A study from Karolinska Institutet links fluoride in drinking water to impaired cognition in children. In particular, the researchers saw a negative impact on children’s verbal abilities.

In Sweden, fluoride is found naturally in low levels in drinking water, while in several countries, such as the United States, Canada and Australia, it is added to municipal water to prevent tooth decay. It is also used in toothpaste to protect teeth against decay.

Researchers at the Karolinska Institutet have investigated how early exposure to fluoride affects children’s cognitive abilities. The study involved 500 mothers and their children in rural Bangladesh, where fluoride is naturally present in drinking water at levels comparable to Sweden. The researchers measured fluoride levels in the mothers during pregnancy and later in the children via urine samples. The children’s cognitive abilities were then tested by psychologists at ages five and ten.

The article was originally published in The Nordic Times on March 23, 2025.

The study, published in Environmental Health Perspectives, found that higher fluoride levels in pregnant women were linked to impaired cognitive abilities in their children at ages five and ten. The impact was most evident on children’s verbal comprehension and their ability to interpret and process sensory input. In contrast, the researchers found no statistically significant link between fluoride levels in the urine of five-year-olds and their cognition.

–  This could be due to the shorter exposure, but also because the measurements are not as reliable in younger children due to greater variations in how fluoride is absorbed and accumulated in the body, especially in the skeleton, says Maria Kippler, associate professor at the Institute of Environmental Medicine at Karolinska Institutet, in a press release.

Even low levels can have negative effects

The fluoride levels that were linked to poorer cognitive development were below the WHO and EU limits for drinking water. However, the researchers point out that toothpaste is rarely a significant source of exposure, as it is not intended to be swallowed, but emphasize the importance of children learning to spit it out.

– Our results support the hypothesis that even relatively low levels of fluoride can have negative effects on children’s early development, says Kippler.

However, the researchers emphasize that this is an observational study and therefore no firm conclusions can be drawn about cause and effect. It is therefore important to assess the overall results of several similar studies.

– Further research is important to inform the assessment of appropriate fluoride limits. Even small changes in cognition at the population level can have large consequences for public health, says Kippler.