Could high fluoride exposure affect children's IQs?

Fluoride has been added to tap water in many U.S. communities for almost 80 years and is credited with helping protect against cavities and tooth decay. According to CDC, research shows that community water fluoridation reduces cavities by roughly 25%.

However, there has been growing debate about the benefits of fluoride and whether it could negatively impact children's IQs.

In August, NIH's National Toxicology Program released a report that found that drinking water with more than 1.5 milligrams of fluoride per liter is associated with lower IQs in children. Although this level of fluoridation is more than twice the recommended level of 0.7 milligrams per liter set by federal health officials, almost 3 million Americans currently drink water with fluoride levels above 1.5 mg/L from wells and some community water systems.

Recently, federal researchers published the analysis behind this report in JAMA Pediatrics. In the analysis, researchers assessed 74 studies from 10 countries, including China, Mexico, Canada, India, and Denmark.

According to the analysis, for every one part per million increase in fluoride in urinary samples, which is used to determine total exposures from water and other sources, children's IQ points decreased by 1.63. There was also evidence of a dose-response relationship in countries with much higher fluoridation levels than the United States, with IQ scores decreasing as fluoride exposure increased.

"There is concern that pregnant women and children are getting fluoride from many sources, and that their total fluoride exposure is too high and may affect fetal, infant and child neurodevelopment," said Kyla Taylor, an epidemiologist at the National Institute of Environmental Health Sciences and the study's lead author.

However, the study was unable to conclusively determine the effects of fluoridation below 1.5 mg/L, including the United States' currently recommended level of 0.7 mg/L.

"There were not enough data to determine if 0.7 mg/L of fluoride exposure in drinking water affected children's IQ," said Christine Flowers, director of NIH's Office of Communication.

Notably, Taylor said that while the analysis was intended to help better understand the safe and effective use of fluoride, it did not address the benefits and was not designed to assess "the broader public health implications of water fluoridation in the United States."

Scientists are divided over the study's findings

So far, responses to the study's findings have been divided, with JAMA Pediatrics publishing two opposing editorials alongside the study.

In one editorial, Steven Levy, a public health dentist at the University of Iowa, criticized the study's methods and disagreed with its findings.

"The major problem is that the science is not as strong as it's presented by these authors," Levy said. He also noted that more recent fluoride studies, which he believes are better designed and should have been given more weight in the study, have found no negative effects of fluoride on IQ.

Lanphear has also urged the U.S. Public Health Service to set up a committee to examine whether fluoride is neurotoxic and as beneficial to oral health as it is currently believed to be. "If that doesn't happen urgently, my concern is there will be growing distrust of public health agencies amid the public, and they will have deserved it," he said.

In general, there has been growing interest in regulating fluoride levels. For example, U.S. District Judge Edward Chen in September ruled in favor of several advocacy groups, finding that the current practice of adding fluoride to drinking water could lead to unreasonable health risks for children's developing brains, and ordered the Environmental Protection Agency to strengthen its regulations for fluoride in drinking water.

So far, it's unclear how much of an effect the Trump administration could have on changing current regulations on fluoridation, particularly since the power to regulate fluoride in drinking water falls to the states and not the federal government.

However, Lawrence Gostin, a global health law professor at Georgetown University Law Center, said the Trump administration could pressure states to ban fluoride and encourage local opposition to fluoridation.