Christine: The Harvard study is a review of 27 fluoride/IQ studies, a meta-analysis, which together show an average deficit of 7 IQ points in children, which is a significant finding, and, unlike most critics information, was published in a scientific peer-reviewed journal. And that journal is published by the federal government (US Dep’t of HHS)

There are now over 40 published human studies linking moderately high fluoride exposures with reduced intelligence and/or neurobehavioral deficits

· Over 40 animal studies showing that prolonged exposure to varying levels of fluoride can damage the brain, particularly when coupled with an iodine deficiency, or aluminum excess;

· 15 animal studies reporting that mice or rats ingesting fluoride have an impaired capacity for learning and memory;

· 4 human studies linking fluoride exposure with impaired fetal brain development.

The following is an explanation by Paul Connett, PhD, Executive Director of the Fluoride Action Network and co-author of the book, The Case Against Fluoride.

“Xiang et al, 2003, one of the 27 studies reviewed by Choi estimated that the threshold for the lowering of IQ was 1.9 ppm. A child drinking two liters of water at 1 ppm fluoride (2 mg of fluoride per day) would get more fluoride than some of the Chinese children drinking one liter of water at 1.9 ppm (1.9 mg/day).

‘Moreover another study ( Ding et al., 2012) found a lowering of IQ in the range of 0.3 – 3 ppm. No matter how you cut it – and no matter how much you want fluoridation to continue for emotional reasons – the science says that there is no adequate margin of safety – by any normal and rational toxicological standard – to protect ALL of America’s children from this serious end point. This outdated practice must be ended QUICKLY before we do further damage to our children and our future. If you must have fluoride, then brush it on your teeth and spit it out but don’t force it on the whole population via our drinking water.”

About whether the F water levels in the 27 original studies are close enough to be relevant to those in US fluoridated cities. Actually, an even better question is whether the TOTAL F intake in the subjects in China overlaps the F intake of Americans.
When you look at the levels of water F in all of the 27 studies (Choi Table 1) in fact many of the low F reference groups had water F that was considerably less than 0.7 mg/L, with several as low as 0.4 mg/L. The high F groups had as little as 0.88 mg/L F in their water, and many high F groups were in the 2-3 mg/L range. Thus some low F groups had water F concentrations lower than in US fluoridated cities and some had high F concentrations only somewhat higher than in US fluoridated cities.

You might argue that a water F concentration of 2 mg/L is more than “somewhat” higher than in US fluoridated cities. But there are two counterarguments:

First, in toxicology, it is common to provide a safety margin of at least a factor of 10. So a safety factor of 2 just isn’t sufficient.

Second, a more relevant measure of F exposure is urine or serum F, both of which reflect the total intake of F from all sources, not just drinking water. In the studies from China, almost none of the children used fluoridated toothpaste, had F supplements, or had dietary sources of F besides drinking water. In the US, all these additional sources of F can easily double the total F intake of a child. So, a Chinese study with a high F group drinking 2 mg/L F would provide a total exposure similar to a population of American children drinking 1 mg/L water.

For references on the urine F level in the Chinese studies, it turns out that 11 reported urine F in addition to water F. For 5 of these the mean urine F was less than 3 mg/L. There is a surprising dearth of information on urine F levels in American children with which to compare these Chinese data. However, a study in the UK (Mansfield 1999) found that about 6% of adults had more than 3 mg/L F in their urine, and the UK has much less fluoridation than the US. Children will tend to have higher total F intake for their body weight and therefore higher urine F because they drink more water for their body weight and are much more likely to swallow toothpaste. That information can be found in the NRC 2006 report.

Most of the Chinese studies are available in translation online at no cost.

So, to put the Choi study into context quantitatively, it suggests that Chinese children with total F exposures that are similar to some American children in fluoridated cities had an average IQ decline of 5-10 points. The levels of F exposure and the consequences are quite pertinent to water fluoridation in the US.

The most important finding of the Choi study is the remarkable consistency of the Chinese studies. Only 1 of the 27 did not find a lowering of IQ in the higher F exposure group. Such consistency is rarely found in meta-analyses. Choi also provides arguments for why it seems unlikely that a systematic bias is creating a spurious effect in all these studies.

Even if the Choi meta-analysis and the studies that underlie it can’t prove that IQ is lowered by F at exposure levels occurring in the US, the fact that no government that supports fluoridation has ever sponsored a single higher quality study to try to provide a better answer does not reassure us of the safety of fluoridation.