http://www.sciencemag.org/news/2019/08/drinking-fluoridated-water-during-pregnancy-may-lower-iq-sons-controversial-study-says

A new controversial study suggests pregnant women who drink fluoridated water could risk their children’s IQ.

First piloted as an experiment to reduce dental cavities in Grand Rapids, Michigan, in 1945, fluoridated drinking water has since been hailed by the U.S. Centers for Disease Control and Prevention in Atlanta as “one of public health’s greatest success stories.” Today, about two-thirds of people in the United States receive fluoridated tap water, as do many people in Australia, Brazil, Canada, New Zealand, Spain, and the United Kingdom. Now, a controversial new study links fluoridation to lower IQ in young children, especially boys whose mothers drank fluoridated water while pregnant.