What to know about fluoride in drinking water, and whether RFK Jr. could really have it removed

A key adviser to President-elect Donald Trump on health policy has pledged to recommend removing fluoride from drinking water.

Robert F. Kennedy Jr., a longtime environmental lawyer and anti-vaccine activist, has targeted a decades-old intervention to prevent tooth decay. A former presidential candidate now serving on Trump’s transition team, Kennedy has criticized fluoride’s use on social media and in a recent interview with NPR.

For years, local water authorities have considered the addition of low concentrations of fluoride to drinking water a public health achievement. The Centers for Disease Control and Prevention recommends it, citing evidence showing that fluoride prevents cavities in children — the No. 1 chronic disease in kids.

But adding fluoride to drinking water can be controversial, and some communities, including many in the Philadelphia area, have long opted not to fluoridate their water.

Here’s a primer on fluoride in the Philadelphia area and research around its effects on the body.

Fluoride is a mineral found naturally in groundwater — in some places in the Southwest, it’s present in much higher concentrations than elsewhere in the United States. Fluoride is also found in food and drinks, including tea, coffee, raisins, potatoes, rice, and grapefruit juice.

As early as the 1900s, dentists began collecting evidence that fluoride in water somehow prevented tooth decay. (One, Frederick Sumner McKay, was a graduate of the University of Pennsylvania’s School of Dental Medicine, and reported in the early 1900s that his patients in Colorado Springs, where fluoride is naturally present in the local drinking water, had teeth “surprisingly and inexplicably resistant to decay.”)

Later research backed up those theories, and communities have been intentionally fluoridating their water since the 1940s.

The CDC now recommends that communities add fluoride to their drinking water at a concentration of 0.7 milligrams per liter. The agency has called fluoridated water one of the 20th century’s 10 greatest public health interventions.

A 2024 study that looked at tooth decay in third graders in Pennsylvania found that children who lived in communities that fluoridated their water had a 16% lower risk of developing cavities than those in communities that didn’t fluoridate.

In children, fluoride can concentrate in enamel, the hard outer layer of a tooth, and dentin, the tissue that comprises most of the inner tooth. This serves to make the tooth less vulnerable to acids.

“The thing that causes tooth decay is that bacteria eat sugar, they poop acids, and the acids dissolve the tooth and make a cavity,” said Mark Wolff, dean of the University of Pennsylvania School of Dental Medicine. “If you can make the tooth resistant to acid, it reduces the amount of dissolution and tooth decay.”

Evidence also suggests that fluoridated water protects adults from tooth decay as well.

“For people who don’t see the dentist regularly, don’t brush well, don’t have the money to buy toothpaste routinely, it has extremely strong effects,” Wolff said. “It’s a great safety net provision.”

He added that he makes sure his four grandchildren, some of whom live in communities that don’t fluoridate their water, all take it either through water or supplements: “I’d never recommend something that would harm them.”

Philadelphia’s water authority adds fluoride to its water at a concentration of 0.7 mg/L and maintains a fluoride concentration of somewhere between 0.6 mg and 0.8 mg/L.

But many municipalities outside the city do not add fluoride to the water: No water authorities in Montgomery County do so, and only 16 of the dozens of water authorities in Bucks, Delaware, and Chester Counties offer fluoridated water.

Overall, Pennsylvania ranks 40th out of 50 states and Washington, D.C. on water fluoridation, according to the CDC: 55.3% of residents who get their water from community water systems have fluoridated water. (Some residents get their water from wells on their properties, not from local water authorities, and that water is also generally unfluoridated.)

New Jersey ranks 50th on water fluoridation, ahead of only Hawaii. Just 16.2% of residents who get their water from a community water system in the state have fluoridated water.

You can check whether your water authority fluoridates its water in this CDC database.

To some, keeping fluoride out of water is a civil liberties issue. Others have raised concerns about its effects on other parts of the body.

Too much fluoride over a long period of time can cause stained teeth and, in rare cases, skeletal fluorosis, a condition that causes chronic joint pain and other bone conditions like osteoporosis and arthritis. But in the United States, most of the drinking water does not have enough fluoride to cause it — even in communities where fluoride is added to the water.

This year, researchers from the National Toxicology Program released a wide-ranging analysis of numerous studies on how fluoride affects children’s IQs.

The review included studies, all conducted outside of the United States, that found that children exposed to high levels of fluoride — more than 1.5 mg/L, well above the recommended concentrations in drinking water in the U.S. — scored slightly lower on IQ tests, a difference of about two to five points. (In a tweet last weekend, Kennedy cited “IQ loss” as one of his concerns with fluoridated water.)

But this report, and others like it, have drawn skepticism from others in the scientific community, including previous peer reviewers and the American Dental Association, which accused the researchers of using “unorthodox research methods, flawed analyses, lack of clarity, failure to follow the norms of peer review and lack of transparency.”

Other scientists have also noted that the study didn’t weigh the benefits of preventing tooth decay against potential risks from fluoride. Untreated tooth decay, Wolff noted, leads to more missed school days than any other noncommunicable disease and costs millions each year. Severe cases can lead to death.

In another research review, scientists found that lower levels of fluoride exposure, closer to the recommended concentrations for drinking water in the U.S., didn’t have an effect on children’s IQs.

The decision to fluoridate water is up to local governments and water authorities, not the federal government. Still, Wolff said, federal authorities’ recommendations on fluoridation go a long way.

“The federal government banning fluoridation, or putting out a negative finding on it — any of those things could have a devastating effect on whether communities continue,” he said.

“If you take fluoride out of the water system, it won’t be a problem for dentists. It will be a problem for patients and society.”