A new study from the Sweden Karolinska Institute provides evidence that exposure to fluoride during pregnancy or early childhood can impair cognitive development in children, even at levels previously considered safe.
The study was published on March 5th in the Environmental Health Perspective, following 500 mother-child pairs in rural Bangladesh over a decade, following the exposure to naturally occurring fluorides and measured cognitive abilities when children were 5 and 10 years old.
“Our results support the hypothesis that even relatively low concentrations of fluoride can affect early development in children,” says Maria Kippler, an associate professor at the Karolinska Institute at the Institute of Environmental Medicine, and the corresponding author of the study.
Although this study was conducted in Bangladesh, the findings raise questions about fluoride exposure worldwide, including areas that are commonly added to public drinking water to prevent tooth decay.
Research reveals cognitive effects at multiple life stages
The researchers found that higher fluoride exposure during pregnancy was associated with a decline in child cognitive scores at both ages 5 and 10 years. Similarly, children with high fluoride exposure at age 10 showed cognitive decline, but this effect appeared above certain concentration thresholds.
Using urine samples to measure fluoride exposure, the team found that pregnant women with higher urinary fluoride levels (median: 0.63 mg/L) had worsened on cognitive tests, particularly in the area of perceptual reasoning and oral skills. The association lasted after several factors including socioeconomic status, maternal education and family environment.
In children, the findings showed that fluoride exposure at age 10 (median: 0.66 mg/L) was associated with a decline in cognitive scores when concentrations exceeded 0.72 mg/L. At younger ages, the relationship was less clear, probably due to variations in how the child’s growing body handles and retains fluoride.
“In young children, more than half of the amount of fluoride ingested can be retained in the skeleton,” the researchers point out, explaining why measuring exposure in younger children is more complicated.
Balancing the benefits of teeth with potential risks
This study has increased concerns about the potential neurotoxicity of fluorides. While decades of research support the role of fluoride in preventing dental cavities, this study highlights trade-offs that may be worthy of careful consideration.
In parts of North America, including the US and Canada, fluoride is typically added to the urban water supply of about 0.7 mg per liter. Some European countries have adopted a more cautious approach, with many choosing to oppose water fluorination.
“Given concerns about health risks, adding fluoride to drinking water is controversial and has been widely discussed in the US and Canada,” says Dr. Kippler.
Researchers emphasize that dental products, such as toothpastes, which typically have much higher fluoride concentrations, are not a major concern when used according to instructions.
“I would like to emphasize that dental products such as toothpaste are not usually sources of exposure because they are not intended to be consumed,” says Dr. Kippler. “Toothpaste fluoride is important for preventing tooth decay, but it’s important to encourage small children not to swallow toothpaste while brushing.”
Impact on water safety standards
This study found adverse effects at levels below the current regulation threshold. The World Health Organization recommends an upper limit of 1.5 mg/L of fluoride in drinking water, but this study suggests that impacts on cognitive development in children can occur at low concentrations.
In the Bangladeshi cohort, fluoride-drinking water (median: 0.20 mg/L) is moderately correlated with urinary fluoride levels, indicating that water is a significant source of exposure. These levels are comparable to the non-fluidic regions of North America, with natural fluoride levels typically ranging from 0.04-0.20 mg/l.
This study reinforces similar findings from studies conducted in Mexico and Canada where maternal fluoride exposure during pregnancy was also associated with cognitive effects in children.
Looking ahead
Researchers acknowledge research limitations, such as reliance on single spot urine samples at each assessment point. They are currently working to investigate these associations in other populations and establish experimental models to determine possible biological mechanisms.
“A further research is needed to create a robust foundation for reviewing the health risks and thresholds of fluoride in drinking water, food and dental products, particularly for children,” says Dr. Kippler. “Even small changes in perception at the population level can have serious public health effects.”
Unlike many previous studies that reported gender differences in the effects of fluoride, some showed strong influences among boys and girls, so this study did not find a consistent pattern of different effects between sexes.
This study was funded primarily by grants from the Swedish Research Council and the Swedish Research Council for Environmental Science and Spatial Planning. The researchers declared no conflict of interest.
Note: This article reports on peer-reviewed observational studies. The findings suggest a link between fluoride exposure and cognitive effects, but do not establish a direct causal relationship. Public health decisions regarding fluoride should consider the overall body of evidence for both benefits and potential risks.
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