Alerts and Reactions

"There are some pretty bizarre theories out there, such as the idea that fluoride is being used to sedate the population."
"I worry that this study -- which the authors note should be replicated, and they call for further analysis and research -- will be presented as definitive. It is not."
Tim Caulfield, health policy researcher, University of Alberta

"[In Mexico], not many people drink tap water. [Intake of fluorides takes place through fluoridation of salt.]"
"[Still], the urinary fluoride levels of these [Mexican] women were definitely not sky high."
"There still may be a level of fluoride exposure among both pregnant women and everybody else that can still preserve the beneficial effects on tooth decay, while avoiding any effects on intelligence [in the developing fetus]." 
"This is a very rigorous epidemiology study. You just can't deny it. It's directly related to whether fluoride is a risk for the neurodevelopment of children. So, to say it has no relevance to the folks in the U.S. seems disingenuous."
Dr. Howard Hu, principal investigator, dean, Dalla Lana School of Public Health, Toronto

"[The study's findings] are not applicable [to the United States] because it's not known how the subjects of the study ingested the fluoride -- whether through salt, water or both -- no conclusions can be drawn regarding the effects of community water fluoridation in the U.S."
American Dental Association statement

U of T research

Fierce debate over the safety of water fluoridation – particularly for children’s developing brains – has fuelled researchers to explore the issue and provide evidence to inform national drinking water standards (photo by Gullherme Jofill via Flickr)

Since fluoridation of the public potable water supply became a staple health intervention many decades ago when research showed that fluoride was hugely effective in protecting against dental caries, there have been reactions from the public, claiming that general fluoridation had deleterious effects, and some municipalities, sensitive to public criticism, have taken steps to reverse the procedure, no longer fluoridating the water supply in their jurisdictions.

Across Canada most cities remain devoted to fluoridation; Ottawa, Edmonton and Toronto, for example. In other cities, such as Calgary, Waterloo and Windsor, fluoridation is no longer used in those municipalities' systems. Opponents of fluoridation allow their imaginations to run amok, claiming among other things that fluoridation is responsible for an proliferation of heart disease, cancer, birth defects, kidney problems, goiters, ulcers, anemia and spontaneous abortions.

"However, these associations are not supported by the scientific literature", researchers from the University of Guelph concluded in a 2014 evidence review under the imprimatur of the National Collaborating Centre for Environmental Health. Now, however, with the publication of the first study of its kind and size to explore the issue of fluoride exposure and its effects on stages of brain development by researchers from the University of Toronto, the issue has been brought back to life.

Data from 287 mother-child pairs in Mexico City were analyzed by the Toronto researchers from 1994 to 2005 when pregnant women were recruited for a study that took in their children as well at ages six to twelve. Levels of fluoride in urine were examined to find how children were seen to score on intelligence and neurocognitive function tests at age four and then once more between ages six and twelve. For every 0.5 milligrams-per-litre increase in mother's urinary fluoride levels beyond 0.8 mg/l, children scored 2.5 to three points lower on IQ tests.

That the children's own urinary fluoride levels measured at the times of testing, appeared not to register a significant effect, appeared to suggest that whatever effect fluoride could have on brain development occurred while in the womb. Most fluoride exposure in both Canada and the United States results from drinking water being fluoridated in the prevention of cavities, as well as fluoride manufactured right into toothpaste.

There were adjustments made in reaching conclusions based on association, inclusive of the baby's weight at birth, whether the mother smoked, intelligence quotient, socioeconomic conditions, and possible exposure to lead. The Mexican study verified that the mothers on average had 0.90 milligrams-per-litre of fluoride in their urine, a number considered to represent the "general range of exposures" comparable to other populations.

On the other hand, a 2012-2013 survey taken in Canada pointed out mean urinary fluoride levels were roughly 0.43 milligrams-per-litre, representing about 50 percent of the Mexican levels. The Toronto research team took pains to emphasize that their findings, while important, require confirmation in similar studies of other populations. According to Dr. Hu, direct comparisons with women in the United States or Canada face difficulties, reflecting the fact that there have been no large population studies of maternal urinary fluoride loads.

In Canada and the U.S., most fluoride exposure comes from the fluoridation of drinking water to prevent cavities, and fluoride in toothpaste and other dental products.  Getty Images