THURSDAY, Aug. 22, 2024 (HealthDay News) -- High levels of fluoride in drinking water may dim the intelligence of children, a new U.S. government report shows.

Based on an analysis of published research, the potentially controversial report marks the first time a federal agency has determined there is a link between drinking twice the recommended amount of fluoride and lower IQs in kids.

"Since 1945, the use of fluoride has been a successful public health initiative for reducing dental cavities and improving general oral health of adults and children," the report stated. "There is a concern, however, that some pregnant women and children may be getting more fluoride than they need because they now get fluoride from many sources, including treated public water, water-added foods and beverages, teas, toothpaste, floss and mouthwash, and the combined total intake of fluoride may exceed safe amounts."

Importantly, "the determination about lower IQs in children was based primarily on epidemiology studies in non-U.S. countries such as Canada, China, India, Iran, Pakistan and Mexico where some pregnant women, infants and children received total fluoride exposure amounts higher than 1.5 mg fluoride/L of drinking water," the report authors stated. "The U.S. Public Health Service currently recommends 0.7 mg/L, and the World Health Organization has set a safe limit for fluoride in drinking water of 1.5 mg/L."

One expert welcomed the findings.

“I think this [report] is crucial in our understanding” of this risk, Ashley Malin, a University of Florida researcher who recently published a study on the effect of higher fluoride levels in pregnant women on their children, told the Associated Press.

The report did not try to quantify exactly how many IQ points might be lost at different levels of fluoride exposure. But some of the studies reviewed in the report suggested IQ was 2 to 5 points lower in children who’d had higher exposures.

The report noted that about 0.6% of the U.S. population -- roughly 1.9 million people -- are on water systems with naturally occurring fluoride levels of 1.5 milligrams or higher.

“The findings from this report raise the questions about how these people can be protected and what makes the most sense,” Malin said.

The American Dental Association, which champions water fluoridation, told the AP that the organization’s experts were still reviewing the report.

Fluoride is a mineral that exists naturally in water and soil. Though it can come from a number of sources, drinking water is the main source for Americans, the researchers said.

In 2015, U.S. officials lowered their recommendation for fluoride levels in drinking water to address a tooth condition called fluorosis, which can cause splotches on the teeth and was becoming more common in U.S. kids, the AP reported.

But more recent research has pointed to a different problem, suggesting a link between higher levels of fluoride and brain development. Studies in animals showed fluoride could impact cell function in brain regions responsible for learning, memory, executive function and behavior, the AP reported.

After more research continued to raise questions, the National Toxicology Program started working on a review of the available studies in 2016. The hope was that it could provide guidance on whether new fluoride-limiting measures were needed.

“Since fluoride is such an important topic to the public and to public health officials, it was imperative that we made every effort to get the science right,” Rick Woychik, director of the National Toxicology Program, told the AP in explaining the length of time it took to complete the report.

More information

The National Institutes of Health has more on fluoride.

SOURCE: National Toxicology Program, report, Aug. 22, 2024; Associated Press