A new study suggests that ceasing the practice of adding fluoride to public water supplies could dramatically increase tooth decay, costing billions of dollars to treat.

The health and human services secretary, Robert F. Kennedy Jr., has pledged to remove fluoride from the American water supply and announced that the Centers for Disease Control and Prevention would stop recommending fluoridation in drinking water systems nationwide. Mr. Kennedy says that fluoride is a “dangerous neurotoxin,” linking it to conditions such as arthritis, bone fractures, and thyroid disease.

Following Mr. Kennedy’s lead, the FDA now claims — after recommending fluoride’s regular use for decades — that studies have suggested an association between fluoride and thyroid disorders, weight gain, and possibly decreased IQ.

Florida and Utah have recently banned fluoride in public water supplies and lawmakers in several other states are considering similar efforts.

The American Dental Association has long touted fluoride as a cavity-fighting savior, and a new JAMA Health Forum study warns of the dramatic costs that would come with the removal of fluoride from water supplies. The authors of the study say the elimination of fluoride would lead to an additional 25.4 million decayed teeth over a five-year period and 53.8 million over 10 years.

They put the treatment costs at approximately $9.8 billion over five years and $19.4 billion over 10 years.

The Brigham and Women’s Hospital-funded researchers conducted a cost-effectiveness analysis using four years of data from the U.S. National Health and Nutrition Examination Survey to come up with the estimates. They claim that increased tooth decay would disproportionately affect publicly insured and uninsured children compared to those with private dental insurance.

The study found that only 40.4 percent of American children have access to optimal fluoride levels that effectively prevent tooth decay, and 45.7 percent have some fluoride protection. The authors estimate that tooth decay levels would drop nearly 7 percent and there would be 22 million fewer decayed teeth in the country if all public water supplies were adequately fluoridated.

The negative health results of removing fluoride from water have already played out in Calgary, Canada. The city ceased adding fluoride to water in 2011, and a 2021 study found a dramatic increase in dental decay in children.

The number of children who had tooth decay reached 65 percent in Calgary. In Edmonton, where fluoridation remained in place, it was about 55 percent. Voters in Calgary approved reversing the fluoride ban and it will be reintroduced to the city’s water supply later this month.