Anti-fluoride activists often claim community water fluoridation (CWF) depresses IQ. But what is the truth? Does fluoride depress IQ? Or is it just another myth?
This claim is usually presented on social media, submissions to local bodies and magazine articles in forms like:
- The Nazis used fluoridated drinking water in the concentration camps to keep the Jews passive;
- Research shows fluoride decreases the IQ of children or
- The general claim that fluoride is a neurotoxin.
So let’s look at what the science actually says about fluoride and human IQ.
First we need to be clear that there are no scientific studies supporting the claim that CWF is related to decline in IQ. Quite the opposite.
Broadbent et al., (2014) is the only detailed study investigating the relationship between CWF and IQ. They found no statistically significant relationship of IQ to fluoridation so their findings do “not support the assertion that fluoride in the context of CWF programs is neurotoxic.”
Dr Ken Perrott recently checked this out for the US using on-line data for the average IQ level in each US state and the corresponding data for the percentage of CWF in each state (see Dr Ken Perrott’s blog article “IQ not influenced by water fluoridation“). The graph shows there is no statistically significant relationship between the two.
IQ was significantly related to other factors like poverty and premature births. These two factors together explained almost 70% of the variation in IQ while CWF explained none of the variation.
Incidentally this is the same method used by Malin and Till (2015) who claimed a relationship between Attention Deficit Hyperactive Disorder (ADHD) and CWF. Anti-fluoride propagandists are currently promoting this paper although it has basic problems because it ignored the role of confounding factors. When these factors are included in the analysis there is no statistically significant relationship of ADHD to CWF. See the blog article “ADHD linked to elevation not fluoridation” for details.
There are studies relating IQ deficits to high natural fluoride concentrations in drinking water. Choi et al., (2012) reviewed most of these and their paper is probably the most frequent citation used by anti-fluoride activists. Reliance on this paper has been criticised because the reviewed articles are usually brief and often of poor quality, confounding factors were rarely considered and the studies were generally made in areas of endemic fluorosis in China. There are also a few reports of IQ deficits in other areas of endemic fluorosis in India and Iran. Natural fluoride concentrations in the water of these areas are usually much higher than used in CWF.
IQ and dental fluorosis
Skeletal and dental fluorosis are common in areas where fluoride concentration in drinking water is high. Dental fluorosis could be a factor in the observed deficits of IQ of children living in those areas (Perrott 2015). Severe dental fluorosis, like severe dental decay, has a negative influence on quality of life and this could result in learning difficulties leading to measured IQ deficits. In a sense dental fluorosis prevalence could be an important confounding factor ignored by researchers concentrating on a simply chemical toxicity hypothesis.
Unfortunately most studies of IQ deficits in areas of endemic fluorosis have concentrated on a chemical toxicity hypothesis. They have therefore measured drinking water fluoride concentrations but few studies have determined dental fluorosis prevalence. However, Choi et al., (2015) did find a relationship of cognitive deficits to severe dental fluorosis, although there was no statistically significant relationship with drinking water fluoride. Sudhir et al (2009) also reported that IQ grades of 13-15 year old children were lower in children with moderate or severe dental fluorosis (see figure).
It is worth considering dental fluorosis in more detail, especially the different forms found in areas where CWF is used and in areas of endemic fluorosis.
Dental fluorosis
Dental fluorosis is an imperfection in teeth resulting from excessive dietary intake of fluoride. It occurs in different degrees of severity and mild or very mild fluorosis is the only confirmed negative effect of community water fluoridation.
Dental fluorosis occurrence has been used to define the upper limit of fluoride concentration for CWF. Severe dental fluorosis only occurs where drinking water concentration is higher than 2 ppm F (National Research Council, 2006). The figure from the National Research Council report illustrates this. In New Zealand F concentrations are adjusted to ensure F concentrations are in the range 0.7 – 1 ppm F.
The NZ 2009 Oral Health Survey (Ministry of Health, 2010) provides dental fluorosis data for New Zealand. The graph shows the frequency of the different forms of dental fluorosis reported. The distribution is very similar to that for the US.
Although the Ministry of Health data does not show any difference between fluoridated areas and unfluoridated areas more detailed studies usually show a small increase in the milder forms of dental fluorosis where water is fluoridated. Importantly, water fluoridation has no effect on the medium and severe forms of fluorosis. The prevalence of medium and severe forms of dental fluorosis is very low in countries where CWF is used and is probably due to industrial contamination, local high levels of natural fluoride or excess consumption of fluoridated toothpaste.
Perception of the different forms of dental fluorosis is also important. People usually judge mild and very mild forms of dental fluorosis positively so they have a positive effect on their quality of life. In contrast people judge moderate and severe forms of dental fluorosis negatively so these have a negative effect on the person’s quality of life. As mentioned above, moderate and severe forms of dental fluorosis could possibly contribute to IQ deficits in children.
This figure compares the prevalence of the different forms of dental fluorosis in New Zealand and the USA (where CWF is common) with that in an area of endemic fluorosis in China where IQ deficits have been found. We have combined the milder forms together to contrast them with the moderate and severe forms (also combined) because of their different perception and influence on quality of life. There is a big difference and this underlines why we should not naively extrapolate from studies in areas of endemic fluorosis to areas like New Zealand and the United States.
Conclusions
Anti-fluoride activists most frequently cite Choi et al., (2012) as “proof” that fluoride causes IQ deficits in children. The will often give it special endorsement by presenting this as a claim that Harvard University have proven that fluoride lowers IQ. Of course, institutions prove nothing and this endorsement is false considering that the deans of the Harvard Medical School, Harvard School of Dental Medicine and Harvard School of Public Health have declared their support for CWF “as an effective and safe public health measure for people of all ages” (Flier et al., 2013).
But the Choi et al., (2012) study is not directly relevant to CWF because it refers to studies in areas of endemic fluorosis where drinking water fluoride concentrations are high. These studies only considered a chemical toxicity hypothesis and did not take confounding factors into account.
Grandjean & Landrigen (2014) are also often quoted by activists as “proof” that fluoride is a neurotoxin (or more correctly a neurotoxicant). Again to give it special endorsement it is often presented in the form of the claim that the “world’s most prestigious medical journal” (The Lancet) has officially declared that fluoride is a neurotoxin. Again, a scientific journal cannot officially make such a declaration.
But the only evidence quoted by Grandjean & Landrigen (2014) is the paper of Choi et al., (2012). When we realise that Grandjean himself was one of the co-authors of the Choi et al., paper these citations start to look a bit incestuous.
These studies only considered a chemical toxicity mechanism and did not look at other possible mechanisms like the physical effects of severe dental fluorosis on the individual and their development.
So far the only study which has looked at community water fluoridation as a possible factor in IQ is that of Broadbent et al., (2014). They found no statistically significant effect of CWF on IQ. The analysis of the percentage of CWF and average IQ in the 50 US states plus DC supports that conclusion.
References
Broadbent, J. M., Thomson, W. M., Ramrakha, S., Moffitt, T. E., Zeng, J., Foster Page, L. A., & Poulton, R. (2014). Community Water Fluoridation and Intelligence: Prospective Study in New Zealand. American Journal of Public Health, 105(1), 72–76.
Choi, A. L., Sun, G., Zhang, Y., & Grandjean, P. (2012). Developmental fluoride neurotoxicity: A systematic review and meta-analysis. Environmental Health Perspectives, 120(10), 1362–1368 /
Choi, A. L., Zhang, Y., Sun, G., Bellinger, D., Wang, K., Yang, X. J., … Grandjean, P. (2015). Association of lifetime exposure to fluoride and cognitive functions in Chinese children: A pilot study. Neurotoxicology and Teratology, 47, 96–101. doi:10.1016/j.ntt.2014.11.001
Grandjean, P., & Landrigan, P. J. (2014). Neurobehavioural effects of developmental toxicity. Lancet Neurol, 13(March), 330–338
Flier, J. S., Donoff, R. B., & Frenk, J. (2013). Letter from Harvard University deans supporting CWF.
Malin, A. J., & Till, C. (2015). Exposure to fluoridated water and attention deficit hyperactivity disorder prevalence among children and adolescents in the United States: an ecological association. Environmental Health, 14.
Ministry of Health. (2010). Our Oral Health Key findings of the 2009 New Zealand Oral Health Survey.
National Research Council. (2006). Fluoride in drinking water. A scientific review of EPA’s standards.
Perrott, K. W. (2015). Severe dental fluorosis and cognitive deficits. Neurotoxicology and Teratology, 48, 78–79.
Sudhir, K. M., Chandu, G. N., Prashant, G. M., & Reddy, V. V. S. (2009). Effect of fluoride exposure on Intelligence Quotient ( IQ ) among 13-15 year old school children of known endemic area of fluorosis , Nalgonda District , Andhra Pradesh. JOURNAL OF THE INDIAN ASSOCIATION OF PUBLIC HEALTH DENTISTRY, 2009(13), 88–94.
Extra reading
IQ not influenced by water fluoridation
ADHD linked to elevation not fluoridation
Severe dental fluorosis the real cause of IQ deficits?
Controversial IQ study hammered in The Lancet
Confirmation blindness on the fluoride-IQ issue
Severe dental fluorosis and cognitive deficits – now peer reviewed