Pregnant mothers exposed to drinking water fluoride levels at or near current U.S. recommended levels had children who scored lower on cognition tests as fluoride levels increased, according to a new study supported by the National Institute of Health’s Environmental Influences on Child Health Outcomes (ECHO) Program.

The study, authored by a 25-member team of scientists and physicians from 13 universities and medical schools across the nation, followed 2,514 children in 23 states. It found that fluoride in public drinking water during pregnancy is linked to lower cognition scores in children – even at levels considered “optimal” for dental health. 

The finding is significant and may effect how fluoridation policy is viewed in the United States, the most heavily fluoridated nation in the world. Staunch advocates of water fluoridation, including the American Dental Association, have long claimed that studies showing IQ/cognition loss from fluoride are due to levels of exposure far above optimal levels. This new study turns that assertion on its head, showing lowered cognition at fluoride levels that U.S. residents are routinely exposed to (.7ppm).

“This study adds to a large body of work that looks at how early exposure to environmental contaminants may be associated with the development of the thinking and learning processes that are important for children’s developmental outcomes,” said co-senior author Amy Margolis, PhD, of the Ohio State University Wexner Medical Center and College of Medicine.

The study found that for every 0.5 mg/L increase of fluoride level above 0.675 mg/L, cognition scores decreased by an average of 3.36 points. However, when tests under age 7 were included, the losses were much higher,13.5 points, as shown in this graph of results:

For the most socioeconomically vulnerable group, the average loss was 5.5 points, compared to the loss for all levels of 3.36 points. For Blacks, the average loss was also higher, 5.5 points, compared to all racial groups combined.

Its findings complement the comprehensive 2024 National Toxicology Program systematic review of studies that consistently linked higher fluoride levels in pregnant women with lower IQs in their children.

The ECHO study found diminished cognition levels s at 0.675 milligrams per liter (mg/L) or higher, close to the current fluoridation levels of 0.7 mg/L. However, this is an average and should not be interpreted to mean that water fluoride concentrations at or below 0.7 mg/L can be considered safe. This study shows there is no margin of safety.

Standard toxicology protocols, including those used by the EPA, apply a factor of at least 10 to a recognized harm level to account for individual variances in resistance to toxins. Thus, to protect everyone in a population, fluoride levels would ideally be reduced to no more than 0.07 mg/L.

Moreover, many people drink more water than average, including pregnant women. If the water is fluoridated, this elevated consumption also increases the risk of cognitive loss in children. About 5% of pregnant women drink 2 to 3 times as much water as average, so their children would have a clear risk of IQ loss at water fluoride concentrations of 0.2 to 0.4 mg/L, well below the 0.7 mg/L of fluoridated water added to 2/3rds of American’s water.

Testing at a younger age is considered a more accurate indicator of physical harm than testing of older children, whose scores are more affected by differing home and educational environments.

“This study addresses an important gap by evaluating prenatal water fluoride and child cognition in a large U.S. sample,” said lead author Katrina Simon, PhD, of Columbia University Mailman School of Public Health. “Findings from this work offer evidence that can inform ongoing guidance aimed at supporting children’s development.”