It has been hailed by the Centers for Disease Control and Prevention as one of the top public health achievements of the 20th century. Numerous studies have proven its safety and efficacy. But fluoride — the naturally occurring compound that prevents cavities and tooth decay — is still sparking heated debates, seven decades after it was first added to America’s water supply.

“Anti-fluoridationists” — a small but vocal minority — are disputing long-established science to say that fluoride added to tap water lowers IQ and causes everything from acne to anemia to Alzheimer’s.

These anti-fluoride believers are active online but also at the polls: In the past five years, 74 cities have voted to remove fluoride from their drinking water, according to the American Dental Association. This year, there have been 13 votes around the country on fluoridation, and at least three more cities have fluoride referendums on the ballot in November: proposed bans in Brooksville, Florida, and Houston, Missouri, and a vote on bringing fluoridated water back in Springfield, Ohio.

The frets over fluoride are reminiscent of the unfounded fear that vaccines cause autism: disproved by science, yet steadfast nonetheless. The persistence of fluoride conspiracy theories — which emerged in the 1950s with claims that fluoridation was a communist plot to dumb down Americans — is alarming public health officials, including the American Dental Association and the American Academy of Pediatrics, who say fluoride is a safe, inexpensive way to boost children’s oral health.

Dr. Johnny Johnson, a retired pediatric dentist who is president of the nonprofit American Fluoridation Society, calls the anti-fluoride efforts “cult-like.”

“You cannot tailor public health to the whims of a small group of people,” he said. “If you are doing that, you are harming a large group of people.”

The anti-fluoridationists, though, say that it’s the fluoride supporters who are harming the public’s health. Some argue that the government uses fluoride as a form of mind control; others believe it's designed to boost the sugar lobby by enabling people to eat more sweets without getting cavities; and still others believe that health officials are afraid to reverse course on fluoride after promoting it for decades.

Paul Bieber, president of the New York State Coalition Opposed to Fluoridation, speaks at a 2012 press conference in New York City. Bryan Smith / Zuma Press file

They spread the word on Facebook groups, like that of the New York State Coalition Opposed to Fluoridation, which blames fluoride for problems including thyroid damage and was slammed in 2012 for falsely claiming that the federal government “recommends avoiding fluoridated water when making infant formula.” (The CDC says it’s fine to use fluoridated tap water for formula, though the agency notes it may cause mild spotting on babies’ teeth, so parents can use low-fluoride bottled water some of the time instead.) Reddit users claim fluoride kills gut bacteria. And on Twitter, fluoride is regularly called a cancer-causing neurotoxin.

The anti-fluoride movement has also made headway offline. In June, the Texas Republican Party opposed water fluoridation in its 2018 platform. In New Jersey, where more than 80 percent of residents do not have fluoridated water, the town of East Brunswick stopped fluoridating three years ago after Mayor David Stahl called it "mass medication of the public," a familiar refrain on anti-fluoridation forums. In Brooksville, Florida, a city of 8,000 about an hour north of Tampa, Mayor Betty Erhard has said for years that fluoride is a toxin and a waste of taxpayer money. Next month, at her urging, Brooksville will vote on removing it.

Dr. Johnny Johnson, president of the American Fluoridation Society, campaigns to keep fluoride in the water in Brooksville, Florida. Courtesy of Dr. Johnny Johnson

“I believe that people should consent to what’s in their water,” Erhard said. Some townspeople agree.

“Fluoride is a dangerous cancer-causing agent. I don't even like taking a shower in it,” one wrote on Erhard’s Facebook page.

CONTROVERSY FROM THE VERY START

The first place in America to receive fluoridated water was Grand Rapids, Michigan, in 1945, when residents there became guinea pigs for the theory that boosting existing natural fluoride levels in water would decrease tooth decay, particularly in children. The experiment, by the United States Public Health Service, was done without residents’ consent — still a point of contention among anti-fluoridationists.

The experiment was so successful that 11 years into what was supposed to be a 15-year study, researchers announced the rate of cavities among Grand Rapids’ 30,000 schoolchildren had dropped by 60 percent. But not everyone was pleased.

"I was called a murderer and a communist," Dr. Winston Prothro, director of public health in Grand Rapids during the early days of fluoridation, told The Washington Post in 1988. "I must have had letters from every city in America, and plenty from other countries, too. It fell on me to defend the physical and moral health of our entire city."

Since then, the conspiracy theories have evolved from fears of a communist plot to other worries about purported dangers of fluoride — an abundant element that occurs naturally in water, even when it’s not added by the government.

“Now, you have this weird backlash where people think that anything that is a chemical is bad, even though everything is a chemical,” said University of Miami associate professor Joseph Uscinski, co-author of the book “American Conspiracy Theories.” “There are groups of people who think that if something isn’t natural, it is somehow impure or bad, and it grosses them out.”

To experts, objecting to fluoride is nonsensical. The compound, consumed in water or applied topically through toothpaste or mouthwash, prevents cavities by replacing weakened structures in the teeth, said Dr. Kerry Maguire, associate clinical investigator of Forsyth, an independent research institute specializing in oral health.

It’s true that too much fluoride can be dangerous — one complication is skeletal fluorosis, which causes stiffening and pain of the joints and bones or abdominal pain, nausea and vomiting — but those effects only occur with prolonged exposure to a far higher level of fluoride than is found in public water systems in the U.S., experts say. In this country, the only common side effect of fluoridation is fluorosis of the teeth — minor staining that is often only visible to a dentist.

THE ANTI-FLUORIDE MOVEMENT

Today, nearly 75 percent of the U.S. receives fluoridated water from community water systems.

That’s a number that Paul Connett, a chemistry professor emeritus at St. Lawrence University in Canton, New York, hopes to get down to zero.

“There’s umpteen ways that fluoride can cause damage,” said Connett, executive director of the nonprofit Fluoride Action Network, which aims to end fluoridation worldwide.

Connett was initially skeptical of concerns about fluoride when his wife asked him two decades ago about its health effects.

“The prevailing attitude is that people who are opposed to fluoride are crazy, so I didn’t want to be stigmatized in that way,” Connett said.

But the more he looked into it, the more convinced Connett became that fluoride was indeed toxic.

He now cites what he bills as a “dynamite” 2017 study that concluded that higher prenatal fluoride exposure was associated with lower cognitive outcomes in children in Mexico.

The findings, he says, are consistent with more than 50 other studies that concluded that fluoride lowers IQ.

But many dental experts dismiss such studies as bogus, particularly because many of them were done in other countries, where natural fluoride levels are far higher than in the U.S. and there may be other factors, like polluted water.

“You can’t do that in science.”

“It’s as though you have something you want to prove, so you look at other countries that have naturally high levels of fluoride at multiples of what we have in the United States, and they see changes and then they backwards extrapolate it to water fluoridation,” said Johnson of the American Fluoridation Society. “You can’t do that in science.”

Some anti-fluoridationists oppose all fluoride, including in toothpaste. (Sales of fluoride-free toothpastes are relatively small but projected to grow; an article in the dental journal Gerodontology in August found that such toothpastes have “no impact” on preventing cavities.) Fluoride opponents seize on the warning label on toothpaste cautioning that a poison control center should be called if a child accidentally ingests too much, saying that proves fluoride is a toxin.

The American Dental Association, which has supported water fluoridation since 1950, disputes that, pointing out that the amount of fluoride in an entire tube of toothpaste wouldn’t be fatal, but other additives would likely cause a child to vomit.

As for fluoride in water, “there have been literally thousands of studies published in peer-reviewed journals that demonstrate the safety of community water fluoridation,” said Dr. Brittany Seymour, the American Dental Association’s consumer spokeswoman, calling it “the single most important public health measure to prevent cavities.”

“Which is more important: protecting your children’s brain, or protecting your children’s teeth?”

The Fluoride Action Network disagrees. The group sued the Environmental Protection Agency in federal court in San Francisco last April to stop water fluoridation.

“Which is more important: protecting your children’s brain, or protecting your children’s teeth?” Connett said.

He expects the case to be heard next August. The EPA said it does not comment on pending litigation.

MORE THAN A TOOTHACHE

Kentucky is the only state to require fluoridation in every community water system that serves 1,500 or more people, and as a result, 99.99 percent of residents receive fluoridated water. Anti-fluoridationists have tried to reverse the law, but it’s not going anywhere, said Dr. Julie Watts McKee, the state dental director of the Kentucky Oral Health Program, a public initiative that carries out community programs to reduce oral disease. The cost to fluoridate water for a person’s entire lifetime is cheaper than the price of a single filling, McKee said.

“The science — the true science — proves its effectiveness over and over again,” she said. “It helps people of all ages. It helps the kids better because they have growing teeth and are at a cavity-prone age, but it helps us all.”

Elsewhere in the country, the percentage of residents receiving water varies, with Hawaii at the low end at 11.7 percent.

It’s not always a health fear that keeps states from raising fluoridation levels; sometimes the decision is budgetary. Either way, the low levels are troubling to fluoridation proponents, who argue that it gives everyone a shot at fighting cavities — regardless of access to dental care.

The effects of cavities, particularly untreated ones, can be far-reaching.

“It’s very, very difficult to concentrate when you have a toothache, and if we are trying to help children succeed in school … this is an important component that is often overlooked,” Maguire said. “It is a winnable war.”

In Brooksville, Florida, where the vote on removing fluoride is just a couple weeks away, Mayor Erhard has high hopes that her townspeople will vote it out. The city has spent about $19,000 on fluoridation over the past five years, and she would like to see that money go someplace else — such as repairing the city’s roads.

Erhard said she doesn’t worry about how kids will fare with nonfluoridated water, so long as parents do their part to encourage good oral health.

“If you’re feeding them a lot of sugar, naturally, you’re going to get a lot of cavities,” she said. “I can tell you firsthand from my experience that I’ve always brushed and I love going to the dentist, and my teeth are healthy.”