A rigorous nine-year research review looking at the relationship between fluoride and intelligence in children concludes that as fluoride levels rise, IQ drops.

Every 1 part per million increase in fluoride in urine — a way of measuring all the sources of fluoride a person consumes — was associated with a roughly 1 point drop in a child’s IQ score, the review concluded.

Although an impact like that may seem small for any one person, on a wider scale, the study authors note, the consequences are significant, especially for those who are vulnerable because of risk factors like poverty and nutrition.

“A 5-point decrease in a population’s IQ would nearly double the number of people classified as intellectually disabled,” they write in their conclusions.

The study, which was published Monday in the journal JAMA Pediatrics, comes with a backstory. It was conducted by scientists at the government’s National Toxicology Program, which evaluates chemicals and other things people are exposed to, like cell phone radiation, for their potential to harm health. It began in 2015 and was subject to several rounds of reviews in a process that some critics charge was designed to delay its public release.

Source: cnn.com