(CNN) - Pregnant women may want to start paying closer attention to the level of fluoride they take in.
A new study says increased exposure to fluoride during pregnancy is tied to lower IQ scores in children.
Researchers followed more than 600 mothers and their children. The kids were given age-appropriate IQ tests at three or four years old.
The study showed that kids of moms with higher levels of fluoride during pregnancy scored lower in intelligence tests. It also found boys were more impacted by higher fluoride levels than girls.
The study was published Monday in the journal JAMA Pediatrics.
The Centers for Disease Control and Prevention calls water fluoridation one of the greatest public health achievements of the 20th century.
It credits fluoride with dramatically reducing tooth decay in children and adults.
About 66 percent of all US residents receive fluoridated water.