“Fluoride Harm: Suppressed Science and Silenced Voices” brings together more than 30 internationally recognized scientists, medical professionals, journalists and citizen advocates to expose the hidden health risks and political corruption surrounding water fluoridation. The newly released anthology reveals how powerful interests silenced critics and distorted science to protect a harmful status quo.
By Kathleen M. Thiessen, Ph.D.
Editor’s note: “It Just So Happened” is the title of Chapter 26 of “Fluoride Harm: Suppressed Science and Silenced Voices — A Collection of 21st Century Essays” edited by Hardy Limeback and Karen Favazza Spencer.
“It is irresponsible to promote or encourage uncontrolled exposure of any population to a drug that, at best, is not appropriate for many …. and for which the risks are inadequately characterized and inappropriately disclosed to the public.” — Kathleen Thiessen, Ph.D.
IT JUST SO happened that my first professional assignment following graduate school was to prepare a draft report on fluoride toxicity for the Environmental Protection Agency (EPA). More specifically, this was to be a review of health effects associated with hydrogen fluoride, with an emphasis on airborne releases and exposures. I had joined the Chemical Hazard Evaluation Program of the Health and Safety Research Division of Oak Ridge National Laboratory (ORNL), which was contracted to provide various reports for the EPA.
The scope of my review was eventually expanded, at my request, to include hydrogen fluoride and related compounds, and EPA published my report in 1988 (USEPA, 1988). This was my first significant involvement with the field of human health risk assessment, at a time when literature searches were not as easy to conduct as they are now.
As a newcomer to the field, I didn’t fully appreciate all of the information that I found, and I now know that some of the information available at the time on beneficial effects was incorrect. Nevertheless, that 1988 report pointed out the dependence of chronic health effects on the total fluoride intake from all sources of fluoride, the slower clearance of fluoride and consequent higher risks for people with renal dysfunction, the likelihood that some of the decline in tooth decay attributed to fluoridated water was due to other causes, and that adverse effects as well as beneficial effects should be considered in setting fluoride levels.
At the time that I wrote the EPA report, I was only dimly aware that there was any controversy about water fluoridation. Looking back, I have wondered whether one of EPA’s purposes in commissioning a review of airborne hydrogen fluoride was to provide support for the assumed safety of fluoride exposure. I vaguely remember having seen something about my hometown in South Carolina planning to fluoridate and thinking that was a good thing. Bette Hileman’s special report in Chemical & Engineering News was also published in 1988 (Hileman, 1988), but I didn’t know about it until some years later. Some of the information on adverse effects considered as speculative in the 1980s has in recent years become much better supported, but at that time it was considered not important or not substantiated and certainly less than the benefits to be gained from water fluoridation.
Following my 1980s fluoride project, I worked on other EPA projects for a few years, while still employed with ORNL. EPA published a 1994 report on health effects associated with mercuric chloride which I drafted in the late 1980s, soon after writing the hydrogen fluoride report (USEPA, 1994). I left ORNL in 1989, did some consulting work for a while, and eventually joined SENES Oak Ridge, Inc., Center for Risk Analysis, when the company started in 1992. In 2014 we changed our name to Oak Ridge Center for Risk Analysis, Inc., of which I am now president. Our company is probably best known in the context of radiological risk assessment, but my background in chemical risk assessment at ORNL helped the company take advantage of opportunities in that area as well.
It just so happened that in 1998, a science teacher in the Lee County, Florida, school system sent a letter to the school board asking them to oppose efforts to start water fluoridation in the county. It also just so happened that my father was serving on the school board at that time. Dad sent the teacher’s letter to his daughter, the scientist. I told him that water fluoridation was a done deal, everybody knows that it’s a good thing. But also, for Dad’s sake, I spent my Thanksgiving break looking at the issue, and I sent a letter through Dad to the school board in early December.
It just so happened that by 1998, the Internet was making a large volume of literature readily available to the public, outside of university and technical libraries. Among other things, there were initial reports of increased lead levels in tap water in fluoridated areas, a finding that could have direct implications for a school board in terms of the neurological and behavioral problems already associated with lead exposure in children. In addition, my brief review found a lack of toxicity studies of the actual fluoridation chemicals or of fluoridated tap water as consumed, the observed trend away from fluoridation in many other countries, and the failure of most studies to consider fluoride exposures in terms of individual fluoride intake rather than the fluoride concentrations in local water supplies. Given the wide range of tap water intakes in the population, considering only the fluoride concentrations in public water supplies means that a study will have significant overlap of exposure groups, potentially obscuring differences in health effects with respect to fluoride intake.
I also suggested in my letter that the Lee County School Board contact the Florida health department. At the time, my company was in the late stages of completing parts of the Oak Ridge Dose Reconstruction for the Tennessee Department of Health, assessing the effects on local populations of past chemical and radiological releases from the U.S. government facilities in and near Oak Ridge. I naïvely assumed that the Florida health officials would do a similarly responsible job with respect to questions from their constituents about water fluoridation. Later on, I came to realize that on the subject of water fluoridation, most health departments and public health agencies are not particularly objective. More than 25 years later, Florida’s Surgeon General referred to community water fluoridation as “public health malpractice” and recommended against fluoridating. Florida’s legislature banned fluoridation in May 2025 (Colombini, 2024; Florida DOH, 2024; Baletti, 2025b).
After my brief review of fluoridation in late 1998, my household started buying bottled water, just to try out. I had previously considered bottled water a justifiable expense mostly for beach locations where the tap water tasted pretty bad. But hey, if fluoride might cause bone and joint pain, I didn’t want that. I didn’t really expect to notice any difference from reducing my tap water consumption. It just so happened, however, that I was pleasantly surprised to find that some long-standing health issues disappeared in weeks. Fluoride sensitivity is real, and eminently testable, although there is relatively little recent literature about it. And it just so happened that I ended up having far more energy in my 40s and 50s than in my 20s and 30s, for which I am extremely grateful.
It also just so happened that, following my letter to the Lee County School Board, I began to hear from people around the country, both scientists and non-scientists, many of whom were concerned about possible harms from water fluoridation. One caller just so happened to be from the NRC. I had to ask her whether she meant the Nuclear Regulatory Commission, for whom I had done occasional work, or the National Research Council. It just so happened that she was organizing a committee for the National Research Council, at EPA’s request, for the purpose of evaluating fluoride exposure and toxicity. The committee’s efforts resulted in the 2006 NRC report (Doull et al., 2006). My work for the committee was my first major opportunity to get into the details of fluoride exposure and toxicity since my 1988 EPA report, but with the benefit of much more literature, much better search capabilities, and much more experience on my part.
Out of Scope
“Assessing the efficacy of fluoride in preventing dental caries is not covered in this report” (NRC 2006, p. 14).
“As noted earlier, this report does not evaluate nor make judgments about the benefits, safety, or efficacy of artificial water fluoridation” (NRC 2006, p. 16).
The NRC report considered community water fluoridation only with respect to its contribution to human exposures in the U.S. Specific consideration of either the safety or benefits of water fluoridation was outside the scope of the committee’s assignment (Doull et al., 2006; Carton, 2006). However, we did not say or assume that fluoridation is safe or that fluoride concentrations of 0.7-1.2 mg/L (the range recommended at the time) in drinking water are safe. We specifically addressed EPA’s health-based standard, the Maximum Contaminant Level Goal (MCLG), for fluoride of 4 mg/L, and we concluded unanimously that the MCLG is not protective of human health and should be lowered. This conclusion was based on the best-known (and hardest to deny) effects of dental fluorosis and skeletal fluorosis, along with increased risk of bone fracture, and should have resulted in a lowering of the MCLG by at least a factor of 10 (EPA’s default minimum safety factor).
As of this writing in 2025, neither the MCLG nor the enforceable standard (the Maximum Contaminant Level, also 4 mg/L) has been lowered. Full consideration of the information now available on more sensitive endpoints such as developmental neurotoxicity and carcinogenicity should result in an MCLG of 0, corresponding to no safe level of fluoride exposure.
The NRC report also noted the wide range of water consumption among members of the population; the very high water intake with respect to body mass of population subgroups such as infants, athletes, and outdoor workers; the importance of looking at individual exposures rather than average exposures of groups having different concentrations of fluoride in drinking water, given the potential for significant overlaps in exposure distributions for the groups; the importance of including all sources of fluoride exposure, not just the contribution from drinking water; and the need for further study of the actual fluoride chemicals used in water fluoridation, particularly the silicofluorides. The report considers fluoride to be an endocrine disrupter, and did not rule out a carcinogenic effect of fluoride. Research since the 2006 NRC report has consistently supported the NRC’s findings with regard to the toxicity of fluoride.
It just so happened that the NRC contacted me again in 2008, to help with a report on potential health effects of selected air contaminants in U.S. Navy submarines. One of those contaminants was hydrogen fluoride. The 2009 NRC report, which has largely escaped widespread notice, dealt only with healthy young adult men. Among other things, the report summarizes estimated average exposures associated with a variety of adverse health effects, based largely on the 2006 NRC report and within the range expected in populations served with fluoridated drinking water (NRC, 2009).
Although the NRC’s 2006 report was prepared at the request of the EPA, and EPA “accepted the NRC (2006) findings as the summary of hazard for inorganic fluoride” (USEPA, 2010a, p. i), it appeared that EPA either did not fully read the report or hoped that no one else would read it. The 2006 NRC report concluded that EPA’s drinking water standards are not protective against several adverse health effects, and, supported by the 2009 NRC report, it demonstrates that exposures from fluoridated water overlap with estimated average exposures of groups in which adverse health effects occurred.
By their usual risk assessment procedures at the time, EPA should have identified a “safe” level of exposure and then applied appropriate safety factors to set the drinking water standards; properly done, this would have meant an end to water fluoridation. Instead, however, EPA inappropriately included an assumption of benefit in its assessment of adverse effects,left some of the most important subgroups out of their exposure assessment, allowed no margin of safety whatsoever (USEPA, 2010a; USEPA, 2010b), and to this date has not revised the drinking water standards that the NRC concluded were not protective.
Eventually, the U.S. Department of Health and Human Services (DHHS) changed its recommended concentration of fluoride in drinking water to 0.7 mg/L, instead of the former temperature-dependent range of 0.7-1.2 mg/L. This was an admission that the previous recommended levels of fluoride in drinking water were too high. The revised recommendation simply used the lower end of the previous range, but without demonstrating that the change would in fact bring about a reduction in dental fluorosis, the only adverse effect considered (USDHHS, 2015).
Expert Opinion v. Misinformation
In 2010, it just so happened that the Association of State and Territorial Dental Directors (ASTDD) wrote to the head of my company, suggesting that I was communicating misinformation about water fluoridation and otherwise being unscholarly and unethical in my research. Several years later, we were provided evidence of the involvement of the Centers for Disease Control and Prevention (CDC), the New York State Department of Health, and others in the sending of that letter. Ironically, a paper that ASTDD said I should use with respect to fluoride effectiveness contained essentially the same data as the paper that ASTDD objected to my using. Both papers used data from a 1986-1987 survey which, in fact, show essentially no difference in caries experience with respect to fluoride concentration in drinking water, but a very clear dose response for both prevalence and severity of dental fluorosis (Heller et al., 1997; Iida and Kumar, 2009). I just wasn’t supposed to point this out.
It also just so happened that for several years, including the time period in which the NRC reports were prepared, I did a considerable amount of contract work for the Radiation Studies Branch of the CDC, representing them in projects at the International Atomic Energy Agency. Naturally, I felt a certain amount of gratification that while the CDC’s Oral Health Division and others were hoping to derail my career, the Radiation Studies Branch of the CDC was sending me to Europe twice a year.
In 2015, it just so happened that I co-authored a paper that examined the significant financial benefit commonly attributed to water fluoridation, along with several key papers underlying the estimates of caries reduction attributed to water fluoridation (Ko and Thiessen, 2015). In fact, benefits are minimal at best, and many costs of fluoridating are typically not included.
A few years later, it just so happened that I was asked to serve as an expert witness for plaintiffs in a lawsuit against the EPA regarding the risk of developmental neurotoxicity from use of fluoridation chemicals in drinking water, a use that potentially exposes 200+ million people in the United States. After several rounds of reports and depositions and two trials, the judge’s ruling in September 2024 concluded that water fluoridation poses an unreasonable risk of injury, and EPA is obligated to regulate it (Chen, 2024). This case would not have been necessary had EPA followed its own risk assessment procedures any time from the 1980s on. EPA’s actual response to the court ruling is still to be seen.
Conclusion
I could not have planned my professional career in the way it turned out, even if I could have imagined it in advance. Providentially, it just so happened that I had the qualifications and experience necessary to contribute to the NRC reports, and later to testify against the EPA. I have simply tried to do a responsible job with the opportunities and challenges in front of me, especially where my efforts could improve the lives and health of others.
“Whatsoever thy hand findeth to do, do it with thy might.” (Ecclesiastes 9:10a)
“And who knoweth, whether thou art come to the kingdom for such a time as this?” (Esther 4:14b)
“The sixth commandment requireth all lawful endeavors to preserve our own life, and the life of others.” (Westminster Shorter Catechism 68. A.)
Kathleen M. Thiessen, Ph.D., has worked in the field of human health risk assessment for more than 35 years, including evaluation of exposures to and health risks from chemical and radiological contaminants. She wrote two reports for the U.S. Environmental Protection Agency, including one on the health effects of hydrogen fluoride and related compounds. She has served on two National Research Council subcommittees, one charged with the review of fluoride exposure and toxicology, and one dealing with guidance levels for air contaminants in submarines, including hydrogen fluoride. Thiessen was involved in the reconstruction of exposures, doses, and health risks to off-site individuals associated with historic releases of contaminants from the U.S. Department of Energy’s Oak Ridge (Tennessee) facilities. She also contributed to the development of a risk-based screening approach to prioritize further investigation of contaminants and exposure situations in various assessment contexts. Thiessen has led several working groups in the International Atomic Energy Agency’s programs on environmental transport modeling. She has also been involved in litigation support for several cases involving chemical or radionuclide contaminants; she recently served as an expert witness for plaintiffs in a federal case involving fluoride toxicity.
Original article online at: https://childrenshealthdefense.org/community/suppressed-science-and-silenced-voices-book-political-corruption-water-fluoridation-chapter-26-thiessen/