The debate over fluoride in drinking water continues with the release of a new study.
A systematic review and meta-analysis published Monday in JAMA Pediatrics found significant inverse associations between high fluoride exposure and children’s IQ scores. The analysis included 74 cross-sectional and prospective cohort studies spanning multiple countries, including Canada, China, Denmark, India, Iran, Mexico, New Zealand, Pakistan, Spain, and Taiwan.
Of the 74 studies, 52 were deemed high risk of bias, while 22 were rated low risk. Despite differences in exposure levels and outcome measures, the study found consistent inverse associations. For studies rated low risk of bias, IQ scores decreased by an average of 1.14 points (95% confidence interval [CI], –1.68 to –0.61; p<.001) per 1-mg/L increase in urinary fluoride.
The findings held even when exposure was limited to fluoride levels below 4 mg/L, 2 mg/L, and 1.5 mg/L in drinking water and urine. The association between fluoride and IQ scores became non-significant only at fluoride concentrations below 1.5 mg/L in drinking water.
Fluoride is added to tap water in some Canadian and U.S. municipalities to help reduce cavities. However, this practice has been questioned in recent years, with opponents arguing it may pose risks to neurodevelopment.
Fluoride debate intensifies
The debate over fluoridating water was intensified when Robert F. Kennedy Jr., a vaccine skeptic favoured by U.S. president-elect Donald Trump to become his health secretary. Kennedy Jr. said in late 2024 that he plans to put an end to water fluoridation in the United States.
In Canada, fluoridation varies by region. Most communities in British Columbia, Newfoundland, and Quebec do not fluoridate their water, while the majority of Ontarians live in municipalities that do.
A U.S. National Toxicology Program review published in August concluded there is “moderate confidence” of a link between higher fluoride levels and lower IQ in children. This review primarily analyzed studies involving fluoride concentrations exceeding 1.5 mg/L—twice the recommended limit for drinking water in Canada and the U.S.
The report stated there was insufficient evidence to determine whether fluoride levels at the recommended limit of 0.7 mg/L negatively affect children’s IQ.
In September, a U.S. federal judge ordered the Environmental Protection Agency to further regulate fluoride in drinking water. The ruling acknowledged uncertainty regarding whether typical fluoridation levels cause lower IQ in children but emphasized research pointing to potential risks.
(With files from the Canadian Press)
