Water fluoridation is widely regarded as one of the great public health achievements of the 20th century, credited with significantly reducing tooth decay. However, there is growing controversy among scientists about whether fluoride may be linked to lower IQ scores in children.
A comprehensive federal analysis of dozens of previous studies, published this week in JAMA Pediatrics, has added to those concerns. It found a significant inverse relationship between exposure levels and cognitive function in children.
Higher fluoride exposures were linked to lower IQ scores, researchers working for the National Institute of Environmental Health Sciences concluded.
None of the studies included in the analysis were conducted in the United States, where recommended levels of fluoridation in drinking water are very low. At these amounts, the data were too limited to draw definitive conclusions.
Observational studies cannot prove a cause-and-effect relationship. However, in countries with much higher levels of fluoridation, the analysis also found evidence of what scientists call a dose-response relationship, with IQ scores falling in step with increasing fluoride exposure.
Children are exposed to fluoride through many sources besides drinking water: toothpaste, dental treatments, and some mouthwashes, as well as black tea, coffee, and certain foods, such as shrimp and raisins. Some drugs and industrial emissions also contain fluoride.
For every one part per million increase in fluoride in urine samples, which reflect total exposures from water and other sources, children’s IQ scores dropped by 1.63, according to the analysis.
“There is concern that pregnant women and children are getting fluoride from many sources,” said Kyla Taylor, an epidemiologist at the institute and lead author of the report, “and that their overall exposure to fluoride is too high and may affect the fetus, the infant and the child. neurodevelopment”.
Dr Taylor said the analysis was intended to contribute to the understanding of the safe and effective use of fluoride. However, he said it was not about the benefits and was not intended to assess “the broader public health impacts of water fluoridation in the United States.”
Several scientists, including several dentists, criticized the report, pointing to what they said were methodological flaws and stressing that the research had no implications for US drinking water.
The issue is so divisive that JAMA Pediatrics commissioned two editorials with opposing views to publish alongside the report.
In one, Dr. Steven M. Levy, a public health dentist at the University of Iowa, said many of the studies included in the analysis were of very low quality. He also cautioned against concluding that any changes should be made to US fluoridation policies.
“A lay reader or policy maker at a water table in a small community somewhere might look at the data and think that any way you analyze it, it’s worrisome,” said Dr. Levi in ​​an interview. “It’s not as clear as they’re trying to make it.”
The report’s findings align in some ways with the statements of Robert F. Kennedy Jr., the choice of President-elect Donald J. Trump to head the Department of Health and Human Services. He questioned the safety of fluoride and said one of the Trump administration’s first actions would be to advise water systems to remove fluoride.
Criticism of fluoridation has surfaced frequently since the practice began in many US communities in the 1950s. However, opposition was initially dismissed, as it was strongest among those with extremist or fringe views and right-wing groups such as the John Birch Society, the which called fluoridation a communist plot.
This is changing. Last September, U.S. District Judge Edward Chen in San Francisco ordered the Environmental Protection Agency to strengthen regulations on fluoride in drinking water because of research suggesting high levels may pose a risk to children’s mental development .
In a second paper published alongside the new study, public health expert Dr. Bruce P. Lanphear, noted that as early as 1944, the editor of The Journal of the American Dental Association expressed concern about the addition of fluoride, which he called “an extremely toxic substance” to drinking water. He wrote that “the potential for harm far outweighs the potential for good.”
Some studies have suggested that dental health has improved not because fluoride was added to the water, but because of fluoride toothpastes and better dental hygiene practices. (In some countries, fluoride is added to salt.)
According to this argument, topical application of fluoride to the teeth is effective enough to prevent caries and ingestion is not necessary. But other studies have reported increases in cavities after public water fluoridation initiatives were discontinued in some countries.
Currently, the recommended fluoride level in the United States is 0.7 parts per million, and the study found no statistically significant inverse association between fluoride levels and IQ scores below 1.5 parts per million based solely on fluoride levels in water.
But nearly three million Americans still drink water with fluoride levels above 1.5 parts per million from wells and some community water systems.
Linda Birnbaum, former director of the National Institute of Environmental Health Sciences, called for more research into the potential effects of fluoride levels below 1.5 parts per million.
He pointed out that the study concluded that the exposure could be harmful to developing brains. “The answer is pretty clear: yes,” said Dr. Birnbaum.
To protect fetuses and babies who are especially vulnerable, she advised parents to avoid drinking fluoridated water during pregnancy and use fluoridated bottled water when preparing formula for their infants.
“My recommendation is that pregnant women and infants should not be exposed to excess fluoride,” said Dr. Birnbaum, who is not an author of the new analysis.
Breastfeeding women need not worry, he added, as very little fluoride is transmitted through breast milk.
“The more we study many chemicals, especially the chemicals that affect IQ, like lead — there’s really no safe level,” said Dr. Birnbaum.
About 74 studies from 10 countries, including China, Mexico, Canada, India and Denmark, were reviewed. Dr. Lanphear noted that consistent relationships between fluoride and IQ were found in very different populations.
He urged the US Public Health Service to set up a committee, perhaps one that would not include researchers who have studied the subject in the past and can take a fresh look at the issue, to seriously consider two questions: whether fluoride is neurotoxic and if it is as beneficial to oral health as it is believed to be.
“If this doesn’t happen urgently, my concern is that there will be a growing distrust of public health services in the public, and deservedly so,” he said.
