Excess fluoride linked to cognitive impairment in kids, massive study finds

Fluorine is perhaps one of the most controversial elements on the periodic table. Its fluoride form is commonly added to drinking water as a way to prevent tooth decay, yet has become the source of numerous conspiracy theories, spread by people who question the government's true motives behind a public health initiative. In fact, such doubts were sown almost as soon as fluoridation programs began rolling out in the 1940's, with The John Birch Society peddling a crackpot theory that fluoride transforms people into communists.

There are some potentially negative health effects from ingesting too much fluoride — just as there are risks to drinking too much water or taking too much vitamin C. As the saying goes in toxicology: dosis sola facit venenum — the dose makes the poison. But without going off the deep end, how serious are these risks really? And are they outweighed by the close connection between dental health and the health of the rest of your body?

The National Toxicology Program (NTP) released a long-awaited fluoridation report last week, reporting that fluoride levels at twice the recommended limit are linked to lower IQs in kids. This is a long way from confirming the anti-fluoride conspiracy theories made famous by classic movies like "Dr. Strangelove," in which Gen. Jack D. Ripper says "Do you realize that fluoridation is the most monstrously conceived and dangerous communist plot we have ever had to face?"

It's probably safe to say that fluoride doesn't possess such extreme properties. Nonetheless, the new systematic review raises a provocative question: How concerned should people be about mass fluoridation?

After reviewing the scientific literature about connections between fluoride exposure and possible neurodevelopmental and cognitive consequences, the NTP scientists — who ultimately work for the Department of Health and Human Services — concluded that eight of the nine high-quality studies on cognitive and neurodevelopmental ailments and fluoride found "reported associations with estimated fluoride exposure."

Out of 19 high-quality studies examining links between fluoride exposure and child IQs, "18 reported an inverse association between estimated fluoride exposure and IQ in children." Those 18 studies were conducted in five different countries, including three prospective cohort studies (or studies that follow a group of people over a long period of time) and 15 cross-sectional studies (or studies that analyze data from a large population during a single point in time).

Overall the NTP report included studies of varying quality from Canada, China, India, Iran, Mexico and Pakistan, with dozens of papers being flagged as "low-quality" for methodology flaws or lacking sufficient rigor in their data. The NTP concluded that drinking water with more than 1.5 milligrams of fluoride per liter is consistently linked with children having lower IQs. Although the report did not specify how many IQ points can be lost due to excess fluoride exposure, some of the reviewed studies suggested the drop would fall between two and five points.

What the report does not do, according to the authors, is "address whether the sole exposure to fluoride added to drinking water in some countries (i.e., fluoridation, at 0.7 mg/L in the United States and Canada) is associated with a measurable effect on IQ." That means correlation does not always equal causation and they further state that they can't "provide a quantitative estimate of the number of IQ points lost for a given increase in fluoride exposure measures." It's not as clear cut it being that if a person drinks a certain amount of fluoride, they will get a worse report card in school.

"The NTP monograph concluded that higher levels of fluoride exposure, such as drinking water containing more than 1.5 milligrams of fluoride per liter, are associated with lower IQ in children," NTP Director Dr. Rick Woychik said in a statement. "The NTP review was designed to evaluate total fluoride exposure from all sources and was not designed to evaluate the health effects of fluoridated drinking water alone. It is important to note, however, that there were insufficient data to determine if the low fluoride level of 0.7 mg/L recommended for U.S. community water supplies has a negative effect on children’s IQ."

Dr. Mattias Öhman, an economist and researcher at the Institute for Housing and Urban Research at Sweden's Uppsala University, praised the study to Salon and said it is consistent with other research on fluoride use. Notably, Öhman's past research has found that fluoride use has a positive effect on dental health.

"Based on the results from our study, as far as I know still the largest sample with reliable data with good identification/methodology, one should not be concerned with levels below 1 mg/l (and most likely as far as it is below 1.5 mg/l)," Öhman said. "We did not find negative effects even for higher levels, however for these levels our sample is scarce and should be interpreted with caution."

Öhman emphasized that people should not respond to the NTP report by becoming anti-fluoridation. "Fluoridation within the limit is good for dental health with no (known) negative health effects – at least not IQ," Öhman said. "However, 'too much' is never good and would not be good for dental health, etc."

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Dr. Philippe Grandjean, a scientist of environmental medicine at the University of Rhode Island, has also done extensive research into fluoridation but he believes that the NTP report was "unusually modest and fails to recognize the substantial and negative public health impact of fluoride."

The report mentions some of Grandjean's research, criticizing a 2012 study he co-authored for excluding "studies with individual-level measures of exposure" and not being "able to perform a formal dose-response analysis. Although software used for the meta-analysis was reported, the study lacked a predefined protocol." Grandjean told Salon that, among other things, fluoridation is unnecessary because people can access fluoride through other methods.

"Fluoridation is an outdated method to prevent caries, as the beneficial effect is in the oral cavity, i.e., on the surface of the teeth," Grandjean said. "Fluoridated toothpaste (and similar local treatment) is a much better solution, but don’t swallow the toothpaste!"

Grandjean argued that fluoride is toxic to humans' central nervous systems, particularly in small children and fetuses because their brains are experiencing critical stages in their development.

"Pregnant women and those who prepare milk substitute for babies should therefore avoid fluoridated drinking water and waters with high 'natural' fluoride content, including some types or bottled water," Grandjean said. "Certain types of black tea are also high in fluoride and should be avoided by pregnant women." When Salon questioned the NTP's use of IQ tests to monitor brain health, given how IQ tests are widely viewed as unscientific, Grandjean pointed to research by the Environmental Protection Agency (EPA) on IQ scores and overall success in life. He argued that higher IQs correspond to higher incomes and better performance in schools, although it remains unclear whether that is due to cause-and-effect or entrenched class differences.

"The U.S. EPA considers a loss of 1 IQ point to be a 'critical' effect," Grandjean said. "Comparisons between children exposed to high and low fluoride levels in drinking water have shown an average of 6-7 lower IQ levels in the highly exposed children. This was our conclusion in our report from 2012, which is essentially confirmed by the NTP report. The EPA has previously regulated other toxic substances, such as lead and mercury, due to their adverse effects on brain development. Allowing fluoride addition to drinking water therefore questions the governmental reasoning in regard to the protection of the next generation’s brain health."

Grandjean added that "public authorities have prevailed for decades in recommending fluoride intake from drinking water, despite the increasing evidence that fluoride is toxic to the brain. With the advent of fluoridated toothpaste, other countries without fluoride in the drinking water have similar caries occurrence as the U.S. So the dental health advantage of fluoride addition is, at best, minimal and certainly questionable and cannot overrule the well-documented neurotoxicity."

By contrast, Öhman pointed to his own research as well as studies conducted by the military, all of which underscore the efficacy of fluoride in protecting dental health.

"In Aggeborn & Öhman (2021), we know that the reliability of the test used in the military is of very high quality and is regularly used in research and confirmed by psychologists," Öhman said. "And as you may know, we didn’t find negative effects in our study." He argued that a lot of the studies finding evidence of negative effects from fluoride use were low quality "which was one of the reasons that we conducted our study, and I recognize many of these studies in the systematic review. I am a bit surprised that our study was not included."

One glaring omission from the report is the supposed mechanism behind fluoride's potential harm. If fluoride in high doses is harmful to the brain, how does it cause this damage?

"Human mechanistic studies were too heterogenous and limited in number to make any determination on biological plausibility," the authors state, essentially saying we don't know yet. "The body of evidence from studies on adults is also limited and provides low confidence that fluoride exposure is associated with adverse effects on adult cognition."

The underlying question, when it comes to fluoridation, is whether the kooky claims about "bodily fluids" lampooned by Stanley Kubrick in "Dr. Strangelove" bear any relationship to the more sober assertions from scientists. A critic can express valid reservations about fluoridation without being on the fringe, yet at the same time the NTP's systematic review itself acknowledged that the vast majority of the studies linking fluoridation to neurological problems are low-quality. In the end, the NTP report leaves much of the fluoridation question open to debate, although it at least reaffirms that fluoride use is good for your teeth. The question which remains regarding exposure limits, underscoring the need for more research.