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'Are fluoride levels in drinking water associated with hypothyroidism prevalence in England? A large observational study of GP practice data and fluoride levels in drinking water': Comments on the authors' response to earlier criticism

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  • Office for Health Improvement and Disparities

Abstract

Academic debate is healthy and helps us to clarify the evidence base for the interested reader. However, it is unusual for a peer-reviewed paper in a reputable journal to receive quite as much criticism as that which greeted publication of the paper by Peckham et al on fluoride and hypothyroidism.1 Two highly critical commentaries were published at the time.2 ,3 A subsequent review article4 in the Journal of Evidence-based Dental Practice concluded that “this study is an ecologic one that has several significant flaws, making it almost meaningless with regard to assessing any possible association between water fluoridation and hypothyroidism.” Published criticisms included lack of a coherent basis for a prior hypothesis, unbalanced citing of the literature, failure to allow for potential confounding, inadequate recognition of the limitations of ecological studies, imprecise measurement of exposure and outcomes, and over interpretation of the results to infer causation. Statistical aspects of the study were particularly heavily criticised by Warren et al 4 for lack of transparency in reporting, the use of arbitrary categorical cut points to analyse a continuous variable, and by us3 for some apparently anomalous results in relation to deprivation. The authors have now responded to the criticism and …
LETTER
Are uoride levels in drinking
water associated with
hypothyroidism prevalence in
England? A large
observational study of GP
practice data and uoride
levels in drinking water:
comments on the authors
response to earlier criticism
Academic debate is healthy and helps us
to clarify the evidence base for the inter-
ested reader. However, it is unusual for a
peer-reviewed paper in a reputable journal
to receive quite as much criticism as that
which greeted publication of the paper by
Peckham et al on uoride and hypothy-
roidism.
1
Two highly critical commentar-
ies were published at the time.
23
A
subsequent review article
4
in the Journal
of Evidence-based Dental Practice con-
cluded that this study is an ecologic one
that has several signicant aws, making it
almost meaningless with regard to asses-
sing any possible association between
water uoridation and hypothyroidism.
Published criticisms included lack of a
coherent basis for a prior hypothesis,
unbalanced citing of the literature, failure
to allow for potential confounding, inad-
equate recognition of the limitations of
ecological studies, imprecise measurement
of exposure and outcomes, and over inter-
pretation of the results to infer causation.
Statistical aspects of the study were par-
ticularly heavily criticised by Warren et al
4
for lack of transparency in reporting, the
use of arbitrary categorical cut points to
analyse a continuous variable, and by us
3
for some apparently anomalous results in
relation to deprivation.
The authors have now responded to the
criticism and readers can draw their own
conclusions as to the adequacy of that
response.
The quote from the NRC report is a
helpful clarication, but extensive discus-
sion in that report of the weaknesses of
the evidence base is still not acknowl-
edged. The relevant studies are mainly
correlation studies in rural developing
world communities with limited data on
intermediate end points and recognised
methodological weaknesses. These studies
have little, if any, relevance to exposures
due to water uoridation schemes in the
UK. Also, Peckham et al accept that hypo-
thyroidism has multiple immediate causes
(auto-immune, surgical etc) but do not
acknowledge that this makes any unifying
hypothesis of association with uoride
exposure intrinsically implausible.
We continue to believe that confounding
has been inadequately considered. Age and
sex may have been partly accounted for
but only at aggregate level not at individual
level (the ecological fallacy). The data pre-
sented in gures 1s and 2s are poorly
explained and are not clearly attributable
to, and indeed postdate, the reference
cited. The figures appear to show different
distributions of iodine intake in uori-
datedcompared to non-uoridated
regions, which if anything suggests that
iodine exposure may indeed be an import-
ant confounder. However, having exam-
ined the source we do not understand how
the National Diet and Nutrition Survey
can be analysed by uoridated and non-
ouridated SHA areasor for women aged
over 40 years, since it does not use such an
age range and is not sufciently precise to
allow small-area aggregation (uoridation
does not occur at SHA level). Peckham
et al are mistaken, we refer in our com-
mentary to a different article by
Vanderpump
5
to the one cited by Grimes.
Other potential confounders mentioned in
the NRC report such as selenium, calcium
and aluminium are not considered,
let alone a myriad of unknown and
unmeasured variables related to popula-
tion or health service factors.
On the comparisons made, there is
still no information on how the two city
areas were dened or why other areas
were excluded. It seems the journal peer
reviewer recommended a categorical
approach instead of the analysis of con-
tinuous variables. Without seeing the
review in question it is hard to comment
further, except to say that it would appear
to us to be poor advice. No explanation is
given as to why tertiles of deprivation and
hypothyroidism, respectively, were com-
bined into binary outcomes differently.
The justication for the uoride exposure
category seems to be related to thera-
peutic efcacy which was not the subject
of the study. As has been pointed out
what we need to be condent about the
analysis is a clear descriptive table to help
us to understand the data not a few coef-
cients presented as outcomes.
We were fascinated to discover that the
direction of association between depriv-
ation and hypothyroidism switched direc-
tion in their model after adjustment for
proportion aged over 40 years (OR
changed from 0.49 to 1.7). Although
good to know that it was not an error,
discovery of such a statistical quirk in the
model (which we believe is an extreme
example of Simpsons paradox
6
) raises
more questions than it provides answers
about the relevance and validity of the
model for the hypothesis being examined.
Returning to the question of interpret-
ation, we do not agree that an association
has been demonstrated let alone a causal
one. Peckham et al quote a recent Irish
review
7
this is what it has to say in con-
clusion about their study: There are
three reasons for assigning a low-quality
rating. First, the study design assigned was
incorrect. Second, the control for con-
founding was incomplete. Third, the
authors infer a causal relationship rather
than a theoretical relationship.
It is a fact that a question has been raised
if not answered by this study. Rather than
continue to debate with its authors we plan
to repeat the analysis ourselves using more
conventional statistical methods. In the
meantime, it is unfortunate that this article
and its claims remain in the literature
despite its weaknesses. The BMJ website
shows that it has achieved an Altimetric
score at the time of writing of 357 with
extensive activity in North America whereas
the critical commentaries have scores of just
14 and 16 with no US coverage.
Water uoridation is a well-established
and highly effective public health inter-
vention with a safety record that spans
many decades. It is important that the
public and policymakers receive clear and
measured advice on its safety and effect-
iveness based on the best available science.
John N Newton,
1
Julia Verne,
2
Mark Dancox,
2
Nicholas Young
3
1
Department of Chief Knowledge Ofcer, Public Health
England, London, UK
2
Department of South West Knowledge and Intelligence
Team, Public Health England, Bristol, UK
3
Department of Knowledge and Intelligence Team,
Public Health England, Bristol, UK
Correspondence to Professor John N Newton,
Department of Chief Knowledge Ofcer, Public Health
England, PHE, Wellington House 135-155 Waterloo
Road, London SE1 8UG, UK; john.newton@phe.gov.uk
Contributors All authors contributed to the drafting
of this response.
Competing interests None declared.
Provenance and peer review Commissioned;
internally peer reviewed.
Open Access This is an Open Access article
distributed in accordance with the Creative Commons
Attribution Non Commercial (CC BY-NC 4.0) license,
which permits others to distribute, remix, adapt, build
J Epidemiol Community Health Month 2017 Vol 0 No 0 1
PostScript
JECH Online First, published on January 16, 2017 as 10.1136/jech-2016-208649
Copyright Article author (or their employer) 2017. Produced by BMJ Publishing Group Ltd under licence.
upon this work non-commercially, and license their
derivative works on different terms, provided the
original work is properly cited and the use is non-
commercial. See: http://creativecommons.org/licenses/
by-nc/4.0/
To cite Newton JN, Verne J, Dancox M, et al.J
Epidemiol Community Health Published Online First:
[please include Day Month Year] doi:10.1136/jech-
2016-208649
Received 14 November 2016
Accepted 18 November 2016
J Epidemiol Community Health 2017;0:12.
doi:10.1136/jech-2016-208649
REFERENCES
1 Peckham S, Lowery D, Spencer S. Are uoride
levels in drinking water associated with
hypothyroidism prevalence in England? A large
observational study of GP practice data and
uoride levels in drinking water. J Epidemiol
Community Health 2015;69:61924.
2 Grimes DR. Commentary on Are uoride levels in
drinking water associated with hypothyroidism
prevalence in England? A large observational study
of GP practice data and uoride levels in drinking
water.J Epidemiol Community Health
2015;69:616.
3 Newton JN, Young N, Verne J, et al. Water
uoridation and hypothyroidism: results of this study
need much more cautious interpretation. J Epidemiol
Community Health 2015;69:61718.
4 Warren JJ, Saraiva MC. No evidence supports the
claim that water uoridation causes
hypothyroidism. JEvidBasedDentPract
2015;15:1379.
5 Vanderpump MP, Tunbridge WM. Epidemiology and
prevention of clinical and subclinical hypothyroidism.
Thyroid 2002;12:83947.
6 Hernán MA, Clayton D, Keiding N. The Simpsons
paradox unraveled. Int J Epidemiol
2011;40:7805.
7 Sutton M, Kiersey R, Farragher L, et al.Health effects
of water uoridation. Ireland: Health Research Board,
2015.
2J Epidemiol Community Health Month 2017 Vol 0 No 0
PostScript
... This political allegation of the last century, in the form of "conspiracy theory," has now been fomented by the allegation that fluoride is a neurotoxin that affects the IQ of people exposed to fluoridated water. These and other allegations, such as fluoride causing hypothyroidism, are based in transversal studies of associations and not cause-effect, which have been scientifically contested with elegance (28)(29)(30)(31). Thus, the adjustment of fluoride concentration during water treatment is still recommended by WHO, because the only systemic side effect associated with optimally fluoridated water ingestion is dental fluorosis, which does not compromise the quality of life of affected people. ...
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Since the 1950s, the benefits and risks of fluoridated water use have been debated worldwide. In the past, it was considered that the systemically ingested fluoride would exert its primary preventive effect after being incorporated into the enamel as fluorapatite, making the enamel more resistant to the caries process; however, it is now recognized that the main effect of water fluoridation is local and post eruptive. On the other hand, irrespective of the caries decline reported worldwide, the anticaries benefit of water fluoridation continues to be observed even in developed countries. Regarding the risks, water fluoridation is considered an acceptable community-based method for fluoride delivery, because the risk of developing dental fluorosis lesions due to the ingestion of fluoride during the enamel formation period has been deemed acceptable when contrasted to the anticaries benefits of fluoride. However, the use of fluoride in water to control caries has created a controversy due to data associating water fluoridation as the cause of some systemic diseases. Therefore, the aim of this descriptive review was to discuss the systemic effects (risks) of water fluoridation use. S y s t e m i c E f f e c t s (R i s k s) o f W a t e r F l u o r i d a t i o n
... This political allegation of the last century, in the form of "conspiracy theory," has now been fomented by the allegation that fluoride is a neurotoxin that affects the IQ of people exposed to fluoridated water. These and other allegations, such as fluoride causing hypothyroidism, are based in transversal studies of associations and not cause-effect, which have been scientifically contested with elegance (28)(29)(30)(31). Thus, the adjustment of fluoride concentration during water treatment is still recommended by WHO, because the only systemic side effect associated with optimally fluoridated water ingestion is dental fluorosis, which does not compromise the quality of life of affected people. ...
Article
Full-text available
Since the 1950s, the benefits and risks of fluoridated water use have been debated worldwide. In the past, it was considered that the systemically ingested fluoride would exert its primary preventive effect after being incorporated into the enamel as fluorapatite, making the enamel more resistant to the caries process; however, it is now recognized that the main effect of water fluoridation is local and post eruptive. On the other hand, irrespective of the caries decline reported worldwide, the anticaries benefit of water fluoridation continues to be observed even in developed countries. Regarding the risks, water fluoridation is considered an acceptable community-based method for fluoride delivery, because the risk of developing dental fluorosis lesions due to the ingestion of fluoride during the enamel formation period has been deemed acceptable when contrasted to the anticaries benefits of fluoride. However, the use of fluoride in water to control caries has created a controversy due to data associating water fluoridation as the cause of some systemic diseases. Therefore, the aim of this descriptive review was to discuss the systemic effects (risks) of water fluoridation use.
... Studies showed that F has some impacts on human health depending on its content in drinking water (Omid et al. 2017;Newton et al. 2017;Näsman et al. 2016;Li et al. 2001;Indermitte et al. 2009). F is used as a compound known for mineralization of bones and teeth. ...
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Fluoride (F) contamination in groundwater can be problematic to human health. This study evaluated the concentration of fluoride in groundwater resources of Isfahan Province, the central plateau of Iran, and its related health issues to the inhabitant populations. For this purpose, 573 drinking groundwater samples were analyzed in 2016 by using the spectrophotometric method. Non-carcinogenic health risks due to F exposure through consumption of drinking water were assessed using the US EPA method. In addition, the associated zoning maps of the obtained results were presented using geographic information system (GIS). The results indicated that F content in drinking water ranged from 0.02 to 2.8 mg/L. The F contents were less than 0.50 mg/L in 63% of the drinking groundwater samples, 0.51–1.5 mg/L in 33.15%, and higher than 1.5 mg/L in 3.85% (Iran and World Health Organization guidelines) of the drinking groundwater samples. The F levels in the west and the south groundwater resources of the study areas were lower than 0.5 mg/L, which is within the recommended values for controlling dental caries (0.50–1.0 mg/L). Therefore, these places require more attention and more research is needed to increase F intake for health benefit. The HQ index for children, teens and male and female adults had health hazards (HQ > 1) in 51, 17, 28, and 18 of samples, respectively. Groundwater resources having a risk of more than one were located in the counties of Nayin, Natanz, and Ardestan. So, in these areas, there are potential risks of dental fluorosis. The most vulnerable groups were children. The F levels must be reduced in this region to decrease endemic fluorosis.
... We count both inbound and outbound links. Our hypothesis is that the presence of a reference to another resource is indicative of a relevant comment (Newton et al., 2017). ...
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Dental caries remains a significant public health problem in many countries and an important cause of health inequalities. In England, almost a third of 5-year-old children and over two-fifths of 15-year-old teenagers are affected, and substantially higher rates of disease are seen among deprived communities.1 Dental disease can cause impaired nutrition and growth,2 ,3 and is one of the most common causes of child hospital admission. Long-term impacts on appearance, speech, schooling and self-confidence may add up to a substantial disadvantage for affected children. Water fluoridation schemes were first introduced in England in the 1950s and around six million people across the country now live in areas where the level of fluoride in drinking water is adjusted to an optimum level for oral health. Worldwide, hundreds of millions of people have experienced the benefits of water fluoridation for many decades. The possible health effects of water fluoridation have been studied and reviewed many times.4 ,5 The dental effects of fluoridation, namely reduced dental decay and dental fluorosis, are well described. Water fluoridation is one of the few interventions that can be expected to directly reduce public health inequalities, although …
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In a famous article, Simpson described a hypothetical data example that led to apparently paradoxical results. We make the causal structure of Simpson's example explicit. We show how the paradox disappears when the statistical analysis is appropriately guided by subject-matter knowledge. We also review previous explanations of Simpson's paradox that attributed it to two distinct phenomena: confounding and non-collapsibility. Analytical errors may occur when the problem is stripped of its causal context and analyzed merely in statistical terms.
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Iodine deficiency is the most common cause of hypothyroidism worldwide. In persons living in iodine-replete areas, causes are congenital, spontaneous because of chronic autoimmune disease (atrophic autoimmune thyroiditis or goitrous autoimmune thyroiditis [Hashimoto's thyroiditis]), or iatrogenic because of goitrogens, drugs, or destructive treatment for thyrotoxicosis. Screening for congenital hypothyroidism exists and its use prevents mental retardation. The prevalence of spontaneous hypothyroidism is between 1% and 2% and is more common in older women and 10 times more common in women than in men. A significant proportion of subjects have asymptomatic chronic autoimmune thyroiditis and 8% of women (10% of women over 55 years of age) and 3% of men have subclinical hypothyroidism. Approximately one third of patients with newly diagnosed overt hypothyroidism have received destructive therapy for hyperthyroidism and indefinite surveillance is required. There is not much that can be done to prevent the occurrence of spontaneous autoimmune hypothyroidism, but if identified early, something can be done to prevent progression to overt disease. Controversy exists as to whether healthy adults would benefit from screening for autoimmune thyroid disease because a significant proportion of subjects tested will have evidence of mild thyroid failure. Case finding in women at menopause or visiting a primary care physician with nonspecific symptoms appears justified.
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The overwhelming health benefits of water fluoridation has been clearly demonstrated for decades; it’s sheer effectiveness and relatively low cost prompted the Centre for Disease Control to declare it as one of the top 10 public health achievements of the 20th century.1 Despite this, as long as there has been water fluoridation there has been an opposition to it on health grounds, although many of the arguments have been debunked.2 ,3 In this respect, water fluoridation remains controversial from a political standpoint. The recent work published in this journal by Peckham et al4 has re-ignited the debate. However, there are numerous reasons to be sceptical of the work. … [Full text of this article]
While previous research has suggested that there is an association between fluoride ingestion and the incidence of hypothyroidism, few population level studies have been undertaken. In England, approximately 10% of the population live in areas with community fluoridation schemes and hypothyroidism prevalence can be assessed from general practice data. This observational study examines the association between levels of fluoride in water supplies with practice level hypothyroidism prevalence. We used a cross-sectional study design using secondary data to develop binary logistic regression models of predictive factors for hypothyroidism prevalence at practice level using 2012 data on fluoride levels in drinking water, 2012/2013 Quality and Outcomes Framework (QOF) diagnosed hypothyroidism prevalence data, 2013 General Practitioner registered patient numbers and 2012 practice level Index of Multiple Deprivation scores. We found that higher levels of fluoride in drinking water provide a useful contribution for predicting prevalence of hypothyroidism. We found that practices located in the West Midlands (a wholly fluoridated area) are nearly twice as likely to report high hypothyroidism prevalence in comparison to Greater Manchester (non-fluoridated area). In many areas of the world, hypothyroidism is a major health concern and in addition to other factors-such as iodine deficiency-fluoride exposure should be considered as a contributing factor. The findings of the study raise particular concerns about the validity of community fluoridation as a safe public health measure. Published by the BMJ Publishing Group Limited. For permission to use (where not already granted under a licence) please go to http://group.bmj.com/group/rights-licensing/permissions.
No evidence supports the claim that water fluoridation causes hypothyroidism
  • Jj Warren
  • Mc Saraiva
Warren JJ, Saraiva MC. No evidence supports the claim that water fluoridation causes hypothyroidism. J Evid Based Dent Pract 2015;15:137–9.
Health effects of water fluoridation. Ireland: Health Research Board
  • M Sutton
  • R Kiersey
  • L Farragher
Sutton M, Kiersey R, Farragher L, et al. Health effects of water fluoridation. Ireland: Health Research Board, 2015.