The benefits of fluoridated water are well-established but when nature rather than science is in charge it can be harmful. The dose makes the poison and over 200 million people worldwide are estimated to be exposed to high fluoride levels in their drinking water.

A new study finds that long-term consumption of water with fluoride levels far above, 1000 percent more, established drinking water standards may be linked to cognitive impairments in children.

The study was conducted in rural Ethiopia where farming communities use wells with varying levels of naturally occurring fluoride ranging from 0.4 to 15.5 mg/L. The World Health Organization recommends fluoride levels below 1.5 mg/L. Researchers recruited 74 school-aged children and rated their ability to draw familiar objects such as a donkey or a house, with scores reflecting any missing details. They used a standard computerized memory test which is language and culture neutral as another tool to measure cognitive ability.

The authors declared a clear association between high fluoride and cognitive impairment, with
 higher exposure to fluoride in drinking water inked to more errors on the drawing and memory tests. Lead author Tewodros Godebo, assistant professor of environmental health sciences at Tulane University, said the “causal relationship between fluoride exposure and neurotoxicity remains unclear” but this is another case where more epidemiology won't help, real studies about any possible neurotoxic effects of fluoride, especially during early brain development and childhood, are needed.

Some animal studies have claimed that fluoride can cross the placenta and blood-brain barriers. In regions with no alternative water sources, this means excess fluoride exposure begins at conception.

Godebo hopes to replicate the results in Ethiopia with a larger cohort of children and study the cognition of children in low-fluoride Ethiopian communities for potential signs of cognitive impact.

"We have a unique opportunity to study low fluoride communities in the same setting as high fluoride communities, so we can determine if fluoride is a neurotoxicant at low levels,” Godebo said. “Such studies are important to the public and government agencies to determine the safety and risk of water fluoridation in drinking water supply systems.”

Co-authors for the study included Nati Pham and Arti Shankar of Tulane University, Marc Jeuland of Duke University, Amy Wolfe of University of Kentucky, and Redda Tekle-Haimanot and Biniyam Alemayehu of Addis Ababa University.