A U.S. government report expected to stir debate has concluded that fluoride in drinking water at twice the recommended limit is linked to lower IQ levels in children.
This report, based on an analysis of previously published research, marks a historic moment as it’s the first time a federal agency has determined—with moderate confidence—that higher fluoride exposure correlates with reduced IQ in kids. Although the report wasn’t designed to evaluate the health effects of fluoride in drinking water alone, it signals a noteworthy acknowledgment of potential neurological risks from high fluoride levels.
According to the U.S. Centers for Disease Control and Prevention, fluoride fortifies teeth and minimizes cavities by replenishing minerals lost through regular wear and tear. The addition of low levels of fluoride to drinking water has long been heralded as one of the most significant public health triumphs of the 20th century.
“I think this report is crucial in our understanding of this risk,” said Ashley Malin, a University of Florida researcher who has studied the influence of higher fluoride levels in pregnant women on their children’s development. She described it as the most rigorously conducted report of its kind.
The much-anticipated report, released Wednesday, comes from the National Toxicology Program, a division of the Department of Health and Human Services. It consolidates a review of studies from Canada, China, India, Iran, Pakistan, and Mexico, concluding that drinking water with more than 1.5 milligrams of fluoride per liter is consistently linked with lower IQs in children.
Although the report did not quantify precisely how many IQ points might be lost at varying fluoride exposure levels, reviewed studies suggested IQs were 2 to 5 points lower in children who had experienced higher exposures.
Since 2015, federal health officials have recommended a fluoridation level of 0.7 milligrams per liter of water, compared to the previous upper range of 1.2 milligrams that was in place for five decades. The World Health Organization has also set a safe fluoride limit in drinking water at 1.5 milligrams.
Approximately 0.6% of the U.S. population—roughly 1.9 million people—are served by water systems with naturally occurring fluoride levels of 1.5 milligrams or higher, the report states.
“The findings from this report raise important questions about how these people can be protected and what the best course of action might be,” Malin remarked.
The comprehensive 324-page report did not draw conclusions about the risks associated with lower levels of fluoride, indicating the need for further study. It also left unanswered questions about what high fluoride levels might do to adults.
The American Dental Association, a staunch advocate for water fluoridation, had criticized earlier versions of the new analysis and Malin’s research. Late Wednesday, a spokeswoman for the organization stated that their experts were still reviewing the report.
Fluoride, a mineral naturally present in water and soil, was recognized about 80 years ago for its dental health benefits, leading to a nationwide push for its use. In 1945, Grand Rapids, Michigan became the first U.S. city to add fluoride to tap water. In 1950, federal officials endorsed the practice to prevent tooth decay, a recommendation that continued even after fluoride toothpaste became available.
In 2015, the recommended fluoride levels in drinking water were lowered to address fluorosis, a condition that causes splotches on teeth and was increasingly common among U.S. children.
Separately, the Environmental Protection Agency has imposed a longstanding requirement that water systems must not exceed 4 milligrams of fluoride per liter, a standard aimed at preventing skeletal fluorosis, a potentially crippling condition that results in weaker bones, stiffness, and pain.
However, mounting studies have suggested a different concern, pointing to a link between higher fluoride levels and brain development. Researchers have examined the impact on developing fetuses and very young children who might consume water mixed with baby formula. Studies in animals indicated that fluoride could affect neurochemistry and cell function in brain areas responsible for learning, memory, executive function, and behavior.
In 2006, the National Research Council, a private nonprofit organization, noted evidence from China suggesting neurological effects in individuals exposed to high fluoride levels and called for additional research into fluoride’s impact on intelligence.
Following a series of studies that continued to raise questions, the National Toxicology Program began a comprehensive review in 2016 to assess whether new fluoride-limiting measures were warranted. Despite earlier drafts, the final document faced delays, partly due to concerns over the available research’s support for early conclusions.
“Given the public and public health officials’ interest in fluoride, we had to ensure we got the science right,” said Rick Woychik, director of the National Toxicology Program.
Malin suggested that pregnant women should consider reducing their fluoride intake, not only from water but also certain types of tea. She also proposed policy discussions on whether to require labeling beverages with their fluoride content.
