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A rigorous nine-year review of research into the relationship between fluoride and cognition in children concluded that IQ decreases as fluoride levels increase.
Each 1-unit increase in urinary fluoride — a way of measuring all sources of fluoride a person consumes — is associated with a roughly 1-point decrease in a child's IQ score, the review concluded.
Although such an effect may seem small to one person, in a broader sense, the authors of the study, the consequences are significant, especially for those who are vulnerable due to risk factors such as poverty and malnutrition.
“A 5-point drop in a population's IQ can double the number of people classified as mentally retarded,” they wrote in their conclusion.
of ResearchPublished Monday in the JAMA Pediatrics journal, it comes with a back story. It was conducted by scientists at the government's National Toxicology Program, which evaluates chemicals and other exposures to human health, such as mobile radiation. In the year It was launched in 2015 and has been subject to several reviews in the process, which some critics say has been designed to delay its official release.
The full review is finally as a A long monograph The study was conducted in August and September basis A federal judge's ruling orders the U.S. Environmental Protection Agency to tighten controls on fluoride to protect children's brain development.
“Simply put, the risk to health at exposure levels in United States drinking water is sufficient to trigger a regulatory response by EPA,” U.S. District Judge Edward Chen wrote in the decision.
In November, Robert F. Kennedy Jr., President-elect Donald Trump, the US Secretary of Health and Human Services, labeled fluoride “industrial waste” and He promised As the Trump administration advises utilities to stop adding to public water supplies.
Fluoride a A naturally occurring mineral It is found in different levels in soil, rock and water. Also a The result of fertilizer production. For decades, many cities have added fluoride to treated drinking water to protect teeth from cavities, according to recommendations from the US Centers for Disease Control and Prevention and the World Health Organization.
When brushing your teeth, fluoride can help stop early decay by returning minerals to the tooth enamel. It also makes teeth More resistant to acid And it interferes with the ability of bacteria to erode teeth.
In some places, including places with well water and naturally high fluoride content, children get too much fluoride, leaving spots and stains on their teeth, called dental fluoride disease. In 2015, HHS He lowered it. Recommended levels Fluoride in drinking water from 0.7 parts per million to 1.2 parts per million to 0.7 parts per million, to prevent fluorosis.
CDC He repeated his faith In the year In 2015, Health Benefits of Fluoride named water fluoridation one of the “10 Greatest Public Health Achievements of the 21st Century.”
But now environmental health experts say health agencies need to reevaluate the risks and benefits of fluoride's neurotoxicity.
“The evidence is sufficient. It's not definitive,” said Dr. Bruce Lanphear, an epidemiologist and professor at Simon Fraser University in Canada. Lanphear wrote a commentary on the new paper, and one of his studies was included in the review, but was not involved in the report's conclusions.
“We need to pause,” he said. Instead of sticking their heads in the sand, we need to review the evidence.
In a separate comment on the study, Dr. Steven Levy, professor of preventive and community dentistry at the University of Iowa, does not speak to the study's conclusions and the way JAMA Children's Treatment is presented because the study itself does not exist. Rounds of reviews and delays in public release.
Levy said that simply publishing a meta-analysis of human studies doesn't provide readers with useful context on animal studies conducted by the National Toxicology Program, which showed no decline in learning or memory in rats exposed to low to moderate levels of fluoride. It indicates that all human beings The studies included in the review were from countries outside the US and most were classified by the study authors as being at high risk of bias.
“Therefore, although there is some evidence that there may be a link between IQ and high levels of fluoride in water, there is no evidence of a negative effect at the lower levels of fluoride commonly used.” [community water fluoridation] Rituals,” he wrote.
On this point, the authors of the study agree with him.
In their statement, they said they don't have enough data to know whether the recommended amount of fluoride in drinking water has any effect on children's IQ.
The new review included 74 studies from 10 countries. Most of the studies – 45 – came from China, where researchers first noticed a difference between communities exposed to high levels of fluoride and communities that were not.
If it came from precise measurements, such as laboratory tests of fluoride in residential water or urine, the researchers looked at how the children's age, intelligence were tested, and how researchers measured their exposure to fluoride, inferring from precise measurements such as fluoride levels.
Some are very strong Studies from Canada and Mexico looked at measurements of fluoride in the urine of pregnant women and then tested their children's IQ years later.
The researchers cut the data into three meta-analyses, or case studies.
In their first study of nearly 21,000 children from 59 studies, they found significant differences in IQ between children with high and low fluoride exposure. Children exposed to the highest levels of fluoride scored 7 points lower on IQ tests than those exposed to the lowest levels of fluoride. When researchers limited their analysis to only high-quality studies, the difference remained smaller: about 3 IQ points.
In a second analysis of group-level studies of fluoride levels in urine and water, the researchers found less than a 2-point drop in IQ between the highest and lowest fluoride levels. When they limited their analysis to the four studies with low risk of bias in their data, they found that children who received 2 parts per million of fluoridated water had IQ scores that were, on average, 5 points lower than those who did not. It is not exposed to low levels. When the researchers looked at millions of people with less than 1.5 units of water, there were no significant differences in IQ.
In four studies with a low risk of bias that reported group-level measurements of urinary fluoride, people found less than 1.5 parts per million in urine—not just water, but all sources they consumed. – had IQ scores on average 1 point lower than those exposed to low levels.
A recent meta-analysis of studies that reported individual measurements of urinary fluoride and IQ scores in nearly 4,500 children found that an increase of 1 part per million in fluoride was associated with an IQ score of 1.63.
Lanphear said the consistency of the findings across all these analyzes was striking.
“Kids who had high fluoride exposure — whether that's measured by fluoride, like a raw measure, or fluoride in water or fluoride in urine — found consistent data that higher exposure was associated with lower IQ,” he said.
Lanphear was involved in a different situation An influential study In the year From Canada, published in 2019 by JAMA Pediatrics. The conclusion was surprising, the editors of the journal added. A note for the study Letting their readers know that you've put a lot of thought into publishing.
of Research They measured fluoride in the urine of 600 pregnant women and then measured their children's IQ scores at 3 to 4 years of age. About half of the women lived in communities where fluoride was added. The researchers found that every 1 part per million increase in urinary fluoride was associated with a 5-point decrease in IQ in men but not women. Lanphear said they don't know why the association was only seen by men.
The fluoride levels measured in their study were compared to levels measured in communities with fluoridated water in the United States, and the difference of 3 to 5 IQ points was not subtle, he said.
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Dr. Howard Hu, a professor of preventive medicine at the Keck School of Medicine at the University of Southern California, said the reduction in IQ associated with fluoride is equivalent to exposure to leaded gasoline. Hu was not involved in the current study.
But weighing the benefits and risks of fluoride is not easy, perhaps as easy as it was for lead, Hu said. Cavities are an important public health problem.
“Cavas is not just about cosmetics or going to the dentist. Increasing cavities has other downstream effects,” he said, including inflammation and oral health that can affect overall physical health.
What seems to be getting attention about fluoride is its danger early in life, when the brain is still developing. Emerging evidence suggests that in addition to IQ, fluoride may be associated with behavioral problems in children, Hu said.
Childhood is the stage where fluoride appears to have no effect on dental health, so it may be useful to advise pregnant women to limit their exposure to all sources. Fluoride can be found in a variety of things — including soft drinks, pesticides and black tea — because the plant bioaccumulates it, Lanphear said.
“For pregnant women, not only in drinking water, we should advise not to use fluoride in black tea during pregnancy, and you definitely do not want to mix fluoride. [in fluoridated water] with formula, because infants absorb fluoride more easily than older children and adults,” Lanphear said.