Fluoridated water harms the development of young brains, argued scientists testifying this month for groups seeking to ban the cavity-fighting element from public water supplies.

State and local governments often add fluoride to drinking water, a practice that dates back to the 1940s. The Centers for Disease Control and Prevention (CDC) reports that more than 200 million Americans receive water from a system that is treated with fluoride.

The experts, drawn from government and academia, testified June 10 on behalf of nonprofit groups that argue water fluoridation poses an “unreasonable” risk of harm and want to end the practice.

Harvard University epidemiologist Philippe Grandjean said that exposure levels to fluoride are far too high in babies and young children and that it has reduced their IQ levels, “endangering the next generation's intelligence.”

University of Washington professor and physician Dr. Howard Hu measured the impact of fluoride consumption on babies by testing their mothers’ urine while pregnant and later testing the children’s IQ scores. Hu said he “absolutely” found that higher levels of fluoride were associated with lower IQs.

Kris Thayer, director of the United States Environmental Protection Agency (EPA) Chemical and Pollutant Assessment Division who also worked at the National Toxicology Program, said that animal studies support the conclusion that fluoride could be neurotoxic in humans. However, he acknowledged that the data has some limitations.

The government has responded that much of the data cited in the case is unreliable and inconsistent, and therefore can’t be used to claim that fluoride damages human health.

Public health and medical organizations generally agree. In a 2018 statement, the CDC said that fluoridated drinking water helps lower barriers to dental care in at-risk communities, including the elderly, people living in low-income areas and racial and ethnic minority groups.

Experts have not found compelling evidence linking fluoride to poor health outcomes, according to the agency’s statement. The American Dental Association also reports that “70 years of scientific research has shown fluoride in water is safe.”

The debate over adding fluoride to drinking water is nearly as old as the practice itself. The first fluoridation project took place in Grand Rapids, Michigan, in 1945, where the United States Public Health Service added fluoride to the water without informing residents. 

Decades later, various anti-fluoride groups continue to take issue with the fluoridation being instituted without Americans’ consent. Many advocates also claim that fluoride can cause cancer and thyroid damage. Other anti-fluoride activists believe that fluoridation is a conspiracy by domestic or foreign governments to harm the American people. 

A 2019 study in JAMA Pediatrics reinvigorated anti-fluoride voices by suggesting once again that fluoride during pregnancy is associated with reduced IQ in children.

While the results were taken as shocking, the study only analyzed 600 mother-baby pairs from six Canadian cities and therefore should not be universally applied.

The next step in the fluoridation-ban case is a status briefing on Aug. 6.