Fluoride/Human IQ Studies

23 published studies report an association of reduced IQ with high fluoride exposure. Click here for complete summary.

In the summer of 2008, the following two reports reviewed the published studies reporting an association of high fluoride exposure and reduced IQ. The fluoride levels in water in these studies range from 0.88 – 9.4 ppm.

Connett M, Limeback H.
Fluoride and its effect on human intelligence. A systematic review.

International Association for Dental Research 83rd General Session and Exhibition. Toronto, Canada.
Poster 2205. July 4, 2008.

Tang Q-Q, Du J, Ma H-H, Jiang S-J, Zhou X-J.
Fluoride and Children’s Intelligence: A Meta-analysis.
Biol Trace Elem Res. 2008 Aug 10. 2008.

The Tang et al. study cites 16 studies, including 5 Chinese studies that we did not know about. FAN plans to have them translated.

The Connett & Limeback review, published prior to Tang et al., found 18 out of 20 studies reporting an association to fluoride exposure and lowered IQ.

The citations for the 23 studies are listed on the FAN site with links to the Chinese and translated versions.

The Fluoride journal published 6 of the translated Chinese studies on fluoride’s impact on IQ in its April-June 2008 edition (Qin-1990, Chen-1991, Guo-1991, Liu-2000, Hong-2001, Li-2003) and will publish more translated studies in later editions.

Twelve (12) the human/IQ studies were originally published in Chinese. Julian Brooke translated these studies into English under contract with Fluoride Action Network.

In their review of the toxicology of fluoride, the committee who authored the 2006 National Research Council of the National Academies report on fluoride (NRC), cited only 3 of the 23 studies in its ‘Findings on Human Cognitive Abilities’, and cited 6 of the 23 studies in its references (Yang et al., 1994; Li et al., 1995; Lin et al., 1991; Zhao et al., 1996; Lu et al., 2000; Xiang et al., 2003). 5 studies (including one untranslated Chinese study) were published after the NRC was released. The NRC report stated:

Human Cognitive Abilities.
In assessing the potential health effects of fluoride at 2-4 mg/L, the committee found three studies of human populations exposed at those concentrations in drinking water that were useful for informing its assessment of potential neurologic effects. These studies were conducted in different areas of China, where fluoride concentrations ranged from 2.5 to 4 mg/L. Comparisons were made between the IQs of children from those populations with children exposed to lower concentration of fluoride ranging from 0.4 to 1 mg/L. The studies reported that while modal IQ scores were unchanged, the average IQ scores were lower in the more highly exposed children. This was due to fewer children in the high IQ range. While the studies lacked sufficient detail for the committee to fully assess their quality and their relevance to U.S. populations, the consistency of the collective results warrant additional research on the effects of fluoride on intelligence. Investigation of other mental and physiological alterations reported in the case study literature, including mental confusion and lethargy, should also be investigated.
Ref: bottom of page 220 to page 221

The NRC report also stated:

On the basis of information largely derived from histological, chemical, and molecular studies, it is apparent that fluorides have the ability to interfere with the functions of the brain and the body by direct and indirect means. To determine the possible adverse effects of fluoride, additional data from both the experimental and the clinical sciences are needed.

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