Concerns Experts Shared About the 2019 Green, et al. Fluoride/IQ Study
Some
explanations on why the Green, et al. fluoride - IQ study
(which makes the claim that "A 1-mg/L increase in Maternal Urinary Fluoride
level was associated with a 4.49-point lower IQ score in boys, but there was no statistically significant association with IQ scores in girls") is not
likely to change the scientific consensus that community
water fluoridation is a safe and effective public health
measure to reduce the risk of dental decay and related
health issues. Correlation is another term often
used when changes in variables are presented as related
to one another.
https://jamanetwork.com/journals/jamapediatrics/fullarticle/2748634
Additional Fluoridation Resources
Statistician,
Rene Najera’s discussion of the Green, et al. paper:
“In
consultation with friends and colleagues, we found a lot
to be worried about in the epidemiological design of the
study and the biostatistical analysis of the resulting
data… And, of course, of the conclusions reached by the
authors and the press (with some help from the authors).
In the [second] part, I will lay out the epidemiological
design of the study and how it is flawed both in terms
of its internal
and external validity.
In the third part, I will lay out the biostatistical
analysis issues we observed.
The
discussion section is standard jargon that researchers
include in their papers where they basically acknowledge
that their study is based on a limited sample of the
entire population and that more research is needed.
(That’s the standard line for asking for more cash to do
another study.) They also state clearly: ‘Nonetheless,
despite our comprehensive array of covariates included,
this observational study design could not address the
possibility of other unmeasured residual confounding.''”
https://epidemiological.net/2019/09/19/the-hijacking-of-fluorine-18-998-part-one/
https://epidemiological.net/2019/09/21/the-hijacking-of-fluorine-18-998-part-two/
https://epidemiological.net/2019/09/23/the-hijacking-of-fluorine-18-998-part-three/
Expert reaction
to study looking at maternal exposure to fluoride and IQ
by eight international experts:
“In summary it
is not correct to imply that the data here show evidence
of a link between maternal fluoride exposure and IQ. The
average change in IQ is not statistically significant.”,
“I don’t think
there is a need to worry.”, “There
are many limitations which could affect the findings
reported in this paper and until these are addressed, I
regard the results as interesting, but not something to
alter fluid or food intake by mothers.”, “There
are numerous other complicating factors that limit the
interpretability of the results…”, “The
reduction in average IQ scores in young children,
associated with higher fluoride intake during their
mothers’ pregnancies, is really fairly small, and there
are reasons to doubt whether the reduction is entirely
caused by fluoride intake anyway.”, “I
would be very cautious about over interpreting this
data. Statistical significance does not equal
‘importance’.”
https://www.sciencemediacentre.org/expert-reaction-to-study-looking-at-maternal-exposure-to-fluoride-and-iq-in-children/
If at first you
don't succeed . . . statistical manipulation might help:
Details of why anti-F interpretations are faulty:
“…
the study itself shows no significant difference in children whose
mothers lived in fluoridated or unfluoridated areas
during pregnancy. Here is the relevant data from Table 1
in the paper..:”
https://openparachute.wordpress.com/2019/08/22/if-at-first-you-dont-succeed-statistical-manipulation-might-help/
No, fluoride
doesn't lower IQ. It fails to satisfy Hill's Criteria Of
Causality, American Council on Science and Health:
“While the
authors conclude that a 1-mg increase in fluoride
detected in the mother's urine is linked to an IQ drop
of about 4.5 points in boys, there is no statistically
significant IQ difference among girls. (Actually, it's
worse than that. The point estimate shows an IQ increase
of 2.4 points for girls.) Obviously, that is incoherent. There is no
sensible biochemical reason for why fluoride would harm
the brains of boys but not those of girls.”
hhttps://www.acsh.org/news/2019/08/19/no-fluoride-doesnt-lower-iq-it-fails-satisfy-hills-criteria-causality-14229
A request from 30
science and health experts to the National Institute of
Environmental Health Sciences for the release
of the Green et al. study data for independent analysis
based on the fact that “In recent weeks, a number of experts in epidemiology, psychology,
statistical methodology and other fields have raised
numerous concerns about the Green article, including the
following:”
1. Focusing on a subgroup analysis amid “noisy data”:
2. Modeling and variable anomalies:
3. Lacking data on relevant factors that can impact
children’s intelligence and cognitive ability:|
4. Omitting crucial findings:
5. Using invalid measures to determine individual
exposures:
6. Defining the final study group:
7. Assessing the impact of fluoride exposure:
8. Reporting anomalies:
9. Internal inconsistency of outcomes:
10. Overlooking research that conflicts with the
authors’ conclusions:
https://www.asdwa.org/wp-content/uploads/2019/10/NIEHSLetter10-23-19.pdf
CADTH RAPID RESPONSE REPORT: Community Water Fluoridation Exposure: A Review of Neurological and Cognitive Effects (10/23/19)
“Key Findings: This review identified one prospective birth cohort study13 examining the association between fluoride exposure of mothers during pregnancy and subsequent children’s intelligence quotient scores at age 3 to 4 years. Both unadjusted and adjusted estimates showed no significant association between an increase of 1 mg/L in mother urine fluoride and Full Scale intelligence quotient score in the total sample of boys and girls, or in girls. Adjusted estimates also showed no statistically significant association between an increase of 1 mg/L in mother urine fluoride and performance intelligence quotient or verbal intelligence quotient in all children. In boys, every 1 mg/L increased in mothers’ urine fluoride levels was associated with a 4.49 point lower intelligence quotient score. Every 1 mg increase in daily fluoride intake of mothers corresponded with 3.66 points lower in total children’s intelligence quotient score.
The interaction between child sex and maternal fluoride intake was not statistically significant. The evidence is weak due to multiple limitations (e.g., non-homogeneous distribution of data, potential errors and biases in the estimation of maternal fluoride exposure and in IQ measurement, uncontrolled potential important confounding factors); therefore, the findings of this study should be interpreted with caution.”
https://mattjacob.s3-us-west-2.amazonaws.com/cwf/CADTH+Evaluation+of+Green+Study+(2019).pdf
American Dental
Association News: Responses to fluoride study flood in
from all over the globe :
“The
American Dental Association remains committed to
fluoridation of public water supplies
as the single most effective public health measure to
help prevent tooth decay,” One of
the study’s authors, Dr. Angeles Martinez-Mier, chair of
cariology, operative dentistry and dental public health
at the Indiana University School of Dentistry, said
while she stands “fully
behind our study’s conclusions, as an individual, I am
happy to go on the record to say that I continue to
support water fluoridation.”
hhttps://www.ada.org/en/publications/ada-news/2019-archive/august/responses-to-fluoride-study-flood-in-from-all-over-the-globe
American Academy
of Pediatrics continues to recommend fluoride following
new study on maternal intake and child IQ
“The Academy
continues to recommend children drink fluoridated tap
water despite a new study linking fluoride intake among
pregnant women with a small dip in their children’s IQ.”
https://www.aappublications.org/news/2019/08/19/fluoride081919
American Dental
Hygienists’ Association Statement Regarding a Study
Linking Maternal Fluoride Exposure during Pregnancy and
the IQ Scores of Their Children:
“In reviewing this
study, it is important to consider the following
limitations identified by the authors:
• The timing of the urine sampling may not have
precisely represented fetal exposure throughout the
pregnancy.
• Maternal IQ was not taken into consideration.
• The reported fluoride intake did not measure the
actual concentration in the tap water in the
participant’s home. Fluoride concentration was estimated
based on the postal code; some locations could be
receiving water from multiple treatment plants.
• The estimated fluoride intake only considered
beverages; dietary sources and oral hygiene products
such as toothpaste were not considered.
• Information on the consumption of tap water and other
water-based beverages was obtained via a self-report,
non-validated questionnaire that may be subject to
recall bias.
• The method for estimating maternal fluoride intake has
not been validated.
• Post-natal fluoride exposure or consumption was not
assessed.”
https://www.adha.org/resources-docs/Press_Release_ADHA_JAMA_response.pdf
Podcast by
Dr. Christopher Labos (cardiologist with a degree in
epidemiology) and Johathan Jarry (a science
communicator) includes “a comprehensive look at the
[Green, et al.] fluoride-and-IQ study that came out”
that begins 30
minutes into the discussion:
“Some of the
things that we have discovered over time have been done
with observational research. So the fact that it’s
observational research in and of itself doesn’t make it
wrong, but you have to realize the limitations. The link
between smoking and lung cancer came out of
observational research. But it
came out of observational research that
was replicated many times over in many different
populations and eventually became incontrovertible.
And you can also get similar evidence using
animal models – convergence of evidence, it all moves in
the same direction. Because with an
observational study you see ‘A’ is associated with ’B’:
‘A’ could be causing ‘B’; ‘B’
could be causing A; it could be a random association; or
there could be some ‘C’ factor that is causing both ‘A’
and ‘B’.”
Listing of study
limitations: a relatively small sample size, urinary
fluoride level issues, potential recall bias on
fluoride/water consumption reporting; a statistical
drop in IQ was found only in boys (but girls’ IQ
increased slightly); the small decrease in boys’ IQ was
only found in performance IQ, not verbal IQ (which went
up); the scatter plots of IQ/fluoride data look almost
random and showed no obvious relationship; parent’s IQ
was not tested; fluoride consumption of children after
birth was not measured; no other IQ/fluoride studies
have reported an IQ difference between boys and girl;
many other possible confounding factors that might
affect young children’s IQ were not measured or included
in the analysis.
“As we go through
all of these issues, you will notice none of them are
terrible, but when you add all of them up, we could
really be off by a lot. It’s a
question of certainty – how certain are you this is
true. The minute you do something
you know is going to have this huge media response, do
you have a responsibility to be more certain.
You have to understand your research has
consequences.
If you are going
to do a study about how fluoride is affecting brain
development of children, maybe you could be a bit more
certain before you publish it because you know you are
going to induce fear in the population.”
http://bodyofevidence.ca/podcast/053-smart-drugs-and-fluoride
Earlier article related to potential dangers of subgroup
analysis:
“Analysis of
subgroup results in a clinical trial is surprisingly
unreliable, even in a large trial. This is the result of
a combination of reduced statistical power, increased
variance and the play of chance. Reliance on such
analyses is likely to be more erroneous, and hence
harmful, than application of the overall proportional
(or relative) result in the whole trial to the estimate
of absolute risk in that subgroup. Plausible
explanations can usually be found for effects that are,
in reality, simply due to the play of chance.
When clinicians
believe such subgroup analyses, there is a real danger
of harm to the individual patient.”
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC59592/
- Debate: Subgroup analyses in clinical trials:
fun to look at - but don't believe them!
Bruce Y Lee, MD,
Senior Contributor@Forbes:
“If you think
these findings prove that fluoride in drinking water
leads to lower intelligence, remember that
associations do not mean that one thing causes another.
Otherwise, we'd be urging Nicholas Cage to stop starring
in movies to prevent drownings in swimming pools.
Observational
studies, like this JAMA Pediatrics one, cannot,
cannot, cannot, cannot prove cause and effect.
People who live in areas where tap water is fluoridated
could also be exposed to other things or have behaviors
that may affect their children's IQ scores. For example,
could they or their children be eating more processed
foods with artificial ingredients? Could they be exposed
to more chemicals in the environment? We do not know
enough about the details of the study participants'
lives to know what really is happening.”
https://www.forbes.com/sites/brucelee/2019/08/20/fluoride-and-iq-what-is-the-link-what-this-study-says/
NHS UK -
No proof that a mother's intake of fluoride in pregnancy
affects their child's IQ:
"The findings need to be interpreted carefully. First, this is an observational study that cannot prove that the mother's fluoride exposure in pregnancy is directly responsible for the child's later IQ. Many hereditary, environmental and lifestyle factors could influence the child's IQ. Although the researchers have tried to adjust for potential confounders, it's very difficult to account for all the things that may be having an influence."
https://www.nhs.uk/news/pregnancy-and-child/no-proof-mothers-intake-fluoride-pregnancy-affects-their-childs-iq/
Dental
Health Services Victoria strongly supports health
benefits of water fluoridation:
“While the
researchers did account for some confounding factors
which could impact IQ scores, such as maternal
education, employment and certain health conditions,
many other factors known to impact brain development
were not accounted for by the study, such as maternal
alcohol intake, breastfeeding practices and nutritional
intake in the early years of life. The accuracy of the
methods used by the researchers to estimate fluoride
intake are also untested, as no external validation of
these methods has been carried out.
It is important to consider this new study in line with
the overwhelming weight of existing scientific evidence
that shows fluoride is safe and beneficial in reducing
tooth decay. Extensive evidence shows
there is no connection between levels of fluoride in
drinking water and IQ in children.
Two recent
studies in New Zealand and Sweden looked at the same
question as the Canadian researchers and found no
association between water fluoridation and IQ scores.”
https://www.dhsv.org.au/news/news-stories/general-news-stories/2019-news/dhsv-strongly-supports-health-benefits-of-water-fluoridation
The Right
Chemistry: Fluoride-IQ link doesn't appear significant
“When it comes to
risk factors that can affect a fetus, I would rank
tobacco smoke, alcohol consumption, air pollution and
exposure to lead, mercury, cadmium and various
potentially endocrine disrupting chemicals such as
phthalates well ahead of worries about fluoride.”
https://montrealgazette.com/opinion/columnists/the-right-chemistry-fluoride-iq-link-doesnt-appear-significant
(Joe Schwarcz is director of McGill
University’s Office for Science & Society)
Science-Based Medicine: Maternal Fluoride and IQ – The Scientific Community Pushes Back – Discussion of the Green, et al. study concerns and the request for independent analysis of the study data.
(Dr. Grant Ritchey) "The NIEHS provided funding for the Green et al. study, and we felt it was imperative to express our concerns to this body, not because the conclusions did not meet with our approval, but because there was a lack of transparency in the data they used as well as fundamental statistical errors in analyzing the data. Our letter to the NIEHS:
…[requested] that NIEHS formally ask the Green authors to release the HIPAA-compliant, Research Identifiable File (RIF) data sets from their study, as well as a complete explanation of their methods and the computer program/codes used in their data management and analysis.
As of this post no release of data has been forthcoming..."
https://sciencebasedmedicine.org/maternal-fluoride-and-iq-the-scientific-community-pushes-back/
Science-Based Medicine: Maternal Fluoride and IQ:
“Further, when you have to do subgroup analysis in order to find significant results that is a red flag for noisy data. There are other red flags as well, like the huge variance in results, and the disconnect between performance and verbal IQ. So we have noisy correlational data at odds with prior research. Perhaps even more damning is that the negative results were driven largely by a small number of boys who had extreme levels of exposure. Take out the outliers, and the overall effect becomes non-significant.” (Steven Novella)
https://sciencebasedmedicine.org/maternal-fluoride-and-iq/
There are many extremely important, potential factors that can significantly contribute to a child’s IQ that apparently were not collected, analyzed and included in the analysis? Without considering any of the possible factors that can have an important impact on a child's IQ, why would any extremely low (boys-only) potential association of IQ with low levels of exposure to fluoride be of any value?
Some of these important, ignored variables include:
- Parental IQ: “IQ and education for both parents were statistically correlated to child IQ. However, paternal IQ and education were not significant after accounting for maternal IQ effects.” (Meador, et al., Epilepsy Behav. 2011) “IQ correlations – father-child, 0.51; mother-child, 0.55. So intelligence clearly has a powerful genetic component.”(Intelligence and IQ, Dr. C. George Boeree)
- Diet and nutrition of mothers during pregnancy & Diet and nutrition of children after birth: “After adjusting for maternal education, socioeconomic status, the Home Observation for Measurement of the Environment (HOME) score, and total caloric intake, the good prenatal and childhood nutrition indices predicted more favorable neurodevelopment, while both poor nutrition indices predicted poorer neurodevelopment. These associations were stronger in prenatal than childhood models.” (Malin, et al., Nutrients 2018)
- Birth weight and early-life weight: “Within this cohort of typically developing children, early-life weight status was inversely associated with children's perceptual reasoning and working memory scores and possibly with full-scale intelligent quotient scores.” (Li, et al., Obesity, 2018)
- Length of time breast-feeding: “Breastfeeding duration of 1 month or shorter compared with longer periods was associated with approximately three points lower IQ… In conclusion, in this large sample with high quality assessment of child IQ, we found support of a beneficial association for breast feeding with child IQ at 5 years of age, while adjusting for maternal IQ and parental education, which only few previous studies have been able to do.” (Strøm, et al., BMJ Open 2019)
- Amount of time parents spent with child: “Using a large longitudinal British dataset, I show that paternal involvement in childhood has positive associations with offspring IQ at age 11, and offspring social mobility by age 42, though not with numbers of grandchildren. For IQ, there is an interaction between father's socioeconomic status socioeconomic status (SES) and his level of involvement, with high-SES fathers making more difference to the child's IQ by their investment than low-SES fathers do.” (Evolution and Human Behaviour, 2008)
- “Maternal education, household income, parents’ skin color, duration of breastfeeding, head circumference and number of siblings were the most powerful predictors of low IQ at age six. Of a broad set of potential social and biological predictors explored those essentially social were the most impactful ones, which could mean that a high proportion of these children may require intervention.” "Another major finding of this study is the effect of growth, nutrition, and breastfeeding during the first year of life on cognitive ability. Children who were breastfed for a longer period were less likely to have low IQ than those who were not breastfed." "Other predictors of low IQ were smoking during pregnancy and maternal perception of the child’s health." (Camargo-Figuera, et al., BMC Pediatr.)
- Amount of time each child spent in front of TV or playing electronic games: “In multivariate models, being a third-born or more child and watching television ≥1 h/day at 24 months were negatively associated with all IQ scores…” (Plancoulaine, et al., Sleep Med. 2017)
- Many
other factors were ignored that influence
intelligence and cognitive development in infants
and young children: that influence intelligence and cognitive development in infants and young children,
for example: Amount of time each child spent outside playing; Amount of time each child spent socializing with others; any environmental stress, genetics, etc.
“The IQ of an individual is multifactorial and is determined by a multitude of factors. Nature and nuture work together in determining human intelligence. Even though the genetic susceptibility plays a crucial role on the IQ of the individual, various modifiable environmental factors like education, premature birth, nutrition, pollution, drug and alcohol abuse, mental illnesses, and diseases can have an influence on an individual’s IQ. These modifiable factors can reinforce or weaken genetic susceptibility.” (Arun Oommen, Journal of Neurology & Stroke, 2014)
As noted above, there are a number of criticisms of the statistical methods used in they Green, et al. study which cast serious doubt on any conclusions that there was an actual, relevant association (or correlation) between fluoride exposure (at levels expected from community water fluoridation) and IQ.
Bottom Line: Trust the Majority of Relevant Science Experts instead of accepting the interpretation of vocal outliers who, after over 75 years of desperately trying, are still unable to provide ANY relevant, quality studies sufficient to change the scientific consensus that community water fluoridation is a safe and effective public health measure for reducing the risk of dental decay and related health issues.
Below are graphs from the Green, et al. study that compared various measurements of prenatal maternal fluoride exposure with children's IQ at 3 - 4 years old (regression lines removed). Along the x-axis are the measured fluoride exposure levels, and along the y-axis are the measured IQ scores. Each dot represents the IQ of a child plotted against the prenatal fluoride exposure of its mother.The highlighted dot in graph A below shows a female child with a measured FSIQ of about 142 and the mother's average urinary fluoride concentration (from three samples during pregnancy) was near 0.8 mg/L. If you follow the 142 IQ line to the left, you will see several children with similar IQs with mothers who had lower average urinary fluoride concentrations, and if you follow the 142 IQ line to the right, you will see several girls and a boy with IQs above 125 who had average urinary fluoride concentrations up to about 2.0 mg/L.
If you follow the 0.8 mg/L down, you will find a large scatter of boys and girls with IQs between about 85 and 125. At the very bottom of the 0.8 mg/L line are the records of two boys with IQs between about 50 and 60 whose mothers' average urinary fluoride concentrations were between 0.6 and 0.8 mg/L. Is it reasonable to assume this level of fluoride exposure would cause such a drop in IQ?
Carefully examine the scatter plot showing a huge variation in how the IQ of children is actually associated (correlated) with an average maternal fluoride level from just three urine samples collected during about 270 days of pregnancy. Then consider what dozens of other graphs might look like that showed possible relationships between a child's IQ and the many other factors described above that have been shown to be associated with IQ development. An example is shown below. The second graph (B) also shows a huge variation between fluoride exposure and IQ.
The wide scatter alone is sufficient to cast serious doubt on the validity and/or relevance of any conclusions without even considering the other study limitations described above by the experts. When a one sees scatter graphs like those in the Green, et al. study where it looks as though the data points are randomly scattered, one should consider any alleged association between the two variables being studied with extreme skepticism.
For some examples of how a graph can be constructed to "prove" almost any association or correlation I went to a site that lists average IQ by country along with other factors that can be demonstrated to be associated/correlated with IQ. The Green, et al. study claimed that a 1-mg/L increase in Maternal Urinary Fluoride level was associated with a 4.49-point lower IQ score in boys. One can easily see from the graphs below that a $20,000 increase in average income is associated with a 10 point increase in IQ. Extremely concerning, however, is the graph that clearly shows an 8 degree increase in average maximum temperature is associated with a 10 point drop in IQ.
https://www.worlddata.info/iq-by-country.php
The main point of this demonstration is to show that finding an association/correlation between two factors - even a statistically significant association - does not prove there is any actual cause and effect relationship between the two factors. The income/IQ association might demonstrate a legitimate cause and effect association, but it could be that a higher IQ causes a higher average income. The temperature/IQ association is probably due to a number of other causes. For additional examples of how relationships between different factors can be presented search on "correlation does not prove causation" or go to:
https://www.tylervigen.com/spurious-correlations