Benefits of adding fluoride to water may be waning, new research suggests

The widespread use of toothpaste and mouthwashes with added fluoride in recent decades appears to have diminished the known public health benefits of water fluoridation, a new study suggests.

But it would be a mistake for municipalities to interpret the findings as a reason to pull back on adding the cavity-fighting mineral to their water systems, researchers said.

“There’s no evidence to suggest that where water fluoridation programs are in place, that they should necessarily be stopped,” said Anne-Marie Glenny, a co-author of the study and a professor of health sciences research at the University of Manchester in the United Kingdom.

Hundreds of U.S. communities, from Amery, Wisconsin, to Union County, North Carolina, are opting out of water fluoridation. City leaders often cite medical freedom as a reason, saying it should be up to voters, not governments, to decide what is and what isn’t added to the municipal water supply. Groups opposed to fluoride also raise concerns that it may affect children’s IQ levels.

Just last month, a federal judge in California ruled that even though he couldn’t conclude with certainty that fluoridated water was a danger to public health, the U.S. Environmental Protection Agency should strengthen water fluoridation regulations.

Benefits of fluoride toothpaste

The new research, published Thursday in the Cochrane Database of Systematic Reviews, included analyses of more than 157 studies that compared tooth decay in kids living in communities that added fluoride to their water supplies with communities that didn’t.

Studies of more than 5,700 children conducted before fluoride-fortified toothpaste became widely available in the mid-1970s found that adding fluoride to water systems reduced the number of decayed teeth by an average of 2.1 per child.

However, studies conducted after 1975, including nearly 3,000 children in the U.K. and Australia, estimated the benefit was lower, at 0.24 fewer decayed baby teeth per child. That’s a quarter of a tooth.

“Most of the studies on water fluoridation are over 50 years old,” Glenny said. Still, she noted, “contemporary studies are showing that water fluoridation is beneficial.”

Before fluoride toothpastes were widely available to consumers, adding the mineral to water provided a clear benefit to teeth. Cavities among children living in Grand Rapids, Michigan, which in 1945 became the first community in the world to add fluoride to its water supply, plummeted by 60% within a decade.

Fast-forward to 2024: About 75% of the U.S. population has tap water with added fluoride at recommended levels of 0.7 milligrams per liter of water.

Major public health groups, including the American Dental Association, the American Academy of Pediatrics and the Centers for Disease Control and Prevention, support the use of fluoridated water. All cite studies that show it reduces tooth decay by 25%.

But some recent research has hinted that water fluoridation may have negative health effects. A study published in May found that women who had higher levels of fluoride during pregnancy said their kids were more likely to have temper tantrums, complain of vague headaches and stomachaches and show other neurobehavioral symptoms by age 3.

Still, Dr. Johnny Johnson, a pediatric dentist and president of the American Fluoridation Society, said the new findings don’t change decades of safety evidence for added fluoride.

“Water fluoridation is still effective at reducing cavities,” he said. “I would say it’s safe for everyone.”

Another co-author of the new review, Janet Clarkson, a professor of clinical effectiveness at the University of Dundee in Scotland, said the research may serve to “open up a dialogue” to further understand the impact of public water fluoridation.

While water fluoridation helps against cavities, it doesn’t make up for high sugar consumption or inadequate oral health behaviors, Clark said in a press release. “It is likely that any oral health preventive program needs to take a multifaceted, multiagency approach.”