Tag Archives: Dental fluorosis

Water fluoridation – what to expect in the near future


Community water fluoridation (CWF) will persist in science news for the foreseeable future – not for any valid scientific reason but because of reaction to political pressures against it. This is particularly so in New Zealand where our parliament will be discussing legislative changes to fluoridation decision-making this year.

This is not to say that all the relevant news will be political. There is still ongoing research into the efficacy, cost-effectiveness and possible health effects of fluoridation. Although much of this is a response to pressure from opponents of this social health policy.

So what scientific and political news about CWF should we expect to see in the coming years?

The legislation

In the immediate future, this will be dominated by the new parliamentary legislation [Health (Fluoridation of Drinking Water) Amendment Bill– at least in New Zealand. However, US anti-fluoride campaigners are following this legislation very closely, and will probably become involved in submission on it, so I expect this will also get coverage internationally. At least in the alternative health media which has stong links to the US anti-fluoride activist organisation, Fluoride Action Network (FAN), and which routinely carry their press releases.

The NZ Parliamentary Health Committee is currently taking written submissions on the fluoridation bill. The deadline for these is February 2. Readers interested in making their own submission can find some information on the submission process in my article Fluoridation: members of parliament call for submissions from scientific and health experts.

The bill itself simply transfers the decision-making process for fluoridation from local councils to District Health Boards. But most submissions will inevitably be about the science and not the proposed changes to decision-making – and, considering the promise of the local anti-fluoride group to shower the committee with “thousands and thousands of submissions,” will misrepresent that science. I will be interested to see what allowance the committee chairman makes for such irrelevant submissions when it comes to the public hearings, which could begin as early as February.

The bill has support from all the parliamentary parties, except the small NZ First which apparently wants councils to keep responsibility for fluoridation decisions, but wants to make binding referendums obligatory. So, I predict the bill will be passed this year. However, there will probably be attempts at the committee stages to amend it to transfer decision-making to central government, probably the Ministry of Health. Such an amendment appears to be supported by the Labour Party, but not by the National Party.

The “IQ problem” – a current campaign

There will be some news about research on the question of possible cognitive effects of fluoride in drinking water in the next few years. Not because there is any concern about this among health professionals. But because the claim that fluoride causes a drop in IQ is pushed very strongly by anti-fluoride activists. While they have a long list of claimed negative health effects of fluoridation the IQ claim is currently central to their political campaigns.

The campaigners claim scientific support for this claim. But that support comes mainly from a number of poor quality papers outlining research results from areas of endemic fluorosis (where drinking water concentrations of fluoride are much higher than the optimum levels used for CWF), mainly in China. FAN has a lot invested in this claim because it financed the translation of many of these otherwise obscure papers into English.There is general agreement among health specialists that these studies are not relevant to CWF. Investigation of areas where CWF is used, and where natural fluoride levels are similar to those used in CWF have not shown any neurological effects due to fluoride.

There is general agreement among health specialists that these studies are not relevant to CWF. Investigation of areas where CWF is used, and where natural fluoride levels are similar to those used in CWF have not shown any neurological effects due to fluoride.

However, FAN is strongly pushing the idea that cognitive effects of fluoride (rather than very mild dental fluorosis) should be the main criteria used in determining the recommended maximum levels of fluoride in drinking water. They currently have a petition in front of the US Environmental Protection Agency (EPA) promoting this claim. This may make the news in the near future as the EPA must respond this month and the likely rejection of the petition will no doubt cause a flurry of press releases.

Paul Connett, who with other members of his family runs FAN, has also attempted to use the scientific publication path to promote this claim. His arguments and calculations defining an extremely low maximum concentration, are very naive and his draft paper has already been rejected by journals several times. However, he no doubt lives in hope for its eventual acceptance somewhere. If he is successful this will be trumpeted to the high heavens by his supporters because while they describe Paul Connett as the international authority of water fluoridation he actually has no proper scientific publications in that area.

Research on neurological effects

We expect some research publications in the next year or so from the current US National Toxicity Program research on claims that fluoride at the concentrations used in drinking water fluoridation could have neurological effects. This research is basically a systematic review – according to the proposal:

an “evaluation of the published literature to determine whether exposure to fluoride is associated with effects on neurodevelopment, specifically learning, memory, and cognition.”

The motivation for this work, apart from the political pressure arising from activist claims, is to attempt to evaluate possible effects at concentration relevant to CWF. (Most published animal and human studies have involved higher concentrations). As the proposal says:

“Previous evaluations have found support for an association between fluoride exposure and impaired cognition; however, many of the studies included exposure to high levels of fluoride. Most of the human evidence was from fluoride-endemic regions having high background levels of fluoride, and the animal studies typically included exposure during development to relatively high concentrations of fluoride (>10 mg/L) in drinking water. Thus, the existing literature is limited in its ability to evaluate potential neurocognitive effects of fluoride in people associated with the current U.S. Public Health Service drinking water guidance (0.7 mg/L).”

I discuss the background to the US National Toxicity Program fluoride research in my article Fluoride and IQ – another study coming up.

Canadian Professor Christine Till will soon start a study looking at cognitive and behavioral factors using a data set for pregnant women exposed to contaminants. She intends to investigate the possibility of relationships with markers for fluoride consumption (see ). Anti-fluoride campaigners hold out great hope for results from this study because Till’s previous research is widely used by them to claim that fluoridation causes increased prevalence of attention-deficit hyperactivity disorder (ADHD). However, that research was flawed because potential confounders were not considered properly. In fact, her reported statistically significant correlations disappears when the confounders are included (see  ADHD linked to elevation not fluoridation).

Problems in areas of endemic fluorosis

Health effects including cognitive deficits: The World Health Organisation recommends that drinking water fluoride concentrations should not be higher than 1.5 mg/L because of negative health effects of high concentrations. Many areas of the world do have high drinking water fluoride concentrations and those areas suffer from endemic fluorosis – dental and skeletal fluorosis. This is, of course, a serious problem and there is a continuous stream of research papers devoted to these areas.

This research is not relevant to CWF (where the optimum concentration of 0.7 mg/L or similar levels is used). But, of course, anti-fluoride campaigners will continue to cite these papers as “evidence” against CWF. We may even see an expert on endemic fluorosis being toured in New Zealand to provide scientific credibility to the anti-fluoride campaign. Dr. Ak.K. Susheela, who works on endemic fluorosis in India and has links with FAN, has been speaking at meetings organised by the anti-fluoride movement in North America and has been suggested as a speaker the local anti-fluoride campaigners should bring to New Zealand.

I expect there will be more papers reporting IQ deficits in areas of endemic fluorosis and these will most probably continue to use a chemical toxicity model to explain their results. I personally am interested in the possibility of researchers considering other models, such as the psychological effects of dental and physical deformities like dental and skeletal fluorosis (see Perrott et al. 2015. Severe dental fluorosis and cognitive deficits). Unlikely, considering how research can get locked into pet paradigms, but one can but hope.

Defluoridation: Another big issue in areas of endemic fluorosis is the need to lower drinking water fluoride concentrations. This if often done by finding alternative sources but there is continuing research on treatment methods to do this.

Again, not relevant to CWF – but I do follow this research and find some of it interesting chemically. Perhaps it reminds me of my own research many years ago.


The controversy around CWF is not going to go away. The opposition is strongly grounded in the “natural”/alternative health industry. It has plenty of financial and ideological resources and its message appeals to a significant minority of the population.

Most of the public interest this year will relate to the new legislation – expect plenty of press releases from the anti-fluoride groups as they organise to make and advertise their submissions, and express their anger at the probably inevitable decision that will go against them.

However, there will be a continuing dribble of research reports of relevance to CWF and to the claims advanced by anti-fluoride campaigners. While it is normal for a social health policy to be continually monitored and its literature reviewed, some of this research is a direct result of concerns raised by campaigners and activists.

Many in the scientific community find this sort of political activity annoying. But it does have its up side. CWF has been one of the most hotly contested social health programmes. Consequently is has received more than its fair share of literature reviews and new research.

And that is a good thing. Anti-fluoride activists often claim there is little research on the health effects of CWF. But that is just not true. Ironically it is the very political activity of such campaigners which has led to CWF being one of the most thoroughly researched social health policy.

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A Chinese study the anti-fluoridation crowd won’t be citing


Tooth brushing programme carried out in kindergartens in a Chinese rural area. Image credit: Supervised tooth brushing programme

Anti-fluoridation campaigners love to cite Dr Q. Y. Xiang to “prove” that community water fluoridation (CWF) can lower IQ. Trouble is – Xiang’s research on fluoride and IQ took place in an area of endemic fluorosis in China where drinking water fluoride levels were much higher than those used for CWF. That hasn’t stopped Paul Connett from making mileage out of Xiang’s data – even though the link between IQ and drinking water fluoride shown by Xiang’s data is very tenuous (see Connett fiddles the data on fluoride).

However, I suspect Connett and his activist organisation, The Fluoride Action Network (FAN), will be very quiet about the latest paper from this group. This is because the research they report supports the scientific consensus – in particular:

  • Fluoride at the concentration used in CWF does reduce tooth decay;
  • Fluoride at the concentration used in CWF does not cause the cosmetically undesirable forms of  dental fluorosis.

The paper is:

Xiang, J., Yan, L., Wang, YJ., Qin, Y., Wang, C. &  Xiang, QY. (2016). The effects of ten years of defluoridation on urinary fluoride, dental fluorosis, defect dental fluorosis, and dental caries, in Jiangsu province, PR China. Fluoride, 49(March), 23–35.

Yes, I know, it is published in Fluoride – which is hardly a credible scientific journal. And the lack of proper peer review sticks out like a sore thumb with mistakes in the text, poor data presentation and poor data statistical analysis.

Fluoride improves dental health

This is shown by data they collected in 2002 for two villages -Wamiao (a “severe endemic fluorosis village” with drinking water fluoride in the “range of 0.57 – 4.50 mg/L”) and Xinhuai (a “non-endemic fluorosis village” with drinking water fluoride in the “range 0.15 – 0.77 mg/L”). They combined the data for the 2 villages to produce the following graphic – from which they concluded that a “possible desirable range for the fluoride level for minimizing the prevalence of dental caries” . . .  [is] “approximately 1.5 – 2.5 m/L.” Considering this is just one study and has limitations the result is similar to the recommended fluoride level for CWF – 0.75 mg/L in the USA and 0.75 – 1.2 mg/L in New Zealand.

DMFT Xiang

OK, this is a poor graphic and I cannot see why they should have divided the data into the nine subgroups instead of statistically analysing the whole dataset (an indication of poor peer review by the journal?). But you get the picture. Dental decay declines as fluoride concentration in the drinking water in increased from near zero to about 1 mg/L.

CWF does not cause dental fluorosis

After 2002 the water sources used in the two villages changed:

“As a defluoridation project, water from two deep wells has been used as a tap water source of drinking water in Wamiao village since the beginning of 2003. The surface water in Yaohe river has been used as a tap water source in Xinhuai village since 2009.”

The current dental fluorosis study occurred in 2013 when the fluoride concentrations in both villages were in the range 0.85 – 0.95 mg/L. This is similar to the levels used in CWF.

In 2013, the researchers found very low levels of total dental fluorosis in both villages (3.1% in Xinhuai and 8.8% in Wamiao – no significant difference). They also measured “defect dental fluorosis” – a Chinese classification which includes some “moderate” dental fluorosis and all “severe dental fluorosis as diagnosed by Dean’s criteria (see  Water fluoridation and dental fluorosis – debunking some myths and the image below).

The prevalence of “defect dental fluorosis” in 21013 was zero for both villages.

This contrast markedly with the situation in 2002 where the prevalence of total dental fluorosis was significantly higher in Wamiao village (89%) than in Xinhuai (4.5%). The prevalence of “defect dental fluorosis” was 39% in Wamiao but zero in Xinhuai (data from Xiang, et al., 2004).

The 2013 data reported in this paper confirm what I have said again  and again in  articles here. CWF does not cause the cosmetically undesirable forms of dental fluorosis – the “moderate” and “severe” forms, or the “defect dental fluorosis” in the Chinese classification). Anti-fluoride campaigners always misrepresent this data by quoting figures for total dental fluorosis and claiming the effects are those only seen with “moderate” and “severe” forms.

Paper’s take home message

The new water supply in these two villages has solved the dental fluorosis problem while also maintaining a fluoride concentration comparable to that used in CWF and helping support a low level of dental decay in children. The data support other findings (and the current scientific consensus) showing that CWF does not cause any cosmetically undesirable dental fluorosis but does help prevent tooth decay.

Once more on the IQ and fluoride myth – why ignore other factors?

The “fluoride damages IQ” myth won’t go away – mainly because it is avidly promoted by campaigners against community water fluoride (CWF). This is despite the fact that no link has even been drawn between CWF and IQ (the only relevant study shows no connection). But that doesn’t stop ideologically driven campaigners who rely on poor quality studies from areas of endemic fluorosis where dietary fluoride intake is higher than in areas using CWF.

There are plenty such studies, but a more recent one illustrates their problems – and the role  confirmation bias seems to play in these studies. It is:

Kundu, H., Basavaraj, P., Singla, A., Gupta, R., Singh, K., & Jain, S. (2015). Effect of fluoride in drinking water on children′s intelligence in high and low fluoride areas of Delhi. Journal of Indian Association of Public Health Dentistry, 13(2), 116.

It’s another study where the IQ values of children from a “high fluoride” area were compared with those for children from a “low fluoride area.” There was a statistically significant difference and the paper goes on to claim:

“High F concentration in the drinking water was found to have marked systemic effects on the IQ of children. Though the precise mechanism by which F crosses the blood brain barrier is still not clean‑cut; enough evidence survives for the influence of F intake via drinking water and low IQ of the child.”

However they do acknowledge:

“Apart from fluoride there are other factors which also affect IQ of children. In the present study, mothers diet during pregnancy also significantly affected the IQ of the children.”

The supporting data is poorly presented and described – for example, no indication is given of the fluoride concentration in the drinking water of the “high fluoride and “low fluoride” areas used. Although they do cite areas in Delhi (where the study was located) with fluoride concentration as high as 32.5 ppm!. And I cannot find any details on “mothers diet during pregnancy” (except perhaps division into two groups – “routine” or “special diet as suggested by the doctor during pregnancy”).

Those confounding factors

These sorts of studies almost always rely on finding a statistically significant difference in the IQ values of children in two different areas or villages. But that statistical significance says nothing about the causal factors involved – it may have nothing to do with differences in fluoride levels.

Kundu et al., (2015) do at least include some data on confounding factors which is often missing from such studies. These show significant difference between the groups from the “high fluoride” and “low fluoride” areas which have no connection with fluoride in drinking water – such as father’s occupation, mother’s education and father’s education) – or only an indirect connection (dental fluorosis).

Here is a summary of the data for the various factors. I have selected the data so to show as two values – equal to “high fluoride” and “low fluoride.”


You get the picture. The areas were chosen according to the concentrations of fluoride in drinking water (whatever they were), but they could equally have been chosen on the basis of parental education, father’s occupation or prevalence of the more severe forms of dental fluorosis.

In fact, rather than concluding drinking water fluoride has a “marked systemic effects on the IQ of children” we could equally have concluded:

  • “The father’s occupation has a marked effect on the IQ of children with the children of unskilled fathers having a lower IQ.”
  • “The mother’s and father’s education has a marked effect on the IQ of children with the children of parents with a higher education having a higher IQ.”
  • “Diet of mothers during pregnancy has a marked effect on the IQ of children.” (The paper did not include data suitable for plotting for this.)

The dental fluorosis factor interests me as I have suggested that, in areas of endemic fluorosis, the physical appearance of defective teeth could lower quality of life and cause learning difficulties which are reflected in lower IQ values (see Severe dental fluorosis the real cause of IQ deficits?Severe dental fluorosis and cognitive deficits – now peer reviewed and Free download – “Severe dental fluorosis and cognitive deficits”).

I think that this is more reasonable as a mechanism than the chemical toxicity mechanism that almost all authors of these sorts of papers assume – but never support with any evidence. Even when dental fluorosis is considered it is usually treated as an indicator of lifetime intake of fluoride (which it is) rather than and independent cause of low IQ.


Most studies like this seem to be motivated by confirmation bias. Despite the possibility of a range of factors being involved, and some of these such as parental education being a more obvious cause, there appears to be an urge to interpret data as evidence of a chemical toxicity mechanism involving fluoride. And there is never any experimental work to confirm this preferred mechanism.

To my mind, if fluoride is implicated in the low IQ values the mechanism involving effects of dental fluorosis on quality of life and learning difficulties appears more credible than an unproven chemical toxicity.

Note: None of this is directly relevant to areas where CWF is used. The prevalence of more serious forms of dental fluorosis is very small in these areas and not related to CWF. Also, no study has yet found an effect of CWF on IQ. Given the higher levels of fluoride used in the studies from areas of endemic fluorosis, and the higher levels of serious forms of dental fluorosis, extrapolation of the results to areas where CWF is used is completely unwarranted.

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Alternative reality of anti-fluoride “science”

Paul Connett made many unsupported claims in his presentation against community water fluoridation (CWF) to Denver Water. Here I debunk a claim where he rejects most scientific studies on the cost-effectiveness of CWF.

Different grades of dental fluorosis

Connett asserted two things in his presentation:

  1. Previous research showing the cost effectiveness of community water fluoridation (CWF) has been made obsolete by a single new paper.
  2. Something about this new paper (Ko & Theissen, 2014) makes it more acceptable to him than previous research – and he implies you

Plenty of research shows CWF is cost-effective

Connett has cherry-picked just one paper, refused to say why and, by implication, denigrated any other research results. And there are quite a few studies around.

Here are a just a few readers could consult:

Of course, the actual figures vary from study to study, and various figures are used by health authorities. But generally CWF is found cost-effective over a large spectrum of water treatment plant sizes and social situation.

Connett relies on a flawed study

Connett relies, without justification,  on a single cherry-picked study:

Ko, L., & Thiessen, K. M. (2014). A critique of recent economic evaluations of community water fluoridation. International Journal of Occupational and Environmental Health, 37(1), 91–120.

This is a very long paper which might impress the uninitiated. To give it credit, it does make lengthy critiques of previous studies on cost effectiveness. But it has a huge flaw – its treatment of the cost of dental fluorosis.

It rejects warranted assumptions made by most studies that the adverse effects of CWF on dental fluorosis are negligible: They say:

“It is inexplicable that neither Griffin et al. nor other similar studies mention dental fluorosis, defective enamel in permanent teeth due to childhood overexposure to fluoride. Community water fluoridation, in the absence of other fluoride sources, was expected to result in a prevalence of mild-to-very mild (cosmetic) dental fluorosis in about 10% of the population and almost no cases of moderate or severe dental fluorosis. However, in the 1999–2004 NHANES survey, 41% of U.S. children ages 12–15 years were found to have dental fluorosis, including 3.6% with moderate or severe fluorosis.”

Two problems with that statement:

  1. The prevalence of “cosmetic” dental fluorosis may be about 10% but this cannot be attributed to CWF as non-fluoridated areas have a similar prevalence. For example, in the recent Cochrane estimates show “cosmetic” dental fluorosis was about 12% in  fluoridated areas but 10% in non-fluoridated areas (see Cochrane fluoridation review. III: Misleading section on dental fluorosis).This is a common, probably intentional, mistake made by anti-fluoride campaigners – to attribute the whole prevalence to CWF and ignore the prevalence in non-fluoridated areas. This highly exaggerates the small effect of CWF on the prevalence of “cosmetic” dental fluorosis – which in  any case does not need treatment. “Cosmetic” dental fluorosis is often considered positively by children and parents.
  2. The small numbers of children with moderate and severe dental fluorosis (due to high natural fluoride levels, industrial contamination or excessive consumption of fluoridated toothpaste) is irrelevant as CWF does not cause these forms. Their prevalence is not influenced by CWF.

So Ko and Theissen (2014) produce a different cost anlaysis because :

“. . . the primary cost-benefit analysis used to support CWF in the U.S. assumes negligible adverse effects from CWF and omits the costs of treating dental fluorosis, of accidents and overfeeds, of occupational exposures to fluoride, of promoting CWF, and of avoiding fluoridated water.”

We could debate all the other factors, which they acknowledge have minimal effects, but they rely mainly on the dental expenses of treating dental fluorosis:

“Minimal correction of methodological problems in this primary analysis of CWF gives results showing substantially lower benefits than typically claimed. Accounting for the expense of treating dental fluorosis eliminates any remaining benefit.”

They managed to produce this big reduction in cost-effectiveness by estimating costs for treating children with moderate and severe dental fluorosis – finding:

“the lifetime cost of veneers for a child with moderate or severe fluorosis would be at least $4,434.”


“For our calculations, we have assumed that 5% of children in fluoridated areas have moderate or severe fluorosis.”

See the  trick?

They attribute all the moderate and severe forms of dental fluorosis to CWF. Despite the fact that research shows this is not caused by CWF and their prevalence would be the same in non-fluoridated areas!

The authors’ major effect – which they rely on to reduce the estimated benefits of CWF – is not caused by CWF.

Connett is promoting an alternative “scientific” reality

The Ko & Theissen (2014) paper is one of a list of papers anti-fluoridation propagandists have come to rely on in their claims that the science is opposed to CWF. In effect, this means they exclude, or downplay, the majority of research reports on the subject – treating them like the former Index Librorum Prohibitorum, or “Index of Forbidden Books,” an official list of books which Catholics were not permitted to read.

The Ko & Theissen (2014) paper is firmly on the list of the approved studies for the anti-fluoride faithful. A few others are Peckham & Awofeso (2014), Peckham et al., (2015)Sauerheber (2013) and, of course, Choi et al., (2012) and Grandjean & Landrigan (2014).  You will see these papers cited and linked to on many anti-fluoride social media posts – as if they were gospel – while all other studies are ignored.

These papers make claims that contradict the findings of many other studies. They are all oriented towards an anti-fluoridation bias. And most of them are written by well-known anti-fluoride activists or scientists.

In effect, by considering and using studies from their own approved list and ignoring or denigrating studies that don’t fit their biases, they are operating in an alternative reality. A reality which may be more comfortable for them – but a reality which exposes their scientific weaknesses.

Lessons for Connett

I know Paul Connett is now a lost cause – he will continue to cite these papers from his approved list and make these claims no matter how many times they are debunked. But, in the hope of perhaps helping others who are susceptible to his claims, here are some lessons from this exercise. If anti-fluoride activists wish to support their claims by citing scientific studies they should take them on board.

Lesson 1: Make an intelligent assessment of all the relevant papers – don’t uncritically rely on just one.

Lesson 2: Don’t just accept the findings of each paper – interpret the results critically and intelligently. How else can one make a sensible choice of relevant research and draw the best conclusions.

Lesson 3: Beware of occupying an alternative reality where credence is given only to your own mates and everyone else is disparaged. That amounts to wearing blinkers and is a sure way of coming to incorrect conclusions. It also means your conclusions have a flimsy basis and you are easily exposed.

Lessons for everyone susceptible to confirmation bias.

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Cochrane fluoridation review. III: Misleading section on dental fluorosis

The Cochrane review did not look at the effect of community water fluoridation (CWF) on dental fluorosis. It simply reviewed data on the prevalence of dental fluorosis at different fluoride drinking water concentrations – up to 7.6 ppm which is well outside the optimum concentration used for CWF.

This is strange for a review specifically about CWF. Strictly speaking, as it stands  this section should have been a separate review on dental fluorosis itself. However, this review did calculate a probable dental fluorosis prevalence at 0.7 ppm (the usual concentration used in CWF) which is misleading because it can be misinterpreted as due completely to CWF when it isn’t. And, of course, anti-fluoridation propagandists have cherry-picked and misinterpreted this.

The forms of dental fluorosis. Questionable, Very Mild and Mild forms are usually considered positively whereas the Moderate and Severe forms are considered negatively. See Water fluoridation and dental fluorosis – debunking some myths

Confusing language

I think is was a serious mistake for the reviewers to include this section in a review on CWF as this can imply the calculated prevalences quoted are caused by CWF. They aren’t.

Strictly, their calculations were reported correctly in the abstract:

“There is a significant association between dental fluorosis (of aesthetic concern or all levels of dental fluorosis) and fluoride level.”

And also in the Plain Language Summary:

“The researchers calculated that, in areas with a fluoride level of 0.7 ppm in the  water, approximately 12% of the people evaluated had fluorosis that could cause concern about their appearance.”

However, in their blog post on the review (see Little contemporary evidence to evaluate effectiveness of fluoride in the water”) they inappropriately claim:

“There is an association between fluoridated water and dental fluorosis.”

Quite wrong – the association was with fluoride concentration (and most studies were of natural fluoride levels) – not with CWF.

They also use the term “water fluoridation” incorrectly in their comment on other possible harm from fluoride:

“Five studies that reported on dental fluorosis also presented data on the association of water fluoridation with skeletal fluorosis (Chen 1993; Jolly 1971; Wang 2012), bone fracture (Alarcon-Herrera 2001), and skeletal maturity (Wenzel 1982), in participants between the ages of six and over 66 years. Four of the studies included a total of 596,410 participants (Alarcon-Herrera 2001; Chen 1993; Wang 2012; Wenzel 1982), and fluoride concentration in all four studies ranged from less than 0.2 ppm to 14 ppm.”

Their use of the term “water fluoridation” to cover natural fluoride concentrations up to 14 ppm is irresponsible and misleading.

What the review did on dental fluorosis

It simply attempted to find a quantitative relationship between “fluoride level” (concentrations of naturally derived fluoride in drinking water) and dental fluorosis prevalence. It did this for all grades of dental fluorosis from “questionable” to “severe” (see figure above for illustrations fo the different grades). It also did this for “dental fluorosis of aesthetic concern” (which they arbitrarily defined as the mild, moderate and severe forms – they acknowledge inclusion of “mild” forms here is debatable). The figure below gives an idea of the data they were working with.


Using this data they produced tables of the probability of any forms of dental fluorosis, and of dental fluorosis of aesthetic concern at fluoride concentrations from 0.1 to 4 ppm. In the figures below I have converted their probability values to a calculated prevalence of dental fluorosis at concentrations up to 0.7 ppm.


As you can see from these figures the calculated prevalence of dental fluorosis at “fluoride exposures” less than the 0.7 ppm is only slightly less that at the 0.7 ppm used in CWF. So  it is very misleading to interpret the review’s statement below as indicating anything about CWF:

“The researchers calculated that, in areas with a fluoride level of 0.7 ppm in the  water, approximately 12% of the people evaluated had fluorosis that could cause concern about their appearance.”

Why should the review have considered differences between fluoridated and unfluoridated areas for its conclusions about tooth decay – but ignore the differences between fluoridated and unfluoridated areas in its consideration of dental fluorosis?

Estimating possible effect of CWF on dental fluorosis

In Misrepresentation of the new Cochrane fluoridation review I estimated what the possible effects of CWF is from the calculated probabilities in the Cochrane review. I am surprised the reviewers do not do this themselves as their review was meant to be about CWF and not natural fluoride levels in general.

At 0.7 ppm (the usual concentration for CWF), the calculated prevalence of all forms of dental fluorosis is 40%. But to calculate the prevalence due to CWF we must subtract the prevalence for non-fluoridated water. So dental fluorosis due to CWF would be 40% – 33% = 7 % of people  (using the review’s concentration for non-fluoridated water of 0.4 ppm) or 40% – 30% = 10 % of people (using a more realistic concentration of 0.2 ppm).

Similarly, if we consider only those forms of dental fluorosis the review considers of “aesthetic concern,”  then calculated prevalence due to CWF amounts to only 12% – 10% = 2% of people (using the reviews definition of non-fluoridated) or 12% – 9% = 3%  of people using a more realistic concentration of 0.2 ppm for non-fluoridated.

Defining “dental fluorosis of aesthetic concern”

The milder forms of dental fluorosis are usually judged positive from the point of view of the quality of life. That is why the review also considered dental fluorosis of aesthetic concern – which they define as the severe, moderate and mild forms of dental fluorosis. But, their inclusion of mild forms here is questionable and they acknowledge that:

“Within the context of this review dental fluorosis is referred to as an ’adverse effect’. However, it should be acknowledged that moderate fluorosis may be considered an ’unwanted effect’ rather than an adverse effect. In addition, mild fluorosis may not even be considered an unwanted effect.”

It is not surprising (considering the data in the figures above) that surveys  usually find no changes in the severe and medium forms of dental fluorosis (usually considered of “aesthetic concern”) due to CWF.

I think the Cochrane reviewers were irresponsible to quote calculations which did not include the difference between fluoridated and non-fluoridated areas. This has enabled anti-fluoridation propagandists to use the authority of the Cochrane name to imply, as they often do, that CWF causes a dental fluorosis prevalence of 40%!


The review section on dental fluorosis should not be read as information on the effects of CWF – although the presented data can be used to calculate possible effects. These calculations confirm findings of published surveys that CWF has no effect of the forms of dental fluorosis of aesthetic concern.

However, the conclusions presented in this section of the review are open to misrepresentation and distortion just as they are with the reviews comments on “bias” and poor quality of research (see Cochrane fluoridation review. II: “Biased” and poor quality research) and their selection criteria (see Cochrane fluoridation review. I: Most research ignored). Misrepresentation and distortion of the review are already happening. Anti-fluoridation activists are heavily promoting this review, together with their distortions and misrepresentations, opportunistically using  the Cochrane name to give “authority.”

Sensible readers will not rely on such misrepresentation or brief media reports. Nor will they rely on the Abstract or Plain Language Summary – which have problems. They will read the whole document – critically and intelligently. This is the only way to find out what the true content of this review is.

See also:

Misrepresentation of the new Cochrane fluoridation review
Cochrane fluoridation review. I: Most research ignored
Cochrane fluoridation review. II: “Biased” and poor quality research

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Free download – “Severe dental fluorosis and cognitive deficits”

S08920362Anyone interested in my article on this subject in Neurotoxicology and Teratology can now download a pdf version:

Perrott, K. W. (2015). Severe dental fluorosis and cognitive deficits. Neurotoxicology and Teratology, 48, 78–79.

The publishers tell me that anyone who clicks on the link until May 3, 2015, will be taken to the final version of on ScienceDirect for free. No sign up or registration is needed – just click and read!

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Severe dental fluorosis and cognitive deficits – now peer reviewed

Last May I raised the possibility that the much touted relationship of small IQ declines for children living in areas with naturally high fluoride in drinking water could be associated with severe dental fluorosis and not a chemical neurotoxicant (see Confirmation blindness on the fluoride-IQ issue). In November I repeated this argument because the recently published work by Choi et al (2015) provided evidence of a statistically significant relationship of cognitive deficits to severe dental fluorosis for Chinese children living in high fluoride areas  (see Severe dental fluorosis the real cause of IQ deficits?).
I am pleased to report the journal Neurotoxicology and Teratology (which published the Choi et al., 2015 paper) have now accepted a peer-reviewed letter to the Editor from me on the subject:

Perrott, K. W. (2015). Severe dental fluorosis and cognitive deficits. Neurotoxicology and Teratology.

Don’t limit possible hypotheses

My letter warns:

“cognitive deficits could have many causes or influences – genetic, environmental and/or social. Researchers need to be careful not to limit their possible hypotheses or research approaches. Unfortunately Choi et al. (2015) appear to be doing just this with their plans for a larger scale study targeted only at “fluoride’s developmental neurotoxicity.””

It points out:

Choi et al. (2012) did highlight the need for further research. Broadbent et al. (2014) showed no effect of fluoride on IQ at the optimum drinking water concentrations used in CWF [community water fluoridation]. However, most of the reports reviewed by Choi et al. (2012) considered data from areas of endemic fluorosis where drinking water fluoride concentrations are higher.”

“Choi et al. (2015) did not find a statistically significant association of drinking water fluoride concentration with any of the neuropsychological measurements. But they did find one for moderate and severe dental fluorosis with the WISC-R digit span subtest.”

This suggests a possible hypothesis involving the effects of negative physical appearance and not a chemical neurotxocant:

“Emotional problems in children have been related to physical anomalies, including obvious oral health problems like severe tooth decay (Hilsheimer and Kurko, 1979). Cognitive deficits can sometimes be related to emotional problems and subsequent learning and behavior problems. Quality of lifeparticularly oral health related quality of life – is negatively related to tooth decay and severe dental fluorosis. It is possible that negative oral health quality of life feelings in children could induce learning and behavior difficulties which are reflected in neuropsychological measurements.”

Difference between areas of endemic fluorosis and CWF

This hypothesis is applicable to children in areas of endemic fluorosis but is not relevant to areas where CWF is used:

“Sixty percent of the children in the Choi et al. (2015) pilot study had dental fluorosis graded as moderate or severe. This likely reflects the endemic fluorosis of the study area. Only a few percent of individuals in areas exposed to the optimum levels of drinking water fluoride used in CWF have dental fluorosis that severe. For example, a recent oral health survey in New Zealand found 2% of individual had moderate dental fluorosis and 0% had severe dental fluorosis (Ministry of Health, 2010). Similarly a US survey found only 2% of individuals exhibited moderate dental fluorosis and less the 1% severe dental fluorosis (Beltrán-Aguilar et al., 2010).”

“Tooth decay and other oral defects negatively impact a child’s quality of life as assessed by children and parents (Barbosa and Gavião, 2008; Nurelhuda et al., 2010; de Castro et al., 2011; Aguilar-Díaz et al., 2011; Biazevic et al., 2008; Abanto et al., 2012Krisdapong et al., 2012; Bönecker et al., 2012; Locker, 2007). Quality of life impacts have also been found for dental fluorosis, but there is a marked difference in physical appearance and quality of life assessments for children with moderate/severe dental fluorosis compared with those having none/questionable or very mild/mild forms.

The physical appearance of moderate and severe forms of dental fluorosis is generally considered undesirable so we could expect these forms to be associated with poor quality of life and this appears to be the case (Chankanka et al., 2010; Do and Spencer, 2007; Chikte et al., 2001). In contrast, most studies report no effect or a positive effect of questionable, very mild and mild forms of dental fluorosis on quality of life (Do and Spencer, 2007; Chankanka et al., 2010; Peres et al., 2009; Biazevic et al., 2008; Büchel et al., 2011; Michel-Crosato et al., 2005).

Given the different patterns of dental fluorosis severity in areas of endemic fluorosis and areas where CWF is practiced and fluoride intakes are likely to be optimal it seems reasonable to expect a difference in ways fluoride intake influences health-related quality of life and possibly cognitive factors.”

My purpose in this letter was to argue that other mechanisms besides chemical neurotoxicity should be considered in these studies. I hope researchers take this on board and look forward to the response of Choi and her co-workers to this suggestion.

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Did the Royal Society get it wrong about fluoridation?

Did the Royal Society of NZ and the Office of the NZ Prime Minister’s Chief Science Advisor make a big mistake in their report Health Effects of Water Fluoridation: a Review of the Scientific Evidence)? Did they misrepresent a scientific paper which reported an effect of fluoride on the IQ of children?

This is what “Connett’s Crowd,” anti-fluoridation activists and propagandists, are saying in their attempts to discredit the review. So, did this review make the mistake its critics claim?

Well, no. It’s just a beat up. But there is a small mistake in the review’s executive summary which the anti-fluoridationists are pouncing on.

The issue

Most critics of community water fluoridation rely heavily on this paper:

Choi, A. L., Sun, G., Zhang, Y., & Grandjean, P. (2012). Developmental fluoride neurotoxicity: A systematic review and meta-analysis. Environmental Health Perspectives, 120(10), 1362–1368.

This was a metareview of mainly obscure and brief reports (see Quality and selection counts in fluoride research) indicating the possibility the fluoride intake by children living in high fluoride areas of China and Iran may suffer IQ deficits. Choi et al., (2012) used a statistical analysis to determine the possible size of the IQ drop averaged over all the studies. They found a small drop and said:

“The estimated decrease in average IQ associated with fluoride exposure based on our analysis may seem small and may be within the measurement error of IQ testing.”

Their abstract reported the:

“standardized weighted mean difference in IQ score between exposed and reference populations was –0.45 (95% confidence interval: –0.56, –0.35).”

(Their use of “standardised weighted mean difference” was poorly explained and has caused confusion with many readers. See below for a brief explanation of the term).

What did the Royal Society Review say about this?

The review discusses the question of possible neurotoxic effects on page 49-50. Their comment relevant to Choi et al., (2014) appears below (click to enlarge):


And this is what is in the executive summary (click below to enlarge). It makes a very small mistake by referring to “less than one IQ point” when it should have said “less than one standard deviation.”


So, the review reported the Choi et al., (2012) findings accurately but made a small mistake in the executive summary. This is really of no consequence because the overall message of the small size of the estimated IQ drop (described by the authors as “small and may be within the measurement error of IQ testing”) is not really altered.

What do the anti-fluoride critics say?

Such mistakes are inevitable and authors will universally say they usually find them only after publication when no correction is possible. I remember picking up 5 mistakes in one of my papers – mainly incorrect spelling of my own name several times and a mistake in the address of my institution – those were the early days of word processing! Of course no one used my mistakes to cast doubts on the scientific content of the paper.

Still, “Connett’s crowd” have been merciless in their criticism. Here is an example from the big man himself (see Water Fluoridation: The “Healthy” Practice That Has Deceived the World):

Gluckman and Skegg (sic)* mistakenly claim “a shift of less than one IQ point” in the 27 studies reviewed by Choi et al. (2012). What they have done here is to confuse the drop of half of one standard deviation reported by the authors with the actual drop in IQ, which was 6.9 points. Such an elementary mistake would not have been made by Gluckman and Skegg (sic)* if they had actually read the report, instead of relying on what fluoridation propagandists were saying about it.

* Of course Gluckman and Skegg – who Connett calls The ‘Hollow Men’ of New Zealand –  did not author this review.

H.S. Micklem, in the Fluoride Free NZ report on the Royal Society review, snipes:

“It is hard to imagine how this mistake could have been made by anyone who had actually read the papers that are disparaged so casually.”

I guess critics should read carefully before indulging in such snaky comments. All they have demonstrated is that they did not read past the executive summary of the review (and certainly did not read the relevant section in the review). Or, more seriously, that they wish to misrepresent the review by highlighting the mistake and ignoring what the review actually says.

(At Least Kathleen Thiessen was more honest in her comments in the FFNZ report because she did refer to page 49 as well as the mistake. However she still concluded “The RSNZ report is not accurate in its characterization of the Choi et al. (2012) article on effects of fluoride on children’s IQ.”)

Update: One of my commenters, picker22, has brought this to our attention – it puts the mistake mentioend above into context.

“The original press release from Harvard School of Public Health News service made the same error stating that the difference was .5 IQ points. This error on the part of Harvard led to more that a couple of mis-statements by fluoridation advocates in the US.

The current web page notes that the sentence reporting the magnitude of IQ change was “updated” Sept 5, 2012. Sadly, I didn’t copy the original.


Is Choi et al (2012) relevant to fluoridation?

Not really.

The only study specific to community water fluoridation (CWF) the Royal Society review mentions is Broadbent, et al., (2014). Community Water Fluoridation and Intelligence: Prospective Study in New Zealand.

The Choi et al., (2012) paper reviews reports mainly from areas of endemic fluorosis where fluoride intake is much higher than areas using CWF. Subsequently the same authors  made their own measurements in a similar area of China and did not find a significant relationship of drinking water fluoride to IQ (see Choi et al., 2014. Association of lifetime exposure to fluoride and cognitive functions in Chinese children: A pilot study).

The did, however, find a relationship of IQ to severe dental fluorosis. I discuss their findings in my article 

What is this “standardised weighted mean difference”

This term caused a lot of confusion with readers and critics. Choi et al., (2012) used this statistical device because they were attempting to estimate the average decrease in  IQ associated with fluoride exposure based on the difference in IQ between children from high fluoride villages and low fluoride villages in a large number of studies. Further, different IQ scales and measurement methods were used in the different studies which had different levels of variation in the data.

They therefore standardised the differences by expressing them as a fraction of the standard deviation for each study. A mean value over all studies was determined, weighting the contribution from each study according to the precision of the IQ measurements.

The standardised weighted mean difference value of 0.45 has meaning because we know it represents less than half of one standard deviation so it gives us an indication of how it compares with measurement error. But a value of 6.9 as used by Paul Connett is meaningless – until we are told the standard deviation. Choi et al. (2012)  did not report a difference of 6.9 implied by Paul Connett who appears to have obtained that value from a response to a letter to the editor where they use a hypothetical example to explain the meaning:

“For commonly used IQ scores with a mean of 100 and an SD of 15, 0.45 SDs is equivalent to 6.75 points (rounded to 7 points).”

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Water fluoridation and dental fluorosis – debunking some myths

Dental fluorosis is really the only “negative” side effect of community water fluoridation (CWF). It occurs in non-fluoridated as well as fluoridated areas but is often a little more common in the fluoridated areas.

However, there is a lot of rubbish about dental fluorosis spouted by anti-fluoride propagandists. It is worth putting dental fluorosis into its proper context and debunking some of the misinformation they promote.

Here are some facts.

1: Diagnosis of dental fluorosis involves grading teeth into 6 levels:

  1. No dental fluorosis
  2. Questionable
  3. Very mild
  4. Mild
  5. Moderate
  6. Severe.

Here are some photos of the different grades

2: The moderate/severe grades are rare in areas considered for CWF and fluoridation does not increase prevalence of those grades of dental fluorosis. However, those more severe forms are more common in areas where dental fluorosis is endemic like parts of China, India and north Africa.

Dental and skeletal fluorosis is a real problem in these endemic areas, but it is not a problem in the areas where CWF is used.

The figure below contrasts data for prevalence of dental fluorosis in NZ and the USA where CWF is common with data for an area of endemic fluorosis in China.


3: The first 4 grades (none – mild) are judged purely “cosmetic. In fact children and parents often judge the grades questionable – mild more highly than none. Research finds these milder forms of dental fluorosis often improve dental health related quality of life (Do and Spencer, 2007; Chankanka et al., 2010; Peres et al., 2009; Biazevic et al., 2008; Büchel et al., 2011; Michel-Crosato et al., 2005).

In contrast research shows that the moderate/severe grades of dental fluorosis have a negative impact on health-related quality of life(Chankanka et al., 2010; Do and Spencer, 2007; Chikte et al., 2001).

4: Anti-fluoride propagandists often lump all grades together – presenting dental fluorosis as always bad. It also enables them to produce high figures to inflate the apparent problem. That is deceptive.

5: Anti-fluoride propagandists often use data from countries like India and China where fluorosis is endemic in their arguments against CWF. The figure above shows this is also deceptive.

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Severe dental fluorosis the real cause of IQ deficits?

A new study finds cognitive function defects, like IQ, in children are not significantly related to fluoride in drinking water. But they are associated with medium and severe dental fluorosis.

This interests me for two reasons:

  1. The report is by Choi and Grandjean who had also authored the 2012 meta-review often used by anti-fluoride activists to claim that community water fluoridation causes a lowering of IQ (the authors subsequently pointed out the high fluoride concentrations in the papers they reviewed meant that conclusion is not valid)
  2. The data reported is consistent with my suggestion in Confirmation blindness on the fluoride-IQ issue that reported relationships between IQ and drinking water fluoride concentration could really indicate a relationship with severe dental fluorosis, and not drinking water fluoride itself.

The new report is:

Choi, A. L., Zhang, Y., Sun, G., Bellinger, D., Wang, K., Yang, X. J., … Grandjean, P. (2014). Association of lifetime exposure to fluoride and cognitive functions in Chinese children: A pilot study. Neurotoxicology and Teratology.

Firstly – this is only a pilot study and has several acknowledged weaknesses – the small number of children studied (51) being the most obvious. However, this is what was found:

“Sixty percent of the subjects examined had moderate or severe fluorosis. These children were exposed to elevated fluoride concentrations in drinking water. Children with normal or questionable Dean Index were all from households with a water fluoride concentration of 1 mg/L and had urinary fluoride excretion levels below 1 mg/L.”

The children were placed in 3 groups according to their degree of dental fluorosis:

  1. Normal/questionable (N=8)
  2. Very mild/mild (N=9)
  3. Moderate/severe (N=26)

The high proportion of children with moderate/sever dental fluorosis indicates the study involved an area of endemic fluorosis.

And the results of neuropsychological tests:

“Results of multiple regression models show that moderate and severe fluorosis was significantly associated with lower total and backward digit span scores when compared to the reference combined categories of normal and questionable fluorosis (Table 4). Although the associations between fluoride in urine and in drinking water with digit span were not significant, they were in the anticipated direction. Motor coordination and dexterity were not significantly associated with fluoride in drinking water and fluorosis although higher levels were associated with poorer scores as well. Other outcomes did not reveal any association with the fluoride exposure.”

The authors used a number of neuropsychological tests. The digit span test results suggest a “deficit in working memory” for the children with moderate and severe dental fluorosis. None of the other tests used show any signficant relationship with indices for fluoride exposure.

So, this pilot study did not show any association of neuropsychological tests with fluoride concentration in drinking water but it did find an association with medium and severe dental fluorosis. This is consistent with my speculation in Confirmation blindness on the fluoride-IQ issue that “a physical defect like dental and skeletal fluorosis could lead to decreasing IQ.”

I argued that:

“minor physical anomalies are known to be associated with learning difficulties and emotional illness in children (seeHilsheimer & Kurko 1979). It seems entirely reasonable that a physical anomaly like severe dental fluorosis could lead to learning difficulties in children which could be seen as lower IQ values.”

There are many problems with the studies anti-fluoride activists promote relating IQ to fluoride in drinking water. But it could be that any real effect seen with the higher fluoride concentrations could simply be explained by effects of the physical anomaly of medium and severe dental fluorosis common at these higher concentrations.

Unfortunately the authors of this study still do not consider this possibility. I guess it could be that someone with a hammer only sees nails, and chemical toxicologists are only capable of considering brain damage caused by toxic chemicals. The effects of physical anomalies on learning difficulties are probably quite outside their training and experience.

Their confirmation bias and mental blockage on this meant they were considering dental fluorosis as just another indicator of dietary fluoride intake. However, even that assumption has its problems because genetic differences are also known to be involved in dental fluorosis.

I think this must be why they ended with a conclusion that could well be quite unfounded:

“This pilot study in a community with stable lifetime fluoride exposures supports the notion that fluoride in drinking water may produce developmental neurotoxicity”

Dental fluorosis and community water fluoridation

Fluorosis is endemic in many parts of China and the high prevalence of medium/severe dental fluorosis (60%) among the children in the Choi et al (2014) pilot study shows their situation is not at all similar to that in areas of New Zealand and USA using community water fluoridation (CWF).

The figures below give some context.

Here are examples of the different degrees of dental fluorosis.

The graph below shows the situation reported for New Zealand in the 2009 New Zealand Oral health Survey (see Our Oral Health). No severe and only 2% moderate dental fluorosis reported.

This figure (taken from Fluorosis Facts: A Guide for Health Professionals) shows the amount  of moderate and severe dental fluorosis in the US is also very small.

Perhaps we can now contrast the situation here, in areas where CWF is common, with the situation in China in areas with endemic fluorosis where these studies were undertaken. The figure below is a slide from a presentation by Xiang (2014) to Paul Connett’s recent anti-fluoride “get-together” (Xiang 2014). This is not the very mild dental fluorosis attributed to CWF.

(Anti-fluoride people also often single out the study of Xiang, et al (2003). Effect of fluoride in drinking water on children’s intelligence. Fluoride, 36(2), 84–94, because unlike the others it is more detailed.  Xiang’s team has studied areas where fluorosis is endemic.)


Anti-fluoride activists often promote the meta-review of Choi et al (2012) in their arguments against CWF. However, there are many problems with these studies including the fact reported IQ effects were associated with much higher drinking water fluoride concentrations than occurs with CWF.

The new study of Choi et al (2014) did not confirm any association of neuropsychiatric measurements with drinking water fluoride concentration. However, it did show association of negative neuropsychological effects with medium/severe dental fluorosis.

This is consistent with the physical anomaly of severe dental fluorosis being the real cause of IQ effects and not any direct chemical toxic effect.

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