Category Archives: SciBlogs

Hip fractures in the elderly and fluoride – contradictory evidence

Room for cherry-picking to confirm a bias. Separate Swedish studies report that fluoride can either prevent or promote the risk of hip fracture in the elderly. Image credit: Are hip fracture patients treated quickly enough?

Anti-fluoride activists are promoting a recent study linking fluoride intake and bone fractures. No surprise there. But they are cherry-picking a single study to support their agenda and scientifically literate people should see the wider picture and not ignore other studies which, on the whole,  convey a different story. This issue illustrates problems with epidemiological studies producing variable results and shows why people should avoid cherry-picking and look at the full range of studies in a field.

Here I consider just two studies on fluoride intake and bone fracture which produced different conclusions. Both studies involved people from Sweden where the natural fluoride levels in drinking water vary across the country.

Drinking water fluoride may protect against hip fractures

First a study from 2013:

Näsman, P., Ekstrand, J., Granath, F., Ekbom, A., & Fored, C. M. (2013). Estimated drinking water fluoride exposure and risk of hip fracture: A cohort study. Journal of Dental Research, 92(11), 1029–1034.

The main findings are illustrated in the figure showing the calculated Hazard Ratios for people of different ages living in areas of Sweden with “very low” (less than 0.3 mg/L), “low” (0.3 – 0.69 mg/L), “medium” (0.7 -1.49 mg/L) or “High” (greater than 1.5 mg/L) fluoride levels in the drinking water. The Hazard Ratio in the figure below is a measure of the number of hip fractures at these levels compared with the number of hip fractures at “Very low” fluoride concentration. The bars represent the 95% confidence intervals. The Hazard Ratios for the “very low” group are 1.0 and Hazard Ratios statistically significantly different to 1 (no effect) are coloured red.

Considering all people there is no statistically significant increase in the number of hip fractures for any level of water fluoride concentration compared with the “very low” levels. The number of hip fractures experienced by people in the two lower age groups (less than 70 years and 70 – 80 years) was significantly lower at higher water fluoride concentrations than at the “very low” concentrations. The authors say:

this “suggests a protective effect of fluoride among the younger (age younger than 80 years): however, the majority of fractures occurred above the age of 80 years (median age at time of fracture, 82.0).”

So a study suggested that the fluoride in Swedish drinking water does not encourage bone fractures and may actually protect against them in the lower age groups.

Fluoride may encourage hip fractures

Now a study from 2021 – the one anti-fluoride activists are promoting (for obvious reasons):

Helte, E., Vargas, C. D., Kippler, M., Wolk, A., Michaëlsson, K., & Åkesson, A. (2021). Fluoride in Drinking Water , Diet , and Urine in Relation to Bone Mineral Density and Fracture Incidence in Postmenopausal Women. Environmental Health Perspectives, 129(April).

Unlike Näsman et al (2013) which used drinking water fluoride concentrations as a measure of fluoride exposure, Helte et al (2021) used urinary fluoride and estimated dietary fluoride intake as measures of fluoride exposure. The Hazard Ratios were calculated from the number of hip fractures in the Tertile 2 groups (0.88 – 1.30 mg/g urinary fluoride or 1.74 – 2.41 mg/day dietary fluoride intake) and Tertile 3 groups (1.30 – 116.51 mg/g urinary fluoride or 2.41 – 11.16 mg/day dietary fluoride intake) compared with hip fractures in the tertile 1 groups (0.14 – 0.88 mg/g urinary fluoride or 0.26 – 1.74 mg/day dietary fluoride intake).

Note: The urinary fluoride units of mg/g represent mg of urinary F/g urinary creatinine. Creatinine levels were used to correct the spot values for dilution.

The Hazard Ratios that statistically significantly different to 1 (no effect) are coloured red in the figure below.

A bit complicated I know, but what the figure shows is no statistically significant increase in hip fracture numbers for the tertile 2 groups compared with the lower F intake tertile one group. But a significant increase in fracture numbers for the tertile 3 groups except for the women exposed to constant water fluoride concentrations since 1982 in the dietary F group.

Hertle et al (2021) also considered other types of fracture. There were no statistically significant increases in fractures in the upper tertiles for either the “all fractures” or “major osteoporotic fractures” classes.

So, a bit of a mixed bag but this paper is currently being promoted by anti-fluoride activists as evidence of a harmful result from community water fluoridation (CWF).

Critically assessing the evidence for bone fractures

It is easy to see why supporters of CWF may cite Näsman et al (2013) as evidence for lack of harm and opponents may cite Helte et al (2021) as evidence of harm from CWF. But neither approach is really scientific. The methodological differences and choice of factors considered can easily explain variable results. One should critically and rationally assess both of these papers, together with the many other papers reporting similar studies, before coming to any conclusion.

On balance, the published studies probably support the findings of Näsman et al (2013) and not Helte et al (2021). In fact, a systematic review and meta-analysis published in 2015 concluded that chronic exposure to fluoride in drinking water was not associated with a significant increase in hip fracture risk. The citation for this review is:

Yin, X.-H., Huang, G.-L., Lin, D.-R., Wan, C.-C., Wang, Y.-D., Song, J.-K., & Xu, P. (2015). Exposure to Fluoride in Drinking Water and Hip Fracture Risk: A Meta-Analysis of Observational Studies. PLOS ONE, 10(5), e0126488. 

It’s worth reproducing one of the figures from that review because it illustrates how epidemiological studies may, individually, support a claim of harm but when considered as a whole these studies do not support the claim. The figure below shows the range of Hazard Ratios obtained by a number of studies.

The lesson here is to be very careful of claims made on the basis of single cherry-picked studies. Especially when those making the claim have a bias they wish to confirm. Every claim should be critically and rationally considered using all the available studies.

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An open letter to Paul Connet and the anti-fluoride movement

Paul Connett and Vyvyan Howard have, through the local Fluoride Free New Zealand activist group, published an open letter addressed to NZ scientists and educators (see An Open Letter To NZ Scientists And Educators). It is strange to encourage scientific exchanges through press releases but if they are seriously interested in an exchange of informed scientific opinion on the research they mention I am all for it.

In fact, I renew my offer to Paul Connett for a new exchange on the new relevant research along the lines of the highly successful scientific exchange we had in 2013/2014 summarised in Conett & Perrott (2014) The Fluoride Debate.

Connett and Howard say they felt “let down” by the reception they received in their 2018 visit. But they should realise this sort of ridicule is inevitable when a supposedly scientific message is promoted by activist fringe groups with known funding by big business (in this case the “natural”/alternative health industry). The science should be treated more respectably and discussed in a proper scientific forum or via a proper scientific exchange rather than political style activist meetings.

It is this sort of respectable, informed and open scientific exchange I am offering to Paul Connett and Vyvyan Hoard.

Connett and Howard argue that there has recently been  “a dramatic change in the quality of these [fluoride] studies.” I agree that new research occurs all the time and there is plenty of scope upgrading of the scientific exchange we had in 2013/2014 to cover that new research. Consideration of the new research requires the objective, critical and intelligent consideration scientists are well used to and this is not helped by activist propaganda meetings. So I encourage Connett and Howard to accept my offer. after all, if they are confident in their own analysis of this research what do they have to lose?

Inaccuracies in “open letter”

One can see an “Open letter” as displaying a willingness to enter into a proper scientific exchange. However, Connett and Vivyan’s open letter includes inaccuracies and misinformation on the new research which simply demonstrates that a one-sided presentation cannot present the research findings properly.

For example, they misrepresent the 2014 New Zealand fluoridation review of Eason et al (2014). Health effects of water fluoridation: A review of the scientific evidence. Even to the extent of mistaking the authors (not Gluckman & Skegg as they claim) and misrepresenting the small mistake made in the summary which was later corrected. That attitude does not bode well for the proper consideration of the research.

Connett and Howard concentrate on new research relating child IQ to fluoride intake but they ignore completely the fact that all the research comparing IQ in fluoridated and unfluoridated areas show absolutely no effect. I have summarised the results for the three papers involve in this table.

Instead, they concentrated on a few extremely weak relationships reported in a few papers. But even here they get this wrong – for example, they say there is “a loss of about 4 IQ points in offspring for a range of 1 mg/liter of fluoride in mother’s urine.” The paper they refer to (Green et al 2019) actually found no statistically significant relationship between child IQ and maternal urinary fluoride for all children considered. The relationship Connett and Howard mention was actually for male children (no relationship for female children or for all children) and was very weak. These sort of weak relationships are commonly found in epidemiological research and are usually meaningless. In this case, Connett and Howard have simply cherry-picked one value and misrepresented it as applying to all children.

Both the Green et al (2019) and Till et al (2020) papers Connett and Howard refer to suffer from selecting a few weak statistically significant relationships and ignoring the larger number of non-significant relationships they found for the data they investigated. Connett and Howard also completely ignored the new studies that don’t fit their claims. For example that of Santa-Marina et al (2019). Fluorinated water consumption in pregnancy and neuropsychological development of children at 14 months and 4 years of age. which showed an opposite positive relationship of child IQ with maternal urinary fluoride. Similar they ignored the large Swedish study of Aggeborn & Öhman (2020). The Effects of Fluoride in the Drinking Water showing no effect of fluoride on IQ but positive effects on oral health and employment possibilities in later life.

In conclusion, I reiterate that genuine open scientific exchanges do not take place via press release and activist meetings. However, the fact that Connett and Howard have issued an “Open Letter” could be interpreted as inviting others to participate in a proper exchange. I endorse that concept and offer Connett and Howard space for a free and open exchange on the new research at this blog site.

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Embarrassing knock-back of second draft review of possible cognitive health effects of fluoride

We have come to expect exaggeration of scientific findings in media reports and institutional press releases. But it can also be a problem is original scientific publications where findings are reported in an unqualified or exaggerated way. Image Credit: Curbing exaggerated reporting

This is rather embarrassing for a US group attempting to get the science right about possible toxic effects of fluoride. It’s also embarrassing for the anti-fluoride activists who have “jumped the gun” and been citing the group’s draft review as if it was reliable when it is not.

The US National Academies of Sciences, Engineering, and Medicine (NAS) have released their peer-review of the revised US National Toxicity Program (NTP) draft on possible neurodevelopmental effects of fluoride (see Review of the Revised NTP Monograph on the Systematic Review of Fluoride Exposure and Neurodevelopmental and Cognitive Health Effects).

This is the second attempt by the NTP reviewers to get acceptance of their draft and it has now been knocked back by the NAS peer reviewers for a second time.

Diplomatic but damning peer-review

Of course, the NAS peer reviewers use diplomatic language but the peer review is quite damning. It criticises the NTP for ignoring some of the important recommendations in the first peer review. One which is quite critical was the lack of response to the request that NTP explains how the monograph can be used (or not) to inform water fluoridation concentrations. The second NAS peer review firmly states that the NTP:

“should make it clear that the monograph cannot be used to draw any conclusions regarding low fluoride exposure concentrations, including those typically associated with drinking-water fluoridation.”

And:

“Given the substantial concern regarding health implications of various fluoride exposures, comments or inferences that are not based on rigorous analyses It seems to me that there is soime internal politicsshould be avoided.”

It seems to me there is some internal politics involved and some of the NTP authors may be promoting their own, possibly anti-fluoride, agenda. Certainly, the revised NTP draft monograph continues to obfuscate this issue. It continues to state that “fluoride is presumed to be a cognitive neurodevelopmental hazard to humans” – a clause which anti-fluoride campaigner consistently quote out of context. Yes, it does state that this is based on findings demonstrating “that higher fluoride exposure (e.g., >1.5 mg/L in drinking water) is associated with lower IQ and other cognitive effects in children.” But this is separated from the other fact that the findings on cognitive neurodevelopment for “exposures in ranges typically found in drinking water in the United States (0.7 mg/L for optimally fluoridated community water systems)” are “are inconsistent, and therefore unclear.”

Monograph exaggerates by enabling unfair cherry-picking

So, you see the problem. The draft NTP monograph correctly refers to IQ and other cognitive effects in children exposed to excessive levels of fluoride. The draft also correctly refers to that lack of evidence for such effects at lower fluoride exposure levels typical of community water fluoridation. But in different places in the document.

The enables activist cherry-picking to support an anti-fluoride agenda and that is a fault of the document itself. It should clearly state that the monograph should not be used to draw any conclusion at these low exposure levels. This is strongly expressed in the peer-reviewers’ comments.

I find the blanket “presumed to be a hazard for humans” quite misleading. For example, no one says that calcium is “presumed to be a cardiovascular hazard to humans.” Or that selenium is “presumed to be a cardiovascular or neurological hazard to humans.” Or what about magnesium – would you accept that it is a “presumed neurological hazard to humans?” Would you accept that iron is a “presumed cardiovascular, cancer, kidney or erectile dysfunction hazard to humans?” Yet all those problems have been reported for humans at high intake levels of these elements.

No, we sensibly accept that various elements and microelements have beneficial, or essential benefits, to humans at reasonable intake levels., Then we sensibly warn that these same elements can be harmful at excessive intake. To proclaim that any of these elements are “presumed” to be hazardous – without clearly saying at excessive intake levels, is simply distorting or exaggerating the data.

What does “presumed” mean?

A lot of readers find the use of “presumed” strange. But it’s meaning is related to the levels of evidence found by reviewers.

No, don’t believe those anti-fluoride activists who falsely claim that “presumed” is the highest level of evidence and that the finding should be treated as factual. They are simply wrong.

Some idea of the word’s use is presented in this diagram from the NTP revised draft monograph.

So “presumed” means that the evidence for the effect is moderate. That the effect is not factual or known. But as further evidence comes in the ranking of fluoride as a hazard may increase, or decline.

As the monograph bases this “presumed” rating solely on evidence from areas of endemic fluorosis where fluoride intake levels are high it is correct to avoid stating the effects as factual. For example, consider these images from areas of endemic fluorosis in China (taken from a slide presentation by Xiang 2014):

Clearly, people in these areas suffer a range of health effects related to the high fluoride intake. The cognitive effects like IQ loss from these areas could result from these other health effects, not directly from fluoride (although excessive fluoride intake leads to the health effects).

So we can “presume” that fluoride (in areas of endemic fluorosis where fluoride intake is excessive) is a “cognitive neurodevelopmental hazard for humans” but we can not factually state that the neurodevelopment effects are directly caused by fluoride. That would require further scientific work to elucidate the specific mechanisms involved in creating that effect.

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Science is often wrong – be critical

Activists, and unfortunately many scientists, use published scientific reports like a drunk uses a lamppost – more for support than illumination

Uncritical use of science to support a preconceived position is widespread – and it really gets up my nose. I have no respect for the person, often an activist, who uncritically cites a scientific report. Often they will cite a report which they have read only the abstract of – or not even that. Sometimes commenters will support their claims by producing “scientific evidence” which are simply lists of citations obtained from PubMed or Google Scholar.

[Yes, readers will recognise this is a common behaviour with anti-fluoride activists]

Unfortunately, this problem is not restricted to activists. Too often I read scientific papers with discussions where authors have simply cited studies that support, or they interpret as supporting, their own preconceived ideas or hypotheses. Compounding this scientific “sin” is the habit of some authors who completely refuse to cite, or even discuss, studies producing evidence that doesn’t fit their scientific prejudices.

Publication does not magically make scientific findings or ideas “true” – far from it. The serious reader of scientific literature must constantly remember that the chances are very high that published conclusions or findings are likely to be false. John Ioannidis makes this point in his article Why most published research findings are false. Ioannidis concentrates on the poor use, or misuse, of statistics. This is a constant problem in scientific writing – and it certainly underlines the fact that even scientists will consciously or unconsciously manipulate their data to confirm their biases. They are using statistical analysis in the way a drunk used a lamppost – for support rather than illumination.

Poor studies often used to fool policymakers

These problems are often not easily understood by scientists themselves but the situation is much worse for policymakers. They are not trained in science and don’t have the scientific or statistical experience required for a proper critically analysis of claims made to them by activists. Yet they are often called on to make decisions which rely on the acceptance, or rejection, of scientific claims (or, claims about the science).

An example of this is a draft (not peer-reviewed) paper by Grandjean et al  – A Benchmark Dose Analysis for Maternal Pregnancy Urine-Fluoride and IQ in Children.

These authors have an anti-fluoride activists position and are campaigning against community water fluoridation (CWF). Their paper uses their own studies which report very poor and rare statistical relationships of child IQ with fluoride intake as “proof” of causation sufficiently strong to advocate for regulatory guidelines. Unsurprisingly their recommended guidelines are very low – much lower than those common with CWF.

Sadly, their sciencey sounding advocacy may convince some policymakers. It is important that policymakers be exposed to a critical analysis of these studies and their arguments. The authors will obviously not do this – they are selling their own biases. I hope that any regulator or policymaker required to make decisions on these recommendations have the sense to call for an independent, objective and critical analysis of the paper’s claims.

[Note: The purpose of the medRxiv preprints of non-peer-reviewed articles is to enable and invite discussion and comments that will help in revising the article. I submitted comments on the draft article over a month ago (Comments on “A Benchmark Dose Analysis for Maternal Pregnancy Urine-Fluoride and IQ in Children”) and have had no response from the authors.  This lack of response to constructive critiques is, unfortunately, common for this group. I guess one can only comment that scientists are human.]

Observational studies – exploratory fishing expeditions

A big problem with published science today is that many studies are nothing more than observational exploratory studies using existing databases which, by their nature, cannot be used to derive causes. Yet that can easily be used to derive statistically significant links or relationships. These can be used to write scientific papers but they are simply not evidence of causes.

Properly designed studies, with proper controls and randomised populations properly representing different groups, may provide reasonable evidence of causal relationships – but most reported studies are not like this. Most observational studies use existing databases with non-random populations where selection and confounding with other factors is a huge problem. Authors are often silent about selection problems and may claim to control for important confounding factors, but it is impossible to include all confounders. The databases used may not include data for relevant confounders and authors themselves may not properly select all relevant confounders for inclusion.

This sort of situation makes some degree of data mining likely., This occurs when a number of different variables and measures of outcomes are considered in the search for statistically significant relationships. Jim Frost illustrated the problems with this sort of approach. Using a set of completely fictitious random data he was able to obtain a statistically significant relationship with very low p values and R-squared values showing the explanation of 61% of the variance (see Jim Frost – Regression Analysis: An Intuitive Guide).

That is the problem with observational studies where some degree of data mining is often involved. It is possible to find relationships wich look good, have low p-values and relatively high R-squared values, but are entirely meaningless. They represent nothing.

So readers and users of science should beware. The findings they are given may be completely false or contradictory. or at least meaningless in quantitative terms (as is the case with the relationships produced by the Grandjean et al 2020 group discussed above).

A recent scientific article provides a practical example of this problem. Different authors used the same surgical database but produced complete opposite findings (see Childers et al: 2020). Same Data, Opposite Results?: A Call to Improve Surgical Database Research). By themselves each study may have looked convincing. Both used the same large database from the same year. Over 10,000 samples were used in both cases and both studies were published in the same journal within a few months. However, the inclusion and exclusion criteria used were different. Large numbers of possible covariates were considered but these differed. Similarly, different outcome measures were used.

Readers interested in the details can read the original study or a Sceptical Scalpel blog article Dangerous pitfalls of database research. However, Childers et al (2020) describe how the number of these sort of observational studies “has exploded over the past decade.” As they say:

“The reasons for this growth are clear: these sources are easily accessible, can be imported into statistical programs within minutes, and offer opportunities to answer a diverse breadth of questions.”

However:

“With increased use of database research, greater caution must be
exercised in terms of how it is performed and documented.”

“. . . because the data are observational, they may be prone to bias from selection
or confounding.”

Problems for policymakers and regulators

Given that many scientists do not have the statistical expertise to properly assess published scientific findings it is understandable for policymakers or regulators to be at a loss unless they have proper expert advice. However, it is important that policymakers obtain objective, critical advice and not simply rely on the advocates who may well have scientific degrees. Qualifications by themselves are not evidence of objectivity and, undoubtedly, we often do face situations where scientists become advocates for a cause.

I think policymakers should consciously seek out a range of scientific expert advice, recognising that not all scientists are objective. Given the nature of current observational research, its use of existing databases and the ease with which researchers can obtain statistically significant relationships I also think policymakers should consciously seek the input of statisticians when they seek help in interpreting the science.

Surely they owe this to the people they represent.

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Even studies from endemic fluorosis areas show fluoride is not harmful at levels used in fluoridation

Most of the claims made by anti-fluoride propagandists are simply wrong. Image source: Fluoridation and the ‘sciency’ facts of critics

Anti-fluoride propagandists continually cite studies from areas of endemic fluorosis in their arguments against community water fluoridation (CWF). But if they critically looked at the data in those papers they might get a shock. Invariably the published data, even from areas of endemic fluorosis, shows fluoride is safe at the concentrations relevant to CWF.

I have completed a detailed analysis of all the 65 studies the Fluoride Action Network (FAN) lists as evidence that community water fluoridation (CWF) is harmful to child IQ. The full analysis is available for download as the document Analysis of FAN’s 65 brain-fluoride studies.

In this article, I discuss the studies in the FAN’s list (see FLUORIDE & IQ: THE 65 STUDIES”) which report relationships between child IQ and fluoride exposure in areas of endemic fluorosis. There are eleven such studies in the FAN list but only six of them provide sufficient data to enable independent statistical analysis.

While those six studies do show a statically significant (p<0.05) negative relationship of IQ with fluoride intake those results are not relevant to CWF because the fluoride as exposure levels are much higher than ever occurs with CWF.

However, it is possible to investigate if the relationships are significant at lower concentrations more relevant to CWF. I have done this with these six studies and illustrate the result obtained with these graphs below using the data extracted from Xiang et al (2003). (This study is often used by anti-fluoride campaigners).

The red data points in the figures below are for lower concentrations of urinary F or creatinine adjusted urinary F. The range for the red points is still quite a bit larger than urinary F levels measured for children in areas where CWF is used. However, we can see that the relationships at these lower ranges are not statistically significant (results from regression analyses cited in figures).

 

This was also the case with the other studies from FAN’s list which provided sufficient data for regression analyses. I summarise the results obtained for five of these studies in the figure below.

This show that none of the studies found statistically significant relationships with fluoride exposure for the low fluoride concentration relevant to CWF. The situation is basically the same for the sixth study, Mustafa et al (2018), which reports average school subject performances for a range of subjects for children in Khartoum state, Sudan. However, it is hard to know what the safe limit for fluoride exposure is in that climate (for climatic reasons the upper permissible F level in drinking water is set at 0.33 ppm for Khartoum state) and the sample numbers are low. Interested readers should consult my report – Analysis of FAN’s 65 brain-fluoride studies.

Conclusion

Anti-fluoride campaigners often cite FAN’s list (FLUORIDE & IQ: THE 65 STUDIES”) in their attempts to argue that fluoridation is bad for the child’s brain. But in these series of articles Anti-fluoride 65 brain-fluoride studies not evidence against fluoridation, I have shown that their arguments are false.

In Child IQ in countries with endemic fluorosis imply fluoridation is safe I showed that while IQ and other health problems may occur where fluoride exposure is very high in areas of endemic fluorosis the reports themselves implicitly assume that the low fluoride exposure in the “low fluoride” areas is safe. It is the data from these areas, not the “high fluoride” areas, that are relevant to CWF. So despite the heavy use of these articles by FAN and anti-fluoride activists these studies do not prove what they claim. If anything these studies show CWF is safe.

In this article, I considered a few of these studies which included data relevant to low fluoride exposure. When the low fluoride exposure data (relevant to CWF)  from these studies were statistically analysed none of them showed significant relationships of child IQ to fluoride exposure. That confirms the implicit assumption from these studies that there is no negative effect of fluoride exposure on child IQ at these low levels.

Finally, in Canadian studies confirm findings of Broadbent et al (2015) – fluoridation has no effect on child IQ I summarise results from the only three studies where comparisons of IQ for children living in fluoridated and unfluoridated areas are compared. These studies were made in New Zealand and Canada and the results were the same. No statistically significant differences in child IQ were found.

However, the authors of the Canadian studies ignored this result and instead used questionable statistical methods to search for possible relationships between fluoride exposure and child IQ. Most of the relationships they report were not statistically significant but, nevertheless, they and their supporters have simply ignored this and concentrated on the few statically significant relationships.

Anti-fluoride activists currently rely strongly on these studies and heavily promote them. I will discuss these few studies further in my next article.

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Canadian studies confirm findings of Broadbent et al (2015) – fluoridation has no effect on child IQ

Readers may remember the scathing reaction of anti-fluoride campaigners to the paper of Broadbent et al (2015). This was the first paper to compare child and adult IQ levels for people living in fluoridated and unfluoridated areas.

The anti-fluoride campaigners were extremely rude in their reaction – accusing the authors of fraud and claiming the paper was “fatally flawed.” Interestingly, several scientists known for their anti-fluoride bias also launched attacks – but more respectably as letters to the editor of the journal. For example, see articles by Osmunson et al (2016),  Grandjean (2015),; and Menkes et al (2014).

And why? Simply because Broadbent et al (2015) showed there was no difference in IQ of people living in fluoridated areas. That the studies from areas of endemic fluorosis used by anti-fluoride activists to argue at CWF were just not relevant (see Child IQ in countries with endemic fluorosis imply fluoridation is safe).

But isn’t it strange? Two more recent papers (Green et al 2019 & Till et al 2020) have effectively repeated the work of Broadbent et al (2015). They found the same result – no difference in IQ of children living in fluoridated and unfluoridated areas. And simply no reaction, no condemnation from anti-fluoride activists or the anti-fluoride scientists.

No condemnation because these anti-fluoride critics promote these papers for other reasons. But this underlines how biased the critics of the Broadbent et al (2015) paper were.

I have completed a detailed analysis of all the 65 studies the Fluoride Action Network (FAN) lists as evidence that community water fluoridation (CWF) is harmful to child IQ. The full analysis is available for download as the document Analysis of FAN’s 65 brain-fluoride studies.

In this article, I discuss the studies in the FAN’s list (see FLUORIDE & IQ: THE 65 STUDIES”) which compare child IQ in areas of “fluoridated” and “unfluoridated” fluoride in Canada. Only two studies – but I include that of Broadbent et al (2015) (which FAN’s list ignores) for completeness. All three studies found no difference in the IQ of children living in fluoridated and unfluoridated areas.

Comparing IQ of children in fluoridated and unfluoridated areas

The table below summarises the results reported by all three studies – Broadbent et al (2015), Green et al (2019), and Till et al (2020).

Table 1: Results from studies comparing IQ of children and adults from fluoridated and fluoridated areas

Notes:
Data from Green et al (2019) for children whose mothers lived in fluoridated or unfluoridated areas during pregnancy.
Data from Till et al (2020) for children either breastfed of formula-fed as babies while living in fluoridated or unfluoridated areas.

There is absolutely no difference in IQ due to fluoridation. Remember, the standard dedication of the values in the table are about 13 to 16 IQ points.

I have presented all the results from these papers graphically below. FSIQ is the normal IQ measurement. VIQ (Verbal IQ) and PIQ (Performance IQ) are subsets of FSIQ.

The only statistically significant differences between fluoridated and unfluoridated areas were for VIQ of breastfed babies (VIQ higher for fluoridated areas) and PIQ of formula-fed babies (PIQ lower for fluoridated areas).

Anti-fluoride campaigners and (biased scientists like Grandjean) love the Green et al (2019) and Till et al (2020) papers because they reported (very weak) negative relationships of some child cognitive measures with fluoride intake ( I discuss this in separate articles). This is largely a result of the statistical methods used – particularly resorting to several different cognitive measures and measures of fluoride exposure, as well as the separation of results according to gender. Reminds me of the old saying that one can always get the results one requires by torturing the data hard enough.

I will return to the statistical problems of these and similar papers in a separate article.

Misrepresentation by anti-fluoride activists

Anti-fluoride campaigners have latched on to the two Canadian studies – often making claims that simply are not supported. But always ignoring the data shown above.

For example – this propaganda poster from FAN promoting the Green et al (2019) study.

This completely misrepresents the results of the study. No difference was found in the IQs of children from fluoridated and unfluoridated areas. These people completely ignore that result while placing unwarranted faith in the weak relationships reported elsewhere in that paper. (In fact, Green et al (2019) found a weak significant relationship only for boys – the relationships for all children and for girls were not significant. See my articles about this statistical torture).

And this FAN propaganda poster promoting the Till et al (2020) study.

Again – completely wrong. There was no difference in IQ of formula-fed babies in fluoridated and unfluoridated areas (see Table 1 above). Even worse – FAN is misrepresenting the statistical relationships reported in this paper as there’s was no statistically significant relationship between child IQ and fluoride exposure for formula-fed our breastfed babies once the influence of outliers and/or confounders were considered.

Misrepresentation by anti-fluoride scientists

It is understandable, I guess, that the authors of the two Canadian papers make a lot of the poor statistical relationships they reported and ignored the fact that they did not see any effect of fluoridation. Perhaps they can be excused some bias due to professional ambition. But this underlines why sensible readers should always critically and intelligently read the papers in this controversial area. One should never rely on the public relations claims of authors and their institutes. But it is sad to see how scientific basis and ambitions can lead scientists to support the claims of political activists. or worse, to attack honest scientists who do post-publication peer review of the studies (see for example When scientists get political: Lead fluoride-IQ researcher launches emotional attack on her scientific critics).

I am also very critical of scientific supporters of these studies who have their own anti-fluoride motivations. Philippe Grandjean, for example, was one of the authors very critical of the Broadbent et al (2015) paper and ignored completely the fact that the Green et al (2019) and Till et al (2020) papers report exactly the same result – no effect of fluoridation on child IQ. Grandjean often makes public comments supporting the claims of anti-fluoride campaigners like FAN. He also behaved in a scientifically unethical way when he refused to allow my critique of the flawed paper by Malin & Till (2015) to be published in Environmental Health – the journal he acts as the chief editor of (see Fluoridation not associated with ADHD – a myth put to rest).

I am repeating myself but it is a matter of “reader beware.” Readers should not simply rely on the scientific “standing” of authors who are only human and suffer from the same biases as others. They should read these papers for themselves and make up their own mind about what the data actually says.

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Child IQ in countries with endemic fluorosis imply fluoridation is safe.

Anti-fluoride activists love to point out that people living in endemic fluorosis areas in countries like China suffer all sorts of health problems, including lower IQ. But studies of these areas show no lowering of IQ in the low fluoride areas relevant to community water fluoridation.

I have completed a detailed analysis of all the 65 studies the Fluoride Action Network (FAN) lists as evidence that community water fluoridation (CWF) is harmful to child IQ. The full analysis is available for download as the document Analysis of FAN’s 65 brain-fluoride studies.

In this article, I discuss the studies in the FAN’s list (see FLUORIDE & IQ: THE 65 STUDIES”) which compare child IQ in areas of “low” and “high” fluoride in countries like China, Mexico, Iran, Egypt, and India where fluorosis is endemic. In fact, all these studies either assume or provide evidence that fluoride at the concentrations used for CWF is harmless.

IQ differences for “high” and “low” fluoride areas

FAN was really dredging through very poor research to find these studies. In fact, FAN had to go to the trouble of translating many of these studies because they were obscure and not available in English.

Of their 65 studies, 17  do not provide data for fluoride intake or for drinking water fluoride concentrations. Instead, they simply describe the “high” areas as endemic fluorosis areas or areas where people suffer severe dental or skeletal fluorosis. Several of the studies used “control” groups from areas of “slight” fluorosis or dental fluorosis in contrast to skeletal fluorosis.

Another 29 studies did provide water fluoride concentrations for the “low” fluoride and “high” fluoride areas. This data is useful as it enables us to consider how relevant the results are to CWF. I have summarised the data in Figure 1.

The take-home message from Figure 1 is that while these 29 studies do show a decrease in child IQ in areas of “high” fluoride those areas are not relevant to CWF. In fact, the only relevance to CWF are the areas of “low” fluoride where there is the implicit assumption that child IQ is not affected. We can also assume this is the case for the 17 studies which do not provide details of fluoride exposure.

Figure 1: Comparison of water fluoride levels in “high” and “low” fluoride areas of 29 of the FAN studies and in areas where CWF is used.

So these 46 studies heavily promoted by FAN over recent years do not show any harm from CWF – in fact, all these studies implicitly assume there is no negative effect on child IQ at the “low” fluoride levels studied – and these are the areas most relevant to CWF. A simple consideration of the health problems faced by people living in areas of endemic fluorosis should have made it obvious that the data for high fluoride areas is simply not relevant. Consider these figures from Das et al (2016) – one never sees people like this in areas where CWF is used:

Dental fluorosis case found in the study area (age: 12, sex: male). Das et al (2016)

Skeletal fluorosis case found in the study area (age: 17, sex: male). Das et al (2016)

FAN is simply silly to suggest these studies, and especially the results for the “high” fluoride areas, area at all relevant to CWF.

Mind you, Paul Connett, FAN Director, likes to draw attention to one of these studies where he claims the “high” fluoride area has a drinking- water fluoride concentration of 0.81 mg/L which is similar to that for CWF. He is simply dredging the data (and ignoring all the other studies he cites)  to make this claim. The study he refers to was made in an area of iodine deficiency and is extremely weak – simply and half pages in a Chinese newsletter. Have a look for yourself – Lin et al (1991).

In a future article, I will discuss the studies in FAN’s list which compare IQ for children from fluoridated and unfluoridated areas.

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Anti-fluoride 65 brain-fluoride studies not evidence against fluoridation

Activists like ant-fluoride and anti-vaccination propagandists are very selective about the studies they promote. But their bias often means they get even these ones wrong. FAN’s 65 brain-fluoride studies are an example of this. Image credit: Don’t let confirmation bias narrow your perspective

Anti-fluoride and anti-vaccination activists suffer from a common activist fallacy – they believe their own propaganda. They also have a network of “natural”/alternative health industry internet sites and magazines to disseminate these beliefs and propaganda. A glaring example is a smug article, The End of Fluoridation Is in Sight, published on the Mercola.com alternative health, anti-vaccination site.

The uninformed reader looking at these alternative health industry sources might be excused for thinking that community water fluoridation (CWF) is about to end. That the scientific evidence against it is damning. But, of course, those conclusions are wrong – the science supporting CWF remains strong and the few studies activists use to argue against CWF have big flaws.

Actually, the situation is even worse than that. The studies commonly cited by anti-fluoride activists actually support CWF when they are read properly. Activists are unaware of this because they rarely read the studies they cite – most don’t get past the title, let alone the abstract, and certainly don’t bother with the real content. And they never subject these studies to critical analysis.

The Fluoride Action Network (FAN) has collected  together all the studies they argue show CWF is bad for children’s brains in a single list – FLUORIDE & IQ: THE 65 STUDIES.I have completed a detailed analysis of all the 65 studies and my full analysis is available for download as the document Analysis of FAN’s 65 brain-fluoride studies.

In fact, none of these studies in FAN’s list provides any credible evidence that CWF is harmful to child IQ. On the contrary, these studies either assume or provide evidence that fluoride at the concentrations used for CWF is harmless.

I will summarise my findings of these studies in a series of upcoming articles as my health permits (I have just spent a couple of stressful weeks in hospital).

  1. Difference studies – a simple comparison of cognitive measures in people living in “low fluoride and “high fluoride” areas. Forty-six studies made in areas of endemic fluorosis – India, China, Mexico, Iran, and Sudan. All these studies implicitly assume no negative health effects at fluoride concentration relevant to CWF
  2. Three difference studies relevant to CWF where populations in non-fluoridated and fluoridated areas are compared. All these studies show no effect of CWF on child IQ.
  3. Studies which derive relationships of cognitive measurements with fluoride exposure in areas of endemic fluorosis. Six of these studies include enough data for testing if there is a statistically significant effect at concentrations relevant to CWF – there is no effect observed in all these cases.
  4. Three studies deriving relationships for cognitive measurements with fluoride exposure in low fluoride areas where concentrations are relevant to CWF. These controversial studies involve considerable statistical manipulations and activists cherry-pick a few statistically significant relationship but ignore the many more non-significant relationships.

Read my article Analysis of FAN’s 65 brain-fluoride studies if you want the detailed analysis. Otherwise, just follow my summaries in future posts.

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Another study used by anti-fluoride activists actually shows community water fluoridation OK

Another study comparing effect in children from nonendemic areas (Dagang) and endemic fluorosis area (Jinghai) about 80km apart in the Tianjin area of China. Hardly sampling the same population.

Anti-fluoride campaigners still use studies from endemic fluorosis area of China in their campaign against community water fluoridation (CWF). This misrepresents the situation. While the control areas they use (non-endemic fluorosis areas where there are no health effects) are relevant to CWF the data from the endemic fluorosis areas where fluoride intake is high are simply not relevant to CWF.

However, some of these studies provide enough information to enable checking for health effects in the control, non-endemic fluorosis areas. I discuss one of these studies below – Cui et al (2018) – and show it finds no health effects at the low fluoride concentration relevant to CWF. The use of this study in anti-fluoride campaigns is therefore misleading.

I also show how even in his misrepresentation of this study the “Research Director” of the Fluoride Action Network (FAN), Chris Neurath, makes basic mathematical mistakes.

The citation for this study is:

Cui, Y., Zhang, B., Ma, J., Wang, Y., Zhao, L., Hou, C., … Liu, H. (2018). Dopamine receptor D2 gene polymorphism, urine fluoride, and intelligence impairment of children in China: A school-based cross-sectional study. Ecotoxicology and Environmental Safety, 165(August), 270–277.

The study used school children (7 to 12 years old) from the districts of Jinghai and Dagang in Tianjin of China (see map above). The endemic fluorosis area had drinking water fluoride concentrations of 1.52–2.49 mg/L and the nonendemic fluorosis area had drinking water fluoride concentrations of 0.20–1.00 mg/L.

Of course, the results for children in the endemic fluorosis area are simply not relevant to CWF where the drinking water concentrations are usually less than 0.8 mg/L.

ONLY THE DATA FROM THE NON-ENDEMIC FLUOROSIS AREA IS RELEVANT TO CWF.

Child IQ values were compared with urinary fluoride levels and regression analysis used to determine if there was any relationship. The children were also tested for the presence of different genes and each of three different genetic groups was considered separately.

Skewed data

The data from both endemic and non-endemic fluorosis areas were combined. That for urinary F was skewed and had to be transformed to provide the normal data distribution required for linear regression analysis. Consequently, the authors report linear regression results for the relationship of child IQ to the logarithm of urinary F [Log(UF)].

No statistically significant relationships were found for two of the genotypes (designated CC & CT) but there was a significant relationship for the genotype designated TT. Less than 14% of the children had this gene.

Figure from Cui et al (2018) showing a negative relationship of child IQ with the logarithm of urinary fluoride. Equation of fitted line is IQ = 117.48 – 9.75*Log(UF). R-squared = 0.142, p = 0.012. 95% CI for coefficient -17.21,-2.29

So, of course, the anti-fluoride campaigners simply go with the results for the children with the TT gene and ignore the results for the other 86% of children.

Nothing new here – they always ignore results that they can not use in their campaigns to confirm their biased presentations.

Analysis of the data for the low fluoride levels relevant to CWF doesn’t support activist claims

Here I will just consider the data relevant to CWF. After digitally extracting the data from the figures in the paper I restricted linear regression analysis to the children with urinary F values of less than 2 mg/L (which is still rather high for areas where CWF is used). The figure below displays that data, together with the results of linear regression analysis. Untransformed values were used because data for urine fluoride concentrations less than 2 mg/ml is normally distributed.

Linear regression analysis for the relationship of child IQ with urinary F. Children with TT gene about 44% of the sample. Children with CC and CT genes about 86% of the sample.

There were no statistically significant (p < 0.05) relationships, either for the TT variant (red triangle) or for the other variants (open circle) (CC & CT combined in this figure).

So, once again we see that if the appropriate data from these studies are used they confirm that there is no relationship of child IQ with measures of fluoride exposure at concentrations relevant to CWF (see also New study touted by anti-fluoridation campaigners actually indicates fluoridation is safe).

FAN’s “Research Director” makes simplistic mistakes

FAN plans to use studies like Ciu et al (2018) in their upcoming case against the US Environmental Protection Agency. Their aim is to attempt to establish cognitive effects as the main harms from CWF and then use studies like these to argue against CWF. Even though studies like this simply establish that there is no harm from fluoride concentration used for CWF. One hopes that the experts testifying for the EPA show how these studies are misrepresented by FAN.

FAN has provided a presentation by their “Research Director,” Chris Nerath, which they claim summarises their arguments. It’s a “pretty” PowerPoint presentation (FAN describes it as “powerful“) and may fool some people, but it just does not stand up to scientific scrutiny.

Quite apart for the misrepresentation of these scientific studies, and use of studies like Cui et al (2018) which are not relevant to CWF, Neurath simply makes basic scientific mistakes.

For example, in his slide 33, he claims that Cui et al (2018) showed a 10 point IQ loss for a 1 mg/L increase in urinary F. But that is simply not true – his mistake is that he ignored the fact that the linear relationship reported by Cui et al 2018) [IQ = 117.48 – 9.75*Log(UF)] is based on log values of urinary F where the value of the coefficient is -9.75. In other words, the 10 point loss is for an increase of urinary by a log value of 1 is equivalent to an increase from a concentration of 1 mg/L [Log(1) = 0] to a urinary F concentration of 10 mg/L ([log(10)=1].

Slide 33 from the presentation by Chris Neurath, FAN’s “Research Director” displaying an embarrassing mathematical mistake.

Let’s do the correct calculation for him. The Cui et al (2018) relationship shows an IQ value 117.48 for a urinary F concentration of 1 mg/L [Log(1)=0] and 114.55 for a urinary F concentration of 2 mg/L [Log(2)=0.301]. So the loss is only 2.9 IQ points.

Neurath thinks it sounds much better for his case to say a loss of 10 IQ points but all he has done is shown either he did not read Cui et al (2018) properly or does not understand a simple mathematical relationship.

However, I should stress Neurath’s argument is irrelevant to CWF, as well as being mathematically wrong because its analysis includes data from endemic fluorosis areas. In fact, there is no statistically significant relationship between child IQ and urinary fluoride either for the overall group or for the separate genetic groups considered.

“Safety threshold”

The graph in Neurath’s slide is adapted from Cui et al (2018) which made an attempt to determine a “safety threshold of urine fluoride levels for IQ
impairment” for the children with the TT gene. They defined this “safety threshold” as the urinary fluoride value corresponding to the mean IQ for the group. This seems arbitrary to me and the authors make no attempt to justify the definition.

They then divided the data into quintiles according to urinary fluoride values. Quintile 4 was the first quintile where the mean IQ value is below the mean IQ for the whole group so they assumed to mean log(UF) for that quintile to represent the “safety threshold.”

It all seems quite hairy to me – but I suppose the method produces a few data points which Neurath was able to plot on a graph and make to appear impressive. But look at the spread of the data (Neurath does not show this) in the graph below where the bars represent the spread of data for each quintile and the dotted line is the mean IQ value for the group. The spread is hardly surprising – the overall data is very scattered and only about 9 data points were used for each quintile.

I frankly think this method of determining a “safety threshold” is meaningless. We could do exactly the same with the data where urinary fluoride is less than 2 mg/L – much more relevant to CWF. This is the result – using quartiles of about 8 data points each.

Quite meaningless.

There are many other misrepresentations and mistakes in Chris Neurath’s Powerpoint presentation and I may return to some of them later. However, let’s hope the court recognises these and rejects FAN’s attempts.

Conclusion

Anti-fluoride activists continually use studies from areas of endemic fluorosis in their campaigns against CWF. However, when the actual data relevant to community water in these studies are considered they usually show no health effect.  There is no doubt that people living in endemic fluorosis areas suffer a range of health problems. But where these studies provide complete data they almost always could be used to support CWF.

Activists like FAN and their “Research Director” simply clutch on to any study they can finds which appears to show harmful effects of fluoride and ignore the fact that they are hardly ever relevant to the fluoride concentration used in CWF. They cherry-pick and ignore, or cover-up, any information not supporting their bias.

This approach is hardly scientific. It is not objective and never undertakes a critical review of the studies used. These activist display a thoughtless approach to scientific research when they opportunistically use scientific studies like this. Their approach is unthinking and it is hardly surprising that they make simple mathematical and statistical errors like the one described here and made by Paul Connett recently (see and Author confirms anti-fluoridation activist misrepresentation of her work).

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When scientists get political: Lead fluoride-IQ researcher launches emotional attack on her scientific critics

age credit: Science and Politics – Skeptically.org

It seems impossible to keep politics out of science. It’s a pity because politics can end up forcing science to produce the results desired by politicians. When this happens the ideal aim of science – the pursuit of objective knowledge – can get lost.

We rightly disapprove of external political and commercial influences on science. But there is another insidious form of politics derived from ego, personal ambition and the promotion of research by institutes and individual researchers. This is very often driven by the competition for research funding – the loudest researcher gets the grant. These days this is a real problem – the classical introverted scientist, no matter how bright, is often at a complete disadvantage when it comes to the fight over research funding.

In my own career, I have seen excellent researchers driven to redundancy simply because they did not have the political skills to fight for research funds. And at the same time, I have seen mediocre scientists, often producing poor quality or even misleading science, get those funds – simply because of their ambition and political skills.

These thoughts came flooding back to me as I read the new opinion piece by Christine Till, the leader of the research group that published several of the recent fluoride-IQ/ADHD and similar papers that I have critiqued here. Papers that have been heavily promoted by the authors and Till’s institute as well as the anti-fluoride/anti-vaccination crowd and, at the same time, extensively critiqued by the scientific community.

The citation  for her article is:

Till, C., & Green, R. (2020). Controversy: The evolving science of fluoride: when new evidence doesn’t conform with existing beliefs. Pediatric Research.

Unfortunately, the article is not a reply to critics or a good faith scientific engagement with the scientific issues. It is simply an attack on those who have made honest and respectful critiques. An attack which attributes unjust motives to her critics and comes close to personal.

Attempt to close down science by personal attacks

I discussed some of these issues before in my articles Scientific integrity requires critical investigation – not blind acceptance and Fluoridation science and political advocacy – who is fooling who?

In this case, I was concerned about the way  Dr William Ghali, one of the promoters of  Christine Till’s work, attacked and attempted to belittle scientific colleagues who were indulging in the normal peer-review process of critiquing published papers which they considered had faults. Nothing new about that scientific critique – it goes on all the time. It is expected by authors and, in the end, it helps to improve the science. I Personally think such critique should be welcomed by researchers.

If the opponents of scientific exchange like Dr Ghali are successful in their attempt to prevent such scientific debate then we are all losers. How can we trust scientific findings that are protected from scrutiny?

This is what is wrong with the opinion piece by Till and Green cited above. Instead of entering into a good-faith scientific exchange with their critics they attribute motives and biases to them. Even accusing them of attempting to prevent the progress of science. They accuse critics of a “tendency to ignore new evidence,” of  “overt cognitive bias” and of promoting  a “polarized fluoride debate.”

But, in fact, these critiques have come because the “new evidence” is not being ignored but is being evaluated. It is being critically considered. The article more or less admits this when it says “critics attacked the methodology of the study [Green et al (2019] and discounted the significance of the results.

True, the so-called “fluoride debate” is polarised. After all, it is being promoted by anti-fluoride/anti-vaccination activists who are attempting to prevent or remove, a health policy known to benefit children. Till & Green may be unhappy that they have not been able to win over the scientific community with their paper but it is hardly honest to reject the critiques of the paper by calling them “attacks” or by claiming they “ignore” the evidence.

An admission the paper had difficulties

The article admits the  Green et al (2019) paper had difficulties right from the beginning. It took three attempts before a journal would accept it for consideration. Even then it ended up having “several additional rounds of review by the JAMA editors until we eventually reached a compromise.” This gives some substance to my speculation of problems in the review process which lead to the unprecedented publication of an editor’s note – a political action  I have never seen before (see If at first you don’t succeed . . . statistical manipulation might help).

They acknowledge that even their colleagues in environmental epidemiology “were initially sceptical.” And so they should have been – all new research should be reviewed sceptically and critically.

Refusing to engage scientifically

But the annoying thing is that these authors attempt to write off the scepticism and critical review of the wider scientific community as being due to “experts” (yes in quotes), “who held strong beliefs . .” This despite the fact that in the published critiques it is not “strong beliefs” which were presented, but detailed consideration of the methodology and statistical analyses used in the original paper.

All these critiques were made respectfully – and often with thanks to the Green et al (2019) for their new work. Yet Till and Green accuse these reviewers of making “vitriolic comments and claims with little scientific basis” – a comment which is, in itself, disrespectful to those who took time to make their critiques. They resort to smearing two of the reviews (by the UK-based Science Media Centre and Dr Berezow, a specialist from the American Council on Science and Health) by accusations these bodies are “both heavily funded by the pharmaceutical and food and beverage industries.” This funding smear is commonly used by anti-science activists who attempt to discredit scientific findings or analysis but refuse to consider the science itself.

They say of these two reviews that they claim “the results are driven by outliers” – yet a simple search shows that this comment simply does not appear in the cited reviews.  The critique of Dr Berezow from the American Council on Science and Health does not include either of the words “outlier” or “driven.”

The only reference to “outliers” in the Science Media Centre review was by Dr Oliver Jones, Associate Professor of Analytical Chemistry, RMIT University who wrote:

“The authors state that an increase of 1 milligram per liter (1 mg/L) increase in fluoride was associated with a 4.49 point lower IQ score but fluoride intake appears to have been below 1 mg/L for most people in the study, even for those with fluoridated water, and nearly everyone (bar a few outliers) had a fluoride intake of less than 2 mg/L (which multiple previous studies have shown is safe) . There is also a Lot of variation in the data – which makes drawing firm conclusions/ predictions from it difficult.”

A valid criticism which needed a response – not a smear.

My search for the word “driven” produced these two comments:

Dr Joy Leahy, Statistical Ambassador, Royal Statistical Society, wrote:

“if a woman is living in an area with fluoridated water during pregnancy, then her child is likely to grow up drinking this same fluoridated water. Therefore, it is difficult to say whether any association found is driven by the fluoride consumption in pregnancy, or an assumed fluoride consumption in the infant after birth.”

Prof Rick Cooper, Professor of Cognitive Science, Birkbeck, University of London, said:

“a significant decrease in IQ was found only in boys – girls showed a non-significant increase in IQ. The negative effect was driven by a small number of boys whose mothers had extreme levels of fluoride exposure, but even these children had IQ in the normal range.”

These are valid points that again deserve a scientific response yet Till & Green describe them as “vacuous claims exemplify attempts to manipulate the scientific evidence and manufacture doubt.”

We all support using new knowledge to adjust policies

Till & Green attempt to claim the high moral ground by asserting:

“Science advances by continuously challenging old ideas and adjusting our beliefs as new knowledge emerges, even if this new evidence conflicts with conventional wisdom or is inconvenient.”

Of course, this is true and I think it is dishonest of them to pretend this is not also the position of those who critiqued their paper. These reviewers were interested in looking at the new results, evaluating them and seeing how relevant they are. Seeing if they do indeed require us to adopt new thinking.

After all, look at what Dr Berozow, one of the critics they smeared by implying he was influenced by industry funding  and was falling back on “vitriolic comments” and “vacuous claim”, says in introducing his critique:

“The investigation by Green et al into the effect of maternal consumption of fluoride on the IQ of children is important. It is always wise to constantly evaluate and reevaluate long-standing public health practices in the light of new evidence.”

Till & Green are simply resorting to attributing motive and asserting their critics are not open to new knowledge as a way of avoiding facing up to the valid criticisms made by experts who reviewed and critiqued their work.

Confirmation bias – the pot calls the kettle black

We all suffer from confirmation bias and scientists (including Till & Green) are not immune. It is well understood that scientists are the last people to recognise problems in their own work. That is why peer review and open critique of scientific reports is so essential. But, in line with the whole approach of this opinion piece, Till & Green attempt to present a picture that only their critics suffer from this problem. They say:

“We typically fret about subtle biases, like recall bias and unmeasured confounding, but confirmation bias, the tendency to ignore or debunk data that does not conform to what we believe, is arguably a much larger problem.”

I find their attempt to belittle concerns about “unmeasured confounding” rather ironic. After all, this was the problem with Till’s original fluoride-ADHD work (which she used to win research grants for her later fluoride research) that I highlighted in Perrott (2018) Fluoridation and attention deficit hyperactivity disorder – a critique of Malin and Till (2015).

I am aware that Till has read my paper in its pre-publication and published forms but studiously ignores it. For example, the ADHD paper of Riddell et al (2109), which she co-authored, simply does not include Perrott (2018) in its discussion and continues to present Malin & Till (2105) as authoritative despite the obvious flaw that it ignored important confounders, and when these are considered their claim of a relationship between fluoridation and ADHD prevalence proved to be false.

So much for her attribution of confirmation bias to others – when she is obviously guilty of it in this case by ignoring “data that does not conform, to what [she] believes.”

The Till & Green opinion piece is unwise

Till & Green seem to have simply reacted emotionally to the reviews and critiques the Green et al (2019) paper received. They, of course, had the right – even the obligation – to respond scientifically to the reviews. But I believe their response in this article is unwise, maybe even professionally damaging,  and they should not have committed these emotional outbursts to print. After a cooling down period, it is possible they will withdraw the article – and that would be best for them in the end.

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