with the number of points associated with this study. Considering this margin of error, it is quite possible there was no significant difference at all. Not to mention the IQ scores were well within the normal range with boys in the fluoridated group at 104.78 and girls in the fluoridated group at 111.47.[3]

As you read the study, though the results in the abstract clearly state “A 1mg higher daily intake of fluoride among pregnant women was associated with a 3.66 lower IQ score in boys and GIRLS”, under the discussion portion it states “the association between high MUF concentrations and lower IQ scores was observed in boys but not girls.”[3] This is a perfect example of why you must read the entire study to know the true outcome.

I’m going to move on to the strengths and weaknesses portion of the study. In this section the authors admit “we did not have maternal IQ data”, this is an important point because studies show IQ is influenced by genetics.[4] This is an observational study in which the participants used self-reporting including self-reporting of such things as exposure to second hand smoke. One of the major disadvantages of observational cohort studies, such as this one, is the susceptibility to selection bias. These studies are not randomized, which can lead to bias in every stage of the study, this includes design, conduct, analysis, and reporting. Observational cohort studies are very useful, however there are shortcomings and limitations.[5]

Now, to my favorite part of this study. The “Conflict of Interest Disclosures”. In this portion it states “Dr. Lanphear reports serving as an expert witness in an upcoming case involving the US Environmental Protection Agency and water fluoridation but will not receive payment.” Remember Paul Connett and his organization that filed a petition against the EPA? Well, Dr. Lanphear, one of the authors of this study, will be an expert witness in that very case. As a matter of fact, this lawsuit is led by Michael Connett, the son of Paul Connett. The EPA recently sought to limit the scope of discovery, which was denied. This will allow this study to be admissible as evidence in their case. Coincidence? I’ll let you decide. No matter your thoughts on the relevance of the study, you can not deny the possibility of bias.


1. Centers for Disease Control and Prevention. Community Water Fluoridation. Retrieved from

2. Lisa Trahan, Karla K. Stuebing, Merrill K. Hiscock, and Jack M. Fletcher. The Flynn Effect: Meta-analysis. Psychol Bull. 2014 Sep; 140(5): 1332-1360. Retrieved from

3. Green R, Lanphear B, Hornung R, et al. Association Between Maternal Fluoride Exposure During Pregnancy and IQ Scores in Offspring in Canada. JAMA Pediatr. Published online August 19, 2019. doi:10.1001/jamapediatrics.2019.1729

4. U.S. National Library of Medicine. Genetics Home Reference. Is Intelligence Determined by Genetics? Retrieved from

5. Jae W. Song, MD and Kevin C Chung MD, MS. Observational Studies: Cohort and Case-Control Studies, Plast Reconstr Surg. 2010 Dec; 126(6): 2234-2242. Retrieved from

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