IIf Donald Trump is elected a second time, his presidency could jeopardize what is considered one of the greatest public health achievements of the 20th century: the addition of fluoride, a mineral that prevents tooth decay, to drinking water.

That's because of Robert F. Kennedy Jr., the notorious vaccine skeptic who Trump said would play a big role in his administration's health care if elected. “On January 20th, the Trump White House will advise all U.S. water systems to remove fluoride from public water,” Kennedy recently wrote on .

Adding fluoride to drinking water reduces tooth decay rates by about 25%, according to the U.S. Centers for Disease Control and Prevention (CDC). Some U.S. communities began doing so in the 1940s, and today, according to the CDC, about 72% of the U.S. population that receives water from public utilities drinks fluoridated water. Decisions about whether to use fluoride are typically made at the state or local level, and at least a dozen states require large municipalities to do so, Stateline reports.

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People in countries like Australia and Canada also consume fluoride in their drinking water. A 2021 study showed that children in Calgary, a Canadian city that stopped fluoridating its water, developed significantly more tooth decay than children in nearby Edmonton, which uses fluoride.

Although fluoride has long been present in U.S. drinking water and celebrated by the federal government, Kennedy is not alone in opposing its use. Fluoridation advocates have been calling for the mineral's removal from water supplies for decades, and a number of communities, including Portland, Oregon, Juneau, Alaska, and Wichita, Canada, have decided not to add fluoride to their water.

Why is there so much controversy over a naturally occurring mineral proven to improve oral health?

Although fluoride has proven benefits, particularly in reducing the risk of tooth decay and tooth decay, some studies also raise questions about its possible link to health problems ranging from cancer to osteoporosis. The CDC maintains that there is no convincing evidence linking fluoride to “any adverse health effects or systemic disorders,” and other major health groups, including the American Cancer Society and the American Dental Association (ADA), agree that Fluoride is safe. However, concerns remain – particularly about the links between fluoride and cognition.

In August, the U.S. National Toxicology Program (NTP) released a report that found with “moderate certainty” that fluoridated water at concentrations more than twice the U.S. recommended fluoride level is associated with slightly lower IQ scores in children . U.S. standards recommend a fluoride level of 0.7 milligrams per liter of water, and the NTP's conclusion applies to water fluoridated at 1.5 milligrams per liter and above.

The first drafts of the report failed to pass an independent review by the National Academies of Science, Engineering and Medicine, which found that the NTP authors had not adequately supported their conclusions with data. Some pro-fluoride organizations, including the ADA, argue that the final version still does not provide conclusive evidence and should not lead to policy changes in water treatment.

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Tewodros Godebo, an assistant professor at Tulane University's Celia Scott Weatherhead School of Public Health and Tropical Medicine who studies fluoride, says studies of very high fluoride exposures don't necessarily apply to the U.S., where water typically contains much less of the mineral.

Still, it's notable that even government scientists disagree about the safety of fluoridated water, says Christine Till, a professor at Canada's York University, whose research has shown a link between fluoride and lower IQ scores in children. “One authoritative group (the CDC) says it is safe for everyone, and another U.S. government expert group (the NTP) says there are concerns about the negative effects of fluoride intake on child development,” Till says. “At the very least, it’s time to acknowledge the evolving science.”

A federal judge in California waded into this debate earlier this year when he ruled that the U.S. Environmental Protection Agency must tighten regulations on fluoride to address its potential risk to children's cognitive development. This decision does not necessarily mean that fluoride must be removed from U.S. drinking water — the EPA can address the situation in a number of ways, including issuing a public notice about the mineral's potential risks and benefits — but it does illustrate the increasing scrutiny This practice of fluoridating water, which some anti-fluoride activists say is no longer necessary since most people can choose to use fluoride in dental products such as toothpaste. (Till says it's important to analyze total fluoride exposure, not just drinking water exposure, when analyzing the mineral's potential risks and benefits.)

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A 2024 Cochrane review article found that adding fluoride to drinking water may result in slightly less tooth decay in children, but concluded that the effects of this practice are less dramatic today than before the widespread use of fluoride Fluoride in toothpaste. The authors also found that adding fluoride to drinking water may increase the number of people with dental fluorosis, a mostly cosmetic condition that can leave white spots, spots or lines on the teeth.

However, Godebo says fluoridated water helps protect people who may not be keeping up with oral hygiene or may not have access to regular dental care – another factor that complicates any discussion about possible adjustments to fluoride levels in water in the United States.

Despite Kennedy's suggestion that fluoride removal would be a top priority in a potential Trump administration, Godebo says “the science is not there” to make a change to U.S. recommendations at this point. “It would be a big decision,” he says. “It should take years before we reach a conclusion.”