A U.S. government report expected to spark debate concluded that fluoride in drinking water at twice the recommended limit is linked with lower IQ in children.
The report, based on an analysis of previously published research, represents the first time a federal agency has determined — “with moderate confidence” — that there is a link between higher levels of fluoride exposure and lower IQ in kids. Although the report was not designed to exclusively evaluate the health effects of fluoride in drinking water, it is a significant acknowledgment of a potential neurological risk from elevated levels of fluoride.
Fluoride, known for strengthening teeth and reducing cavities by replacing minerals lost during normal wear and tear, has long been lauded as one of the greatest public health achievements of the last century, according to the U.S. Centers for Disease Control and Prevention.
“I think this is crucial in our understanding of this risk,” remarked Ashley Malin, a University of Florida researcher who has studied the effect of higher fluoride levels in pregnant women on their children. She called it the most rigorously conducted report of its kind.
The comprehensive report, released Wednesday, comes from the National Toxicology Program, part of the Department of Health and Human Services. It encapsulates a review of studies conducted in several countries, including Canada, China, India, Iran, Pakistan, and Mexico. These studies concluded that drinking water containing more than 1.5 milligrams of fluoride per liter is consistently associated with lower IQs in children.
The report did not quantify exactly how many IQ points might be lost at different levels of fluoride exposure, but some of the studies reviewed suggested that IQ was 2 to 5 points lower in children with higher exposures.
Since 2015, federal health officials have recommended a fluoridation level of 0.7 milligrams per liter of water, with the previous upper range for five decades set at 1.2 milligrams. The World Health Organization has set a safe limit for fluoride in drinking water at 1.5 milligrams per liter.
Approximately 0.6% of the U.S. population, or about 1.9 million people, are on water systems where naturally occurring fluoride levels reach 1.5 milligrams or higher.
“The findings from this report raise questions about how these people can be protected and what makes the most sense,” Malin said.
The 324-page report did not draw a conclusion about the risks of lower levels of fluoride, suggesting that more study is needed. It also did not address what high levels of fluoride might do to adults.
The American Dental Association, which supports water fluoridation, had criticized earlier versions of the new analysis as well as Malin’s research. Late Wednesday, a spokesperson indicated that the organization’s experts were still reviewing the report.
Fluoride is a mineral that naturally exists in water and soil. About 80 years ago, scientists discovered that people whose water naturally had higher fluoride levels also had fewer cavities, spurring a campaign to get more Americans to use fluoride for better dental health.
In 1945, Grand Rapids, Michigan became the first U.S. city to start adding fluoride to tap water. In 1950, federal officials endorsed water fluoridation to prevent tooth decay, continuing to promote it even after fluoride toothpaste became available. While fluoride can come from multiple sources, drinking water remains the primary source for Americans, according to researchers.
Officials adjusted their recommendation for drinking water fluoride levels in 2015 to address a tooth condition known as fluorosis, marked by splotches on teeth and becoming more common among U.S. children.
Separately, the Environmental Protection Agency has long mandated that water systems cannot contain more than 4 milligrams of fluoride per liter. This standard aims to prevent skeletal fluorosis, a potentially crippling disorder causing weaker bones, stiffness, and pain.
However, numerous studies increasingly point to a different problem, suggesting a connection between higher fluoride levels and impaired brain development. Researchers are particularly concerned about the impact on developing fetuses and very young children who might ingest water with baby formula. Animal studies have shown that fluoride can impact neurochemistry cell function in brain regions responsible for learning, memory, executive function, and behavior.
In 2006, the National Research Council highlighted limited evidence from China suggesting neurological effects in people exposed to high fluoride levels. It called for more research on fluoride’s impact on intelligence.
Continued research raising questions led the National Toxicology Program to commence a review in 2016 of available studies to determine if new fluoride-limiting measures were necessary.
Earlier drafts of the report were challenged, with a committee of experts stating that existing research did not support the initial conclusions.
“Since fluoride is such an important topic to the public and public health officials, it was imperative that we made every effort to get the science right,” said Rick Woychik, director of the National Toxicology Program, in a statement.
Malin suggested that it might be prudent for pregnant women to lower their fluoride intake, not only from water but also from certain types of tea. She also proposed considering policy discussions about requiring fluoride content on beverage labels.
