Water fluoridation is widely regarded as one of the great public health successes of the 20th century, credited with substantially reducing tooth decay. But there has been growing controversy among scientists over whether fluoride may be linked to lower IQ scores in children.
A comprehensive federal analysis of results from previous studies, published this week in JAMA Pediatrics, added to these concerns. He 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. For these amounts the evidence was too limited to draw definitive conclusions.
Observational studies cannot demonstrate 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 decreasing as fluoride exposure increased .
Children are exposed to fluoride through many sources other than drinking water: toothpaste, dental treatments, and some mouthwashes, as well as black tea, coffee, and some foods, such as shrimp and raisins. Some drugs and industrial emissions also contain fluoride.
For every part per million increase in fluoride in urine samples, which reflects total exposures to water and other sources, IQ points in children fell by 1.63, according to the analysis.
“There is concern that pregnant women and children receive fluoride from many sources,” said Kyla Taylor, an epidemiologist at the institute and lead author of the report, “and that their total fluoride exposure is too high and could affect the fetus , the newborn and the child.
Dr Taylor said the analysis aims to contribute to understanding the safe and effective use of fluoride. But it said it does not address the benefits and is not intended to evaluate “the broader public health implications of water fluoridation in the United States.”
Several scientists, including many dentists, criticized the report, pointing out what they said were methodological flaws and pointing out that the research had no implications for drinking water in the United States.
The topic is so controversial 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 that many of the studies included in the analysis were of very low quality. He also cautioned against concluding that changes should be made to America’s fluoridation policies.
“A lay reader or a politician on a water board in a small community somewhere may see the evidence and think that any way you analyze it, it’s a concern,” Dr. Levy said in an interview. “It’s not as clear as they’re trying to make it.”
The report’s findings are somewhat in line with statements by Robert F. Kennedy Jr., President-elect Donald J. Trump’s pick to run the Department of Health and Human Services. He questioned the safety of fluoride and said one of the Trump administration’s first acts will be to advise water systems to remove fluoride.
Criticisms of fluoridation have surfaced frequently since the practice was introduced in many U.S. communities in the 1950s. But opposition was initially rebuffed, as it was strongest among those with extremist or fringe views, and right-wing groups such as the John Birch Society, which called fluoridation a communist plot.
Things are changing. Last September, U.S. District Judge Edward Chen in San Francisco ordered the Environmental Protection Agency to tighten rules on fluoride in drinking water because of research that suggested high levels could pose a risk to children’s intellectual development.
In a second editorial published alongside the new study, a public health expert, Dr. Bruce P. Lanphear, noted that as early as 1944, the editor of the Journal of the American Dental Association had expressed concern about the addition of fluoride, which he had defined it as “a highly 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 improved not because fluoride was added to water, but because of fluoridated 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 tooth decay and ingestion is not necessary. But other studies have reported an increase in tooth decay after public water fluoridation initiatives ended in some countries.
Currently, recommended fluoride levels in the United States are 0.7 parts per million, and the study did not find a statistically significant inverse association between fluoride levels and IQ scores below 1.5 parts per million based solely on levels of fluoride 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 exposure may be harmful to brain development. “The answer is pretty clear: yes,” Dr. Birnbaum said.
To protect particularly vulnerable fetuses and infants, she advised parents to avoid drinking fluoridated water during pregnancy and to use fluoride-free bottled water when preparing formula for their babies.
“My recommendation is that pregnant women and newborns should not be exposed to excess fluoride,” said Dr. Birnbaum, who is not the author of the new analysis.
Breastfeeding women need not worry, she added, as very little fluoride is transmitted through breast milk.
“The more we study many chemicals, particularly those that affect IQ, such as lead, the more there is no safe level,” Dr. Birnbaum said.
Some 74 studies from 10 countries were reviewed, including China, Mexico, Canada, India and Denmark. Dr. Lanphear noted that consistent links between fluoride and IQ have been found in very different populations.
He urged the U.S. Public Health Service to set up a committee, perhaps one that does not include researchers who have studied the topic in the past and who can take a fresh look at the topic, to seriously examine two questions: whether fluoride is neurotoxic, and whether it is as beneficial to oral health as you think.
“If this doesn’t happen urgently, my concern is that there will be growing distrust among the public towards public health agencies, and they will have deserved it,” he said.