Category Archives: Science and Society

Debunking a “classic” fluoride-IQ paper by leading anti-fluoride propagandists


Three of the paper’s authors – Quanyong Xiang (1st Left), Paul Connett (2nd Left) and Bill Hirzy (far right) – preparing to bother the EPA.

Anti-fluoride groups and “natural”/alternative health groups and websites are currently promoting a new paper by several leading anti-fluoride propagandists. For two reasons:

  1. It’s about fluoride and IQ. The anti-fluoride movement recently decided to give priority to this issue in an attempt to get recognition of possible cognitive deficits, rather than dental fluorosis,  as the main negative health effect of community water fluoridation. They want to use the shonky sort of risk analysis presented in this paper to argue that harmful effects occur at much lower concentrations than currently accepted scientifically. Anti-fluoride guru, Paul Connett, has confidently predicted that this tactic will cause the end of community water fluoridation very soon!
  2. The authors are anti-fluoride luminaries – often described (by anti-fluoride activists) as world experts on community water fluoridation and world-class scientists. However, the scientific publication record for most of them is sparse and this often self-declared expertise is not actually recognised in the scientific community.

This is the paper – it is available to download as a pdf:

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.


Co-author Bruce Spittle – Chief Editor of Fluoride – the journal of the International Society for Fluoride Research

I have been expecting publication of this paper for some time – Paul Connett indicated he was writing this paper during our debate in 2013/2014. FAN newsletters have from time to time lamented at the difficulty he and Bill Hirzy were having getting a journal to accept the paper. Connett felt reviewers’ feedback from these journals was biased. In the end, he has lumped for publication in Fluoride – which has a poor reputation because of its anti-fluoride bias and poor peer review. But, at last Connett and Hirzy have got their paper published and we can do our own evaluation of it.

The authors are:


Co-author David C. Kennedy – past president of the International Academy of Oral Medicine and Toxicology – an alternative dentist’s group.

Bill Hirzy, Paul Connett and Bruce Spittle are involved with the Fluoride Action Network (FAN), a political activist group which receives financial backing from the “natural”/alternative health industry. Bruce Spittle is also the  Chief Editor of Fluoride – the journal of the International Society for Fluoride Research Inc. (ISFR). David Kennedy is a Past President of the International Academy of Oral Medicine and Toxicology which is opposed to community water fluoridation.

Quanyong Xiang is a Chinese researcher who has published a number of papers on endemic fluorosis in China. He participated in the 2014 FAN conference where he spoke on endemic fluorosis in China.

xiang-Endemic fluorosis

Much of the anti-fluoridation propaganda used by activists relies on studies done in areas of endemic fluorosis. Slide from a presentation by Q. Xiang to an anti-fluoride meeting organised by Paul Connett’s Fluoride Action Network in 2014.

Critique of the paper

I have submitted a critique of this paper to the journal involved. Publication obviously takes some time (and, of course, it may be rejected).

However, if you want to read a draft of my submitted critique you can download a copy from Researchgate – Critique of a risk analysis aimed at establishing a safe dose of fluoride for children.  I am always interested in feedback – even (or especially) negative feedback – and you can give that in the comments section here or at Researchgate.

(Please note – uploading a document to Researchgate does not mean publication. It is simply an online place where documents can be stored. I try to keep copies of my documents there – unpublished as well as published. It is very convenient).

In my critique I deal with the following issues:

The authors have not established that fluoride is a cause of the cognitive deficits reported. What is the point in doing this sort of risk analysis if you don’t actually show that drinking water F is the major cause of cognitive deficits? Such an analysis is meaningless – even dangerous, as it diverts attention away from the real causes we should be concerned about.

All the reports of cognitive deficits cited by the authors are from areas of endemic fluorosis where drinking water fluoride concentrations are higher than where community water fluoridation is used. There are a whole range of health problems associated with dental and skeletal fluorosis of the severity found in areas of endemic fluorosis. These authors are simply extrapolating data from endemic areas without any justification.

The only report of negative health effects they cite from an area of community water fluoridation relates to attention deficit hyperactivity disorder (ADHD) and that paper does not consider important confounders. When these are considered the paper’s conclusions are found to be wrong – see ADHD linked to elevation not fluoridation, and ADHD link to fluoridation claim undermined again.

The data used by the Hirzy et al. (2016) are very poor. Although they claim that a single study from an area of endemic fluorosis shows a statistically significant correlation between IQ and drinking water fluoride that is not supported by any statistical analysis.

The statistically significant correlation of IQ with urinary fluoride they cite from that study explains only a very small fraction of the variability in IQ values (about 3%) suggesting that fluoride is not the major, or maybe not even a significant, factor for IQ. It is very likely that the correlation between IQ and water F would be any better.

Confounders like iodine, arsenic, lead, child age, parental income and parental education have not been properly considered – despite the claims made by Hirzy et al. (2016)

The authors base their analysis on manipulated data which disguises the poor relations of IQ to water fluoride. I have discussed this further in Connett fiddles the data on fluorideConnett & Hirzy do a shonky risk assessment for fluoride, and Connett misrepresents the fluoride and IQ data yet again.

Hirzy et al. (2016) devote a large part of their paper to critiquing Broadbent et al (2014) which showed no evidence of fluoride causing a decrease in IQ  using data from the Dunedin Multidisciplinary Health and Development Study. They obviously see it as a key obstacle to their analysis. Hirzy et al (2016) argue that dietary fluoride intake differences between the fluoridated and unfluoridated areas were too small to show an IQ effect. However, Hirzy et al (2016) rely on a motivated and speculative estimate of dietary intakes for their argument. And they ignore the fact the differences were large enough to show a beneficial effect of fluoride on oral health.


I conclude the authors did not provide sufficient evidence to warrant their calculation of a “safe dose.” They relied on manipulated data which disguised the poor relationship between drinking water fluoride and IQ. Their arguments for their “safe dose,” and against a major study showing no effect of community water fluoridation on IQ, are highly speculative and motivated.

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Non-fluoridated Christchurch does not have better teeth than fluoridated Auckland


It seems every time anti-fluoride propagandists present data it is either cherry-picked, distorted or misleading. Often all three. So it is hardly a surprise to find local anti-fluoride propagandists are telling porkies again.

They have been promoting the above graphic claiming it shows people in “non-fluoridated Christchurch have “better teeth.” But the graphic is based on naive cherry-picking of the data, it ignores the effect different ethnic groups have on the data and it uses a single cherry-picked year which fits their bias.

On top of that, axis values have been chosen to exaggerate differences and the labels are incorrect. The “non-fluoridated Christchurch” category uses data for Canterbury and the “fluoridated Hamilton” category uses data of the Waikato.

It seems that several of the commenters on the Fluoride Free NZ Facebook page where this graphic was first used saw the problems and raised them. All they got is insults for their time. These organisations do not seem capable of a rational discussion.

The Ministry of Health data they use is freely available on the MoH website. It provides oral health data for 5-year-old children and year 8 children. The data is presented annually and for different regions.

So let’s have a look at what the data really says – using more normal axis ranges and separating out ethnic groups.


The top graph here is still misleading because it does not take into account the effect of different ethnic groups. However, the correct categories are used and the more rational axis really cuts the exaggerated difference down to size.

In the second graphic the data for Māori and Pacifica have been removed – the MoH describes this group as “Other” – it is mainly Pakeha. We can see that the caries-free % is actually greater for fluoridated Auckland than it is for non-fluoridated Canterbury – exactly the opposite of what the anti-fluoride propagandists were claiming.

It is the same story for Māori – the caries-free % is actually higher in fluoridated Auckland than in non-fluoridated Canterbury.

The problem with the “Total” data is that Pacifica have a large effect – particularly in Auckland where Pacifica are concentrated. Pacifica generally have poorer oral health but are concentrated in fluoridated regions. This drives down the caries-free % figures for the fluoridated areas if the differences are not accommodated.

I referred to this effect of Pacifica on the data in my article A challenge to anti-fluoridationers to justify their misrepresentation of New Zealand research. There I was referring to a similar way anti-fluoride campaigners were misrepresenting data from recent New Zealand research. In this case, they were using data from a paper (Schluter & Lee 2016) and completely ignoring the distortions introduced by inclusion of Pacific – even though the authors had warned against the anomaly introduced by this.

There are other effects which should also be considered in a proper understanding of these data. It is easy to cherry-pick the data for a single year when differences are small – the anti-fluoride people do that a lot. OK if you want to confirm your biases but consideration of the data over multiple years helps indicate trends, identify anomalies and provide an idea of variations in the data. It is also important to consider the numbers in each region. For example, I have not included Pacific in the graphs above because they are concentrated in Auckland and the numbers in Canterbury and Waikato are very low (eg., 45 in Waikato in 2014).

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Debunking anti-fluoridationist’s remaining 12 reasons for opposing fluoridation

New Zealand anti-fluoride campaigners have whittled their list of objections to community water fluoridation (CWF) down to 12 reasons. Maybe that’s progress – they used to tout a list of 50 reasons!

Let’s go through that list one by one and see if any stand up. I am responding here to each reason given in the Fluoride Free New Zealand’s (FFNZ) document Top 12 Reasons why Fluoridation Should End.

You can download a printable version of my responses.

1: Fluoride works by a surface reaction with existing teeth but research shows that it has a beneficial systemic effect with developing teeth.

The document asserts that “Fluoride promoters now claim that if there is any benefit from fluoride it is from contact with the surface of the tooth” and cite as their authority a High Court judge (incidentally, from a ruling that went against anti-fluoride campaigners). A High Court Judge is hardly an authority on scientific matters

Yes, the surface or “topical” action at the tooth surface is understood to be the predominant mechanism for existing teeth. The US Center for Disease Control illustrates this in its figure from the document Recommendations for Using Fluoride to Prevent and Control Dental Caries in the United States).

But, I pointed out in my article Cherry-picking and misinformation in Stan Litras’s anti-fluoride article, research also suggests fluoride is incorporated into the developing teeth of children and this helps provide protection.

Newbrun (2004), for example, stressed in a review of the systemic role of fluoride and fluoridation on oral health:

“The role of systemic fluoride in caries prevention is neither “minimal” nor “of borderline significance.” On the contrary, it is a major factor in preventing pit and fissure caries, the most common site of tooth decay. Maximal caries-preventive effects of water fluoridation are achieved by exposure to optimal fluoride levels both pre- and posteruptively.”

Cho et al (2014) presented data showing that children exposed to CWF during teeth development retained an advantage over those never exposed to it. Systemic fluoride may not play a role with existing teeth but it does during tooth development – even if it is difficult to determine the relative contributions of systemic fluoride and “topical” or surface fluoride to lasting oral health.

2: Too much fluoride causes dental fluorosis but this is not relevant to CWF.

Some children from both fluoridated and non-fluoridated areas do exhibit dental fluorosis. This is thought to be due to excessive consumption of fluoridated toothpaste and one important factor used in determining the optimum concentration of fluoride used in CWF is to prevent the development of dental fluorosis.

Anti-fluoride propagandists usually cite horrific figures for dental fluorosis because they incorporate all forms of dental fluorosis, from the mildest to the most severe, into their figures. For example, they will cite Ministry of Health Oral Health Survey data to claim that New Zealanders have a prevalence of 45% dental fluorosis caused by fluoridation. In fact, the dental fluorosis of concern (the severe and moderate forms) is very rare and the NZ Oral Health survey (from which this data is taken) showed no difference between fluoridated and unfluoridated areas.

3: Fluoride is not a neurotoxin (or neurotoxicant) at concentrations used in CWF.

Sure, animals studies show effects at high concentrations and there are studies of possible negative cognitive effects from areas of endemic fluorosis where drinking water concentrations of fluoride are relatively high. However, studies from areas where CWF is used (Broadbent et al, 2014) or natural levels of fluoride in drinking water are similar (see More nails in the coffin of the anti-fluoridation myths around IQ and hypothyroidism) do not show any negative effect on cognitive ability. In fact, the research suggests that fluoride may actually improve cognitive ability and improve chances of employment and income in adults (see the last link).

The Lancet article cited by FFNZ did not classify fluoride as a “neurotoxin” and the only discussion of fluoride in that article related to the poor quality studies from areas of endemic fluorosis referred to above. Scientific journals publish research findings and reviews – they don’t pass regulations or get into classifications.

4: FFNZ’s reference to dose is simply an attempt to claim evidence from high concentrations studies is relevant to CWF. It isn’t.

All the research indicates that the optimum recommended concentrations used in CWF are high enough to help reduce tooth decay but low enough to have no negative health effects. Only very mild dental fluorosis. which is often judged positively by teenagers and parents, is a possible result of such low concentrations.

The US National Toxicology Review referred to will simply extend previous reviews of animal studies to include human studies. This research programme also plans to include some animal studies using low fluoride concentrations – precisely because most former studies have used high concentrations unrepresentative of CWF.

The fact that new research like this commonly occurs is a good thing as it helps guarantee that social health measures like CWF are safe and they provide confidence to the public that there is continuous monitoring that would pick up any formerly unseen problems.

5: Skeletal and dental fluorosis occurs in parts of the world with high drinking water fluoride concentration but this is not relevant to CWF

The World Health Organisation recommends that drinking water fluoride concentrations should be in the range  0.5 – 1.5 mg/l. High enough to support dental health but low enough to prevent skeletal fluorosis or dental fluorosis of any concern.

Anti-fluoride campaigners commonly refer to the negative health effects in areas of endemic fluorosis (eg., China, India, and Senegal) where drinking water fluoride concentrations are much higher than used for CWF. But those facts are completely irrelevant to the situation in countries like New Zealand. And they are irrelevant to CWF which uses much lower drinking water concentrations.

6: There is no credible evidence to suggest that fluoride is an endocrine disruptor at concentrations used for CWF

A number of animal and human studies have produced conflicting results for endocrine effects of fluoride. These studies suffer from the use of high or unspecified fluoride concentrations. Effects have sometimes been seen for human in areas of endemic fluorosis. Studies have often been confused because of confounding effects due to iodine deficiency (known to cause thyroid problems), calcium and water hardness.

This means that it is easy to cherry-pick individual studies to support claims of harm from fluoride but these are usually for areas of high fluoride concentration or the studies are flawed by the problem of confounding effects.

The authoritative 2014 New Zealand Fluoridation Review (Eason et al. Health effects of water fluoridation: A review of the scientific evidence) considered “alleged effects of CWF on health outcomes  . . . including effects on reproduction, endocrine function, cardiovascular and renal effects, and effects on the immune system. “ It concluded:

“The most reliable and valid evidence to date for all of these effects indicates that fluoride in levels used for CWF does not pose appreciable risks of harm to human health.”

7: Bottle-fed babies do not receive harmful amounts of fluoride.

The FFNZ claim they do is a common anti-fluoride misrepresentation of the health recommendations concerning CWF and bottle-fed babies. These recommendations advise that use of fluoridated water to reconstitute baby formula is not harmful. They simply suggest that parents who are concerned should occasionally use non-fluoridated water for that reconstitution – a peace of mind thing.

For example, the American Dental Association advises:

“Yes, it is safe to use fluoridated water to mix infant formula. If your baby is primarily fed infant formula, using fluoridated water might increase the chance for mild enamel fluorosis, but enamel fluorosis does not affect the health of your child or the health of your child’s teeth. ”

Where parents want to reduce the risk of dental fluorosis they:

“can use powdered or liquid concentrate formula mixed with water that either is fluoride-free or has low concentrations of fluoride.”

Arguments based on low concentrations in human breast milk simply rely on the naturalistic fallacy – the claim that something is good or right because it is natural (or bad or wrong because it is unnatural). There are common concerns about deficient levels of some beneficial elements in human breast milk and recommendations for using supplements. See, for example, Iron and fluoride in human milk.

8: Fluoridation chemicals are not contaminant-laden waste products.

For example, fluorosilicic acid, the most commonly used fluoridation chemical in New Zealand, is a by-product of the fertiliser industry. When used for water treatment it must pass rigorous restrictions on contaminant levels. Certificates of analysis are required.


With these regulations and checks for water treatment chemicals, the concentration of any contaminant introduced into tap water by their use is much lower than the concentration of those contaminants already naturally present in the source water used. See Chemophobic scaremongering: Much ado about absolutely nothing for data based on a typical certificate of analysis for fluorosilicic acid and the natural concentrations of contaminants for the source water used by Hamilton City. The concentration of contaminants introduced into drinking water is well under 1% of the levels already naturally present in the water source (see graph).

9: Fluoridation is not a medicine and it does not violate human basic rights.

That was determined in High Court rulings – cases brought by anti-fluoride campaigners financed by the “natural”/alternative health industry. All appeals so far against those rulings have been rejected.

10:   Community water fluoridation is not suitable or necessary for many countries

A claim that only 5% of the world uses community water fluoridation is not relevant. Consider that just over 10% of the world do not have access to safe clean water so their people have more pressing concerns that water fluoridation. Many countries like China, India, and parts of North Africa use drinking water with fluoride concentrations that are excessive – fluoride removal or searches for alternative sources are their priority.

Even many developed countries or regions do not have reticulation systems which enable cost-effective fluoridation. This may be the case in Christchurch where the use of a number of bores may mean fluoridation of much of the city is not cost-effective.

Many countries already have natural concentrations of fluoride in their drinking water that are near optimum – making any supplementation unnecessary.

A recent review (O’Mullane et al., 2016) summarised the numbers of people around the world with access to beneficial levels of fluoride in their drinking water:

“General estimates for the number of people around the world whose water supplies contain naturally fluoridated water at the optimum level for oral health are around 50 million. This means that, when the numbers of people with artificially (369.2 million) and naturally fluoridated water supplies (50 million) at the optimum level are added together, the total is around 437.2 million.”

11: The effectiveness of community water fluoridation in reducing tooth decay is well established.

This fact is very often misrepresented by anti-fluoride campaigners. For example, in the FFNZ document, a recent New Zealand study is cited to argue that “there is no difference in decay rates between non-Māori children in fluoridated and non-fluoridated areas.” In fact, the authors of that study warned that the data for “non-Māori” children were misleading because it included data for Pacific Island children who have generally poorer dental health than other ethnic groups and are concentrated in fluoridated regions, thus distorting the data for non-Maori. When the data for all ethnic groups are considered separately it clearly shows the beneficial effects of community water fluoridation. This figure shows the non-Māori data corrected by removing the data for Pacific Island children. iut confirms that there is a difference in decay rates between fluoridated and non-fluoridated area.

Comparison of data for “other” (non-Māori/non-Pacifica) children in fluoridated (F) and unfluoridated (UF) areas. 5-year-old New Zealand children. dmft = decayed, missing and filled teeth.

FFNZ claims about the Cochrane Review and data from the District Health Boards and Ministry of Health are also incorrect. While the Cochrane Review did specifically exclude most recent studies because of its selection criteria it still concluded:

“Data suggest that the introduction of water fluoridation resulted in a 35% reduction in decayed, missing or filled baby teeth and a 26% reduction in decayed, missing or filled permanent teeth. It also increased the percentage of children with no decay by 15%. These results indicate that water fluoridation is effective at reducing levels of tooth decay in both children’s baby and permanent teeth.”

12: Community water fluoridation is only one part of successful dental health policies

These included regular fluoride varnishes, regular dental examinations, registering children into dental programmes, education measures such as guided toothbrushing, presenting children with toothpaste and toothbrushes, the involvement of parents in dental health and plaque checking and in dental health programmes generally. Health professionals see all these elements, including water fluoridation, as complementary. There is absolutely no suggestion that community water fluoridation means no other social dental health programme is used. However, in areas where community water fluoridation is not available health professionals will often introduce extra measures, such as wider use of fluoride dental varnishes, to help protect child dental health.

FFNZ misleads when it claims other aspects of a dental health programme can simply be substituted for water fluoridation. All parts of these programmes are complementary, one cannot normally be substituted for another.


So, none of the 12 reasons given by FFNZ for their opposition to CWF stand up to critical scrutiny.

Having whittled their original list down from 50 to only 12 reasons perhaps they should bite the bullet, face the facts, and continue whittling it down to zero.

That would then conform to the scientific information available.

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New research confirms adults benefit from community water fluoridation as well as children


Community water fluoridation is beneficial to adults as well as children.

A new Australian study confirms that lifetime access to community water fluoridation (CWF) is associated with reduced tooth decay for adults – at least in the age groups 15 – 34 years and 35 – 44 years.

The study is reported in the paper:

Do et al., (2017). Effectiveness of water fluoridation in the prevention of dental caries across adult age groups. Community Dentistry and Oral Epidemiology.

Other workers reported similar results. But Do et al., (2017) had a closer look at the data, because of the difficulties in assessing both access to CWF, and tooth decay, in adults. In particular, they carried out a secondary analysis which looked at lifetime access to CWF and tooth decay within defined age groups as well as across age groups of adults aged between 15 – 91 years.

They found the association of access to CWF with reduced tooth decay was strongest for the youngest adult age group, 15 – 34-year-olds.  The association was weaker, but still significant, for the 35 – 44 years age group. However, they did not see a significant association for the remaining age groups, 45 – 54 years and 55+ years.

The authors discuss possible reasons for what they call the “fading” of apparent benefits from CWF with age.

1: Lack of exposure to CWF during childhood for the older age groups. This is because CWF was not present when they were young. The authors say:

“there is some evidence among children at least of the importance of a critical period of exposure, where either the incorporation of fluoride into the developing tooth may be crucial or the establishment of a positive mouth ecology may set a child on a lifelong trajectory.”

This would be in line with research showing a systemic effect of fluoride for developing teeth in children. There is also that those older adults were exposed to risks of tooth decay before later being exposed to CWF.

2: A limit to the measurement of tooth decay in adults because the measures of tooth decay:

“increasingly shows saturation of all susceptible surfaces, whereby more members of an age group approach a ceiling in the sum of the surfaces with past or present caries experience. . . .  It should be emphasized that, for the older age groups, this saturation might have occurred before access to FW had become available in Australia.”

So, yet another confirmation of the benefits of CWF for adults as well as children.

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Premature births a factor in cognitive deficits observed in areas of endemic fluorosis?


Could the increased incidence of premature births explain cognitive deficits observed in areas of endemic fluorosis? Image credit: New Kids-Center.

Anti-fluoridation activists are soon likely to be promoting a new paper reporting a study which found a relationship between maternal (in utero) exposure to fluoride and cognitive development delay in infants. Of course, they will be unlikely to mention the study occurred in an area of endemic fluorosis where drinking water fluoride concentrations are much higher than used in community water fluoridation (CWF). They are also unlikely to mention the possible role of premature births in cognitive development delay observed in the study.

The paper is:

Valdez Jiménez, L., López Guzmán, O. D., Cervantes Flores, M., Costilla-Salazar, R., Calderón Hernández, J., Alcaraz Contreras, Y., & Rocha-Amador, D. O. (2017). In utero exposure to fluoride and cognitive development delay in infants . Neurotoxicology

Valdez Jiménez et al., (2017) studied 65 mother-baby pairs in an area of endemic fluorosis in Mexico. The mothers had high levels of fluoride in their urine and this was negatively associated with cognitive functions (Mental Development Index – MDI) in the infants.

The concentration of fluoride in the tap water consumed by the mothers ranged from 0.5 to 12.5 mg/l, with about 90% of water samples containing fluoride above the World Health recommended maximum of 1.5 mg/l.

Fluoride in the mothers’ urine was also high – with the mean concentration for all the mothers of 1.9 mg/l  for the 1st trimester, 2.0 mg/l for the 2nd and 2.7 mg/l for the 3rd trimester. Urinary fluoride concentrations as high as 8.2 mg/l were found. This compares with a mean value of F in urine of 0.65 mg/L) for pregnant women residents in areas with low levels of F in drinking water (0.4 to 0.8 mg/l – similar to that recommended in community water fluoridation).

The MDI test used evaluates psychological processes such as attention, memory, sensory processing, exploration and manipulation, and concept formation. This was negatively associated with maternal urine fluoride concentrations – the association explaining about 24% of the variance.

Room of other influences

This data suggests that other confounding factors which weren’t measured could also contribute to the variation of the MDI results, and if such confounders were included in the statistical analysis the contribution from urinary fluoride may be much less than 24%.

However, I am interested in the data for premature births that were, unfortunately, not included in the statistical analysis. The paper reports “33.8% of children were born premature i.e. between weeks 28-36 and had a birth weight lower than 2.5 kg.” This is high for Mexico – as they say:

“The World Health Organization (WHO) in Mexico reported a rate of 7.3 cases per 100 births; compared with 33.8% of cases per 100 births that we observed in our study. We have 26.5% more cases than expected.”

According to their discussion, other researchers have also reported higher premature births in areas of endemic fluorosis, compared with non-endemic areas.

Is premature birth a mechanism explaining cognitive deficits?

This study differs from many others in that fluoride exposure to the pregnant mother, rather than the grown child, was investigated. While the authors tended to concentrate on possible chemical toxicity effects on the cognitive development of the child in utero it is also possible that indirect effects could operate. For example, premature birth and low birth weights could themselves be a factor in child cognitive development.

In fact, a quick glance a the literature indicates this may be the case. For example, Basten at al., (2015) reported that preterm birth was associated with “decreased intelligence, reading, and, in particular, mathematics attainment in middle childhood, as well as decreased educational qualifications in young adulthood.” It was also associated with decreased wealth at 42 years of age.

The influence of endemic fluorosis on premature births and birth weights may not involve fluoride directly. Health problems abound in endemic areas – as well as the obvious dental and skeletal fluorosis complaints also involve muscles, blood vessels, red blood cells, the gastrointestinal mucosa and other soft tissues. It is easy to see such health problems influencing the prevalence of premature births and birth weights.

Not relevant to CWF

Of course, none of this is relevant to community water fluoridation. Such fluoridated areas do not have the health problems of areas with endemic fluorosis where drinking water concentrations are much higher. But, of course, this does not stop opponents of CWF claiming that similar problems occur at the lower concentrations.

In case anyone attempts to use this suggestion as an argument against CWF I should mention the only study I could find that makes the link between CWF and fluoridation. Often cited by anti-fluoride campaigners it is a poster paper:

Hart et al., (2009). Relationship between municipal water fluoridation and preterm birth in Upstate New York.

Presented at an Annual Meeting of the American Public Health Association the study appears not to have been published in a peer-reviewed journal. While the authors claim to have found a small, but statistically significant, increase in premature births in fluoridated areas this could be due to a number of possible confounding factors.With only a brief abstract to go on it is impossible to critically assess the study  – in fact, I suspect the non-publication is probably an indication of poor quality.

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More nails in the coffin of the anti-fluoridation myths around IQ and hypothyroidism


Large Canadian study finds no effect of fluoridation on thyroid health

A new Canadian study shows no relationship of cognitive deficits or diagnosis of hypothyroidism with fluoride in drinking water. This work is important because it counters the claims made by anti-fluoride campaigners. While the campaigners cite scientific studies to support their claims, those studies are usually very weak, or irrelevant because they involve areas of endemic fluorosis where drinking water fluoride concentrations are much higher than in situations where community water fluoridation (CWF) is used.

The study is reported in:

Barberio, A. M. (2016). A Canadian Population-based Study of the Relationship between Fluoride Exposure and Indicators of Cognitive and Thyroid Functioning; Implications for Community Water Fluoridation. MSc Thesis, University of Calgary

This new study is important as it has the advantages of using a large representative sample of the Canadian population, with extensive data validation and quality control measures. It also uses individual-level estimates of fluoride exposure on the one hand, and thyroid health and cognitive problems on the other.

Fluoride exposure was measured both by concentration in tap water for selected households and concentration in urine samples from individuals.

Thyroid health

The Canadian study found:

“Fluoride exposure (from urine and tap water) was not associated with impaired thyroid functioning, as measured by self-reported diagnosis of a thyroid condition or abnormal TSH level.”

This contradicts the conclusions from the population-level study of Peckham et al., (2015) which reported that fluoridation was correlated with the prevalence of hypothyroidism. That study is quoted extensively by anti-fluoridation activists but has been roundly criticised because it did not include the influence of confounders – particularly iodine which is known to influence thyroid health.

Barberio (2016) also suggests that the different recommended fluoride concentrations used for CWF in Canada and the UK, and the fact that the Peckham et al (2015) study did not involve individual measures, could also be factors in the different findings.

Cognitive functioning

The Canadian study reported:

“Fluoride exposure (from urine and tap water) was not associated with self-reported diagnosis of a learning disability.”

Barberio (2016) did also investigate a more detailed diagnosis for cognitive problems and found:

“Higher urinary fluoride was associated with having ‘some’ compared to ‘no’ cognitive problems . . . . however, this association:

  • Was weak;

  • Was not dose-response in nature; and

  • Disappeared when the sample was constrained to those for whom we could discern fluoride exposure from drinking water.”

I guess anti-fluoride activists might latch on to this last point regarding urinary fluoride but, at least as far as tap water fluoride is concerned, there was no relationship with learning difficulties.


So – yet another large-scale study contradicts anti-fluoridationist claims. It shows that CWF has no influence on cognitive problems or thyroid health.

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Water fluoridation – what to expect in the near future


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

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

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

The legislation

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

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

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

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

The “IQ problem” – a current campaign

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

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

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

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

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

Research on neurological effects

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

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

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

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

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

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

Problems in areas of endemic fluorosis

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

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

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

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

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


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

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

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

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

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

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Large Swedish study finds no effect of fluoride on IQ


Fluoride levels in Swedish drinking water (mg/L). Variation between municipalities. Source: Aggeborn & Öhman (2016)

A significant new Swedish study shows fluoride in drinking water, at the concentrations used for community water fluoridation, has no effect on IQ or other measures of cognitive ability. Similarly, it has no effect on diagnosis or prescription of medicines for ADHD, depression, psychiatric illnesses, neurological illnesses or muscular or musculoskeletal diseases.

On the other hand, the study showed positive effects of fluoride on income and employment status – most probably because better dental health is beneficial in the labour market.

This work is reported in:

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

The study covers most of the health effects that anti-fluoride campaigners complain about. It really should put all these complaints to rest as the quality of this new study is much better than anything the campaigners rely on for the following reasons:

  • It involved a much large sample. Over 700,000 individuals were involved. The numbers included in specific measurements varied but they were much greater than those used in the studies cited by anti-fluoride campaigners. For example, almost 82,000 were involved in the cognitive ability comparisons – compared with a few hundred at the most in the comparable studies cited by anti-fluoride campaigners.
  • Estimates of effects were much more precise (as expected with large numbers of subjects) than for previous studies. The effect of fluoride on cognitive ability was always close to zero and for practical purposes was zero.
  • Statistical analyses were based on continuously varying fluoride levels – a much better approach than the simple comparison of data for low and high fluoride villages used in the studies cited by anti-fluoride campaigners.

Sweden is an ideal country for studying effects of fluoride at these low concentrations. It does not have artificial water fluoridation but its drinking water contains naturally occurring fluoride. The fluoride concentration in drinking water depends on the geology of the region so different Swedish communities consume water with different fluoride concentrations.

This graphic from the paper shows the number of people drinking water with various concentrations of fluoride. Note – the steps are 0.1 mg/L and although concentrations above 2.0 mg/L occur they are relatively rare. Sweden makes no attempt to remove excess fluoride until the concentrations exceed 1.5 mg/L – the maximum recommended by the World Health Organisation. For comparison, the recommended optimum concentration in  New Zealand is 0.7 mg/L.


Histogram of numbers people drinking water containing naturally occurring fluoride at different concentrations. Source: Aggeborn & Öhman (2016)

Effects of fluoride on dental health

The Swedish data showed positive effects of fluoride on oral health. For example, the share of dentists visits “decreased by approximately 6.6 percentage points if fluoride is increased by 1 mg/l. This should be considered as a large effect.” Tooth repairs are closely related to fluoride. “If fluoride would increase with 1 mg/l, the share of 20-year-olds that had a tooth repaired would be decreased approximately 3.4 percentage points considering the 2013 sample. Again, this effect is large, especially for this cohort.”

Cognitive ability

Relevant data was used from national education tests and psychological tests during the years of the Swedish military conscription. The statistical analysis produced estimates which were all very small and often not statistically significant. The estimates were sometimes negative and sometimes positive. For example, an estimate including covariates showed that “cognitive ability is increased by 0.045 Stanine points [equivalent to about 0.3 IQ points] if fluoride is increased by 1 mg/l (a large increase in fluoride). This should be considered as a zero-effect on cognitive ability.”

Other possible health effects

The authors considered the effects of fluoride on the prescription of medicines for ADHD, depression, and psychoses. They also looked at psychiatric and neurological diagnoses from outpatient and inpatient registers, as well as diagnoses of muscular and skeletal diseases. Anti-fluoride campaigners often claim fluoride has a harmful effect on these health problems.

The was no effect of fluoride on the possibilities of being prescribed any of these medicines.  For example “the probability of receiving ADHD medicines is decreased by 0.2 percentage points if fluoride is increased by 1 mg/l. In economic terms, this effect is a zero-effect.”

It was the same for all the diagnoses considered –  “The estimated effects are small and often statistically insignificant.”

According to the authors:

“In conclusion, we do not find that fluoride has any effects on these health outcomes. This further strengthens our argument that fluoride does not have any negative effects for levels below 1.5 mg/l on human capital development or health outcomes related to human capital development. It is also interesting that we do not find any effects on diagnoses for muscular and skeleton diseases, which has been a question also discussed in connection to fluoride.”

Annual income and employment status

The lack of any effect of fluoride on IQ and other psychological and non-psychological estimates suggest that fluoride would have no effect on long-term outcomes like income and employment status. However, the authors suggested that it could have a positive influence on these outcomes because of better dental health.

And this was the case. Estimates of the effect of fluoride on income were always positive and usually statistically significant. The authors estimated that “income increases by 4.2 percent if fluoride increases by 1 mg/l. This is not a negligible effect and the estimate should be considered as economically significant.”

Similarly for employment status. “If fluoride is increased by 1 mg/l, then the probability that the person is employed is increased by 2 percentage points. This result thus point in the same direction as the results for log income where both these results are significant in economic terms.”

Further analysis indicated “that when dental repairs increases by 1 percentage point, income decreases by 2 percent on the same aggregate level. This effect is clearly economically significant. This indicates that fluoride improves labor market outcomes through better dental health.”


This is an important study. It involved large numbers of people, estimated outcomes were far more precise than in previous studies, it used continuously varying concentrations of fluoride instead of simply comparing high fluoride and low fluoride villages, and it considered possible long-term outcomes like income and employment chances.

The advantages of this study compared with the generally poor quality studies cited by anti-fluoride campaigners should put to rest arguments used by those campaigners. In particular, it should make the current campaigns relying on to IQ and cognitive effects irrelevant.

The authors comment that their data shows there is no need to consider negative health effects on consideration of the cost-effectiveness of community water fluoridation. I wonder if, in fact, these results will encourage policy makers to consider the cost benefits of improved income and employment chances in future calculations of the cost-effectiveness of fluoridation programmes.

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Fluoridation: New research confirms it is cost effective – yet again


Yet again a cost-benefit analysis shows community water fluoridation to save far more than it costs.

A new study has found, once again, that community water fluoridation (CWF) saves more than it costs. Carrying on from the previous most comprehensive study in 2001 this new study is based on updated costs of CWF and the averted lifetime costs of dental treatment in the United States.

It estimates savings from averted tooth decay in 2013  as a result of CWF to be about $32 per capita. The estimated costs of CWF in 2013 was $324 million. The net saving (savings minus costs) from CWF was estimated to be $6,469 million.

The estimated return on investment (annual net saving/annual costs), averaged across all sizes of water systems, was 20.

The study is published in this paper:

O’Connell, J., Rockell, J., Ouellet, J., Tomar, S. L., & Maas, W. (2016). Costs And Savings Associated With Community Water Fluoridation In The United States. Health Affairs, 35(12), 2224–2232.

These figures strongly show that further savings could be achieved by extending CWF in the USA. the authors say:

“During 2013 more than seventy-eight million people had access to a public water system that served 1,000 or more people that did not fluoridate the water. Our findings suggest that if those water systems had implemented fluoridation, an additional $2.5 billion might have been saved as a result of reductions in caries.”

This study found large saving from CWF despite using a lower estimate of tooth decay present when  there is no fluoridation than used by some other studies. The present study relied on estimations of decayed and filled teeth, rather than the more sensitive measure of decay and filled tooth surfaces.

The authors also investigated the robustness of their conclusion by estimating the return on investment for different figures of reduced tooth decay due to CWF. This varied from 16.5 when CWF effectiveness was assumed to be 20% (less effective than the estimated 25%) to 23.7 when  CWF was assumed to be 30% (more effective than the estimated 25%).

Of course, anti-fluoridation propagandists will rubbish this study – just as they have every other study which does not support their message. And their message will be the same they have used to attack every other high-quality cost-effectiveness study of CWF. They will claim it is biased because it does not include consideration of adverse effects of CWF. In particular, costs related to dental fluorosis.

In recent years their argument relies strongly on the flawed work of Ko & Thiessen (2014) – A critique of recent economic evaluations of community water fluoridation. This is flawed because it includes the cost of treatment fo moderate and severe forms of dental fluorosis.  This is despite acknowledging in their discussion that CWF is not responsible for any moderate or severe forms of dental fluorosis. I have discussed this further in Alternative reality of anti-fluoride “science”.

Mind you, I still expect anti-fluoride commenters here to the Ko and Thiessen study at me.

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Fluoridation: members of parliament call from submissions from scientific and health experts

The new community water fluoridation legislation is now on the way in the New Zealand parliament. The Health (Fluoridation of Drinking Water) Amendment Bill was introduced on Tuesday and the parliamentary health committee has invited submissions.

It’s worth watching the videos of the twelve speakers in the first reading. These give an idea of how the legislation will be received by the different political parties. They also give an impression that members of our parliament are well aware of the tactics of the anti-fluoride pressure groups – they fully expect to be inundated with irrelevant and pseudoscientific submissions. But they are also aware that the science currently finds community water fluoridation to be both effective and safe.

After watching the debate these are my initial conclusions:

  1. The bill has almost unanimous support. Only New Zealand First voted against it.
  2. Many of the speakers see the legislation as only a little better than the current situation. The describe it as a half-way house – kicking the can down the road. District Health Boards (DHBs) will be subjected to the same uninformed or misleading pressure that the councils are at present. The government should have gone the whole hog and handed over responsibility for fluoridation decision to the Ministry of Health.
  3. All the speakers declared their support for the science that shows community water fluoridation effective and safe. Most showed they are aware of, and accept, the New Zealand Fluoridation review commissioned by the Royal Society of New Zealand and the Office of the Prime Minister’s Chief Science Advisor.
  4. None of the speakers showed any support for the arguments or activities of anti-fluoridation campaigners. In fact, there were many derogatory comments made about tin foil hats, etc.
  5. New Zealand First is opposed because they prefer that communities make fluoridation decisions by referenda and are calling for these referenda to be binding. They criticised those councils like Whakatane and Hamilton that had ignored the wishes of the community.

Health Committee calling for submissions

The Parliamentary health select committee has called for submissions on the bill. Written submission will be accepted until February 2, 2017.

Information on making a submission is available on the Health (Fluoridation of Drinking Water) Amendment Bill website. And you can make your submissions online.

You can also give notice that you wish to make an oral submission to the Health Committee.

Possible issues of contention

From what speakers in the debate had to say I do not think the anti-fluoride lobby will get much sympathy. MPs are expecting the usual deluge of submissions from them but know from experience how worthless they will be.

However, several MPs stressed they did welcome submissions and particularly encouraged submissions from scientific and health experts. The Royal Society of NZ and the Prime Minster’s Chief Scientific advisor may be specifically invited to make submissions.

The bill is not really about the science, however, and MPs expect that the real content – the processes for making fluoridation decisions and the body responsible for these, should be thoroughly discussed.

I expect there will be a strong push to strengthen the bill by moving responsibility to central government, the Ministry of Health, as MPs still see problems with DHB responsibility.

The issue of community consultation should also come up – particularly as New Zealand First is promoting the idea of binding referenda in communities. As it stands the bill does not define how consultation should occur so this may well be made more specific.

The Green Party seems keen to introduce mechanisms for better informing of the public about the science behind fluoridation. They are conscious that the anti-fluoride groups are fear-mongering on this issue and feel that this can be countered by better information. If this is discussed in depth in the hearings there may well be some interest in defining more specifically how government updates its understanding of the research on fluoridation and how they disseminate new research results to the public.

A role for you, the reader

Well, the process is underway. If you have views or concerns on the bill or on the decision processes involved with fluoridation now is the time to put pen to paper, punch away on your computer keyboard, or prepare for making an oral submission to the health committee. If you want advice on how to do this have a read of Making a Submission to a Parliamentary Select Committee and the linked documents.

Remember, written submissions are accepted until February 2, 2017, and we would expect the Health committee hearings to start soon after that.

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