Contrary to the Trump administration’s suggestions that fluoride in drinking water will affect children’s IQ or decrease cognitive abilities, a large-scale study appears to have disproved this theory, reports Healthline.
The research, published in the Proceedings of the National Academy of Sciences (PNAS), reports that there seems to be no difference at any stage of life between people who grow up with water fluoridation and those who do not.
“We find no evidence that (community water fluoridation) is negatively associated with adolescent IQ or adult cognitive functioning,” the study authors wrote.
The findings are in contrast to Health and Human Services (HHS) Secretary Robert F Kennedy’s announcement in April that he would require the Centres for Disease Control and Prevention (CDC) to revise its long-standing recommendation that fluoride be added to drinking water.
They also contradict previous research, including a January study, that has suggested a possible link between fluoride and children’s IQ levels. Researchers noted that the studies were conducted in China and other countries with higher fluoride concentrations than permitted in the United States.
Scott Tomar, DMD, a spokesperson for the American Dental Association, said this research provides important information for the public at a critical time. Tomar wasn’t involved in the study.
“Despite misinformation out there, the best available evidence indicates that community water fluoridation has no effect on IQ, cognition, or other measures of neurodevelopment,” said Tomar, who is also a Professor and Associate Dean for Prevention and Public Sciences at the College of Dentistry at the University of Illinois Chicago.
No evidence to support negative impact
The new study was led by Rob Warren, PhD, a sociologist and population health expert at the University of Minnesota.
Warren used data from the Wisconsin Longitudinal Study, which has followed more than 10 000 people in that state since they graduated from high school in 1957. Participants took IQ tests at 16, then had cognitive testing done at ages 53, 64, 72 and 80.
The original purpose of the Wisconsin study wasn’t focused on fluoride, so there were no data available on urine or blood tests that would have measured exact levels of fluoride.
Warren’s team based its estimates on exposure from records of when community water fluoridation began in certain areas.
The new findings follow a November 2025 study led by Warren that found no link between community water fluoridation in early life and brain function in people at age 60.
Experts note that fluoridation at appropriate levels doesn’t appear to cause any negative health effects.
“At the levels of fluoride that we use for community water fluoridation in the United States and other countries, there are no adverse health effects,” Tomar told Healthline.
Graham Tse, MD, a paediatrician and chief medical officer of MemorialCare Miller Children’s & Women’s Hospital in California, agreed that the low levels of fluoride in US drinking water pose no threat. Tse wasn’t involved in the study.
He added that fluoride, like vitamins or other substances, can pose some issues if people are exposed to high levels. “That’s the case with many, many things,” Tse said.
Health benefits of fluoride in drinking water
The health benefits of fluoride in drinking water were first studied in 1909 in Colorado. In 1962, the US Public Health Service recommended fluoridation in drinking water.
The CDC states that the optimal level of fluoride in drinking water to prevent cavities is 0.7 milligrams (mg) per litre (L). The legal limit for drinking water in the United States is 4 mg/L.
Today, more than 70% of people in the country on public water systems receive fluoridated water. That represents more than 200m Americans.
However, that number is shrinking. Two states – Utah and Florida – have enacted bans on fluoride in drinking water, while several other states have pending legislation to limit fluoride.
In addition, 86 Wisconsin communities have stopped adding fluoride to municipal water systems since 1995.
Health organisations such as the American Dental Association and the American Academy of Paediatrics (AAP) support the fluoridisation of drinking water.
Fluoride, a chemical found in nature as well as in toothpaste and drinking water, works by inhibiting the growth of bacteria that cause cavities, strengthening the hard outer enamel of teeth, reversing the damage caused by cavities, and supporting new bone formation.
Experts say the benefits are numerous and widespread.
“We have extremely consistent evidence that water fluoridation helps to prevent tooth decay and reduces its severity,” said Tomar. “We also have very consistent evidence that community water fluoridation saves money for families, communities, and state governments by reducing dental costs and missed days of work or school due to dental problems.”
See more from MedicalBrief archives:
FDA moves to restrict fluoride supplements
Experts call for more water fluoridation to fight tooth decay
UK water fluoridation report dismisses claims of health danger