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

Robert F. Kennedy Jr., a longtime environmental attorney and anti-vaccine activist, has taken aim at a decades-old intervention to prevent tooth decay. Kennedy, a former presidential candidate who is now part of Trump’s transition team, has criticized the use of fluoride on social media and in a recent interview with NPR.

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

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

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

What is fluoride and why is it added to drinking water?

Fluoride is a mineral that occurs naturally in groundwater; in some places in the Southwest it is present in much higher concentrations than elsewhere in the United States. Fluoride is also found in foods and beverages, including tea, coffee, raisins, potatoes, rice and grapefruit juice.

As early as the twentieth century, dentists began gathering evidence that fluoride in water could somehow prevent tooth decay. (One person, Frederick Sumner McKay, was a graduate of the University of Pennsylvania 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, “surprisingly and inexplicably “teeth resistant to decay.”)

Later research supported these theories, and communities have been deliberately 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 ten greatest public health interventions of the 20th century.

A 2024 study that looked at tooth decay in third-graders in Pennsylvania found that children who lived in communities where their water was fluoridated had a 16% lower risk of developing cavities than children in communities that did not fluoridate.

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

“What causes tooth decay is bacteria eat sugar, poop acids, and the acids dissolve the tooth and form a cavity,” says 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 solution and tooth decay.”

There is also evidence that fluoridated water also protects adults against tooth decay.

“For people who don’t go to the dentist regularly, don’t brush properly and don’t have the money to routinely buy toothpaste, this has extremely strong effects,” Wolff said. “It’s a great safety net facility.”

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

How many communities in the Philadelphia area have fluoridated water?

The Philadelphia 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 authority in Montgomery County does 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 DC in 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 boards, and that water is also generally non-fluoridated.)

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

In this GGD database you can check whether your water board fluoridates its water.

Why would a community choose not to fluoridate its water?

For some, keeping fluoride out of water is a matter of civil liberties. Others have expressed concerns about its effects on other parts of the body.

Too much fluoride over a long period of time can cause discolored teeth and, in rare cases, skeletal fluorosis, a condition that causes chronic joint pain and other bone disorders such as osteoporosis and arthritis. But in the United States, most drinking water does not contain enough fluoride to cause this – even in communities where fluoride is added to the water.

This year, researchers from the National Toxicology Program released a comprehensive analysis of numerous studies on fluoride’s impact on children’s IQ.

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

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

In another study, scientists found that lower levels of fluoride exposure, closer to the recommended concentrations for drinking water in the US, had no effect on children’s IQ.

How does the federal government’s opinion on fluoride affect local policy?

The decision to fluoridate water is a matter for 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 passing judgment on it — all of these things could have a devastating effect on whether communities survive,” he said.

“If you remove fluoride from the water system, that is not a problem for dentists. It will be a problem for patients and society.”