The Warren study addressed lifelong impact on cognitive ability and found no evidence of a negative effect of fluoridation and possibly even a small benefit. It was consistent with a Swedish study that similarly related early life exposure to fluoridated water to adult cognitive capability and likewise found no indications of adverse cognitive outcomes but did report favourable dental health outcomes.
In New Zealand in 2024 the Ministry of Health directed 14 communities around the country to add fluoride to drinking water and a second group, including Queenstown Lakes District Council, were earlier put on notice that it could be required to.
Central Otago District Council does not, and was not required to, fluoridate its water.
University of Otago Professor of dental epidemiology and public health Jonathan Broadbent said the US study addressed an important knowledge gap as few studies had investigated the link between fluoride and cognitive issues at the levels consumed from drinking water supplies.
"It is reassuring that no association was found. This is consistent with findings from a recent Australian study and an older NZ study. However, some other studies have found associations between fluoride and cognitive issues, generally at higher concentrations than used in fluoridation programmes."
With new fluoridation programmes being launched in New Zealand the research was needed as recent research was limited, he said.
"New fluoridation programmes in NZ have been focused on areas with higher proportions of deprived New Zealanders and so should have good benefits for oral health, which tends to be worse in areas with greater deprivation. On the other hand, other health issues that occur at greater rates in deprived areas so spurious associations could be found. It is essential that the outcomes of these new programmes are monitored carefully."
In the 1950s health officials agreed fluoridation prevented dental caries. However, some groups have claimed fluoride produces adverse neurodevelopmental health effects and fluoridation no longer provided dental health benefits.
While earlier studies looked at exposure to very high levels of fluoride, far beyond recommended standards, the new paper in Science Advances looked at more representative water fluoridation levels.
Researchers looked at language and maths test results from tens of thousands of US high schoolers in 1980 and the water fluoride levels they were exposed to since conception. After accounting for other factors, those exposed to at least 0.7 mg/L of water fluoride had better results.
Follow up cognitive tests with a subset of participants until about 60 years old showed although that edge became insignificant, growing up with recommended water fluoride levels did not contribute to cognitive decline.
— Allied Media
