[oaktrout]

My first sentence in my original post was " The conclusion from the largest and strongest studies is that there is a certain level of fluoride that harms IQ." I did not move the goal posts from there.

I was replying to a comment that said "fluoride in the drinking water concentrations is proven safe" (there is actually no proof of this).

I never claimed that all fluoride levels harm IQ.

It's great that the US recommends that fluoride doesn't exceed levels that are proven to harm children's IQ, instead they only recommend levels for which there is "insufficient data".

I suppose we will ignore the people who are still drinking water with levels above what is known to be harmful.

[jakelazaroff]

To be clear, about whom exactly are we talking here? Who are the actual people drinking water with known harmful levels of fluoride that we’re ignoring?

[newtonsmethod]

If we take the known harmful level of fluoride as being >1.5mg/L then the NTP monograph itself has some information ():

> areas including central Australia, eastern Brazil, sub-Saharan Africa, the southern Arabian Peninsula, south and east Asia, and western North America (Podgorski and Berg 2022). Regions of the United States where CWS and private wells contain natural fluoride concentrations of more than 1.5 mg/L serve over 2.9 million U.S. residents (Hefferon et al. 2024). The U.S. Geological Survey estimates that 172,000 U.S. residents are served by domestic wells that exceed EPA’s enforceable standard of 4.0 mg/L fluoride in drinking water, and 522,000 are served by domestic wells that exceed EPA’s non-enforceable standard of 2.0 mg/L fluoride in drinking water (USGS 2020). [https://ntp.niehs.nih.gov/sites/default/files/2024-08/fluori... Page 2 or Page 22 of the PDF]

Note in the US this is almost all people drinking well water. So if we take the known harmful level at 1.5mg/L, then there are lots of people known to be drinking water above these concentrations. I'm not sure I would say we're necessarily ignoring them, but could argue regulations aren't up to date: the current EPA MCL is 4.0mg/L and secondary MCL is 2.0mg/L.

For more in depth data, we can take the EPA's Review of Fluoride Occurrence for the Fourth Six-Year Review (2024) [https://www.epa.gov/system/files/documents/2024-04/syr4_fluo...]. Page 15 of the PDF shows artificially fluoridated water nowadays has fluoride concentrations between 0.6mg/L and 1.2mg/L. Page 18 shows that ~4.7 million are being served with concentrations of fluoride >1.5mg/L. This is higher than the Hefferon et al figure but it seems this figure is based on data from 2006-2011 (where the population was lower, but also the recommended fluoride concentration was higher, with the max at 1.2mg/L pre-2015). I also am not convinced Hefferon et al has any figures on private wells (although maybe I misread the paper).