This past August (2019), a prospective cohort study by Green et al. was published in JAMA Pediatrics, a well-respected, high impact medical journal, entitled “Association Between Maternal Fluoride Exposure During Pregnancy and IQ Scores in Offspring in Canada“. Steve Novella covered it on SBM previously (I encourage you to read through it before finishing this post); in a nutshell, the study claimed that maternal exposure to fluoride while pregnant results in a small but significant decrease in a child’s IQ at 3-4 years of age. Dr. Novella addressed the study, some of the flaws therein, and how the scientific community immediately criticized the paper.

As a dentist, I took a special interest in the study. I have written about fluoride and fluoridation before in SBM (here, also here, and also also here), so anytime new research comes out, I am keen on seeing what it has to say. It’s no secret that I am pro-fluoride; the evidence for benefit in conjunction with its low risk and cost is overwhelming. That said, I am also open minded enough to objectively evaluate new claims. I am not beholden to fluoride and fluoridation as an ideology, nor do I receive huge checks from the Fluoride Lobby that critics seem to think is lurking in dark alleyways. Fluoride is simply one tool among many we employ to fight the most prevalent disease in children and adolescents. If solid evidence overturned current thinking – either challenging the efficacy of caries (tooth decay) prevention or the safety of fluoride at proper doses – I would be on the forefront to not only change my stance but to educate my patients, community, and the public. That is why I wanted to ensure that the scientific community’s response to the JAMA Peds paper was sound, thorough, and based upon data, not merely a knee-jerk emotional reaction to the questioning of established doctrine.

The first wave of response by experts was swift and concise, pointing out many of the concerns that scientists and health care professionals had about the study’s methodology and statistical analysis. Some of the findings (e.g. why was there an IQ drop only in one sex?) seemed to be incongruous and defied plausibility, while some aspects of the methodology (e.g. the accuracy of self-reporting of fluoride intake is questionable, as well as possible “p-hacking“) seemed suspect. Of course, it must be stated that just because some aspects of a study are questioned or challenged doesn’t automatically make it invalid or wrong. That is the purpose of peer review and transparency in research. Put the findings under the microscope, see if they hold up to scrutiny, and replicate them if possible. That is what was done in this case, and after the initial response, a more in-depth follow-up challenge was launched – but more on that later.

Of course, the anti-fluoridationists are screaming foul. They are accusing those of us who are challenging the study of summarily rejecting the findings simply because it goes against our pre-established dogmatic stance on the subject. They believe that we are either willfully ignorant or are in some way part of a conspiracy. Unfortunately, the feeling is for the most part mutual, which makes it difficult if not impossible to engage in any sort of respectful, meaningful dialogue with critics.

Checks and balances

One of the main tenets of the scientific process is that no hypothesis or theory should shy away from interrogation and critique. If it can stand up to rigid scrutiny, then it becomes part of the scientific canon and be used to advance the boundaries of human knowledge and utility. If it withers under the light of inquisition, that too is a good thing, because not only will we not base future endeavors upon shaky foundations, but our valuable and finite resources (time, talent, and money) can be directed in more fruitful and promising directions. These “checks and balances” keep the arc of scientific progress moving forward, sometimes by leaps and bounds but more commonly in fits and starts, progress gained and lost, false starts and false hopes, serendipitous discoveries, followed by incremental victories.

Recognizing the importance and impact the Green et al. paper could have in policy as well as personal decisions, on October 23rd 2019, a group of thirty concerned health care professionals and scientists drafted a letter to Rick Woychik, PhD, Acting Director, National Institute of Environmental Health Sciences (NIEHS) and Gwen W. Collman, Ph.D. Acting Deputy Director of the same institute. The NIEHS provided funding for the Green et al. study, and we felt it was imperative to express our concerns to this body, not because the conclusions did not meet with our approval, but because there was a lack of transparency in the data they used as well as fundamental statistical errors in analyzing the data. Our letter to the NIEHS:

…[requested] that NIEHS formally ask the Green authors to release the HIPAA-compliant, Research Identifiable File (RIF) data sets from their study, as well as a complete explanation of their methods and the computer program/codes used in their data management and analysis.

As of this post no release of data has been forthcoming, but we hope that will change in the upcoming days and weeks. If the data can be independently analyzed (and I’m confused as to why the authors would want to withhold the data), it could shed light on the validity and applicability of the research. As a dentist, a parent, soon-to-be grandparent, and all-around science guy, I want to see what the data really show. If the findings of the Green paper are confirmed and maternal fluoride intake is indeed harmful to cognitive development in young children, what should be done about it? I would certainly follow the evidence wherever it leads and adjust my thinking and practice accordingly. However, if the re-analysis refutes the initial findings, parents (and prospective parents) can breathe easier, knowing that their li’l nuggets aren’t having their precious bodily fluids sapped and impurified. And if the erstwhile flawed study winds up being used by municipalities to support discontinuation of community water fluoridation (or to prevent fluoride from being added to the water in the first place), it could have significant public health implications, as we have already seen in Calgary.


Since our letter was sent to the NIEHS last week, there have been a few developments, with more rolling in daily. Here are some of the more significant ones as of publication, but I encourage you to stay abreast on future developments by following us on social media (especially Twitter):

  1. We received an initial response from the NIEHS, which read in part:

    Thanks very much for your letter to Drs. Woychik and Collman, and the detailed information you provided regarding the Green et al. MIREC study. Your letter was carefully reviewed and then was forwarded to the NIEHS Office of Communications and Public Liaison for response.

    Please know that the NIEHS does encourage the sharing of data when we have supported its collection. We are currently working to understand the challenges and barriers to sharing data from this study.

    This is promising and shows a willingness by the NIEHS to be scientifically rigorous in their funding processes and review.

  2. A leading Canadian health agency has completed an evaluation of the article written by Green et al. Last week, the Canadian Agency for Drugs and Technologies in Health (CADTH) published a report evaluating the Green study. CADTH’s evaluation reached this conclusion:

    The evidence is weak due to multiple limitations (e.g., non-homogeneous distribution of data, potential errors and biases in the estimation of maternal fluoride exposure and in IQ measurement, uncontrolled potential important confounding factors); therefore, the findings of this study should be interpreted with caution.

    If you would like to read the CADTH evaluation, it is accessible at

  3. The National Post (one of Canada’s largest newspapers) wrote an article about the NIEHS letter. The link is below. The story includes this quote from Dr. Joe Schwarcz a chemistry professor at Montreal’s McGill University: “What are you hiding? Whoever owns the data should be willing to release it.” If you would like to read the Post article, the link is:


Blog posts like this one serve two overarching purposes. The first is to report the news, as it were, so that the readers of SBM can stay current on developments that could impact them and the public at large. The second is to show the important role the science-based community plays in fact checking published research, pushing back against dubious claims and flawed methodologies, and flat out fighting against pseudoscience. Often it feels as though we are losing the battle and it’s easy to get discouraged, but through coordinated efforts such as the one I’ve described, involving people from scientific disciplines across the spectrum in a short period of time, we can mobilize in a common and unified effort that suggests that there is hope for science and critical thinking after all.



Posted by Grant Ritchey

A Science-Based Dentist. Co-host of the Prism Podcast with Clay Jones, where we analyze the spectrum of scientific, rational, and critical thought. Find us on Twitter: Grant: @skepticaldds Clay: @skepticpedi Prism Podcast: @prismpodcast