Does fluoride lower your IQ?

Some controversial claims – that the world is flat, for instance, or that apricot kernels can cure cancer – are really easy to disprove. What happens, though, when a claim appears to have solid research behind it – by scientists from America’s prestigious Harvard University, no less? This is the case with fluoride in drinking water, a practice that has been going on for decades and has been repeatedly shown to reduce tooth decay in children and adults.

But some people believe fluoridation is dangerous – and try to have it stopped by spreading scare stories.

A very small group think it is downright evil, alleging that it was invented by Nazis, or the American government, or lizards from outer space, as a form of mind control, to turn us all into zombies. This is very easy to debunk. When was the last time you saw a zombie with nice teeth?

In recent times it has been claimed there is scientific evidence that fluoride in the water reduces the IQ of children, and that this has been “proved” by scientists from Harvard.

So, does fluoride in drinking water make you stupid, and did Harvard scientists say so? No, and no.

The study usually quoted by anti-fluoride activists dates from 2012. It was indeed written by Harvard scientists – a team led by Anna Choi, from the university’s Department of Environmental Health – and it does indeed say “the results support the possibility of an adverse effect of high fluoride exposure on children’s neurodevelopment”.

So that much is true, but to say this means your drinking water can make you dumb is wrong.  The anti-fluoride folk rely on two assumptions: that you won’t actually read the scientists’ paper; and that, if you do, you won’t understand it.

The key to the paper’s conclusion is the term “high fluoride exposure”. Choi’s team looked at previous studies that investigated if large amounts of fluoride were dangerous. Some of the studies involved sample sizes too small to be useful; but most of the other studies did find that large amounts of fluoride in water were toxic.

But this wasn’t really a surprise to anyone. Lots of substances that are good for you in small doses are really dangerous when you have a sackload: nutmeg, for instance, or salt, or even water.

The studies looked at by Choi and her team concerned parts of the world – Iran and China, mostly – where natural fluoride levels in the water were extremely high, sometimes up to 10 or 11 milligrams per litre.

Fluoride levels in ordinary drinking water are about 1 milligram per litre in Australia, and between 0.7 to 2 milligrams per litre in the US. These levels are way below the US Environmental Protection Authority’s maximum safe limit of 4 milligrams per litre.

Indeed, study after study has found that 1 to 2 milligrams per litre fluoride in the water is not only safe but good for you – assuming you’d like to avoid fillings and extractions as much as possible.

So the next time you hear that the fluoride in your tap water is rotting your brain and was probably put there by extraterrestrial lizards, you can safely ignore it.

Except for the lizards bit. Lizards from space would be a real problem.