EXPERT REACTION: Mum's fluoride exposure might affect bub's IQ

Reporting links between environmental exposures and human health is particularly important when there are new high quality studies, or breakthrough technologies that provide new insights on existing data.

The publication in JAMA Pediatrics of a study associating maternal fluoride exposure and child intelligence regrettably does not meaningfully advance our knowledge in either domain.
 
Using a highly selected sub-group of mothers to be, the authors calculated a correlation between fluoride consumption and child intelligence. Nether the method for collecting maternal fluoride exposure data nor the method for calculating total fluoride exposure have been validated, making the size and source of associations unreliable. To quote the authors (emphasis added):

'We obtained information on consumption of tap water and other water-based beverages (tea and coffee) from a self report questionnaire completed by mothers during the first and third trimesters. This questionnaire was used in the original MREC cohort and has not been validated. Also, for this study, we developed methods to estimate and calculate fluoride intake that have not yet been validated.

The journal editor is aware of the contentious nature of the paper, and has taken the unusual step of publishing their own personal letter in the journal, in addition to the editorial, stating that that this study is neither the first nor last word on the topic. I agree, and very much look forward to more appropriately designed studies on the topic.

While this paper’s title (which hints that fluoride may affect your children’s intelligence) might at first sound scary, I think there are several factors that should be kept in mind when reading it.
 
The key words in the paper are “higher levels”. The authors state that an increase of 1 milligram per litre (1 mg/L) increase in fluoride was associated with a 4.49 point lower IQ score but, fluoride intake appears to have been below 1 mg/L for most people in the study, even for those with fluoridated water, and nearly everyone (bar a few outliers) had a fluoride intake of less than 2 mg/L which multiple previous studies have shown is safe. There is also a lot of variation in the data - which makes drawing firm conclusions/predictions from it difficult.
 
There are also a number of potential confounding factors include the fact that the water intake was self-reported and, as the authors admit, some of the methods used are not validated. One observed assertion also only seems to occur in boys and not girls but no explanation is given as to why this should be the case?
 
In conclusion, while the work in interesting and the authors have tried to be thorough in the end they only claim to have shown an association between two factors - not prove they are linked; the “possibility” of an effect justifying future research is not the same as concluding that there is an effect and; nearly everyone in this study had low levels of fluoride intake anyway. So although the work is interesting and I don’t think there is a need to worry.

This appears to be a weak study and fails to acknowledge existing and robust evidence from New Zealand and Swedish studies that showed there is no association between levels of fluoride in water and a child’s IQ.

The Australian Dental Association’s position is consistent with the National Health and Medical Research Council which confirms that fluoride strengthens and protects teeth in people of all ages, and does so safely.

This paper from Green et al provides an interesting analysis on fluoride and cognitive development. Whilst the paper reports a lower IQ score in boys at aged 3-4 years based on maternal urinary fluoride output, there were no differences in girls.

The reported IQ difference for boys was 4.5 points for a 1 mg/L increase in maternal urinary fluoride, yet the mean maternal urinary fluoride in the non-fluoridated communities was 0.40 mg/L and in the fluoridated communities was 0.69 mg/L – a differences of only 0.29 mg/L – suggesting that the actual differences in reported IQ would be much smaller than the 4.5 points for a 1 mg/L increase.

For mothers in the 25-75th percentile, the IQ difference in boys was only 1.48 points, and there was no difference in girls (with girls having a slightly higher IQ in fluoridated communities).

The authors note a number of limitations for their study, including the fact that post-natal fluoride exposure or consumption was not measured in the children. It would be important to see the results of this study replicated in other locations.

This is one of the most controversial papers that I’ve read in quite a while!  Whilst we need to remember that it is only one study, and the results weren’t completely clear (as the effect was shown in boys, but not in girls), as a prenatal dietitian, I will now be advising my pregnant clients to drink filtered water – at least until more conclusive research is undertaken.  The NHMRC states that adding fluoride to the water supply has reduced tooth decay by up to 44%, so it has clearly done a lot of good and therefore I don’t believe that everyone needs to avoid fluoridated water at this stage. 
 
It’s also important to remember that boiling the water doesn’t reduce fluoride levels, so filtered water is the best choice.  I believe that filtered water is a better choice than bottled water during pregnancy due to the possible risks of BPA (bisphenol A) found in many plastic bottles.  
 
It’s also important to note that not all fluoridated water needs to be avoided, there was a dose-respondent relationship, so drinking small amounts of fluoridated water is not going to hurt.  Water is still the best choice for us all, pregnant women included, to drink, it just might be beneficial to filter it during pregnancy.

While no single observational study provides a definitive test of a hypothesis, the results of the prospective cohort study conducted in Canada by Green et al. (2019) are consistent with those of a previous prospective cohort study conducted in Mexico by Bashash et al. (2017).

Furthermore, a meta-analysis of 27 epidemiological studies found higher fluoride intakes to be associated with lower children’s intelligence (Choi et al 2012). Studies on rodents have found negative impacts of fluoride on memory and learning.

Therefore, as the editorial in JAMA states, “the hypothesis that fluoride is a neurodevelopmental toxicant must now be given serious consideration”.

Since water fluoridation became an icon of public health in heavily fluoridated USA and Australia, it has been very difficult to publish in leading medical or dental journals any article that raises doubts about the safety or claimed benefits of fluoridation.

Authors who have succeeded in publishing have received personal attacks and their work has been misrepresented. Although the article by Green et al. rigorously addressed possible limitations of the study and had “additional scrutiny”, according to the editor’s note, the authors and editor should expect hostile unscientific responses from pro-fluoridationists.