Fluoride, which is added to drinking water in many countries, including the United States, may affect the intelligence level of children, according to a scientific study published on Monday that has begun to receive criticism, reviving a heated scientific and political debate in North America.
The study, conducted by researchers from the US government institute NIHS, is a meta-analysis of 74 studies conducted in 10 countries, including China and Canada, and the United States is not among these countries.
The study observed a decrease in IQ in children who were exposed to certain levels of fluoride in running water in 54 countries.
The study’s authors said in a statement received by Agence France-Presse, “For every increase of 1 mg/L of fluoride in urine (…) a decrease of 1.63 points in children’s IQ is recorded.”
A number of experts have questioned the result of this study, which was published in the journal “Jamma Pediatrics”, specifically pointing to gaps in the methodology and major errors in the basic studies.
Others, in contrast, emphasized that the study is “the most rigorous meta-analysis ever conducted” and called for “a re-evaluation of the potential risks of fluorosis during early brain development.”
But with Donald Trump about to officially take office, some scientists fear that the study will lead to a decline in public confidence in health institutions, as Trump supports Robert Kennedy Jr. (a fierce opponent of adding fluoride to water) to take over the Department of Health.
The threshold at which it becomes toxic
Fluoride is naturally present in groundwater in several countries, specifically in Africa and Asia, but in concentrations that can exceed the healthy limit recommended by the World Health Organization, which is 1.5 mg/L. The presence of fluoride in running water may be due to industrial pollution.
There are a few areas in the United States whose water naturally contains fluoride. Since the 1950s, health authorities in the rest of the country, with some exceptions, have been adding fluoride to their water, which helps prevent tooth decay.
According to a government website, 200 million Americans will receive fluoride-added water in 2022.
Although everyone agrees on the danger of high levels of fluoride, the scientific community is divided regarding the “threshold at which this substance becomes toxic.”
In the study, the researchers indicate – based on a small number of studies – that a rate of less than 1.5 mg/L (the minimum recommended by the World Health Organization) may affect the IQ of children.
Stephen Levy, a professor at the Iowa Oral Health Institute, points out that “almost all studies were conducted in environments containing other pollutants,” pointing to coal pollution in China, for example.
Other studies included in the analysis reached opposite results. There is still “uncertainty” about the effects of this concentration, according to the analysis’ authors.
They point out that there is not “sufficient data” to determine whether the 0.7 mg/L level recommended by US authorities for added fluorine affects IQ.
For his part, David Eaton, professor emeritus at the University of Washington and former president of the American Society of Toxicology, says, “There is simply not enough data” to definitively determine the threshold at which fluoride becomes toxic.
Great success
The study authors and scientists interviewed by AFP agree on one point: the need to conduct other studies to evaluate the effects of low concentrations of fluoride on cognitive development.
More broadly, the scientific community is questioning the need to continue adding fluoride to drinking water, a practice hailed as a great public health success.
Since there are other sources of fluoride, especially toothpaste, the benefits of this practice should be re-evaluated by studying the effects observed after “stopping adding fluoride to water in several areas,” said dental public health researcher Fernando Hugo.
In September, a federal judge, based on a document drawn up by the study’s authors, called on the American authorities to look into the matter.
Advocates of adding fluoride to water assert that this step helps reduce social and economic disparities, as poor populations are unable to adequately care for their teeth.
However, critics of fluoride supplementation point out that these same communities may be more at risk of negative effects of fluoride such as lower IQ in children.
David Eaton says, “Stop adding fluoride to water without conducting a clear assessment of the current benefits would be a grave mistake, because this step has undoubtedly had a significant positive impact on public health in the past,” stressing that the study only addresses the dangers of fluoride.