Challenging Research

"[It's possible some] mystery variable [is related to both fluoride and IQ, but we controlled for everything we could think of]."
"Four-and-a-half IQ points is not negligible. People have been calling this a small effect. I'm shocked. [The effect on IQ] of lead exposure is of this magnitude. It's a big deal."
"The impact is going to be felt -- it means fewer people in the gifted [IQ] range and more people falling in the range of intellectual disability."
Dr.Christine Till, professor of psychology, York University

"[The size of the sample was reasonable and the study is] methodologically sound [making an important contribution]."
"Public policy is ideally informed not by any one study, but by the best available evidence as a whole."
Dr.Lindsay McLaren, community health sciences professor, University of Calgary

"What we know about the effects of lead on IQ doesn't come from one study. It is ... based on a far larger set of research findings that extend over many more populations and many more years."
"At the end of the day, it is still one study. Although I like a lot of what was done in this particular paper, at the end of the day, you're left scratching your head -- why aren't the results internally consistent?"
"I've had that discussion with many, many colleagues, in many different research areas, over many years. And my advice to them is: I'm with you on the research. It's really neat stuff ... but the policy-makers have to consider far more than just one paper. And some of my research colleagues get that more than others. For some, it's a really tough sell."
Dr.Ray Copes, chief of environmental and occupational health, Public Health Ontario

Despite the benefits, adding fluoride to tap water will always be contentious, a chemistry professor says. (Craig Chivers/CBC)

Several generations ago fluoride was being introduced for the first time to drinking water in Canadian jurisdictions. Some municipalities started using fluoride in 1945. Medical science argued for its use in reducing cavities in children. Fluoride strengthens teeth, helping in the prevention of bacterial decay, as a mineral that binds to teeth.

Public health, medical and dental groups all recommended fluoridation of community water, among them the Canadian and American Dental Associations, the Chief Dental Officer of Canada, the World Health Organization. Its contribution to cavity decline in children saw the U.S. Centers for Disease Control and Prevention naming it one of the  ten great public health achievements of the 20th Century.

From the very beginning right to the present time some in the scientific community and in municipal leadership have called its usefulness into question, citing the possibility that the use of fluoride led to other health problems. Some municipalities ceased using fluoride, the result of which saw a dramatic rise in cavities among children living there. Fluoride's qualities as a cavity preventive are lauded. And fears of its possible darker side are cited by opponents.

A new study led by York University's Christine Till -- published in the journal JamaPediatrics -- found what the researchers believe to be a link between fluoride exposure in drinking water during pregnancy and the eventuality of lower IQs in children. On publication, the study and its conclusions caused an international stir, leaving Dr. Till professing "shock" at the way the study has been received.

Fluoride has been one of the most positive public health interventions in human history, public health experts say.

Levels of fluoride in some 500 pregnant women's urine was measured for the study on three occasions during pregnancy. Self-reported information on individuals' consumption of tap water and black tea -- known to be naturally high in fluoride -- was collected. The women's children's IQs were tested -- once -- at ages three or four. Self-reported fluoride was then associated with lower IQs both in girls and boys.

Only in boys, however, was urinary fluoride concentration associated with lower IQ. A drop of 4.5 IQ points was found for every one milligram-per-litre increase in urine fluoride. A variety of other factors including economic status, parents' education, exposure to other environmental chemicals that could account for IQ differences was controlled for in the study.

Given that the research was subject to "review after review after review" prior to funding, then underwent extensive scrutiny during peer review, the authors going so far as to hire a third-party statistician to look over the numbers to ensure everything was in order, the study is considered to be the largest, most rigorous of its kind to have been conducted to date.

Routine since the mid-20th Century across Canada, fluoride added to drinking water helps in tooth enamel strengthening; its beneficial role in cavity reduction unquestioned. Other studies indicate that those who benefit the most from fluoride use in drinking water are those with poor oral health and compromised access to dentistry.

Dr. Copes at Public Health Ontario is perplexed by the observed sex differences in the study. An indication, he feels, that the use of different research methods might be indicated, along with replication of research conducted by other researchers prior to informing pregnant women they are advised to limit fluoride consumption. His position on the other hand, puzzles Dr. Till who believes ample evidence exists to inform pregnant women to limit their fluoride exposure immediately.

Ayesha Drouillard in her home in Windsor on Friday, February 17, 2012. Drouillard was hoping to push city officials to remove fluoride from the drinking water in Windsor.