Fluoride and IQ – once more

I guess anti-fluoridation propagandists will soon be pushing another “scientific” paper claiming to show that fluoride decrease IQ. Of course, this paper is published in the anti-fluoride journal Fluoride – which gives you a clue to how unreliable it is. You can download and read it for yourself – I suggest you do:

Karimzade, S., & Aghaei, M. (2014). Investigation of intelligence quotient in 9–12-year-old children exposed to high- and low-drinking water fluoride in west Azerbaijan province, Iran,  47(March), 9–14.

In summary, it compares the IQ levels of children in two Iranian towns, one with low fluoride drinking water (0.25 ppm F) and one with high fluoride drinking water (3.94 ppm F). Guess what – the children in the high fluoride area had lower IQ than those in the low fluoride area. Standard “evidence” for the anti-fluoride activists.

But here is the problem – the only data presented was for fluoride concentration and IQ. There was absolutely no consideration of any other factors known to influence IQ! Parental education levels, for example.

Dr Jonathan Broadbent pointed me to some easily available information ignored by the authors but highly relevant to the situation.  The population sizes and education levels of the areas.

The “low fluoride” area Piranshahr

( This paper is so poorly written and reviewed there was no way of identifying which area was which from the paper itself. I had to hunt down likely fluoride levels by my own internet search – I will comment on the question of quality and reviewing below).

Piranshahr city, Iran.

According to Wikipedia this city:

“is one of the fastest-growing cities in Iran. The government’s mid-year estimate for 2013 puts Piranshahr’s population at 270,138 compared with the 2012 figure of 220,000.The city is forecast to have a population of approximately. 320,000 by 2014 and 350,000 by 2015.”


“Piranshahr has an educated population and its literacy rate is very high: of Piranshahr’s population over 28.60% (vs. a national average of 24%) hold a bachelor’s degree or higher; 94% (vs. 82% nationally) have a high school diploma or equivalent. In fact, Piranshahr has the highest percentage of college graduates of any city in the entire country.”

 The “high fluoride” area Poldasht

Poldasht city Iran. Same magnificaiton as map above.

This is the capital of Poldasht CountyWest Azerbaijan ProvinceIranAt the 2006 census, its population was 8,584, in 2,205 families. It, and the county, are smaller than Piranshahr. From Google maps it seems pretty much in the middle of nowhere, right on the Iran/Armenian border.

I couldn’t find any information on educational levels in Poldasht (it is after all a small, remote place). However, I think it is safe to infer that it is culturally and educationally less developed than Piranshahr. As Dr Broadbent commented – these towns are not comparable (and consequently neither would their satellite villages be). It appears the authors may have indulged in a bit of confirmation bias through sample selection.

Mind you, the authors assured readers:

“The two rural areas studied had very similar population, educational, economic, social, cultural, and general demographic characteristics but differed in the concentration of F in drinking water.”


“Questionnaires were completed by the parents to measure potential confounding factors involving educational, economic, social, cultural, and general demographic characteristics.”

Trouble is, the authors did nothing to share data supporting these claims with their readers! Why not? And why didn’t the reviewers and journal editors ask such information be included? After all, it is absolutely central to the case being made. This brings us to the quality and refereeing standards of the journal Fluoride.

Fluoride again excluded from MEDLINE indexing

In my exchange with Paul Connett I was very critical of the journal Fluoride.  Despite supporting the journal Paul did nothing to answer my criticisms. You can see our discussion in The Fluoride Debate. My comments on the journal are in The journal Fluoride.

I am not the only observer critical of the quality and standards of Fluoride. Last year the editor made another application for inclusion in the MEDLINE Index. This was again rejected on quality grounds. The score of 1.5 out of 5 was well below the 3.75 or greater required for selection for indexing.

The image below is from the review committee report on Fluoride.

Fluoirde-1 fluoride-2

This report confirms my criticism of Fluoride. It should not be treated as a reliable source of research findings. The deficiencies in the paper discussed above illustrates some of the problems.

Similar articles

5 responses to “Fluoride and IQ – once more

  1. Steve Slott

    Excellent, Ken. A big part of the problem still remains with media who portray there to be “two sides” to this issue, refusing to accurately characterize it as science versus “junk science”. Anybody can say whatever they please, as antifluoridationists constantly do, but when media do not discern fact from fiction, the misinformation and junk gain false credibility that negatively impacts everyone.

    Steven D. Slott, DDS


  2. There are so many flaws in this study it would not pass muster at an undergraduate level at many universities in Australia or New Zealand. The fact that the authors reference such unreliable sources tells us that they are heavily invested in their own confirmation biases.

    A good example of diluted thinking. Thanks for this article Ken.


  3. Steve Slott

    And here what the new Broadbent study in J of Public Health has to say:

    “Results. No significant differences in IQ because of fluoride exposure were noted. These findings held after adjusting for potential confounding variables, including sex, socioeconomic status, breastfeeding, and birth weight (as well as educational attainment for adult IQ outcomes).

    Conclusions. These findings do not support the assertion that fluoride in the context of CWF programs is neurotoxic. Associations between very high fluoride exposure and low IQ reported in previous studies may have been affected by confounding, particularly by urban or rural status.”

    (Am J Public Health. Published online ahead of print May 15, 2014: e1–e5. doi:10.2105/AJPH.2013.301857)

    Steven D. Slott, DDS


  4. bdcguard-19

    Can you shill off the quality of this study please? http://ehp.niehs.nih.gov/1104912/


Leave a Reply: please be polite to other commenters & no ad hominems.

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s