(The Hill) — A federal judge has ordered the Environmental Protection Agency (EPA) to address the potential impacts of fluoride in drinking water on IQ levels. 

In a new ruling this week, Obama-appointed Judge Edward Chen ordered the EPA to take regulatory action over the issue. 

Chen wrote that “a preponderance of the evidence” shows that there is an “unreasonable risk” stemming from fluoride in drinking water.

Specifically, he wrote that there is “ample support” in the scientific record that the U.S. population is at risk of losing more than four IQ points due to fluoride exposure. 

Fluoride is intentionally added to drinking water to prevent tooth decay. About 200 million Americans drink water with added fluoride. 

The substance’s health impact has been the subject of significant debate.

The Department of Health and Human Services’s National Toxicology Program found in August that higher levels of fluoride exposure is linked to lower IQs in children. 

But, following that report, the American Academy of Pediatrics stood by its recommendation in favor of adding fluoride to water and toothpaste. 

In May, the Centers for Disease Control and Prevention said in a statement that “expert panels … have not found convincing scientific evidence linking community water fluoridation with any potential adverse health effect,” including low intelligence. 

Chen, in his ruling, said that his unreasonable risk finding “does not conclude with certainty that fluoridated water is injurious to public health; rather, … the Court finds there is an unreasonable risk of such injury.”

He wrote that this risk is “sufficient to require the EPA to engage with a regulatory response” but does not dictate what the outcome of that EPA action will be. 

A spokesperson for the EPA said that the agency was reviewing the decision, but did not comment further.