New review finds fluoride is not a developmental neurotoxicant at exposure levels relevant to fluoridation

Proper consideration of the best science shows community water fluoridation does not have a negative effect on child IQ. Image credit: Africa Studio / Shutterstock.com

A new extensive review of the scientific literature has concluded that fluoride is not a human developmental neurotoxicant at the current exposure levels in Europe. This is of course just as valid for New Zealand, the USA and other countries which use community water fluoridation (CWF).

Forty-one pages long, it’s a very extensive and detailed review. The full text can be downloaded  and its citation is:

Guth, S., Hüser, S., Roth, A., Degen, G., Diel, P., Edlund, K., … Thomas, H. (2020). Toxicity of fluoride: critical evaluation of evidence for human developmental neurotoxicity in epidemiological studies, animal experiments and in vitro analyses. Archives of Toxicology. 2020 May 8.

The anti-fluoridation crowd won’t be happy with this review. They have tended to have things their own way as they have argued that fluoridation is harmful to child IQ using irrelevant studies from endemic fluorosis areas where people suffer a range of health effect from overexposure to fluoride and other contaminants. Anti-fluoride campaigners have also misrepresented and misused recent studies from areas where fluoride exposure is lower.

So this review is timely because it critically examines all the recent studies and identifies their limitations. It identified 23 relevant epidemiological studies published between January 2012 and August 2019. One of these examined an association between fluoride exposure and school performance. The other 22 examined possible relationships with IQ.

Limitations of fluoride-IQ studies

The authors reported that:

“So far, almost all studies investigating the effect of fluoride intake on intelligence were performed in relatively poor, rural communities, e.g., in China, Iran, and Mongolia, where drinking water may contain comparatively high levels of fluoride (‘exposed population’), whereas the ‘reference populations’ often had access to water that was fluoridated at the recommended level.”

Figure 1: People in endemic fluorosis area sufferer a range of health problems – studies from these areas are not relevant to CWF

This means that anti-fluoride campaigners usually rely on studies which actually show no effect at F intake levels relevant to CWF. They base their arguments on the known negative health effects at high fluoride intake (people in areas of endemic fluorosis suffer a range of health problems) but ignore, or cover-up the fact the data actually does not show any harmful effects at levels similar to that experienced by people in areas of CWF.

Figure 2: Drinking water concentrations reported by Duan et al. (2018) from “high F” and “low F” villages compared with tap water F in areas of CWF

Figure 2 above shows this using data from 26 studies reported in the review of Duan et al. (2018). Here the blue range represents the drinking water concentration range for the control groups where no health problems were reported, or it was assumed none occurred (that is why it was a control group). The green range represents drinking water fluoride concentration common in areas of CWF.

We should be drawing our conclusions about the possible effects of CWF from the blue range of data – not the red range.

Confounding effects

Guth et al (2020) stress that most studies they considered ignored many confounding effects.  For example:

” . .rural regions with unusually high or unusually low fluoride in drinking water may be associated with a less developed health-care system, as well as lower educational and socioeconomic status. Furthermore, in these regions the overall nutritional status and the intake of essential nutrients may be lower and the exposure to environmental contaminants such as lead, cadmium, mercury, or manganese may be higher—factors that are also discussed to have a potential impact on intelligence”

Only two of the studies were from areas using CWF – Broadbent et al (2015) and Green et al (2019) – and their conclusions were different. Guth et al (2020) considered these two studies in detail.

Both studies were limited by the lack of IQ data for mothers – parental IQ is a strong confounder for child IQ studies. But Guth et al (2020) are quite critical of the lack of consideration of confounders in the Green et al (2019) study:

“Green et al. (2019) did not consider breastfeeding and low birth weight as possible confounders (both factors significantly associated with IQ in the study of Broadbent); they considered some of the relevant confounders (city, socioeconomic status, maternal education, race/ethnicity, prenatal secondhand smoke exposure), but did not adjust for others (alcohol consumption and further dietary factors, other sources of fluoride exposure, exact age of children at time point of testing). Furthermore, the study (Green et al. 2019) did not include assessment of children’s postnatal fluoride exposure via, e.g., diet, fluoride dentifrice, and/or fluoride tablets, which is considered to be a noteworthy limitation.”

Problems like poor consideration of confounders, contradictory results and the vague results reported by Green et al (2019) (no overall effect of fluoridation on child IQ, a statistically significant relationship of drinking water F concentration with male child IQ but not with female child IQ) caused Guth et al (2020) to conclude:

“The available epidemiological evidence does not provide sufficient arguments to raise concerns with regard to CWF in the range of 0.7–1.0 mg/L, and to justify the conclusion that fluoride is a human developmental neurotoxicant that should be categorized as similarly problematic as lead or methylmercury at current exposure levels.”

To repeat – this review is very detailed and thorough. Unlike the recent review of Grandjean (2019) (Developmental fluoride neurotoxicity: an updated review) which was superficial and somewhat biased (Grandjean is well known for his opposition to CWF) it made a detailed assessment of problems like the poor consideration of confounders or important risk-modifying factors and the concentration on poor quality studies from areas of endemic fluorosis.

Hopefully, policymakers will read this new review and take its conclusions into account.

Similar articles