Tag Archives: Broadbent

Anti-fluoridationists rejection of IQ studies in fluoridated area.

US anti-fluoride activist Paul Connett claims studies cannot detect an IQ effect from fluoridated water because total fluoride intake is the real problem – but still campaigns against community water fluoridation. Image credit: MSoF “Activist Spouts Nonsense – The Evidence Supports Fluoridation”

This is another article in my critique of the presentation Paul Connett prepared to present to a meeting at Parliament in February.

I deal with his coverage of the studies of IQ effects where community water fluoridation (CWF) is used. There are now actually three such studies (Broadbent et al. 2015, Barberio et al. 2017  and  Aggeborn & Öhman 2016), but Connett pretends there is only one – the Broadbent et al. (2015) New Zealand study.

Maybe because it was the first one to provide evidence challenging his extrapolation of the fluoride/IQ studies (see The 52 IQ studies used by anti-fluoride campaigners) results in areas of endemic fluorosis to areas where CWF is used. It is also the study which seems to have resulted in the most hostility from anti-fluoride campaigners.

So here I will just be sticking with his criticism of the New Zealand study Broadbent et al (2015):

Slide 76 from Paul Connett’s presentation prepared for his February meeting at  parliament buildings

Broadbent’s findings do not “negate all other human studies”

Paul allows emotion to get the better of him as no one is suggesting this at all. The studies Connett refers to are all from areas of endemic fluorosis (see  The 52 IQ studies used by anti-fluoride campaigners), not from areas of CWF.

Broadbent et al (2015) simply concluded that their “findings do not support the assertion that fluoride in the context of CWF programmes is neurotoxic.”  That is a modest statement and Broadbent et al. (2015) simply do not draw any conclusions about the studies Connett relies on. But, of course, Connett is upset because this and similar studies just do not support his attempt to extrapolate results from areas of endemic fluorosis to areas of CWF.

The health problems suffered by people in areas of endemic fluorosis are real and it is right they should be studied and attempts made to alleviate them. But this has absolutely nothing to do with CWF.

“Fatally flawed” charge is itself fatally flawed

Again, Paul has allowed emotions to get the upper hand. It is possible, and necessary, to critique published papers – but critiques should be evidence-based and realistic. Paul’s “fatally flawed” charge (slides 77 & 78) simply displays how much this paper has put his nose out of joint.

But let’s look at the specific “flaws” Paul (and other critics associated with the Fluoride Action Network) claim.

The two villages mindset: Paul alleges that the Broadbent et al (2015) study “essentially compared two groups.” He is stuck in the mindset of most of his 52  studies from areas of endemic fluorosis (see  Fluoride & IQ: The 52 Studies). The mindset of simply comparing the IQ levels of children in a village suffering endemic fluorosis with the IQ levels of children in a village not suffering endemic fluorosis. This simple approach can identify statistically significant differences between the villages but provides little information on causes. For example, most of these studies used drinking water fluoride as a parameter but there could be a whole range of other causes related to health problems of fluorosis.

Professor Richie Poulton, current Director of the Dunedin Multidisciplinary Health and Development Research Unit

In contrast, Broadbent et al. (2015) used “General Linear models to assess the association between CWF and IQ in childhood and adulthood, after adjusting for potential confounders.” The statistical analysis involved includes accounting for a range of possible risk-modifying factors besides CWF., This was possible because the study was part of the Dunedin Multidisciplinary Health and Development Study. This is a highly reputable long-running cohort study of 1037 people born in 1972/1973 with information covering many areas.

The fluoride tablets argument: Connett and other critics always raise this issue – the fact that “In New Zealand during the 1970s, when the study children were young, F supplements were often prescribed to those living in unfluoridated areas.” Often they will go further to claim that all the children in the unfluoridated area of this study were receiving fluoride tablets – something they have no way of knowing.

But the fact remains that fluoride tablets were included in the statistical analysis. No statistically significant effect was seen for them.  Overlap of use of fluoride tablets with residence in fluoridated or unfluoridated areas will have occurred and their influence would be reflected in the results found. Presumably, the effect would be to increase the confidence intervals. As the critics, Menkes et al. (2014), say “comparing groups with overlapping exposure thus compromises the study’s statistical power to determine the single effect of CWF.”  I agree. But this does not negate the findings which are reported with the appropriate confidence intervals (see below).

The point is that the simplistic argument that effects of fluoride tablets were ignored is just not correct. Their effect is reflected in the results obtained.

Potential confounders: Many poor quality studies have ignored possible confounders, or considered only a few. This is a general problem with these sort of studies – and even when attempts are made to include all that the researchers consider important a critic can always claim there may be others – especially if they do not like the results. Claims of failing to consider confounders can often be simply the last resort of armchair critics.

In this case, there is no actual reported association to be confounded (unlike my identification of this problem with the Malin & Till 2015 ADHD study – see Perrott 2017). However, Osmunson et al. (2016) specifically raised possibilities of confounding by lead, manganese, mother’s IQ and rural vs urban residence. Mekes et al. (2014) also raised the rural vs urban issue as well as a possible effect from breastfeeding reducing fluoride intake by children in fluoridated areas.  In their response, Broadbent et al (2015b & 2016) reported that a check showed no significant effect of lead or distance from the city centre and pointed out that manganese levels were too low to have an effect. Broadbent et al (2015b) also reported no significant breastfeeding-fluoride interaction occurred.

Numbers involved: Connett claims the study was fatally flawed because “it had very few controls: 991 lived in the fluoridated area, and only 99 in non-fluoridated” (Slide 77). But the numbers are simply given by the longer term Dunedin study themselves – they weren’t chosen by Broadbent and his co-workers. That is the real world and is hardly a “fatal flaw.”

The 95% confidence intervals

Yes, statisticians always love to work with the large numbers but in the real world, we take what we have. Smaller numbers mean less statistical confidence in the result – but given that Broadbent et al (2015) provides the results, together with confidence intervals, it is silly to describe this as fatally flawed. These were the results given in the paper for the parameter estimate of the factors of interest:

Factor Parameter estimate 95% Confidence interval p-value
Area of residence -0.01 -3.22 to 3.20 .996
Fluoride toothpaste use 0.70 -1.03 to 2.43 .428
Fluoride tablets 1.55 -0.38 to 3.49 .116

Connett did not refer to the confidence intervals reported by Broadbent et al (2015). However, Grandjean and Choi (2015) did describe them as “wide” – probably because they were attempting to excuse the extrapolation of “fluoride as a potential neurotoxic hazard” from areas of endemic fluorosis to CWF.

The argument over confidence intervals can amount to straw clutching – a “yes but” argument which says “the effect is still there but is small and your study was not large enough to find it.” That argument can be never ending but it is worth noting that Aggeborn & Öhman (2016) made a similar comment about wide confidence intervals for all fluoride/IQ studies, including that of Broadbent et al. (2015).  Aggeborn & Öhman (2016) had a very large sample (almost 82,000 were involved in the cognitive ability comparisons) and reported confidence intervals of -0.18 to 1.03 IQ points (compared with -3.22 to 3.20 IQ points reported by Broadbent et al 2015). Based on this they commented, “we are confident to claim that we have estimated a zero-effect on cognitive ability.”

The “yes but” argument about confidence intervals may mean one is simply expressing faith in an effect so small as to be meaningless.

Total fluoride exposure should have been used: Connett says (slide 77) “Broadbent et al did not use the proper measure of fluoride exposure. They should have used total F exposure.  Instead, they used only exposure from fluoridated water.” Osmunson et al. (2016) make a similar point, claiming that the study should not have considered drinking water fluoride concentration but total fluoride intake. They go so far as to claim “the question is not whether CWF reduces IQ, but whether or not total fluoride intake reduces IQ.”

This smacks of goalpost moving – especially as the argument has specifically been about drinking water fluoride and most of the studies they rely on from areas of endemic fluorosis specifically used that parameter.

In their response to this criticism Broadbent et al (2016) calculated estimates for total daily fluoride intake and used them in their analysis which “resulted in no meaningful change of significance, effect size, or direction in our original findings.”

It’s interesting to note that Connett and his co-workers appear to miss completely the point about “wide” confidence intervals made by Grandjean and Choi (2015). Instead, they have elevated their argument to the claim that fluoride intake is almost the same in both fluoridated and unfluoridated areas so that any study will not be able to detect a difference in IQ. Essentially they are claiming that we are all going to suffer IQ deficits whether we live in fluoridated or unfluoridated areas.

This is the central argument of their paper – Hirzy et al (2016). However, the whole argument relies on their own estimates of dietary intakes – a clear example where motivated analysts will make the assumptions that fit and support their own arguments. This argument also fails to explain why the Dunedin study found lower tooth decay in fluoridated areas.

Last time I checked the anti-fluoride campaigners, including Connett, were still focusing on CWF – fluoride in drinking water. One would think if they really believed their criticism that they would have given up that campaign and instead devoted their energies to the total fluoride intake alone.


All studies have limitations and of course, Broadbent et al. (2015) is no exception. However, the specific criticisms made by Connett and his fellow critics do not stand up to scrutiny. Most have been responded to and shown wrong – mind you this does not stop these critics from continuing to repeat them and disregard the responses.

I believe the relatively wide confidence intervals could be a valid criticism – although it does suggest a critic who is arguing for very small effects. A critic who may always find the confidence intervals still exclude their very small effect – no matter how large the study is.

In effect, the narrow confidence intervals reported by Aggeborn & Öhman (2016) should put that argument to rest for any rational person.


Aggeborn, L., & Öhman, M. (2016). The Effects of Fluoride In The Drinking Water

Barberio, A. M., Quiñonez, C., Hosein, F. S., & McLaren, L. (2017). Fluoride exposure and reported learning disability diagnosis among Canadian children: Implications for community water fluoridation. Can J Public Health, 108(3),

Broadbent, J. M., Thomson, W. M., Ramrakha, S., Moffitt, T. E., Zeng, J., Foster Page, L. A., & Poulton, R. (2015). Community Water Fluoridation and Intelligence: Prospective Study in New Zealand. American Journal of Public Health, 105(1), 72–76.

Broadbent, J. M., Thomson, W. M., Moffitt, T., Poulton, R., & Poulton, R. (2015b). Health effects of water fluoridation: a response to the letter by Menkes et al. NZMJ, 128(1410), 73–74.

Broadbent, J. M., Thomson, W. M., Moffitt, T. E., & Poulton, R. (2016). BROADBENT ET AL. RESPOND. American Journal of Public Health, 106(2), 213–214. https://doi.org/10.2105/AJPH.2015.302918

Grandjean, P., Choi, A. (2015). Letter: Community Water Fluoridation and Intelligence. Am J Pub Health, 105(4).

Hirzy, J. W., Connett, P., Xiang, Q., Spittle, B. J., & Kennedy, D. C. (2016). Developmental neurotoxicity of fluoride: a quantitative risk analysis towards establishing a safe daily dose of fluoride for children. Fluoride, 49(December), 379–400.

Malin, A. J., & Till, C. (2015). Exposure to fluoridated water and attention deficit hyperactivity disorder prevalence among children and adolescents in the United States: an ecological association. Environmental Health, 14.

Menkes, D. B., Thiessen, K., & Williams, J. (2014). Health effects of water fluoridation — how “ effectively settled ” is the science? NZ Med J, 127(1407), 84–86.

Osmunson, B., Limeback, H., & Neurath, C. (2016). Study incapable of detecting IQ loss from fluoride. American Journal of Public Health, 106(2), 212–2013.

Perrott, K. W. (2017). Fluoridation and attention deficit hyperactivity disorder – a critique of Malin and Till ( 2015 ). Br Dent J.

Similar articles



Combatting anti-fluoride Gish gallopers

gishWe have all experienced this problem. Claims made on the internet which rely on nothing more than constant assertion – and moving on, when challenged, to new claims, similarly relying only on assertion. The old Gish gallop.

truth boots

The conscientious defender of science is often loaded down with the task of checking out claims, finding the literature – and reading it to find what it actually says. So it is useful, when there is a debate on a specific subject, to have access to a source where all the claims are considered together.

Community water fluoridation is one subject where all sorts of weird and wonderful (and unscientific) claims are peddled. Now we have a document which critically analyses many of these claims in one place. What’s more – it is in a peer-reviewed publication. And it is local – dealing with common claims made by anti-fluoridation campaigners in New Zealand.

The paper is:

Broadbent, J., Wills, R., McMillan, J., Drummond, B., & Whyman, R. (2015). Evaluation of evidence behind some recent claims against community water fluoridation in New Zealand. Journal of the Royal Society of New Zealand, 6758(October), 1–18.

Unfortunately, it is behind a pay wall – but many readers may have institutional access – or know someone who has.

I am not going to go through the whole paper here – nor present the analysis of each claim ( I have already done this for many common anti-fluoride claims – interested readers can do a topic search here, or browse the fluoridation list of articles). Instead, I list below all the claims considered in the paper below

Chemistry of fluoride

Claim: ‘[F]luorine is an inherently toxic element’ (Gross 1956; Atkin 2013).

Claim: ‘Fluorine naturally presents as calcium fluoride in water supplies’ (Guha 2011; Atkin 2013).

Claim: ‘Water fluoridation systems use either hydrofluorosilicic acid or derivative hexafluorosilicate. These compounds have never been tested for human health safety’ (Waugh 2012; Atkin 2013).

Claim: ‘Silicofluorides do not fully dissociate to form free fluoride ions in aqueous solution and revert to the silicofluoride ion in acid stomach conditions’ (Atkin 2013; Sauerheber 2013).

Claim: ‘Silicofluorides do not completely dissociate to form free fluoride ions, as proved by Crosby (1969)’ (Royal 2010).

Claim: ‘The World Health Organization states that 40% of ingested fluoride is absorbed through the stomach wall as molecular hydrofluoric acid (a known mutagen). This negates the “all fluoride ions are the same” deception’ (Atkin 2013).

Health and safety

Claim: ‘In 2000, the US National Sanitation Foundation released test results showing fluoridation chemicals typically add 0.43 parts per billion (ppb) arsenic to the finished water’ (Connett 2001; Atkin 2013; Hirzy et al. 2013).

Claim: ‘Adjusting for NZ parameters, applying the EPA’s risk factor (3.5 × 10–5 deaths per 70 year lifetime per microgram arsenic per day), we would expect 1.1 extra lung and bladder cancer deaths per year in NZ due to the contaminated fluoridation chemicals used’ (Atkin 2013).

Claim: ‘A report by environmental risk consultant, Declan Waugh, showed that across all major health conditions, the 70%-fluoridated Republic of Ireland had significantly higher disease rates than never-fluoridated Northern Ireland, often by several 100%’ (Atkin 2013; Waugh 2013).

Claim: ‘The recent Harvard review of IQ studies found that there was a genuine concern about developmental neurotoxicity’ (Atkin 2013).

Claim: ‘In the US court case of Aitkenhead v Borough of West View it was found proven that fluoridation increased cancer rates by 5%. This finding has never been  overturned’ (Atkin 2013).

Claim: ‘In 2006, Dr Elise Bassin published high quality research showing that boys (but not girls) exposed to fluoridated water between the ages of 5 and 10 had 500% more osteosarcoma in their teens (Bassin et al. 2006). No study has ever refuted Bassin’s findings, as they look at total lifetime exposure or exposure at time of diagnosis, both of which are irrelevant. This equates to two osteosarcoma deaths per year in New Zealand (NZ)’ (Atkin 2013).

Claim: ‘In 2006 Dr Elise Bassin published research in Cancer Causes and Control, demonstrating that it is likely that males exposed to fluoride, including fluoridated water, between the ages of 6 and 8 years inclusive, had at least a five-fold increased risk in developing osteosarcoma (bone cancer) in their teens’ (Atkin 2011).

Claim: ‘A range of studies, using different modalities, has shown a correlation between fluoride and heart disease’ (Takamori et al. 1956; Singh et al. 1961; Atkin 2013).

Claim: ‘[A] direct correlation [exists] between the fluoride level in arteries, including coronary arteries, and atherosclerosis’ (Li et al. 2012; Atkin 2013).

Claim: ‘Perhaps one of the most alarming potential consequences of water fluoridation, as highlighted in recent research, is that a significant correlation exists between fluoride uptake and calcification of the major arteries, including coronary arteries’ (Li et al. 2012; Waugh 2012).

Claim: ‘Following fluoridation’s introduction into the US, deaths from heart attacks sky-rocketed in the fluoridated communities, compared with non-fluoridated ones’ (Miller 1952; Atkin 2013).

Claim: ‘Between 1% and 3% of the population have a chemical intolerance to fluoride. This manifests in a range of conditions, including gastrointestinal problems and debilitating chronic fatigue’ (Feltman & Kosel 1961; Moolenberg 1987; Atkin 2013).

Claim: ‘In one study, which lasted 13 years, Feltman & Kosel (1961) showed that about 1% of patients given 1 mg of fluoride each day developed negative reactions, (Connett 2012).

Claim: ‘Research by the State University of New York in 2009 showed women in fluoridated communities had a 15% higher incidence of preterm births, and that this rate was greater for poor non-white mothers. Further research also shows higher preterm birth rates and lower birth weights connected with fluoride (Susheela et al. 2010). Based on NZ statistics, we would expect at least 3.3 extra neonatal deaths per year just from extra extreme preterm births caused by fluoridation, disproportionately affecting Maori and Pacific’ (Atkin 2013).

Claim: ‘Those whom fluoridation is claimed to most benefit, poor non-whites, not only receive little if any such benefit, as found by the York Review, but are most at risk from fluoride’s toxicity’ (Atkin 2013).

Research and mechanisms

Claim:‘The biggest reason [for reduction of dental caries] in New Zealand is that the Ministry of Health directed school dental nurses to stop filling teeth unnecessarily. They stopped filling tiny surface enamel defects during the Hastings experiment, producing an overnight 25% reduction in ‘decay’, attributed to fluoridation in the report (Colquhoun & Mann 1986). In 1976, they stopped drilling and filling perfectly healthy molars—a 64% reduction over five years’ (de Liefde 1998; Atkin 2013).

Claim: ‘The claimed reductions in decay [in the Hastings fluoridation trial], which were greatest for the younger children, were brought about partly if not mainly by a local change in diagnostic procedure following introduction of fluoridation’ (Colquhoun & Mann 1986).

Claim: ‘The original belief was that fluoride had to be ingested to harden teeth during enamel formation. This was discredited in 1999 (Featherstone 1999). Any significant effect from fluoride is topical, not systemic, through high fluoride concentrations (such as toothpaste), not through fluoridated water washing over the teeth during the day’ (Atkin 2013).

Note: Many of the claims considered are sourced from an article by Mark Atkins – formerly the “science and legal advisor” for Fluoride Free NZ. That article is:

Atkin, G. M. (2013). New Zealand drinking water should be fluoridated: No. Journal of Primary Healthcare, 5(4), 332–334.

Similar articles




Fluoridating water does not lower IQ – New Zealand research

Here is a press release from University of Otago today. If you want to read the original paper these links work:

Community Water Fluoridation and Intelligence: Prospective Study in New Zealand.
Community Water Fluoridation and Intelligence: Prospective Study in New Zealand

New University of Otago research out of the world-renowned Dunedin Multidisciplinary Study does not support claims that fluoridating water adversely affects children’s mental development and adult IQ.

The researchers were testing the contentious claim that exposure to levels of fluoride used in community water fluoridation is toxic to the developing brain and can cause IQ deficits. Their findings are newly published in the highly respected American Journal of Public Health.

The Dunedin Study has followed nearly all aspects of the health and development of around 1000 people born in Dunedin in 1972-1973 up to age 38.

Lead author Dr Jonathan Broadbent says the new research focused on Study members’ fluoride exposure during the first five years of their lives, as this is a critical period in brain development, after which IQ is known to be relatively stable.

Dr Broadbent and colleagues compared IQs of Study members who grew up in Dunedin suburbs with and without fluoridated water. Use of fluoride toothpaste and tablets was also taken into account.

They examined average IQ scores between the ages of 7-13 years and at age 38, as well as subtest scores for verbal comprehension, perceptual reasoning, working memory and processing speed. Data on IQ were available for 992 and 942 study members in childhood and adulthood, respectively.

Dr Broadbent says the team controlled for childhood factors associated with IQ variation, such as socio-economic status of parents, birth weight and breastfeeding, and secondary and tertiary educational achievement, which is associated with adult IQ.

“Our analysis showed no significant differences in IQ by fluoride exposure, even before controlling for the other factors that might influence scores. In line with other studies, we found breastfeeding was associated with higher child IQ, and this was regardless of whether children grew up in fluoridated or non-fluoridated areas.”

Dr Broadbent says that studies that fluoridation opponents say show that fluoride in water can cause IQ deficits, and which they heavily relied on in city council submissions and hearings, have been reviewed and found to have used poor research methodology and have a high risk of bias.

“In comparison, the Dunedin Multidisciplinary Study is world-renowned for the quality of its data and rigour of its analysis,” he says.

“Our findings will hopefully help to put another nail in the coffin of the complete canard that fluoridating water is somehow harmful to children’s development. In reality, the total opposite is true, as it helps reduce the tooth decay blighting the childhood of far too many New Zealanders.”

This work was supported by the New Zealand Ministry of Education, the New Zealand Department of Health, the New Zealand National Children’s Health Research Foundation, US National Institute of Dental and Craniofacial Research Grant R01 DE-015260-01A1, UK Medical Research Council Grant MR/K00381X/1, US National Institute on Aging Grant AG032282, and a programme grant from the Health Research Council (HRC) of New Zealand. The Dunedin Multidisciplinary Health and Development Research Unit is supported by the HRC.