Fluoride again!
Don't tell me! The aluminium industry's not making enough money again, and needs help in getting rid of a poisonous waste product in addition to its Government subsidy.
It's exceedingly difficult to do a controlled experiment with human beings, but one of the nearest approaches ever made was the Napier/Hastings twin city scenario in about the 1960s. One with its water containing fluoride, the other not.
The fact that the un-fluoridated one showed the best results was recorded in this excellent newspaper, along with some lame excuse about the presence of Molibdenum in its soil.
I've been wondering ever since when someone was going to advocate "molybdenising" water. But then, of course, that isn't somebody's industrial waste.