A comprehensive new study has confirmed that the addition of fluoride to public water supplies, a practice aimed at preventing tooth decay, does not harm children’s health. The research found no adverse effects on birth weight or other birth outcomes.

Health Secretary Robert F. Kennedy Jr. has consistently criticized the fluoridation of public water, describing it as a form of “mass medication” that he claims could pose serious health risks, particularly to children’s neurological development. However, his stance lacks conclusive supporting evidence.

Opponents of water fluoridation often point to studies suggesting potential health issues such as impaired cognitive development and thyroid dysfunction. For example, a study published in January 2025 noted a correlation between higher fluoride exposure and lower IQ scores in children.

Nevertheless, it’s crucial to note that this particular study did not include any data from the United States. The majority of the research was conducted in countries like China and India, where fluoride exposure levels are much higher than those typically found in U.S. water systems.

Decisions to cease water fluoridation lie with local and state governments. Recently, Florida and Utah became the first states to ban the practice outright. Although Kennedy cannot directly enforce a nationwide cessation, he has the potential to influence policy by instructing the CDC and EPA to update their guidelines and safety standards regarding fluoride use.

But now, a sweeping new study from Columbia University accounted for more than 11 million births across 677 US counties over two decades as fluoridation in community water systems became more common and widely accepted, largely due to its ability to help prevent tooth decay.

To measure the effect, researchers tracked changes in birth weight, gestation, and prematurity in counties that started adding fluoride between 1968 and 1988, and compared these trends to counties without fluoridation. They did not measure IQ. 

There were no statistically significant changes. Any difference in weight was so tiny – less than one percent of an average baby’s weight – that it holds no statistical or real-world significance.

The Columbia University study tracked over 11 million US births for two decades. It found that adding fluoride to drinking water did not cause any significant changes in birth weight, length of pregnancy or rates of premature birth (stock)

In the latest study, published in JAMA Network Open, researchers analyzed over 11 million singleton births from 1968 to 1988 across 677 counties. 

Researchers tracked what happened to babies before and after individual US counties began adding fluoride to their water. They compared these changes to counties that never added fluoride during the same 20-year period. 

The study group comprised 408 counties that adopted fluoridation during the study period. 

Each county’s birth outcomes were compared before and after fluoridation adoption. The control group consisted of the remaining 269 counties that were never fluoridated, providing a baseline for comparison.

This staggered rollout design allowed researchers to compare treated counties to not-yet-treated and never-treated counties over the same time periods.

The primary analysis showed no statistically significant change in average birth weight following community water fluoridation (CWF) adoption.

The estimated effects were minuscule in magnitude, ranging from a decrease of 8.4g to an increase of 7.2g, with zero being well within the margin of error, and are clinically meaningless, representing less than one percent of average birth weight, and pose no known health risk to infants. 

Similarly, the study found no association between CWF and the incidence of low birth weight, the length of gestation or the rate of premature births.

Health and Human Services Secretary Robert F Kennedy, Jr, a long-time opponent of fluoride in water, calling it a ‘neuroxin,’ is pictured in Utah last April during a press conference about the new statewide ban

The CDC map shows the states that participate in federal fluoride reporting

Researchers said: ‘Our findings provide reassurance about the safety of community water fluoridation during pregnancy.’ 

This is not the first study to rule that fluoride in water poses no long-term adverse health effects. Among the first major breakthroughs in fluoride science came in 1970, 25 years after the city council of Newburgh, New York began fluoridating its water.

For a decade, researchers compared the dental health of Newburgh’s children with those in the similar, non-fluoridated ‘control’ city of Kingston.

The results showed children who grew up drinking fluoridated water had 60 to 70 percent fewer cavities, far lower dental costs, and fewer tooth extractions. 

Comprehensive health monitoring over 25 years found no harmful effects, confirming its safety.

Then-75-year-old dentist Dr Maxwell Serman, whose practice predated fluoridation, told The New York Times in 1970: ‘Today, whenever I see a child with a mouthful of cavities, I know immediately he’s not from Newburgh.’

But even then, the public health measure sparked controversy, as some people believed that adding what they equated with medication without their say-so encroached on their bodily autonomy.

Public health experts have cited decades of robust evidence demonstrating that fluoride, at the optimal level used in US water systems, dramatically reduces tooth decay by as much as 25 percent across all socioeconomic groups, making it a powerful tool for nearly every American.  

The graph shows how the number of counties adding fluoride to their water grew steadily over the study’s 21-year timeline. By 1988, fluoride had been introduced in over 2,056 counties, representing nearly 90 percent of the counties and 46 percent of the US population 

The graphic displays the key result: that water fluoridation had no meaningful effect on birth weight. The data show no concerning trends in counties before fluoridation began, and the changes after adoption [the dips and rises] were trivial, ranging from a very slight decrease to a slight increase

The American Dental Association maintains that fluoride in community water supplies is ‘the single most effective public health measure to prevent tooth decay,’ while the CDC lists it among the Ten Great Public Health Achievements. 

But some studies, particularly from regions with naturally high fluoride levels, such as parts of China, India and Iran, where levels can exceed four to 10 parts per million, have found associations with skeletal fluorosis, cognitive effects or thyroid changes.

And long-simmering skepticism about the use of fluoride in water, as well as supplements and toothpaste, has increased in recent years, RFK Jr at the forefront. 

In April 2025, he said as he stood alongside Utah lawmakers at a press conference: ‘The evidence against fluoride is overwhelming.’

Kennedy believes fluoride is best as a topical ingredient, such as toothpaste, and is harmful systemically.  

During the Utah event, EPA head Lee Zeldin thanked RFK Jr for pushing the agency to accelerate its review of fluoride safety standards in water, a process not formally due until 2030.

The FDA is also launching a multi-agency fluoride research initiative, while the CDC has eliminated its core oral health division as part of major budget cuts.