A long-term US study shows water fluoridation at recommended levels doesn't reduce cognitive ability.

The 40-year study found children who drank such water did slightly better in school tests.

By 60, that edge was insignificant, but fluoride didn't contribute to cognitive decline.

Dentist Justin Wall says this puts this particular argument to bed - but theories about fluoride are bound to continue.

"People would probably blame fluoride for mullet haircuts and not getting the Lotto numbers right if they could. But at the end of the day, fluoride is very highly researched."

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