Problematic National Toxicology Report into water fluoridation finally released
Following multiple drafts, reviews and major revisions, the NTP report has finally seen the light of day, finding no link between community water fluoridation and cognition or neurodevelopment.
Last month the US National Toxicology Program (NTP) finally released their long-awaited final report on water fluoridation, following two previous drafts in 2019 and 2020 which had previously caused significant concern across the dental community. It’s an important milestone, because this final report backtracks many of the claims made in the prior drafts that were seized on by groups opposed to water fluoridation, despite the fact that those drafts continually failed to complete a proper peer review process.
The NTP report has gone from initially concluding that water fluoridation at levels that are generally used around the world posed a neurodevelopmental hazard, to making it clear in the final report that this risk may only be associated with exposures that are significantly higher than that.
How did we get to this situation, and what does it tell us about the politics of water fluoridation? First, it’s important to note that the evidence is overwhelmingly clear that water fluoridation is effective in reducing the burden of dental caries (tooth decay) in both children and adults, and that it is particularly important because it helps to tackle the social inequities that are evident in the distribution of dental caries across populations.
It’s worth looking at who the National Toxicology Program is, and why they were looking at water fluoridation in the first place. The NTP is a division of the National Institute of Environmental Health Sciences (NIEHS), which is part of the National Institute of Health (NIH) under the umbrella of US Department of Health and Human Services. The NTP mission is to build knowledge and advance toxicological sciences to protect and promote human health by identifying potentially hazardous substances and evaluate their effects for human health.
In 2015 the Fluoride Action Network, an anti-fluoride lobby group whose stated aim is to end ‘water fluoridation and other involuntary exposures to fluoride,‘ urged the NTP to investigate the cognitive impact of prenatal and postnatal exposure to fluoride. The NTP’s initial review of animal studies found only low-moderate evidence of an effect, which they deemed to be cause for serious public health concern. This led them to conduct their own animal neurotoxicity experiments which, in contrast to their own literature review, found no evidence of neurotoxic harm.
Nonetheless, NTP pushed ahead with a review of the literature on human studies, which forms the basis of this newly released report, and they asked the National Academies of Sciences to serve as peer reviewer. Early drafts of the report made substantial claims about the risks of water fluoridation. For example, one of the drafts had a section titled ‘Strengths of the Evidence Base’ with statements that included:
Reported responses to fluoride exposure and lower children’s IQ are consistent in studies of both low and high quality.
Reported responses to fluoride exposure and lower children’s IQ are consistent across different study populations, study designs, and exposure measures.
The reviewers recommended making it clear that the included studies related to ‘higher’ fluoride exposure to acknowledge that most of the studies did report on fluoride exposures that were much higher than is found in community water fluoridation. Interestingly, when it comes to the final report – there is no longer a ‘Strengths of the Evidence Base’ section.
The 2022 draft report also made the following conclusion:
‘This review finds, with moderate confidence, that higher fluoride exposure (e.g., represented by populations whose total fluoride exposure approximates or exceeds the World Health Organization Guidelines for Drinking-water Quality of 1.5 mg/L of fluoride) is consistently associated with lower IQ in children. More studies are needed to fully understand the potential for lower fluoride exposure to affect children’s IQ.’
However, by the final report, the conclusion now states:
‘The current monograph concludes with moderate confidence that higher estimated fluoride exposures (e.g., as in approximations of exposure such as drinking water fluoride concentrations that exceed the WHO Guidelines for Drinking-water Quality of 1.5 mg/L of fluoride) are consistently associated with lower IQ in children. The moderate confidence in the inverse association between fluoride exposure and children’s IQ is based primarily on studies with estimated fluoride exposures higher than what is generally associated with consumption of optimally fluoridated water in the United States.’
Importantly, the final report notes:
‘This Monograph and Addendum do not 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.’
The NTP makes it clear in their final report that their review of the literature was not designed to evaluate the health effects of fluoridated tap water, and that it did not in fact collect enough data to perform that task anyway – which makes you wonder what the purpose of the report was. The NTP also notes that they only have moderate confidence in the fluoride-IQ association that they found at fluoride exposures greater than 1.5 parts per million.
There has been significant criticism of the NTP report, including the methodology and the quality of the studies it relied on. For example, two thirds of the studies that they reviewed were published in journals of questionable quality, which is often a red flag. Many relied on spot urine samples to measure exposure to fluoride, which is not a reliable methodology. Many had other significant methodological flaws, and the reviewers went so far as to note concerns about the inconsistencies in the risk-of-bias decisions made by the NTP in evaluating the quality of the literature they relied on. A separate meta-analysis in 2023 looking at fluoride exposure and cognitive neurodevelopment noted that all but one of the 30 studies included were assessed as having a moderate or high risk of bias, and the only study with a low risk of bias found no link between fluoride exposure and IQ scores. I have previously commented on this issue when the most recent study claiming links to a higher risk of neurobehavioural problems was published.
The Fluoride Action Network made the explosive claim in March 2023 (based on the draft report which had not yet successfully gone through peer review), that ‘the National Toxicology Program finds no safe level of water fluoridation’ and that ‘water fluoridation policy is threatened.’ What is clear now though is that this final report does not vindicate their concerns that water fluoridation is linked to brain impairment in babies, or attention deficit disorders and lower IQ’s in infants born to mothers who drank fluoridated water during pregnancy and in babies fed formulas mixed with fluoridated tap water.
Why is all of this important?
Water fluoridation remains a live issue for many regional communities around Australia. For example, right now the residents of Cairns are campaigning to have water fluoridation reinstated, after it was withdrawn following a 2012 decision by then Queensland Premier Campbell Newman to hand decision making responsibility back to councils. Ensuring that these decisions are made on the basis of high quality evidence is critical if we are to reduce the significant burden of oral diseases in these communities.
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