Fluoride Action Network

New Evidence on Fluoride and the Developing Brain

Fluoride Action Network | January 2008 | By Michael Connett

In 2007, the question of how fluoride affects the developing brain gained renewed attention from researchers around the world. Research teams from Brazil, China, India, Italy, Mexico, and the United States conducted important new analyses, including 3 new studies investigating fluoride’s impact on childhood IQ (1,2,3), and several new animal studies investigating fluoride’s effects on learning, memory, and behavior (4,5).  The studies, which strengthen the concerns expressed by the US National Research Council in 2006, further highlight that it’s not just the teeth, but the brain, that may be impacted by too much fluoride during infancy and childhood. As noted in a review presented this fall by Harvard scientists Philippe Grandjean and Anna Choi:

“In humans, only five substances have so far been documented as developmental neurotoxicants:  lead, methylmercury, polychlorinated biphenyls, arsenic, and toluene. From this evidence, including our own studies on some of these substances, parallels may be drawn that suggest that fluoride could well belong to the same class of toxicants, but uncertainties remain” (6).

While uncertainties remain — as is common in science — several of the studies published this year made important advances in addressing some of the shortcomings of previous research. In particular, a study (1) linking high-fluoride (5 ppm) water to reduced IQ among a group of Mexican children made important steps in the right direction by simultaneously controlling (via multiple regression analysis) for other key factors known to affect IQ, including parent’s education, income, and childhood lead exposure. In addition to controlling for these factors the Mexican researchers helped eliminate a source of bias by “blinding” the psychologist conducting the IQ tests so that the examiner did not know which children had, or did not have, high fluoride exposures.

According to the authors:

“We found that exposure to F (fluoride) in urine was associated with reduced Performance, Verbal, and Full IQ scores before and after adjusting for confounders. The same pattern was observed for models with F in water as the exposure variable…. The individual effect of F in urine indicated that for each mg increase of F in urine a decrease of 1.7 points in Full IQ might be expected.”

In addition to assessing the effect of fluoride on IQ, the Mexican team studied the effect of arsenic as well and found similar results.  Based on their data, the authors conclude that

“fluoride and arsenic in drinking water have a potential neurotoxic effect in children. It is urgent that public health measures to reduce exposure levels be implemented. Millions of people around the world are exposed to these pollutants and are therefore potentially at risk for negative impact on intelligence. This risk may be increased where other factors affecting central nervous system development, such as malnutrition and poverty, are also present. The risk is particularly acute for children, whose brains are particularly sensitive to environmental toxins. Furthermore, it would be advisable to reexamine the benefits of fluoride given the documented health risks.”

While some pro-fluoride supporters may attempt to dismiss the results of this study — since the levels of fluoride in the water (5-9 ppm) are higher than the levels added to water in fluoridation programs (0.7-1.2 ppm) —  it would be short-sighted to dismiss such important findings on this basis. After all, the study was able to detect a statistically significant effect within a rather small (n=132) group of children. Since individuals vary widely in their sensitivity to chemicals, it is plausible, and indeed likely, that — if fluoride can cause IQ loss at 5 ppm in a small group of children (e.g. hundreds) — it could also cause IQ loss at lower levels in a much larger group of children (e.g. many millions).

Moreover, as noted by Dr. Kathleen Thiessen, a panelist from the National Research Council’s review of fluoride, there is “almost certainly overlaps” in the daily doses ingested by some of the Mexican children in the study and the daily doses ingested by some American children – especially when considering the myriad other sources of fluoride exposure now available in the US.


1) Rocha-Amador D, et al. (2007). Decreased intelligence in children and exposure to fluoride and arsenic in drinking water. Cadernos de Saude Publica 23(Suppl 4):S579-87. [See study]

2) Wang SX, et al. (2007). Arsenic and fluoride exposure in drinking water: children’s IQ and growth in Shanyin county, Shanxi province, China. Environmental Health Perspectives 115(4):643-7.

3) Trivedi MH, et al. (2007). Effect of high fluoride water on intelligence of school children in India. Fluoride 40(3):178-183.

4) Bera I, et al. (2007). Neurofunctional effects of developmental sodium fluoride exposure in rats. European Review for Medical and Pharmacological Sciences 11(4):211-24.

5) Chioca LR, et al. (2007). Subchronic fluoride intake induces impairment in habituation and active avoidance tasks in rats. European Journal of Pharmacology Oct 25; [Epub ahead of print]

6) Choi A, Grandjean P. (2007). Potentials for developmental fluoride neurotoxicity. XXVII Conference of the International Society for Fluoride Research, October 9-12, 2007, Beijing, China.