Anti-fluoride campaigners say that our water is being poisoned by a toxic and dangerous chemical. Ignorant or downright scheming scientists and journalists are causing significant harm to public health while a largely compliant public – the “sheeple” who do what they are told – are being misled.

Earlier this month, the campaigners scored a major victory when Dublin city councillors voted in favour of removing fluoride from Ireland’s public water supplies. It’s the second council to do so, following Cork city’s lead last March.

Do the anti-fluoridation arguments hold water? No. The science is clear: decades of research and verifiable evidence say that fluoride at low concentrations has no ill-effects on human health. Dentists say that it is a public health initiative that helps save people, especially children and those on lower incomes, from tooth decay (see panel).

Effectively, the anti-fluoridation campaign is communicating a form of contemporary folklore, says Dr Billy Mag Fhloinn, a lecturer in Irish folklore at the University of Limerick. And, ironically, it is likely that technologies such as Google and Facebook are reinforcing these folkloric beliefs.

Much of the anti-fluoridation narrative takes the form of perceived folk wisdom, belief statements, rumour and conspiracy theory. According to one conspiracy theory, fluoride is being dumped in the water as a cheap industrial disposal method; another claims that it is a plot to keep the population docile.

These stories are “metanarratives”, says Mag Fhloinn, that express particular worldviews and thought patterns. “Conspiracy theory is structurally similar to traditional mythology, although anti-fluoride lore is not sacred and lacks deities.

“Believers are often personally offended by opposition from science. Most anti-fluoridation campaigners believe and express the view that the overwhelming majority of scientists are are, at best, misguided; at worst, part of a dark scheme. This, like mythology, has explanatory power; every fact that seems to rebut the conspiracy is then seen as a tool of the conspiracy or a failure by the ‘sheeple’ to understand.”

Accelerated panic

Believing that fluoride is dangerous is not completely irrational, says Mag Fhloinn. “People have genuine fears for themselves and for their children, and there’s a distrust of government and the pharmaceutical industry, especially in the United States, where much of the anti-fluoride campaigns and lore flourishes.

“That said, there’s a lack of understanding that chemicals and compounds which will kill you at high doses, including Vitamin A, are, at low doses, necessary for good health.

“Stories and moral panics once spread through word of mouth and literature. Now they move at rapid speed through social media. We’re only beginning to understand the impact this has. People aren’t necessarily being irrational; they feel they have a logic to their beliefs. But they are being unscientific. We live in a scientific world, and perhaps to survive, we need to understand science.”

Confirmation bias

Dr Frank Doyle is a senior lecturer in psychology at the Royal College of Surgeons in Ireland. “We are all susceptible to confirmatory bias – only paying attention to evidence which fits in with our current beliefs. Nowadays, this could be even more problematic, as Facebook and Google have algorithms to show what they think you are more interested in, meaning that you are less exposed to ideas you don’t agree with.”

In practice, this means that people who oppose fluoridation or vaccines are more likely to be shown pages that confirm their worldviews purely because they have previously interacted with such pages or comparable search results.

Last year, research by Prof Stephen Lewandowsky, a psychologist at the University of Bristol, found a strong correlation between belief in conspiracy theories and the rejection of science. But should these beliefs influence health policy?

Dr David Robert Grimes, a physicist and cancer researcher, wrote to every member of Dublin City Council before the vote, saying: “It is scientific bodies like [the World Health Organisation and Irish dentists], and the decades of peer-reviewed science upon which their conclusions are based, that should be underpinning your decision.

“Otherwise, you’re giving a public statement that you’re willing to let angel-healing, anti-vaccine activists [a description that applies to at least one of Ireland’s leading anti-fluoridation campaigners] dictate health policy and that cynical populism trumps the health of your electorate.”

Several Labour Party, Fine Gael and Fianna Fáil councillors responded to express support for water fluoridation. Nobody from Sinn Féin, whose councillors led the anti-fluoride motion, engaged with Grimes.

“Some people are so ideologically married to a certain position that their conviction is hard to change,” says Grimes. “The evidence is disregarded. The data is disputed. The media feels a need for false balance: they try to be fair and so give credence to beliefs that don’t deserve any credibility and have no reliable evidence. Very few people have the time and luxury to dig into science data, and journal access is limited. Conspiracy makes you feel like you have a sense of superior knowledge.”

Grimes says that some people are entrenched in their positions. However, he believes that most people can be reached by presenting the evidence and being encouraged to decide for themselves.

“Those who post online and write angry emails are not the majority.”

FLUORIDE FINDINGS: PEER-REVIEWED DATA

Individual studies in science should be treated with caution. But meta-analyses, or studies of studies, can give a wider picture of peer-reviewed science compiled over decades.

Cochrane Review meta-analyses are internationally recognised as the gold standard in evidence-based medicine. In 2000, a review of 214 scientific studies found that fluoridation was associated with a reduction in dental decay and that there was no evidence of adverse potential effects.

Based on numerous studies and meta-analyses, the US Centers for Disease Control says that water fluoridation is one of the top ten public health interventions of the 20th century. The American Dental Association says it is safe, effective and necessary to prevent tooth decay.

The Irish Dental Association recognises that fluoridation is contentious but says evidence shows it is “the most practical, cost-effective and safe public health measure to control the occurrence of tooth decay in Ireland . . . [we] recommend that policymakers be guided by high-quality, peer-reviewed evidence.”