A US study suggesting a potential link between fluoride exposure during pregnancy with neurodevelopmental issues in infants has drawn the ire of Australian experts.
They argue that methodological shortcomings rendered the findings ‘unreliable.’
In what the authors claimed was the first US-based cohort study to examine associations of prenatal fluoride exposure with child neurobehavior, they said the results showed that women with higher fluoride exposure during pregnancy tended to rate their children higher on overall neurobehavioral problems and internalising symptoms, including emotional reactivity, anxiety, and somatic complaints by three years of age.
Furthermore, each 0.68mg/L increase in MUFSG was associated with nearly double the odds of total neurobehavioral problems being in the borderline clinical or clinical range. Women with higher MUFSG during pregnancy also tended to rate their children higher on autism spectrum disorder (ASD) symptoms.
The researchers claimed the effects observed in this study were sizable considering the relatively low urinary fluoride levels of participants.
But Professor Loc Do, a Professor of Dental Public Health in the School of Dentistry at the University of Queensland, joined his voice with other experts to point out that the paper authored by Dr Ashley Malin (from the University of Florida) and her team did not add to the body of knowledge due to major shortcomings with its exposure, outcome measurements, and small sample size.
“Exposure to fluoride in this study was measured by spot urinary fluoride analysis, which is highly variable within a person even during a day. This major shortcoming was even acknowledged in a paper (https://www.mdpi.com/1660-4601/18/12/6203), of which Dr Malin was a co-author,” Professor Do said.
“Even 24-hour urinary fluoride measurement (a much more reliable exposure measurement) cannot measure chronic fluoride exposure in individuals. An inexplainable observation when those with the highest income or education had markedly high mean urinary fluoride levels, pointing to the unreliability of this measure in this study.”
He was concerned that as the sample was very small (only 229 individuals), it was not adequate to balance expected measurement errors, meaning that even a few individuals with biased measurements could completely alter the overall findings.
“The outcome measure has high measurement error, requiring relatively high literacy, and close attention to the child. Those with the highest income or education (also with the highest mean urinary fluoride in this study) could observe and report more problems about their child than others, leading to assessment bias,” Professor Do said.
“The paper did not cite all the literature that contradicted their findings. An Australian nationwide study (https://journals.sagepub.com/doi/10.1177/00220345221119431) with a large population-based sample (2,682 children) did not find any effect of early life exposure to fluoride on child neurobehavioral development and executive functioning. The exposure measurement of fluoride exposure in this study was objective and fixed. It used two sophisticated instruments of child neurobehavioral development and executive functioning.”
Instead, the US authors noted that other studies conducted in Canada and Mexico have found associations of higher prenatal fluoride exposure at US-population–relevant levels with poorer neurocognitive outcomes, including lower IQ.
Dr Oliver Jones, a Professor of Chemistry at RMIT University in Melbourne, said that if fluoride really did cause problems with brain development in children, the effect would be seen consistently worldwide, but that was not the case.
“In fact, at least two recent studies found that maternal fluoride levels were associated with better cognitive scores in children,” he said.
“Fluoride is a naturally occurring substance found in water and some foods. It is not toxic at the levels we are exposed to and there is no robust evidence of any relationship between fluoride exposure and IQ level or behaviour issues. This study does not change that.”