The Science Behind Fluoride in Drinking Water

Donald Trump's second term may threaten what's lauded as one of the top public-health triumphs of the 20th century: adding fluoride, a mineral that helps prevent tooth decay, to drinking water.

That’s due to Robert F. Kennedy Jr., the notorious vaccine skeptic whom Trump has said will play a big role in health care in his administration if he is elected. “On January 20, the Trump White House will advise all U.S. water systems to remove fluoride from public water,” Kennedy recently wrote on X. (Trump, in an interview with NBC News, said Kennedy’s proposal “sounds OK.”)

Adding fluoride to drinking water reduces rates of cavities by around 25%, the U.S. Centers for Disease Control and Prevention (CDC) says. Some U.S. communities began doing so in the 1940s, and today about 72% of the U.S. population that receives water from public utilities drinks fluoridated water, according to the CDC. 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 including Australia and Canada also consume fluoride in drinking water. A 2021 study demonstrated that children living in Calgary, a Canadian city that stopped fluoridating its water, developed significantly more cavities than children living in nearby Edmonton, which does use fluoride.

Despite fluoride’s long-standing, federally celebrated presence in U.S. drinking water, Kennedy is not alone in opposing its use. Anti-fluoridation advocates have for decades called for the mineral to be removed from water supplies, and a number of communities, including Portland, Ore., Juneau, Alaska, and Wichita, Kans., have decided not to add fluoride to their water.

Why all the controversy over a naturally occurring mineral that has been shown to improve oral health?

Although fluoride has demonstrated benefits, namely in reducing the risk of cavities and tooth decay, some studies have also raised questions about its potential link to health problems ranging from cancer to osteoporosis. The CDC maintains that there is no convincing evidence linking fluoride to “any potential adverse health effect or systemic disorder,” and other major health groups, including the American Cancer Society and the American Dental Association (ADA), agree that it is safe. But concerns remain—particularly about links between fluoride and cognition.

In August, the U.S. National Toxicology Program (NTP) published a report that found with “moderate confidence” that—at concentrations more than twice the recommended fluoride level in the U.S.—fluoridated water is associated with modestly lower IQ scores in children. U.S. standards recommend fluoride levels of 0.7 milligrams per liter of water, and the NTP’s conclusion applied to water fluorinated at 1.5 milligrams per liter and above.

Initial drafts of the report failed to clear independent review by the National Academies of Science, Engineering, and Medicine, which found that the NTP’s authors hadn’t adequately supported their conclusions with data. Some pro-fluoride organizations, including the ADA, argue that the final version still falls short of providing conclusive evidence and should not lead to policy changes around water treatment.

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

Still, it’s noteworthy 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 kids. “One authoritative group [the CDC] is saying it’s safe for everyone, and another expert group from the U.S. government [the NTP] is saying there are concerns about adverse 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 that debate earlier this year, when he ruled that the U.S. Environmental Protection Agency must strengthen regulations on fluoride to address its potential risk to children’s cognitive development. That decision does not necessarily mean fluoride must be removed from U.S. drinking water—the EPA can choose to address the situation in a number of ways, including releasing a public notice about the mineral’s potential risks and benefits—but it highlights growing scrutiny on the practice of fluoridating water, which some anti-fluoride activists argue is no longer necessary now that 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 exposure through drinking water, 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 lead to slightly less tooth decay among children, but concluded that the practice’s effects are less dramatic today than they were before fluoride was widely found in toothpaste. The authors also noted that adding fluoride to drinking water may increase the number of people with dental fluorosis, a mostly cosmetic condition that can leave the teeth with white flecks, spots, or lines.

Fluoridated water, however, helps protect people that may not keep up with oral hygiene or have access to regular dental care, Godebo says—another factor that complicates any discussion about potentially adjusting the level of fluoride in U.S. water. 

Despite Kennedy’s suggestion that removing fluoride would be a day-one priority in the Trump administration, Godebo says “the science is not there” to make a change to U.S. recommendations at this point. “It would be a huge decision,” he says. “It should take more years to come to a conclusion.”