For decades, water fluoridation has played a key role in improving the oral health of North Americans, experts say, but the practice is coming under scrutiny in some communities as opponents gain new prominence in the U.S., pointing to research that cautions about the risks of exposure to the mineral in high doses.
A low level of fluoride has been added to tap water in parts of Canada and the U.S. since the 1940s to help reduce tooth decay and cavities.
It varies by region and municipality – most British Columbia, Newfoundland and Quebec communities, for instance, do not fluoridate water, while the majority of Ontarians live in places where water is fluoridated.
Recently, opponents have questioned the science that supports this practice, including U.S. president-elect Donald Trump’s pick for health secretary, Robert F. Kennedy Jr., who says he plans to put an end to water fluoridation in the United States.
Here's what you need to know about where Canadian communities and researchers stand on the issue:
WHAT ARE THE BENEFITS?
Health Canada, the Canadian Dental Association and the Canadian Medical Association say decades of scientific evidence shows fluoridating water has dental-health benefits, particularly for people who don't have the means to go to the dentist or brush their teeth.
Fluoride, a mineral naturally present in soil and water, strengthens tooth enameland can prevent tooth decay, which is the most common childhood chronic disease in Canada and around the world, according to Health Canada and the World Health Organization.
The Ontario Dental Association says water fluoride can reduce tooth decay in children’s primary teeth by up to 60 per cent, and in their permanent teeth by up to 35 per cent. Adults with a lifelong exposure to water fluoridation can see a 20 to 40 per cent reduction in tooth decay.
A University of Calgary study published in 2021 compared the dental health of children in Calgary and Edmonton over a seven-year period. Calgary stopped fluoridating its water supply in 2011 and Edmonton has kept doing it.
Researchers found “significantly” more cavities in the Calgary kids – 64.8 per cent compared to 55.1 per cent in Edmonton.
In 2021 Calgary voted in favour of reintroducing fluoride to its water supply, and it's expected to resume in 2025.
WHAT DO WE KNOW ABOUT THE RISKS?
A U.S. National Toxicology Program review of scientific literature published in August concluded with “moderate confidence” that there is a link between higher fluoride levels and lower IQ in children.
The review only included studies involving fluoride levels at about twice the recommended limit for drinking water, containing more than 1.5 milligrams of fluoride per litre.
The report says that there was "insufficient data" to determine if the low fluoride level of 0.7 mg/L that is currently recommended in Canada and the U.S. has a negative effect on children’s IQ.
The U.S. Environmental Protection Agency was ordered in September to further regulate fluoride in drinking water. A federal judge ruled that while it's not certain the amount of fluoride typically added to water is causing lower IQ in kids, some research points to a risk that it could be.
York University research published in JAMA Pediatrics in 2019 associated fluoride exposure during pregnancy to lower IQ scores in children.
The study used information from a Health Canada database on maternal-infant exposure to environmental chemicals. Researchers analyzed fluoride in pregnant women's urine samples, and then their children's IQ levels between the ages of three and four. They found an increase of one milligram of fluoride in pregnant women was associated with a decrease of 3.7 IQ points in children.
None of the mothers were drinking more than the recommended level of fluoride in their tap water. Christine Till, one of the study's authors, said the urine samples could have captured other sources of fluoride consumed, such as black tea or toothpaste.
“Now that's just one study. I always say we need to look at the totality of the evidence when we're talking about this topic,” Till, also a clinical neuropsychologist and professor of psychology at York University, said.
A similar study in the U.S., published in JAMA in 2024, also found prenatal fluoride exposure may increase risk of neurobehavioral problems in children.
“Adding fluoride to water should only be considered if scientific evidence clearly demonstrates substantial benefit accompanied by minimal risk. And I will leave it up to the policymakers to determine that risk-benefit for a particular community,” Till said. She continues to study this subject, recently researching fluoride exposure and maternal thyroid hormone levels. Juliet Guichon, a professor at the University of Calgary’s Cumming School of Medicine, co-authored a critique of the study in the journal Community Dentistry and Oral Epidemiology. See more on our website
