(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 I.Q. scores in children.
Researchers followed more than 600 mothers and their children. The kids were given age-appropriate I.Q. 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 affected by higher levels of fluoride than girls.
The study was published Monday in the journal JAMA Pediatrics. An editor's note was attached to the article saying the decision to publish the study was "not easy."
"Given the nature of the findings and their potential implications, we subjected it to additional scrutiny for its methods and the presentation of its findings," it read.
The Centers for Disease Control and Prevention calls water fluoridation one of the greatest public health achievements of the 20th century. The agency credits it with dramatically reducing tooth decay in children and adults.
About 66 percent of all U.S. residents receive fluoridated water.