Should Windsor close the tap on fluoridation?

We’re not positively sure flouride helps prevent caries. But there’s no evidence at all it causes cancer.

Nothing showcases the human potential for creativity better than conspiracy theories. A search of “fluoridation” on YouTube gives a pretty good sense of the fantastically diverse views of anti-fluoridation campaigners, some of whom believe that adding more of the mineral to the water supply is akin to Nazi-inspired mass medication–and that it can cause all kinds of afflictions, from cancer to hip fractures and a diminished IQ.

A few cities across Canada (most recently Windsor) and the U.S. have been moving to phase out fluoridation. This, in turn, has spurred some commentators to squawk in dismay and defer to authorities like the U.S. Centers for Disease Control and Prevention, which touted fluoridation as “one of the 10 great public health achievements of the 20th century.”

Now, as much Science-ish likes to bust a dubious conspiracy theory, it also doesn’t like to rely on  authority alone to draw conclusions. So what does the science show?

The best-available study remains a systematic review of water fluoridation, published in the British Medical Journal in 2000. (There are some U.K. researchers working on an update of this review as you read this.) According to this synthesis of 214 studies, water fluoridation was associated with a reduction in dental caries as well as fluorosis—or mottled teeth—which is mostly an aesthetic concern. Importantly, the review found no adverse effects related to fluoridation.

Still, the researchers called for better evidence. “Given the level of interest surrounding the issue of public water fluoridation, it is surprising to find that little high quality research has been undertaken.” Estimates of the increase in the proportion of children without dental caries in fluoridated versus non-fluoridated areas varied widely: from five to 22 percent with a median difference of 15 per cent.

A more recent overview of the policy issues around fluoridation, published in the BMJ in 2010, similarly noted that there is little sound research in this area, particularly as it relates to one of fluoridation’s great promises: that it’s a social equalizer. “Water fluoridation aims to reduce social inequalities in dental health but few relevant studies exist. The quality of research was even lower than that assessing overall effects of fluoridation.”

Dr. Paul Wilson, a research fellow at the University of York and one of the authors on the 2000 systematic review, shared his views with Science-ish. What he had to say wasn’t very reassuring. “From the available evidence, it’s not possible to make confident statements about the extent to which water fluoridation may reduce the prevalence of tooth decay in children and adults.” He pointed out that what policymakers chose to do with the evidence “is really not for me to say but for local jurisdictions to decide for themselves about whether the available evidence is sufficient to justify a population-wide intervention.”

To get a better understanding of the delicate balancing act public health officials must make, Science-ish called Dr. David Mowat, medical officer at Peel Public Health, which made the unanimous decision last April to continue fluoridating the water supply. He reiterated Dr. Wilson’s point. “Putting aside massive amounts of allegations that aren’t based on evidence at all about the adverse effects of fluoride—cancer, hip fractures—the nub of the matter is really a policy decision based on values around risks and benefits, the benefit being a reduction in caries.”

The best medical officers can do, he added, is make policy decisions based on the best available evidence. This can be tricky with public health matters. Unlike drug trials, “there are no double-blind controlled trials (the gold standard of evidence) of fluoridation. When you’re talking about public health measures, that’s rarely achievable. With that standard, we would have to close down public health entirely. There would not be anything we do that would meet that standard, with the exception of giving vaccines.”

So while this dearth of high-quality evidence on fluoridation could be seen as ammunition to quit treating the local water supply, medical officers may read it another way. Like concerns over WiFi and cell phones, the weight of evidence shows no adverse effects, and, in the case of fluoridation, actual health gains. So though the science isn’t conclusive—leaving room for creative interpretations and conspiracy theories—at least in Canada, most jurisdictions have ruled that the benefits of fluoridation outweigh the harms. 

Science-ish is a joint project of Maclean’s, The Medical Post, and the McMaster Health Forum. Julia Belluz is the associate editor at The Medical Post. Got a tip? Seen something that’s Science-ish? Message her at [email protected] or on Twitter @juliaoftoronto