Anti-fluoridation activists call it ‘the biggest moment in the history of this whole debate.’ It’s the response health policy experts — and some of the authors themselves — feared
Already there are people who claim fluoridated water is doing bad things to us. Now comes a new study suggesting a link between fluoride exposure in pregnancy and lower IQs in children.
Anti-fluoridation activists are calling it “the biggest moment in the history of this whole debate” and that any government that continues to add fluoride to tap water is condoning “one huge, awful human experiment.”
It’s exactly the response health policy experts — and some of the authors themselves — feared.
“There are some pretty bizarre theories out there, such as the idea that fluoride is being used to sedate the population,” said University of Alberta health policy researcher Tim Caulfield.
“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.”
In what is being described as the first study of its kind and size exploring fluoride exposure and different stages of brain development, University of Toronto-led researchers analyzed data from 287 mother-child pairs in Mexico City. The study recruited pregnant women from 1994 to 2005, and has followed the women and their children since.
The researchers measured fluoride in archived urine samples taken from the women when they were pregnant, as well as from their children when they were between ages six and 12.
Next they looked at how levels of fluoride in urine related to how children scored on intelligence and neurocognitive function tests when they were four, and again when they were between six and 12.
Children scored 2.5 to three points lower on IQ tests for every 0.5 milligram-per-litre increase in their mother’s urinary fluoride levels beyond 0.8 mg/L.
There was no clear association between IQ scores and values below 0.8 mg/L. As well, the children’s own urinary fluoride levels, measured when they were being tested, didn’t seem to have a significant effect.
That suggests that whatever effect fluoride might have on brain development occurs in the womb.
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.
In Mexico, “not many people drink tap water,” said Dr. Howard Hu, the study’s principal investigator and founding dean of the University of Toronto’s Dalla Lana School of Public Health. Instead, the women were exposed to fluoridated salt. In 1991, that country became the seventh in the world to introduce a national salt fluoridation program to prevent cavities.
The researchers adjusted for numerous “confounders,” including the baby’s birth weight, the mother’s smoking history, IQ, socioeconomic status and lead exposure.
The Mexican mothers had, on average, 0.90 milligrams per litre of fluoride in their stored urine, which the researchers said is in the “general range of exposures” reported for other populations.
According to Hu, one 2012-2013 survey showed the mean urinary fluoride levels for Canadians were about 0.43 milligrams per litre, about half the Mexican levels.
Still, “the urinary fluoride levels of these (Mexican) women were definitely not sky high,” Hu said.
However, the findings may mean that “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,” Hu said.
The paper adds to studies that have been trickling out of China hinting that fluoride may be neurotoxic to children exposed to exceptionally high levels of fluoridated water. Rat studies have shown fluoride can accumulate in rat brain tissue after chronic exposure to high levels, Hu and his colleagues from the National Institute of Public Health of Mexico, University of Michigan, McGill University, Indiana University, Mount Sinai School of Medicine and Harvard School of Public Health write in the journal, Environmental Health Perspectives. A 2006 report by the U.S. National Research Council, meanwhile, also cited experimental and epidemiological evidence that fluoride may retard neurodevelopment.
“It’s clear from human studies that fluoride can cross the human placenta without a problem,” Hu said, adding that animal studies suggest it collects in the hippocampus, important for learning and memory.
The team cautions their findings need to be confirmed in other populations. And Hu said it’s hard to make direct comparisons with women in the U.S. or Canada, where there haven’t been large population studies of maternal urinary fluoride levels.
But he said the study raises a red flag. “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.”
In a statement, the American Dental Association said the findings “are not applicable” to the U.S. “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.,” the ADA said, adding that more than seven decades of research have shown fluoridation is safe and helps prevents cavities.
Across Canada, where fluoride was first added to public drinking water in the 1940s, numerous cities, including Ottawa, Edmonton and Toronto, still fluoridate their water in keeping with guidelines from Health Canada. Others like Calgary, Waterloo and Windsor have been taking it out.
Opponents claim fluoridation causes, among other things, heart disease, cancer, birth defects, kidney problems, goiters, ulcers, anemia and spontaneous abortion. “However, these associations are not supported by the scientific literature,” University of Guelph researchers wrote in a 2014 evidence review for the National Collaborating Centre for Environmental Health.
Paul Connett begs to differ. “Why would anybody rate the equivalency or supremacy of reducing tooth decay by about one cavity a lifetime when what’s at stake is the mental development of your children? It’s utterly preposterous,” said Connett, executive director of the Fluoride Action Network.
Excess amounts of fluoride can cause dental fluorosis, which causes teeth staining and pitting. “You can see it with the naked eye,” Connett said. “What we’ve also said is, what’s happening to the developing baby’s tissues? What is happening to the brain, the thyroid? Now we’ve got the evidence. It says you are lowering the IQ of your children.”
The paper concludes no such thing, the University of Alberta’s Caulfield argues: it’s just a correlation, not a cause of effect.
Hu said the research team, and the paper’s publisher, expected the findings would stoke the fluoride debate. “We’re going to stay out of that policy question. We prefer to just stick to the science,” he said.
But he gets the controversy.
“If you just Google ‘fluoride’ and ‘water,’ you’ll see lots of public health agencies saying this is really important for dental health and that the science suggesting it’s a problem is weak,” Hu said.
“But then there are these anti-fluoridation groups that say these are Nazis trying to kill us, and they’re denying the evidence and fluoride is just another of the various poisons that governments are subjecting us to without regard for our children.”
However, he said the science base for fluoride having an impact on health such as neurodevelopment at the levels of exposure seen with fluoridated water in the U.S. and Canada has been weak and spotty.
“Naturally it’s controversial, because anything that involves government making a decision for you — ‘I’m going to put fluoride in your water whether you like it or not’ — is so antithetical to a lot of what Americans believe,” Hu said.
“I think in the U.S. in particular there has been a very loud feeling that there’s some evidence it may not be the best thing.”