Cosmos - - Contents - — AN­DREW MASTER­SON

— Does flu­o­ride in wa­ter 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 2012.1 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.

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