Last night we were watching the news and saw a piece which caused a groan from both of us – the report of a study claiming fluoridation of water reduces the IQ of children born to mothers who have ingested that water as part of their diet. Kevin Drum saw it as well and doesn’t think much of it:
A 1 milligram increase in maternal urinary fluoride levels was associated with a decrease of 4.49 IQ points in boys and an increase of 2.40 IQ points in girls. This seems implausibly large, doesn’t it? But I can think of at least one crude way to check it. In 1950 virtually no water in the US was fluoridated. Today, fluoridated water reaches more than 70 percent of the population. At a minimum, this suggests that over the last 70 years the IQ levels of boys and girls (a) should have gone down, and (b) should have diverged by about 7 points. Has this happened?
In a word, no. Overall IQ scores in the United States have increased since 1950 and that steady upward trend has continued at least through 2014.
I don’t know where this study was published, and that can matter a lot. If you run into a anti-fluoridation proponent, this might give you a bit of ammunition.
