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US Court To Decide Whether Fluoride In Drinking Water Lowers IQ

There's no current evidence to suggest that low levels of fluoride pose a health risk.

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Ben Taub

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Ben Taub

Freelance Writer

Benjamin holds a Master's degree in anthropology from University College London and has worked in the fields of neuroscience research and mental health treatment.

Freelance Writer

Edited by Laura Simmons
Laura Simmons - Editor and Staff Writer

Laura Simmons

Editor and Staff Writer

Laura is an editor and staff writer at IFLScience. She obtained her Master's in Experimental Neuroscience from Imperial College London.

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Fluoride drinking water

Fluoridation of drinking water dramatically reduces tooth decay.

Image credit: New Africa/Shutterstock.com

A legal battle over the safety of adding fluoride to drinking water in the US is currently in full swing, with plaintiffs arguing that the chemical poses a threat to the neurodevelopment of children. Judge Edward Chen of the US District Court for the Northern District of California has been hearing expert testimony since January 31, and could order the Environmental Protection Agency (EPA) to ban fluoridation if claimants can prove that the practice is linked to a lowering of IQ.

Fluoride has been routinely added to US drinking water supplies since 1946 in order to protect people’s teeth from decay. However, opponents of the policy have repeatedly pointed to animal studies showing that exposure to high levels of the mineral may lead to cognitive impairment.

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The issue came to a head in 2017 when a group of plaintiffs led by the non-governmental organization Food and Water Watch (FWW) brought an action against the EPA under the Toxic Substances Control Act. The hearing began in June 2020, but Chen halted proceedings shortly afterwards in order to wait for a report by the government’s National Toxicology Program (NTP) to be published.

It is on this report that the case hinges, and while the document has still not been published, Chen has now allowed the trial to resume. 

Initiated in 2016, the NTP assessment consists of a systematic review of all the available data on the neurodevelopmental effects of fluoride exposure in both humans and animals. Overall, the review found “with moderate confidence, that higher fluoride exposure […] is consistently associated with lower IQ in children.”

For instance, of the 19 reliable studies on children included in the review, 18 demonstrated a link between exposure to high levels of fluoride and lower IQ. However, in all such cases, total fluoride exposure was equal to or greater than 1.5 milligrams per liter of water. In the US, however, drinking water contains less than half this concentration, with just 0.7 milligrams of the mineral in every liter.

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Nonetheless, the NTP initially proposed a “hazard classification” for fluoride when it published the first draft of its report in 2019. This was later retracted after peer review by the National Academies of Science, Engineering, and Medicine (NASEM) found that the authors’ conclusions were “not adequately supported.”

In its second draft, the NTP wrote that fluoride’s “effects on cognitive neurodevelopment are inconsistent, and therefore unclear.” However, this statement was left out of the most recent draft, which was presented to the NASEM in September 2022.

Displeased by this omission, the NASEM has requested that the NTP amend the report once again. Specifically, the peer reviewers have asked the study authors to include the following paragraph:

“When focusing on findings from studies with exposures in ranges typically found in drinking water in the United States (0.7 mg/L for optimally fluoridated community water systems) that can be evaluated for dose response, effects on cognitive neurodevelopment are inconsistent, and therefore unclear.”

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The NTP, however, disagrees with this recommendation, and believes the report should simply state that “more studies are needed to fully understand the potential for lower fluoride exposure to affect children’s IQ.”

While these disagreements continue to hold up the publication of the report, Chen has now heard the opening arguments put forward by attorney Michael Connett, representing the plaintiffs. Addressing the court, he reportedly said that infants fed baby formula with tap water represent a “critical vulnerable group being exposed to the highest dose of fluoride of any age group in the population.”

Ultimately, the onus is on the FWW and co to prove that fluoride poses an “unreasonable risk” to the health of fetuses and children. Experts on both sides of the divide are now expected to give evidence over nine days, after which Chen will rule on whether or not the EPA must regulate fluoridation.


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  • tag
  • health,

  • IQ,

  • drinking water,

  • fluoridation,

  • Water fluoridation,

  • fluoride

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