Utah just became the first U.S. state to ban fluoride in public water systems.

Gov. Spencer Cox, a Republican, signed a bill into law on Thursday that prohibits any person or government entity from adding the mineral, which can prevent tooth decay, to water systems in the state.

The bill was introduced in January, then passed in the state Senate on Feb. 21. It will go into effect May 7.

Cox’s signature was the final step needed for the ban, though he told ABC4 Utah earlier this month that “it’s not a bill I care that much about.”

As of 2022, roughly 44% of Utah’s population was receiving fluoridated water — one of the lowest percentages in the county, according to the Centers for Disease Control and Prevention.

“You would think you would see drastically different outcomes with half the state not getting it and half the state getting it. I’ve talked to a lot of dentists. We haven’t seen that,” Cox told ABC4. “So it’s got to be a really high bar for me if we’re going to require people to be medicated by their government.”

Major medical associations and public health groups — including the American Academy of Pediatrics, the American Dental Association and the CDC — support adding fluoride to drinking water on the grounds that it helps prevent cavities.

But Health and Human Services Secretary Robert F. Kennedy Jr. has criticized fluoridation, associating it with illnesses such as bone cancer and thyroid disease, despite scientists saying there’s not enough evidence to support a link. Kennedy said days before the presidential election in November that if elected, Trump would recommend removing fluoride from all water systems.

Dr. Marty Makary, who the Senate confirmed this week to lead the Food and Drug ministration, suggested at the same time in early November that adding fluoride to drinking water was potentially harmful — a claim that most public health experts reject.

Some studies have suggested that fluoride may negatively impact children’s neurodevelopment, including one recently published in the journal JAMA Pediatrics, which found an association between higher fluoride exposure and lower IQ scores in children.

According to the authors, though, most of the 74 studies they reviewed were from countries that use far higher levels of fluoride in their water systems than the United States does.

A study out of Australia last year found no link between children drinking fluoridated water and negative cognitive development. And a 2018 study found that a greater availability of fluoridated water in a county was associated with fewer cavities among children.

According to the CDC, the only documented health risks of fluoridation are cosmetic issues such as discolored tooth enamel and small holes in the teeth.

Still, the push to remove fluoride from drinking water has gained popularity across the country. More than 150 towns or counties have voted to do so since 2010, according to the Fluoride Action Network, an anti-fluoride group. 

Lawmakers in Kentucky, Montana and Tennessee have filed bills to make fluoridation optional for water systems or prevent the mineral from being added to systems altogether. And in Florida, a bill proposed in the current legislative session aims to ban “additives” including fluoride from drinking water.