Image credit: Do new mothers doing a Ph.D. get enough support?
The anti-fluoride movement has certainly mobilised over the prenatal maternal urinary fluoride study which reported an association with child IQ. They see it as the best thing since sliced bread and believe it should lead to the end of fluoridation worldwide.
They also seem to be putting all their eggs in this one basket and have started a campaign aimed at stopping pregnant women from drinking fluoridated water (See Warning to Pregnant Women: Do Not Drink Fluoridated Water).
So I was not surprised to see a newsletter this morning from the Fluoride Action Network reporting another output from this study – a conference paper (most likely a poster) presented at the 3rd Early Career Researchers Conference on Environmental Epidemiology. The meeting was in Freising, Germany, on 19-20 March 2018.
I had been aware of the poster for the last week so had expected FAN to gleefully jump on it and start promoting it in their campaigns.
Here is a link to the abstract:
Thomas, D., Sanchez, B., Peterson, K., Basu, N., Angeles Martinez-Mier, E., Mercado-Garcia, A., … Tellez-Rojo, M. M. (2018). Prenatal fluoride exposure and neurobehavior among children 1-3 years of age in Mexico. Occupational and Environmental Medicine, 75(Suppl 1), A10–A10.
It’s only an abstract and it may be some time before a formal paper is published, if at all. Posters do not get much in the way of peer review and often not followed by formal papers. So I can’t say much about the poster at this stage as I never like to make an assessment of studies on the basis of abstracts alone.
But, in this case, I have Deena Thomas’s Ph.D. thesis which was the first place the work was reported. If you are interested you can access it from this link:
Thomas, D. B. (2014). Fluoride exposure during pregnancy and its effects on childhood neurobehavior: a study among mother-child pairs from Mexico City, Mexico. University of Michigan.
I will wait for a formal paper before properly critiquing the poster, but at the moment I find a big discrepancy between the Thesis conclusions and the conclusions presented in the poster abstract.
In her work, Deena Thomas used the Mental Development Index (MDI) which is an appropriate way of determining neurobehavioral effects in young children.
She concluded in her thesis (page 37):
“Neither maternal urinary or plasma fluoride was associated with offspring MDI scores”
And (page 38):
“This analysis suggests that maternal intake of fluoride during pregnancy does not have a strong impact on offspring cognitive development in the first three years of life.”
And further (page 48):
“Maternal intake of fluoride during pregnancy does not have any measurable effects on cognition in early life.”
So – no association found of child MDI score with maternal prenatal urinary F concentrations.
But the poster tells a different story.
The abstract concluded:
“Our findings add to our team’s recently published report on prenatal fluoride and cognition at ages 4 and 6–12 years by suggesting that higher in utero exposure to F has an adverse impact on offspring cognitive development that can be detected earlier, in the first three years of life.”
So her conclusions reported in her thesis are exactly the opposite of the conclusions reported in her conference poster!
What the hell is going on?
Obviously, I do not have access to the data and she does not provide it in her thesis. But from her descriptions of the data in her thesis and her poster perhaps we can draw some tentative conclusions.
The table below displays the data description, and a description of the best-fit line determined by statistical analysis, in her thesis and her poster.
|Information on data||Thomas Ph.D. Thesis||Conference abstract|
|Number of mother/child pairs||431||401|
|Maternal Urinary F range (mg/L)||0.110 – 3.439||0.195 – 3.673|
|Mean maternal urinary F (mg/L)||0.896||0.835|
|Model p-value||0.391 – Not significant|
|95% CI for β||-4.38 to -0.40|
*β is the coefficient, or slope, of the best-fit line
Apparently at least 30 data pairs have been removed from her thesis data to produce the dataset used for her poster. Perhaps even some data pairs were added (the maximum urinary F value is higher in the smaller data set used for the poster).
This sort of change in the data selected for the statistical analysis could easily swing the conclusion from no effect to a statistically significant effect. So the reasons for the changes to the dataset are of special interest.
Paul Connett claims this poster “strengthens” the findings reported in the Bashash paper. He adds:
“This finding adds strength to the rapidly accumulating evidence that a pregnant woman’s intake of fluoride similar to that from artificially fluoridated water can cause a large loss of IQ in the offspring.”
But this comes only by apparently removing the conflicting conclusions presented in Deela Thomas’s Ph.D. thesis. We are still left with the need to explain this conflict and why a significant section of the data was removed.
To be clear – I am not accusing Thomas et al. (2018) of fiddling the data to get the result they did. Just that, given the different conclusions in her thesis and the poster, there is a responsibility to explain the changes made to the dataset.
From the limited information presented in the poster abstract, I would think the scatter in the data could be like that seen in the Bashash et al. (2017) paper. The coefficient of the best fit line (β) is relatively small and while the 95% CI indicates the fit is statistically significant its closeness to zero suggest that it is a close thing.
However, let’s look forward to getting better information on this particular study either through correspondence or formal publication of a research paper.
Other articles on the Mexican study
Fluoride, pregnancy and the IQ of offspring,
Maternal urinary fluoride/IQ study – an update,
Anti-fluoridation campaigners often use statistical significance to confirm bias,
Paul Connett “updates” NZ MPs about fluoride?
Paul Connett’s misrepresentation of maternal F exposure study debunked,
Mary Byrne’s criticism is misplaced and avoids the real issues