Actually one of the bigger recent studies that showed IQ decrease with increasing fluoride levels was done in China using Han Chinese.
"Han" Chinese are not homogeneous on a DNA level, which is what you'd expect of a continental-sized nation with a record of conquering and absorbing hundreds of kingdoms speaking thousands of languages many of which are extinct today. If this blogger is to be believed, the Chinese studies related to fluoride poisoning due to groundwater pollution that added toxic amounts to water systems, not the addition of fluoride to municipal water systems for dental hygiene purposes. I'm highly skeptical of anti-fluoride material, mainly because the countries that have adopted fluoridation (Singapore, Hong Kong, Brazil, Chile, Australia, New Zealand) are uniformly in the top half of the per capita income scale whereas those that have not run the gamut from the EU (which bans all kinds of American agricultural products due to scientistic superstitions that also extend to man-made global warming) to North Korea.