There appears to be no evidence suggesting community water fluoridation (CWF) has a harmful effect on adolescent IQ or adult cognitive function, according to a study recently published in Proceedings of the National Academy of Sciences.
Furthermore, the study may have improved upon previous research by using adolescent IQ rather than academic performance as a measure and by better accounting for how long participants lived in communities with consistent exposure to CWF, the authors wrote.
“We find no evidence that CWF is negatively associated with adolescent IQ or adult cognitive functioning,” wrote the study's lead author, John Robert Warren of the University of Minnesota Institute for Social Research and Data Innovation (PNAS, April 13, 2026, Vol. 123:16, e2536005123.)
Researchers used data from the Wisconsin Longitudinal Study, which included 10,317 individuals from a 1957 high school graduating class in Wisconsin. By linking school addresses and census records from 1940 and 1950, they identified participants who remained in the same communities during childhood and tracked their exposure to CWF through age 14.
Participants were considered exposed from birth if their county had naturally high fluoride levels in untreated well water. Otherwise, exposure began when their community started water fluoridation. Adolescent IQ was measured using the Henmon-Nelson test, while cognitive function in adulthood was assessed at ages 53, 64, 72, and 80 using standardized cognitive tests. Also, the researchers accounted for factors like parental education, family income, father’s occupation, and community size, they wrote.
Participants exposed to CWF showed no significant differences in cognitive performance compared to those who were never exposed. This finding remained consistent across all ages when cognition was measured and even when the analysis was limited to individuals who had lived in the same community since ages 11 or 1. Unlike studies referenced in decisions to end CWF in places such as Utah and Florida, this research found no evidence that CWF has a negative impact on cognitive function or IQ.
However, the study had limitations. The researchers could not directly measure how much fluoride adolescents consumed, such as through urine sample testing, the authors added.
“Participants exposed to CWF did not perform significantly worse (or better) than their peers who were never exposed,” Warren and colleagues wrote.
