New research has identified 1.5 milligrams of fluoride per liter as a key threshold for child development safety concerns.
Following the August 2024 release of a U.S. government report linking higher levels of fluoride in drinking water to lower IQ in children, a new review conducted by the National Institutes of Health appears to confirm those findings.
The new analysis, published in JAMA Pediatrics on Monday, found that fluoride exposure exceeding 1.5 milligrams per liter (mg/L) was associated with reduced intelligence among children.
The study, conducted by the U.S. National Toxicology Program (NTP), took nine years to complete and is the largest meta-analysis to date on the health effects of fluoride.
The studies reviewed measured fluoride levels in drinking water and in urine. The authors used urinary fluoride as a proxy for total fluoride exposure.
74 Studies Reviewed
Among the 74 reviewed studies, 64 found that higher levels of fluoride exposure were linked to lower IQ in children. The strength of this association is considered moderate to large.
Thirty-one studies reviewed noticed a dose-response, such that increased fluoride levels in drinking water were linked to further decreases in children’s IQ results.
However, the relationship between fluoride and lower IQ scores only persisted when fluoride concentrations in drinking water were above 1.5 mg/L, higher than the current fluoride drinking water standard of 0.7 mg/L.
The 1.5 mg/L cutoff is the same concentration identified in the NTP’s August 2024 report. The report was cited over 120 times in a lawsuit that led the court to rule that the Environmental Protection Agency (EPA) must revise its current drinking water standard of 0.7 mg/L.
When evaluating urinary fluoride, the researchers found that every increase of 1 mg/L in urinary fluoride was associated with an average decrease of between 1.14 and 1.63 IQ points.
Fluoride can cross the blood-brain barrier and accumulate in areas of the brain responsible for cognition and memory, although its effects on the brain remain unclear.
The study’s findings inform future risk-benefit assessments related to fluoride exposure, the authors wrote, especially highlighting the significant contributions of water and drinks made with fluoridated water, like soft drinks, fruit juice, beer, and some bottled water, to total fluoride ingestion.
