The US government just cut down the amount of fluorine in the water supply. Everyone is overexposed to it. And it is detrimental to brain development.
From the article: "But opponents of fluoridation and even some scientists maintain the new standard doesn't go nearly far enough. They say there's evidence that overexposure to fluoride might increase the risk for other health issues, including possibly thyroid problems, attention deficit hyperactivity disorder and even lower IQs."
Sort of funny how everyone is on the fluorine wagon, and anyone who says otherwise is a conspiracy nut.
Low = good, high = bad. "Sola dosis facit venenum". The dose makes the poison.
So I provided the source for GP's other statement, "And it is detrimental to brain development."
In contrast you've provided a generic source for an old adage. Anyhow the Harvard study mentions all the levels studied, some of which are comparable to US levels.
"all but one (Chinese) study suggested that high fluoride content in water may negatively affect cognitive development."
The source does not support claims that US levels of flouridation are too high nor that it is detrimental to brain development.
.88, 1.8, 2.97, 1.81-2.69, 4.12, 2.0, 3.15, 2.9, 2.97, .57-4.5, 2.5, 1.24-2.34, 2.47, 2.38