Fluoride Action Network

Water Fluoridation & the Quality of Evidence Problem

Fluoride Action Network | August 2012

Advocates of fluoridating water often state that there are “thousands” of studies that prove fluoridation to be both safe and effective. In 2000, however, a systematic review of the literature commissioned by the British Government (“York Review”) found that, under current standards for what constitutes good medical evidence, there has not yet been a single high-quality study demonstrating fluoridation’s benefits — despite over 50 years of fluoridating water.

Notably, the York Review found that there was not a single “randomized controlled trial” (RCT) demonstrating water fluoridation’s safety or effectiveness. As the York Review noted, an RCT is “the gold standard” for proving the safety and effectiveness of a medical treatment. Even more striking, the York Review found that there had yet to be a single study on fluoridation’s alleged benefits to teeth that had ever “addressed three or more confounding factors.”

As the York Review noted:

“No randomised controlled trials of the effects of water fluoridation were found. . . . None of the included studies were of evidence level A. The reason for this among the studies evaluating dental caries was that none addressed three or more confounding factors.”

Subsequent to releasing its report, the York Review committee issued a statement to correct common misunderstandings of the report’s findings. According to the statement:“We were unable to discover any reliable good-quality evidence in the fluoridation literature world-wide.”

Sir Iain Chalmers, a scientist who served on the advisory board of the York Review, summarized the quality of evidence proving fluoridation’s safety and effectiveness as follows:

“The quality of evidence for topical fluoride is in a different league from the evidence for water fluoridation. I mean, absolutely no question about that. The evidence on topical fluoride has been generated from randomized controlled trials, many of them, I think it’s well over 50, for example, just for toothpaste, let alone the varnishes and other things which can be used. So, those studies are, as I say, in a different league from the studies on water fluoridation. As far as the York team were able to determine, there are no randomized controlled trials for water fluoridation. It’s not that they couldn’t have been done. Of course they could have been done. But there are none.”

In 2007, Chalmers co-authored a 2007 review on fluoridation in the British Medical Journal. In the review, Chalmers and colleagues summarized the York Review’s findings as follows:

“Given the certainty with which water fluoridation has been promoted and opposed, and the large number (around 3200) of research papers identified, the reviewers were surprised by the poor quality of the evidence and the uncertainty surrounding the beneficial and adverse effects of fluoridation. Studies that met the minimal quality threshold indicated that water fluoridation reduced the prevalence of caries but that the size of the effect was uncertain. Estimates of the increase in the proportion of children without caries in fluoridated areas versus nonfluoridated areas varied (median 15%, interquartile range 5% to 22%). These estimates could be biased, however, because potential confounders were poorly adjusted for. 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.”
SOURCE: Cheng KK, et al. (2007). Adding fluoride to water supplies. British Medical Journal 335:699-702.