Fluoride, a chemical commonly added to drinking water in many countries, has recently become a topic of debate in the US.

Recently appointed US health secretary Robert F. Kennedy Jr has said that he wants to remove fluoride from water supplies.

This is despite the Centre for Disease Control in the US, the World Health Organisation and the EU all advocating in favour of fluoride.

Prof Luke O’Neill told the Show Me The Science podcast that this statement from Mr Kennedy has upset many dentists, who say fluoride helps to prevent tooth decay.

“Many plants have fluoride in them, and some of the fluoride in plants leaches out into the water,” he said.

“What they’ve been doing really is adding a little bit of extra fluoride – I guess early on, they noticed scientifically that areas where there was more fluoride naturally, there was less tooth decay.

“Now, this is over 100 years ago, that’s when it began, and that’s when the evidence began to build up that adding fluoride might be a good thing.”

Prof O'Neill said that while fluoride can be harmful if ingested in large quantities, the amount added to drinking water is far too small to do any damage.

Human skeleton jaw bone.

Prof O’Neill also said that science has further proved that fluoride can prevent gum disease by protecting teeth from bacteria.

“It turns out that fluoride will form again a natural derivative of fluoride, if you will – it's called fluorapatite,” he said.

“Now, fluorapatite goes into your enamel in your teeth, and what does fluorapatite do? It makes the teeth much stronger.

“So fluoride in the water will correlate and actually mechanistically make teeth stronger, and the enamel becomes much more resistant to bacteria.

“Of course, the big cause of gum disease and tooth decay are bacteria in your teeth, and the bacteria eat into the teeth and infect them and cause decay, and fluorapatite is like a barrier against teeth.”

Scientific evidence

According to Prof O’Neill, Mr Kennedy’s reasons for wanting fluoride to be removed from water supplies are not based on any scientific evidence.

“He said there’s a link of fluoride in the water to things like osteoporosis, which is when your bones kind of wear away... and really disturbingly, he said IQ,” he said.

“He said high fluoride means lower IQ – none of this is true at the level of fluoride that we see in drinking water.

“Very high levels, as I say, can cause a bit of damage to bones – but it’s not true that levels in drinking water would do that.

“Especially the IQ one, there was never any evidence for that.”

Prof O’Neill said the US's national toxicology programme has made it clear that the current fluoride limit is safe.

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