My Facebook feed includes a report that fluoride has recently been officially classified as a neurotoxin.

A big step has been made here recently. In the most prestigious medical journal. One known as The Lancet. fluoride has been at last classified as a neurotoxin one hundred percent. This puts it in the same category as things like lead, arsenic, and mercury.

This news was released by the author Stefan Smyle who actually cited a report that had been published in The Lancet Neurology, Volume 13, Issue 3 to be exact in the March of 2014 edition.

I am not entirely sure what it means to be "officially classified", but has such a classification been made?

(Whether fluoride actually is a neurotoxin is a separate claim, if anyone wants to ask a separate question about it.)

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    I'm sure this has been resolved before, but what is the standard for notability when it comes to claims found in Facebook feeds? Apr 12, 2018 at 15:24
  • @iamnotmaynard: I went with "Awareness Act" being notable, rather than the feed entry. There are a stack of other similar sites I can add if it is in doubt: [1], [2], [3]
    – Oddthinking
    Apr 12, 2018 at 15:40
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    I repeat the deleted comments: the idea that something is a neurotoxin is usually meaningless unless you also specify what dose you are talking about. Plenty of essential compounds are neurotoxic at some level. It isn't a binary classification. If the claim does not specify a dose, then the claim itself is dubious.
    – matt_black
    Apr 14, 2018 at 23:48
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    @matt_black: I think it's common sense that, in texts like this, if the amount of a substance is unspecified, it can be assumed to be "an amount at which the average reader is likely to interact with". In this case that would be whatever amount of flouride you find in toothpaste, etc.
    – user541686
    Apr 15, 2018 at 3:17
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    @Mehrdad No you cannot assume that. far too many compounds are toxic at some does but not at others. In important scientific reports we should never have to guess what dose they were talking about. Consider that paracetamol is a liver toxin. Can you assume that this is true at the levels you normally take for headaches? No, you need to take maybe 30 times the normal dose.
    – matt_black
    Apr 15, 2018 at 12:49

2 Answers 2



Quoting user Yaverland from Reddit:

This blog goes into great detail about the paper published by The Lancet.

In addition to the point that "The Lancet" doesn't classify anything, rather it published a paper online that may or may not stand up to further scrutiny...

There was one reference to fluoride in the entire study, which was repeating the claims in another paper. This paper has been met with much scepticism.

Some commentary repeated in the blog:

In comments prepared by the Science Media Centre, epidemiologist Jean Golding of the University of Bristol accused the pair [Grandjean and Landrigan] of issuing scare statements.

“To implicate high fluoride, which they quote as one of the new chemicals… they quote only one paper; this only compares the mean IQs of children in villages with different levels of fluoride, with no allowance made for any other differences, and no actual measurement of fluoride in individual children and comparison with their IQs. This is not good evidence.”

Read the whole blog, it is scathing.

I don't quite know what to add to that.

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    @Bent: The claim in the question is explicitly about The Lancet Neurology, Volume 13, Issue 3. There are scores of ways some A might be "officially" B somewhere, and a question to that end would get my close vote for "too broad", as it's hard to prove non-existence.
    – DevSolar
    Apr 12, 2018 at 13:37
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    In addition to not being good evidence, unless they were observing extremely low IQ levels (like below 70) then their results would not support classifying fluoride as a neurotoxin anyways. Things classed as neurotoxins have many effects, none of which are as mild as causing minor drops in IQ after years of chronic exposure.
    – aroth
    Apr 13, 2018 at 1:08
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    @aroth: What is interesting to me about your comment is that it accepts the premise that there is some way that substances are classified as neurotoxins. Are there organisations that do that?
    – Oddthinking
    Apr 13, 2018 at 16:06
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    @Oddthinking: I think the CDC's list would count?
    – Kevin
    Apr 14, 2018 at 2:01

The Grandjean (China) studies could be not replicated in other countries using a lower standard of water fluoridation, particularly in New Zealand, which uses a similar level of fluoridation as the US. Quoting relevant bits of the 2015 PHS recommendation on this matter:

IQ and other neurological effects. The standard letters and approximately 100 unique responses expressed concern about fluoride's impact on the brain, specifically citing lower IQ in children. Several Chinese studies considered in detail by the NRC review reported lower IQ among children exposed to fluoride in drinking water at mean concentrations of 2.5–4.1 mg/L—several times higher than concentrations recommended for community water fluoridation.[81–83] The NRC found that “the significance of these Chinese studies is uncertain” because important procedural details were omitted, but also stated that findings warranted additional research on the effects of fluoride on intelligence.[6]

Based on animal studies, the NRC committee speculated about potential mechanisms for nervous system changes and called for more research “to clarify the effect of fluoride on brain chemistry and function.” These recommendations should be considered in the context of the NRC review, which limited its conclusions regarding adverse effects to water fluoride concentrations of 2–4 mg/L and did “not address the lower exposures commonly experienced by most U.S. citizens.”[6] A recent meta-analysis of studies conducted in rural China, including those considered by the NRC report, identified an association between high fluoride exposure (i.e., drinking water concentrations ranging up to 11.5 mg/L) and lower IQ scores; study authors noted the low quality of included studies and the inability to rule out other explanations.[84] A subsequent review cited this meta-analysis to support its identification of “raised fluoride concentrations” in drinking water as a developmental neurotoxicant.[85]

A review by SCHER also considered the neurotoxicity of fluoride in water and determined that there was not enough evidence from well-controlled studies to conclude if fluoride in drinking water at concentrations used for community fluoridation might impair the IQ of children. The review also noted that “a biological plausibility for the link between fluoridated water and IQ has not been established.”[79] Findings of a recent prospective study of a birth cohort in New Zealand did not support an association between fluoride exposure, including residence in an area with fluoridated water during early childhood, and IQ measured repeatedly during childhood and at age 38 years.[86]

The Grandjean papers are refs 84 and 85, above; the latter one is with Landrigan, in Lancet Neurology 2014. As you can see above the PHS opinion on it is that it is overstating its case, particularly as it applies to other countries.

And from a 2018 paper

However, some debate remains about the health risks of CWF [community water fluoridation]. For example, in 2012, a systematic review and meta-analysis was published to assess developmental fluoride neurotoxicity (5). The authors suggested that exposure to “high” levels of fluoride may affect children’s neurodevelopment. Reversely, a prospective study in New Zealand published in 2015 which was conducted to examine the possible correlation of CWF and intelligence, found that, after following up participants between 1972 and 2012, there was no significant association between fluoride exposure due to CWF and intelligence quotient (IQ) (6). Some researchers maintain there is not enough evidence to conclude that fluoride in drinking water may impair IQ (7).

Yet, the digitization of mass media communications has led to the far-reaching spread of unrestricted and inaccurate fluoridation information across the web through media and social networks (8). For example, based on the 2012 Choi et al. article (5), an article was released in 2014 by one of the coauthors. According to their review, the authors listed fluoride as one of six newly identified developmental toxins in children (9). Several limitations in this article were addressed by the scientific community (10,11); however, its publication immediately triggered adverse coverage for fluoridation in the popular press, generating tens of thousands of views and shares over social media within 48 hours of publication, disseminating flawed messages about fluoridation (12). The safety and benefits of CWF continue to be debated online, with reference to the 2014 publication, despite robust scientific evidence that CWF is safe, protective, and effective (1-4).

In this latter paper, ref 5 is 84 from PHS (Choi,.., Grandjean) and 9 from the latter quote corresponds to 85 from PHS (Grandjean and Landrigan). And if you want to read the direct rebuttals of Grandjean and Landrigan (refs 10 and 11 above) they're freely available on Lancet's website: here and here which reiterate the same concerns. Quoting from the latter letter:

Grandjean and Landrigan did not acknowledge the animal study[3] that showed no evidence of a neurotoxic effect of fluoride, even at levels up to 230 times the recommended concentration; an earlier study showing that fluoride causes no harm to children;[4] two formal reviews that delineate weaknesses in the Chinese fluoride and IQ studies;[5, 6] and the conclusion by one of these sets of investigators[6] that biological plausibility for a link between fluoridated water and IQ has not been established.

And from the former letter, which has broader criticism of how Grandjean and Landrigan put together their list of "neurotoxicants":

In their Review of neurological toxicants,[1] Grandjean and Landrigan make unsubstantiated claims and misquote previous studies to pull together heterogeneous elements and drugs into a group of substances termed neurotoxicants.

[...] Their “strong evidence” for adding fluoride was a finding from Grandjean's own review of older Chinese studies. [...] By contrast with this review of Chinese studies, all of problematic methodological robustness, more than 3000 studies of the safety of water fluoridation stretch over 65 years. During this time, as fluoridation increased from 0% to 72% of US households, average US IQs have not decreased, but have instead increased by 15 points.[5]

The investigators also added manganese to their list of neurotoxicants writing that “might cause” or has been “linked to” neurological disorders: prenatal exposure to ADHD and postnatal exposure to parkinsonism. However, recent reviews have shown no link between manganese and ADHD or parkinsonism.[6, 7]

Their assumption that “neurotoxicants might lurk undiscovered” behind even low doses of all chemicals can't be disproved. But it denies dose-response concepts. By seeing manganese and fluoride alongside repeated analogies to lead, a reader would naturally associate these elements with the situation with lead, in which no safe level of exposure exists. Manganese, however, as a trace element, does have a safe level.

(For meaning of "trace elemement" in this context see Mineral (nutrient) on Wikipedia)

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    Does this answer the question? The question focused on whether fluoride was classified as a neurotoxin, by The Lancet. Whether it is a neurotoxin and whether that status has any actual effect on human health in the real-life dosages is an answer for a different question [one that would be quite on-topic on Skeptics.SE if anyone wants to ask it.]
    – Oddthinking
    Apr 13, 2018 at 0:51
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    @Oddthinking Then the simple answer is "no" because the Lancet has no powers to "officially classify" such things. It "simply" prints papers of what others (claim) to have found.
    – TripeHound
    Apr 13, 2018 at 9:38
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    @Oddthinking: I think you're splitting hairs here. Obviously The Lancet (which is not even the same journal as Lancet Neurology) doesn't classify any substances. If that's the answer you want to hear, it doesn't require any sources. Apr 13, 2018 at 11:42
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    And in fact you could have read that answer on reddit, 3 years ago: reddit.com/r/skeptic/comments/2705ij/… Apr 13, 2018 at 11:52
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    @Oddthinking: there's not going to be an article rejecting every crank theory on FB. In this case there are some rejecting (or rather limiting) the substantive claims of the papers involved.. but no scientific journal is going to bother with the FB extra-distortion version thereof. Even Snopes doesn't have a page for your particular version of the question, only for the more substantive one: snopes.com/fact-check/water-fluoridation-reduces-iq In the Snopes article ref 84 from my/PHS answer is referered to as the "Harvard study". Apr 13, 2018 at 16:17

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