[BorgHunter]

Fluoride has two major differences that would complicate such a study: First, fluoride is a natural component of lots of drinking water (often at levels far higher than artificial fluoridation creates), while lead contamination in drinking water is rare and usually human-caused. Second, lead is known to be bad for one's health in any amount, while fluoride is only known to cause IQ drops above a certain dose.

You might find this meta-analysis interesting: https://jamanetwork.com/journals/jamapediatrics/fullarticle/... Part of that conclusion (note that water fluoridation in the US is recommended to a level of 0.7 mg/L):

> This systematic review and meta-analysis found inverse associations and a dose-response association between fluoride measurements in urine and drinking water and children’s IQ across the large multicountry epidemiological literature. There were limited data and uncertainty in the dose-response association between fluoride exposure and children’s IQ when fluoride exposure was estimated by drinking water alone at concentrations less than 1.5 mg/L.