Tap water across America has, for decades, been fortified with fluoride, a negatively charged ion of the chemical element fluorine, in order to strengthen the public’s teeth. But a scientific review published in 2024 by America’s National Toxicology Programme, an arm of the country’s health department, suggested that high levels of fluoride are associated with lower IQ in children.
Even though no conclusive causal link has been found, a growing number of cities are planning to end fluoridation, and specialised water filters, which remove any fluoride present, are flying off the shelves. Public-health experts caution that the evidence of harm is thin, and fluoridated tap water keeps teeth healthy. But is it really necessary?
One of fluoride’s main functions is to strengthen and restore enamel, the top layer of teeth. This is vital to help them resist the acids that form in the mouth when bacteria ferment the sugars in food and drink. Coating or bathing the teeth in fluoride-rich substances can thus directly protect the teeth while also introducing fluoride into the saliva. This has additional health benefits, as fluoride in saliva inhibits bacterial metabolism, reducing acid production and the growth of plaque on tooth surfaces. Fluoride can also be effective when swallowed, making its way to the saliva via the bloodstream. (In children, circulating fluoride also enters the enamel of developing teeth.)
Trace amounts of fluoride are naturally present in a variety of foods, including vegetables and shellfish. Higher quantities can be found in tea and coffee, whose plants readily absorb fluoride from soil. A cup of tea made with distilled water contains as much fluoride as anywhere between 100ml and two litres of fluoridated water, depending on a range of factors including the variety of tea and composition of the soil where the leaves were grown; a cup of brewed coffee prepared in the same way contains as much as 300ml of fluoridated water. Toothpastes, mouth washes and fluoride gels are also rich in the stuff.
Of all the ways of getting fluoride to teeth, brushing reigns supreme. Effective tooth-brushing means some of the fluoride present in toothpaste gets deposited directly onto the enamel, some ends up in saliva and some is swallowed. The resulting boost in fluoride levels far exceeds that produced by drinking fluoridated water.
In a report published in 2006, America’s National Research Council estimated the typical amounts of fluoride ingested daily from tooth-brushing across different segments of the population. The Economist calculates that, for six- to 12-year-olds, the figure is equivalent to somewhere between 300ml and 450ml of water fluoridated to the national standard. For toddlers and young children it is between 150ml and 300ml; for adults it is around 150ml.
Fluoride mouth washes, as well as the fluoride-rich gels and varnishes that dentists apply to teeth, also offer big fluoride boosts, but are used less often. An evidence review conducted in Britain in 2004 found that they offer only modest additional protection to those already regularly brushing their teeth.
In this environment, fluoridated water still has a place. In a country the size of America, tooth-brushing and access to dental care differ widely even between adjacent neighbourhoods. For the sake of those without good dental hygiene and, therefore, who are most at risk of tooth decay, this safety-net should be dismantled with caution.■
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