Last May, the National Toxicology Program (NTP), a federal research agency, was set to release its eagerly awaited report into the cognitive and neurodevelopmental impacts on humans from fluoride exposure.

The report was anticipated for several reasons, including its review of studies linking fluoridated water to cognitive harm in children. Water fluoridation is the long-established public policy of adding fluoride to drinking water to fight tooth decay. The report was also set to play a key role in an ongoing lawsuit, filed by government accountability nonprofit Food & Water Watch, to get the Environmental Protection Agency to regulate water fluoridation because of fluoride’s possible neurotoxic harm. More than two years ago, the judge put the case on hold in expectation of the NTP report’s public release.

Before the NTP could release the report, however, “They were blocked,” said Linda Birnbaum, NTP director until 2019. According to Freedom of Information Act (FOIA) records obtained by the plaintiffs and shared with Capital & Main, the U.S. Department of Health and Human Services (HHS) held back the release of the report after criticism of its findings from health and dental organizations that advocate for community water fluoridation. Those groups challenged the report’s scientific validity and expressed concern that it could jeopardize water fluoridation, which they said could especially impact the dental health of low income communities.

The report found that a link between typical levels of fluoride added to water and possible harm to brain development is unclear, with a recommendation for more studies, according to records. But the report did find a possible link to cognitive harm at approximately two times the current recommended water fluoridation level, records show. Some health experts believe this finding makes current water fluoridation levels potentially unsafe for developing fetuses and young children. Because many common foods and drinks contain fluoride, consuming them along with fluoridated water could amount to harmful exposure levels, these experts say.

Leading up to the report’s intended release, individuals from dental organizations including the American Dental Association (ADA) scrutinized the report’s scientific credibility in communications with staff from other dental groups and health agencies including the National Institutes of Health and the NTP, divisions of HHS, records show.

This January, Birnbaum issued a scathing legal declaration as part of the lawsuit, writing, “The decision to set aside the results of an external peer review process based on concerns expressed by agencies with strong policy interests on fluoride suggests the presence of political interference in what should be a strictly scientific endeavor.” Birnbaum said she issued the legal declaration in part over concerns the report might never be publicly released.

The NTP has announced that it will now release the report on March 15, alongside an updated version of the same document that includes the NTP’s responses to what it describes as a “significant number” of comments and criticisms received from experts at various federal health agencies.

Birnbaum, however, remains adamant that the science proves there is “no real benefit” from ingesting fluoride. “The benefit from fluoride is from topical applications,” she said.

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Water fluoridation is described as one of the 10 greatest public health achievements of the 20th century for its part in reducing tooth decay in adults and children by roughly 25%. According to the latest figures, nearly 73% of people connected with community water systems receive fluoridated water, accounting for more than 200 million people, or just under two-thirds of the overall U.S. population. Advocates argue that fluoridation is especially needed in low income communities where rates of tooth decay are generally higher than in wealthier neighborhoods.

At the same time, a growing body of research links fluoride exposure to neurotoxicological impacts in humans, including IQ loss and a higher prevalence of ADHD in children.

The NTP has been working since 2016 on its systematic review of the science into these impacts. By the time the report was set for release last May, it had already undergone more rounds of peer review than is typically the case for such a document, court records show — twice with the National Academies of Sciences, Engineering, and Medicine (NASEM), and external peer review by five experts in the field. According to Birnbaum, similar reports are typically sent out for public comment, peer reviewed by an on-site panel, then finalized by the NTP.

Despite this unusually rigorous review process, a network of health officials and influential dental groups argued that the NTP had failed to address several issues raised by the NASEM review committee. These issues include a need to consider more studies in the review, and a failure to properly account for bias among some of the studies selected. One key health official wrote that if the Centers for Disease Control and Prevention (CDC) had been given the option to clear the report, “We would have non-concurred,” records show.

Birnbaum said she strongly disagrees that the NTP had failed to address NASEM’s concerns. In her declaration, Birnbaum wrote that various sources told her the five external peer reviewers agreed with what was then the final report’s conclusions, and that “NTP’s staff and leadership considered the monograph to be complete and ready for publication by May 2022.”

The report’s critics also feared its findings could erode public trust in water fluoridation, with the head of one leading dental research organization calling it “potentially very bad fluoride news.”

In April of last year, American Fluoridation Society President Johnny Johnson wrote an open letter to “Oral Health Advocates and Public Health Leaders” warning how the NTP’s findings were already causing public health officials to second guess their stance on community water fluoridation (CWF).

“In at least one U.S. state the NTP’s draft Monograph has led to that state’s Toxicologist not being willing to support CWF as safe, when in the past that same Toxicologist was supportive. This is directly due to the NTP’s report,” Johnson wrote.

In response to questions, Johnson wrote in an email that “since the NTP report is not yet publicly available, it would be premature to comment on something that I haven’t seen.” Johnson did not answer when asked which state toxicologist had reversed their stance on water fluoridation.

Though the report has not been public, records suggest that in the lead-up to last May’s scheduled release it had been shared with members of nongovernmental dental groups like the ADA.

If federal health agencies shared the report with outside organizations, “That was completely inappropriate,” said Birnbaum. “It’s either everybody gets a chance to look at it, or only very restricted government entities,” Birnbaum added. “That trust, I would say, was broken.”

In a February 2022 email to various senior health officials including HHS Assistant Secretary for Health Rachel Levine, ADA senior manager for strategic advocacy and public policy Robert Burns asked the NTP to “exclude — or carefully consider how to characterize — any lingering neurotoxin claims” from the upcoming report. He wrote that “such claims are often taken out of context,” and might “undermine national, state, and local efforts to expand community water fluoridation” at the CDC’s recommended levels.

Jayanth Kumar, who sits on the board of the nonprofit Association of State & Territorial Dental Directors (ASTDD), wrote in June to other figures within the organization that the NTP “has dug in and doesn’t want to change its recommendations. The report gives the impression that the effect observed at high level [sic] of fluoride is causal although the report doesn’t state it. NTP recommends more studies at low F [fluoride] levels.”

Neither Burns nor the ADA responded to repeated requests for comment.

Kumar, state dental director for the California Department of Public Health, forwarded an email request for comment to an agency spokesperson, who wrote “CDPH does not comment on pending litigation or on studies in which it did not participate.”

Last May, current NTP Director Rick Woychik sent the document for yet another round of peer review with the agency’s Board of Scientific Counselors (BSC). Once the BSC has made its recommendations, Woychik will decide about “publication and dissemination” of what is now expected to be the final version of the report.

The decision to put the report on hold last May appears to have come from Levine, communications show. Levine’s office did not answer questions about whether she made the decision to shelve last May’s report and if so, why. A spokesperson for Levine instead linked to the NTP webpage summarizing the report’s scientific progress.

Christine Flowers, communications director for the National Institute of Environmental Health Sciences (NIEHS), where the NTP is headquartered, did not answer questions about who ultimately decided to shelve NTP’s report last year. Instead, she pointed to the same NTP webpage.

“It is important to note that the NTP is an INTERAGENCY organization made up of the NIH [National Institutes of Health], FDA [Food and Drug Administration] and the CDC, which work collaboratively,” Flowers wrote in an email.

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The EPA’s legal drinking water limit for fluoride is 4 parts per million (ppm), but that level was established for naturally occurring fluoride. The CDC uses a nonenforceable guideline of 0.7 parts per million (ppm) as a safe level to counter problems like dental fluorosis, which is a change in the appearance of tooth enamel.

Communications between federal health officials and others show that the report the NTP was set to issue last May found that at typical fluoridated water levels in drinking water in the U.S., the effects on brain development are unclear. But it found a possible statistical association with cognitive harm and fluoridated water exposure at approximately 1.5 ppm and above, records show.

That level is not low enough to be safe because of fluoride in other foods and drinks consumed daily, said population health scientist Bruce Lanphear, an expert witness for the plaintiffs. This includes certain teas, coffee, canned shellfish, as well as oatmeal, raisins and potatoes. “Even if there’s no effects at the optimally fluoridated levels, people are going to be exposed to other sources of fluoride like black tea,” explained Lanphear. “For pregnant women or avid drinkers of black tea, they’re going to get more fluoride because it’s a hyper accumulator of fluoride.”

The CDC provides guidelines for fluoride intake in small children and babies in the womb, including a recommendation for youngsters under 8 years old living in communities where fluoride occurs naturally at levels above 2 ppm to be given alternative drinking water.

The CDC recommends breastfeeding infants, as breastmilk contains significantly less fluoride than fluoridated drinking water. If breastfeeding is not possible, the CDC also endorses using fluoridated water in infant formula, though it suggests mixing the formula with low-fluoride bottled water to lessen the risk of dental fluorosis.

Infants who are fed formula made with fluoridated tap water can have three to four times higher fluoride exposure than adults, warned Lanphear. He added that before an infant’s teeth erupt, there’s no benefit to fluoride exposure. “There are vulnerable groups we have to be worried about,” he said, “and that’s not being brought out adequately by these agencies.”

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