That is what the US data for average state IQ and percent water fluoridation tells us.
I thought I would check out the US IQ and fluoridation data for each state after reading Malin and Till (2015). That paper compared the prevalence of ADHD by state with the percent fluoridation in each state. There are problems with the paper (see ADHD linked to elevation not fluoridation and Poor peer-review – a case study) but what is good for the goose is good for the gander. How do the corresponding statistics for IQ compare?
IQ data for US states are not readily available but I managed to find a data set of IQ estimates by state in 2000 based on Scholastic Aptitude Test scores. The correlation of these average IQ scores with water fluoridation (1992) is not at all significant statistically. The slope of the trend line in the plot below is not significantly different to zero (-0.04 to +0.01 at the 95% confidence level as represented by the dashed lines).
This lack of correlation is not at all surprising. After all, the only published study to compare IQ and community water fluoridation (CWF) is that of Broadbent et al., (2014) – they also did not find any statistically signficant relationship.
So what are the anti-fluoride propagandists on about?
They do not rely on studies involving CWF but instead claim support in studies from areas where fluorosis due to excess fluoride is endemic – eg Choi et al., (2012). These and similar studies have reported a correlation of IQ with drinking water fluoride- but there are 2 problems:
- Very little was done in these studies to consider confounding factors. There is the possibility that inclusion of these confounding factors in correlations would show that fluoride does not make a statistically signficant contribution to IQ changes.
- Generally the authors have assumed a chemical toxicity explanation without any real justification. The data can be explained by other mechanisms such as the influence of the disfiguring effect of severe dental fluorosis on quality of life and learning (Perrott, 2015). In the few cases where data for severe dental fluorosis was included its relationship with IQ is statistically significant (eg Choi et al., 2015) (see Severe dental fluorosis the real cause of IQ deficits?). Severe dental fluorosis is not a problem in areas where CWF is used.
There is no need to consider confounding factors for the correction in the above figure as CWF does not explain any of the variation in IQ. But I did find statistically significant relationship for IQ with a number of factors. The plots below show the data for premature births in 1990-1991 and average percent poverty in 2002-2004. These correlations by themselves explain 50 and 63% of the variation in IQ. Combined they explain 69% of the variation.
The percentage of CWF in each state explains none of the variation.
It would be more rational for those concerned about CWF to get active on issues related to poverty and premature births.
The community water fluoridation issue is a dead duck as far as IQ is concerned.