Anti-fluoride propagandists continually cite studies from areas of endemic fluorosis in their arguments against community water fluoridation (CWF). But if they critically looked at the data in those papers they might get a shock. Invariably the published data, even from areas of endemic fluorosis, shows fluoride is safe at the concentrations relevant to CWF.
I have completed a detailed analysis of all the 65 studies the Fluoride Action Network (FAN) lists as evidence that community water fluoridation (CWF) is harmful to child IQ. The full analysis is available for download as the document Analysis of FAN’s 65 brain-fluoride studies.
In this article, I discuss the studies in the FAN’s list (see “FLUORIDE & IQ: THE 65 STUDIES”) which report relationships between child IQ and fluoride exposure in areas of endemic fluorosis. There are eleven such studies in the FAN list but only six of them provide sufficient data to enable independent statistical analysis.
While those six studies do show a statically significant (p<0.05) negative relationship of IQ with fluoride intake those results are not relevant to CWF because the fluoride as exposure levels are much higher than ever occurs with CWF.
However, it is possible to investigate if the relationships are significant at lower concentrations more relevant to CWF. I have done this with these six studies and illustrate the result obtained with these graphs below using the data extracted from Xiang et al (2003). (This study is often used by anti-fluoride campaigners).
The red data points in the figures below are for lower concentrations of urinary F or creatinine adjusted urinary F. The range for the red points is still quite a bit larger than urinary F levels measured for children in areas where CWF is used. However, we can see that the relationships at these lower ranges are not statistically significant (results from regression analyses cited in figures).
This was also the case with the other studies from FAN’s list which provided sufficient data for regression analyses. I summarise the results obtained for five of these studies in the figure below.
This show that none of the studies found statistically significant relationships with fluoride exposure for the low fluoride concentration relevant to CWF. The situation is basically the same for the sixth study, Mustafa et al (2018), which reports average school subject performances for a range of subjects for children in Khartoum state, Sudan. However, it is hard to know what the safe limit for fluoride exposure is in that climate (for climatic reasons the upper permissible F level in drinking water is set at 0.33 ppm for Khartoum state) and the sample numbers are low. Interested readers should consult my report – Analysis of FAN’s 65 brain-fluoride studies.
Anti-fluoride campaigners often cite FAN’s list (“FLUORIDE & IQ: THE 65 STUDIES”) in their attempts to argue that fluoridation is bad for the child’s brain. But in these series of articles Anti-fluoride 65 brain-fluoride studies not evidence against fluoridation, I have shown that their arguments are false.
In Child IQ in countries with endemic fluorosis imply fluoridation is safe I showed that while IQ and other health problems may occur where fluoride exposure is very high in areas of endemic fluorosis the reports themselves implicitly assume that the low fluoride exposure in the “low fluoride” areas is safe. It is the data from these areas, not the “high fluoride” areas, that are relevant to CWF. So despite the heavy use of these articles by FAN and anti-fluoride activists these studies do not prove what they claim. If anything these studies show CWF is safe.
In this article, I considered a few of these studies which included data relevant to low fluoride exposure. When the low fluoride exposure data (relevant to CWF) from these studies were statistically analysed none of them showed significant relationships of child IQ to fluoride exposure. That confirms the implicit assumption from these studies that there is no negative effect of fluoride exposure on child IQ at these low levels.
Finally, in Canadian studies confirm findings of Broadbent et al (2015) – fluoridation has no effect on child IQ I summarise results from the only three studies where comparisons of IQ for children living in fluoridated and unfluoridated areas are compared. These studies were made in New Zealand and Canada and the results were the same. No statistically significant differences in child IQ were found.
However, the authors of the Canadian studies ignored this result and instead used questionable statistical methods to search for possible relationships between fluoride exposure and child IQ. Most of the relationships they report were not statistically significant but, nevertheless, they and their supporters have simply ignored this and concentrated on the few statically significant relationships.
Anti-fluoride activists currently rely strongly on these studies and heavily promote them. I will discuss these few studies further in my next article.