Two New York towns on either side of the Hudson River experimented in 1944 — Newburgh would add fluoride to its water, while Kingston would not.

The results were striking. Newburgh children had half as much tooth decay as those in Kingston.

Today, over 70% of the U.S. population receives fluoridated drinking water. The Centers for Disease Control and Prevention hails the fluoridation of water as one of the top 10 achievements in health in the 20th century, alongside things like vaccination, workplace safety and recognition of the dangers of tobacco.

The impact of fluoridated water alone has declined over time, with the reliance on increasingly available toothpaste, rinses and supplements with fluoride. The CDC says fluoridated water can still reduce the prevalence of cavities by 25%, on average.

Those fluoride-laden alternatives and a post-pandemic movement to elevate personal choice are causing some places to rethink whether fluoride programs are worth it.

“Times have changed. The urgency of people getting fluoride in 2024 is not what it was in 1950, because there are so many ways to get it. It’s kind of common knowledge, and there are so many products with it,” said Jeffrey A. Singer, a working surgeon and a senior fellow at the Cato Institute. “It’s time to revisit this, do we need to be doing this?”

Studies about the potential link between high levels of fluoride and lower IQ in children, plus comments from President-elect Donald Trump’s pick for health secretary, are throwing fuel on the debate to the chagrin of dental experts who say fluoridated water is an irreplaceable tool.

The city of Abilene, Texas, decided in September to stop adding fluoride to its water after a federal judge in California ordered the Environment Protection Agency to draft regulations in response to plaintiffs’ concerns that community levels of the mineral might pose a risk to pregnant women or IQ levels in their children.

The judge did not conclude with certainty that fluoride is “injurious to public health” but that there is an “unreasonable risk of injury” requiring a response.

Robert F. Kennedy Jr., who Mr. Trump picked for health secretary, pointed to the ruling in calling for the end to fluoridation after the Jan. 20 inauguration. He dubbed fluoride an “industrial waste” capable of causing multiple bodily defects, from bone cancer to thyroid issues.

“This has always been a political issue since day one,” said Catherine Hayes, chair of the Department of Oral Health Policy and Epidemiology at the Harvard School of Dental Medicine. “There’s always been this argument it causes cancer. There is no evidence of that.”

Fluoride is a chemical ion of fluorine, a common element found in soil, rocks and water but added to food, beverages and oral care products. It strengthens dental enamel by fighting against mouth bacteria that produce harmful acids.

Today, many toothpastes and mouthwashes have fluoride, something that wasn’t prevalent when the fluoridated water program began in the mid-20th century. Fluoride is also found in some foods like russet potatoes and black tea leaves.

The American Cancer Society says there is no demonstrated link to cancer, and the American Dental Association promotes fluoridated water as effective and safe.

Still, some public health experts, including ones who are not Mr. Kennedy’s allies, say it is worth scrutinizing the fluoridation program given warning signs in some research and the availability of alternate sources of fluoride.

“The safety of low-level fluoridation has been demonstrated by decades of research, though emerging studies suggest it could be a risk to pregnant women,” Leana Wen, a former Baltimore health commissioner, wrote in a recent op-ed for The Washington Post. “Moreover, although the data are clear that community fluoridation dramatically reduced cavities before fluoride toothpaste became available, the current benefit is much smaller.”

Ms. Wen pointed to a JAMA Network study from 2019 that found a link between Canadian women who drank fluoridated water during pregnancy and lower IQ in children ages 3 and 4, and Mexican studies that suggested a link between prenatal exposure and lower test scores of ADHD in their children.

The federal National Toxicology Program found higher levels of fluoride exposure, such as drinking water containing more than 1.5 milligrams of fluoride per liter, are associated with lower IQ in children.

The authors said their review “was designed to evaluate total fluoride exposure from all sources and was not designed to evaluate the health effects of fluoridated drinking water alone.”

Mr. Singer said he is skeptical of papers indicating neurotoxicity from fluoride.

“They are very weak studies and they’re all associations — correlation is not causation,” he said, adding that “IQ is not a good metric of neurotoxicity.”

He said he agreed with Mr. Kennedy for a different reason — personal choice.

“There’s plenty of other ways for people who want fluoride to get it,” Mr. Singer said. “As a matter of public policy, I don’t think we have a right to put fluoride in the water supply so long as some people might not want it. It’s violating the doctrine of informed consent.”

Experts say most common filters, such as Brita, do not remove fluoride. Some filters can, however, remove some fluoride, and a specific type — a reverse osmosis filter — is effective at it.

Policymakers from both sides of the political aisle have grappled with how much fluoride is too much in the modern age.

The federal government revised fluoride levels as recently as 2015. It changed its recommended level of water fluoridation from a range — 0.7 to 1.2 milligrams per liter — to strictly the lower end, at 0.7 mg/L. This is equivalent to about three drops of water in a 55-gallon barrel.

In 2019, the CDC urged parents to monitor toothpaste use among children to ensure they are not swallowing large amounts and causing dental fluorosis, which is marked by discoloration and pitting in the teeth.

This year, authors of the federal National Toxicology Program report said its review “was designed to evaluate total fluoride exposure from all sources and was not designed to evaluate the health effects of fluoridated drinking water alone.”

U.S. District Court Judge Edward Chen, an appointee of former President Barack Obama, cited the study in ordering the EPA this fall to take regulatory action to address any “unreasonable risk” from fluoride levels in water. His ruling didn’t prescribe what steps must be taken.

Dental experts are worried politicians will go too far by eliminating fluoridated water, instead of considering the correct amount or special guidance for certain populations.

They also fear policymakers will lean on alternate sources of fluoride within recognizing the unique benefits of having the mineral in drinking water.

While toothpaste is very important in terms of your daily oral hygiene, it “doesn’t get into the tooth as it’s forming,” Ms. Hayes said.

“So our children benefit most from community water fluoridation, but there’s lots of evidence to show that adults also benefit as well because of the strong topical benefits of community fluoridation,” she said. “Getting the fluoride into the tooth structure is a systemic benefit which is lasting, and the topical benefits you need to have on a daily basis.”

Another benefit, she said, is that fluoridated water is accessible to all.

“The best argument for keeping fluoride in the water is that we have over 70 years of research showing that it’s safe and effective and it’s an equitable public health measure,” Ms. Hayes said. “People don’t have to have access to a dentist or the health care delivery system in order to benefit.”

Others say there has been an explosion of tooth-destroying diets alongside the development of new products, making the water program essential.

“Although fluorides are more available today, unfortunately our diet has changed a lot since the 1940s. Most of what we consume has added sugars these days. So while toothpastes and mouth rinses are available to consumers, sugars are also omnipresent,” said Athanasios Zavras, a professor at Tufts University School of Dental Medicine.

Local entities decide whether to fluoridate their water, and a dozen states require large communities to do it: California, Delaware, Georgia, Illinois, Kentucky, Louisiana, Minnesota, Mississippi, Nebraska, Nevada, Ohio and South Dakota.

In some places, the natural level of fluoride is already high, so communities do not add it.

So far, Mr. Kennedy’s push to eliminate fluoride appears to be an attempt to persuade local governments through the bully pulpit. His social media post on the topic said the administration would “advise” towns to drop fluoride, and Mr. Trump has tried to avoid heavy-handed federal actions, saying issues like abortion and education standards should be left to the states.

Dr. Zavras said he opposed Mr. Kennedy’s push not because of politics “but rather due to the deleterious public health consequences that I foresee this policy will bring about — especially for the poor, the vulnerable, the disabled and children.”

“I am concerned about the removal of fluoride from the water supplies,” he said. “As a practicing pediatric dentist, I see the devastating effects of dental disease every day.”

• Tom Howell Jr. can be reached at thowell@washingtontimes.com.