Kennedy Jr. took a fresh swipe at fluoride, saying the chemical used to protect teeth is making Americans 'stupider' as he touted his plan to scale it back in the country's drinking water.

The studies relied upon are predominantly from communities in China, where the water is naturally fluoridated with much higher concentrations of fluoride than is found in U.S. water. While the CDC recommends 0.7 milligrams of fluoride per liter of water, some of the data was as high as 16 milligrams per liter.