President-elect Donald Trump’s incoming administration could try to remove fluoride from drinking water, according to Robert F. Kennedy Jr.

Kennedy, who campaigned with Trump after dropping his own presidential bid in August, called fluoride an “industrial waste” and linked it to cancer and other diseases and disorders.

“On January 20, the Trump White House will advise all U.S​. water systems to remove fluoride from public water. Fluoride is an industrial waste associated with arthritis, bone fractures, bone cancer, IQ loss, neurodevelopmental disorders, and thyroid disease,” Kennedy wrote Nov. 2 on X. Kennedy linked to a video from an attorney who recently successfully sued the Environmental Protection Agency to take additional measures to regulate fluoride in drinking water.

Kennedy, who has long advocated ending water fluoridation, persisted with his pledge following Trump’s election win. Trump, meanwhile, has said that Kennedy, who previously worked as an environmental lawyer, would have a role in the Trump administration. When asked whether his administration would remove fluoride from drinking water, Trump said, “Well, I haven’t talked to him about it yet, but it sounds OK to me. You know it’s possible.”

Kennedy is an influential vaccine skeptic whose campaign of conspiracy theories earned PolitiFact’s 2023 Lie of the Year.

Longtime research has found that adding fluoride to U.S. drinking water is a safe way to boost children’s oral health. Since 2015, the recommended level in the U.S. has been 0.7 milligrams per liter. Public health organizations, including the American Dental Association, the American Academy of Pediatrics and the U.S. Centers for Disease Control and Prevention, support the practice.

Recent studies, however, have shown possible links between fluoride, bone problems and children’s IQ, particularly when fluoride is above the U.S. recommended levels.

“There is evidence that fluoride exposure has been associated with the diseases (and) disorders that RFK listed, but with caveats,” said Dr. Ashley Malin, an assistant professor in the University of Florida’s Epidemiology Department who has studied fluoride’s effects in pregnant women.

Malin referred to studies showing that higher fluoride exposure, particularly during pregnancy, is associated with reduced child IQ, and that prenatal exposure also is linked to decreased intellectual functioning and executive function. For high exposure in pregnancy, the studies showed symptoms associated with other neurobehavioral issues, such as attention deficit hyperactivity disorder.

However, many of these studies took place in countries other than the United States and looked at fluoride in drinking water at sometimes twice the U.S.’ recommended level. Also, some of the other ailments that Kennedy listed, such as an association with bone cancer, have less robust evidence and need more study.

“Aside from fluoride’s impacts on neurodevelopment, I think that there is more that we don’t know about health effects of low-level fluoride exposure than what we do know, particularly for adult health outcomes,” Malin said.

David Bellinger, a Harvard Medical School neurology professor and professor in Harvard School of Public Health’s Environmental Health Department, said the risk-benefit calculation of added fluoride differs depending on whether typical fluoride exposure levels cause health problems, or if problems occur only when recommended levels are exceeded.

“In toxicology, ‘the dose makes the poison’ is a long-standing principle,” he said. “So a general statement that fluoride is associated with diseases X, Y, and Z is not very helpful unless the dose that might be responsible is specified.”

PolitiFact contacted Kennedy through his Children’s Health Defense organization, but received no reply. The organization sued PolitiFact and Meta related to a 2020 fact-check. That lawsuit was dismissed by a federal court. The dismissal was upheld on appeal, and the case is pending a possible appeal to the U.S. Supreme Court.

What is fluoride and what are its benefits?

Fluoride is a mineral naturally occuring in soil, water and some foods that helps prevent tooth decay and cavities. It strengthens tooth enamel that acid from bacteria, plaque and sugar can wear away.

Water fluoridation has been happening in the U.S. since 1945.

The federal Public Health Service first recommended fluoridation of tap water in 1962, but the decision still lies with states and municipalities. Around 73% of the U.S. population, or about 209 million people, have access to fluoridated water, the CDC reported. Fluoride also has been added to oral care products such as toothpaste and mouth rinse.

In 2015, U.S. health officials lowered the recommended amount of fluoride in drinking water to 0.7 milligrams per liter, saying a higher level was less necessary given other sources of fluoride, and that the lowered amount would still help protect teeth without staining them.

Pediatric dentists note that applying fluoride with toothpastes and rinses is beneficial, but small amounts circulating in the body via water consumption helps younger children who still have their baby teeth, because it can benefit the developing permanent teeth.

The American Dental Association says studies have shown that fluoride in community water systems prevents at least 25% of tooth decay in children and adults and that “for more than 75 years, the best scientific evidence has consistently shown that fluoridation is safe and effective.”

The association says on its website, “It’s similar to fortifying other foods and beverages — for example, fortifying salt with iodine, milk with vitamin D, orange juice with calcium and bread with folic acid.”

According to the CDC, health experts and scientists from the U.S. and other countries have so far “not found convincing scientific evidence linking community water fluoridation with any potential adverse health effect or systemic disorder such as an increased risk for cancer, Down syndrome, heart disease, osteoporosis and bone fracture, immune disorders, low intelligence, renal disorders, Alzheimer disease, or allergic reactions.”

The agency says risks of water fluoridation are limited to dental fluorosis, which can alter dental enamel and cause white flecks, spots, lines or brown stains on the teeth when too much fluoride is consumed.

Do studies show fluoride posing any other risks?

Some studies have said that excess fluoride exposure, often at higher levels than the recommended U.S. limit, can harm infants’ and young children’s developing brains and that higher levels of fluoride exposure during pregnancy were associated with declines in children’s IQs.

A study published in May that Malin led with University of Southern California researchers suggested that fluoride exposure during pregnancy was linked to an increased risk of childhood neurobehavioral problems and said more studies were “urgently needed to understand and mitigate the impacts in the entire U.S. population.”

Experts noted prenatal fluoride exposure is most strongly linked to children’s IQ loss, and said timing of fluoride consumption might need to be considered when making recommendations.

A federal review of dozens of studies published in August by the Department of Health and Human Services’ National Toxicology Program concluded that higher levels of fluoride exposure were linked to  lower children’s IQs. But the report was based primarily on studies in countries such as Canada, China, India, Iran, Mexico and Pakistan and involved fluoride levels  at or above 1.5 milligrams per liter, twice the recommended U.S. limit. The authors said more research is needed to understand whether lower exposure has any adverse effects.

In the report, researchers said they found no evidence that fluoride exposure adversely affected adult cognition.

Bellinger, from Harvard, pointed to the review as an example of how the amount of fluoride matters. He noted how researchers concluded that a very small percentage of people in the U.S. are exposed at levels that correlate with IQ loss.

“Second, the fact that there are now multiple pathways of exposure to fluoride besides fluoridated water (toothpaste and other dental products, etc.) makes it really difficult to attribute a particular adverse effect to the fluoride added to the water,” he wrote via email. “It is the cumulative exposure from all sources that contribute to any adverse health effects.”

In September, a federal judge ordered the Environmental Protection Agency to further regulate fluoride in drinking water because of the potential risk that higher levels could affect children’s intellectual development.

U.S. District Judge Edward Chen wrote that the court’s finding didn’t “conclude with certainty that fluoridated water is injurious to public health,” saying it’s unclear whether the amount of fluoride typically added to water is causing children’s IQs to drop. But he wrote that there was enough risk to warrant investigation and that the EPA must act to further regulate it. The ruling did not specify what actions the agency should take, and the EPA is reviewing the decision.

After the ruling, the American Association of Pediatrics issued a statement that fluoride in drinking water is safe for children and said the policy is based on a robust foundation of evidence.

Besides dental fluorosis, experts say that fluoride exposure over many years above the U.S. recommended amount can cause skeletal fluorosis, a rare condition that causes weaker bones, stiffness and joint pain. Although the Public Health Service recommends a fluoride concentration of 0.7 milligrams per liter for community water systems, the EPA, under the Safe Drinking Water Act, sets enforceable standards for drinking water quality. Currently, to prevent skeletal fluorosis, the EPA requires that water systems not exceed 4 milligrams of fluoride per liter of water.

Malin said she and her research team are investigating a potential link between fluoride and bone fractures. She said although several studies have found high fluoride exposure associated with increased risk of bone fractures, and some have linked fluoride with thyroid disease, there haven’t been rigorous, U.S.-based studies.

The CDC concluded that recent research found no link between cancer and high levels of fluoride in drinking water.

The American Cancer Society reviewed a possible link between water fluoridation and cancer. An organization spokesperson pointed PolitiFact to its review and said it has no data showing a definitive answer.

This fact check was originally published by PolitiFact, which is part of the Poynter Institute. See the sources for this fact check here.