A new study published in the Journal of Dental Research provides reassuring evidence regarding the safety of early childhood fluoride exposure. Researchers found that exposure to fluoride in the first five years of life, whether through drinking water or as indicated by dental fluorosis, was not associated with lower intelligence scores in young adulthood.
Water fluoridation, the controlled addition of fluoride to public water supplies, and the use of fluoridated toothpaste are widely recognized as effective ways to prevent tooth decay. But there has been ongoing discussion about the potential effects of fluoride on brain development, especially in young children whose brains are still developing and may be more sensitive to environmental factors.
While several major reviews of existing research have concluded that fluoride levels typically found in water fluoridation programs do not harm children’s brain development, some researchers have continued to express concerns. These concerns often stem from studies that have reported links between fluoride exposure and lower intelligence scores, although the quality and reliability of these studies have been questioned.
To address this ongoing debate, a team of researchers led by Loc Do at The University of Queensland in Australia set out to investigate if there was any connection between early life fluoride exposure and cognitive development in a group of young Australian adults. They aimed to use detailed measures of fluoride exposure and a well-established intelligence test to provide robust evidence.
“I am an oral epidemiologist with research interests in the effectiveness and safety of fluoride use in preventing dental caries,” said Do, a professor of dental public health. “I have conducted multiple research studies evaluating the balance of risk and benefit of fluoride use. The recent debate on the potential effect of fluoride on child development, including intelligence, has interested me. We succeeded in winning an Australia National Health and Medical Research Council grant to conduct a population-based longitudinal study to investigate the topic.”
The researchers used data from a large, long-term study called the Australia’s National Child Oral Health Study, which had collected information on children’s dental health and related factors between 2012 and 2014. This original study involved a carefully selected group of children from across Australia, designed to represent the broader Australian population. As part of the original study, parents answered detailed questionnaires about their children’s health, behaviors, and family backgrounds.
Trained dental professionals also examined the children’s teeth to assess dental fluorosis. Dental fluorosis is a condition that can occur when children are exposed to too much fluoride while their teeth are forming. It appears as faint white lines or spots on the tooth enamel and serves as a visible marker of fluoride intake during early childhood.
Years later, between 2022 and 2023, the researchers contacted a subset of these original participants, who were now young adults aged 16 and older. They invited them to participate in intelligence testing. To ensure a balanced comparison, they first invited individuals who had been identified as having dental fluorosis in the original study. Then, they selected a random group of participants who did not have dental fluorosis, making sure these individuals were of similar age and gender to those with fluorosis.
To measure intelligence, the researchers used the Wechsler Adult Intelligence Scale, Fourth Edition, often referred to as the WAIS-IV. This is a widely respected and comprehensive test used to assess intellectual abilities in adults and older adolescents. The WAIS-IV involves a series of tasks designed to measure different aspects of intelligence, including verbal comprehension, perceptual reasoning, working memory, and processing speed. From these tasks, a full-scale intelligence quotient, or IQ, score is calculated, providing an overall measure of intellectual ability.
All intelligence tests were administered individually in standardized testing environments, such as psychological clinics or specially arranged offices. This ensured that the tests were given under optimal conditions to obtain accurate and reliable results. The psychologists administering the tests were not informed about the participants’ fluoride exposure status to prevent any unconscious bias from influencing the testing process.
“We paid particular attention to collecting reliable IQ data by using qualified trained and calibrated psychologists,” Do noted.
To understand fluoride exposure, the researchers used two primary measures. First, they calculated the percentage of each participant’s life, up to the age of five, that they had lived in areas with fluoridated water. The second measure of fluoride exposure was the presence or absence of dental fluorosis, as assessed during the original child oral health study.
In their analysis, the researchers also considered other factors that could potentially influence intelligence scores. These included age, gender, family income, parental education, parents’ country of birth, whether the participant had been diagnosed with any neurodevelopmental conditions such as attention deficit hyperactivity disorder or autism, duration of breastfeeding, and frequency of toothbrushing with fluoride toothpaste in early childhood. By accounting for these factors, the researchers aimed to isolate the potential effects of fluoride exposure on intelligence.
The study’s findings revealed that, on average, the participants had a full-scale IQ score of 109.2, which is above the average population score of 100. Interestingly, when comparing groups based on fluoride exposure, the researchers found that those who had no exposure to fluoridated water in their first five years of life actually had slightly lower average IQ scores compared to those who had been exposed to fluoridated water for some or all of that time. However, statistical analyses indicated that these differences were not large enough to be considered statistically significant, meaning they could be due to chance.
Similarly, when comparing participants with and without dental fluorosis, there was no meaningful difference in their average IQ scores. Further sophisticated statistical tests, called equivalence tests, were used to determine if the intelligence scores of those exposed to fluoride were practically equivalent to those not exposed. These tests confirmed that the IQ scores of the fluoride-exposed groups were indeed equivalent to, and certainly not inferior to, the scores of the non-exposed groups.
The researchers also conducted additional analyses, looking at different subgroups of participants based on factors like gender, socioeconomic status, and neurodevelopmental diagnoses. These analyses consistently showed no negative association between early life fluoride exposure and intelligence scores. Furthermore, they examined scores on the different sub-indices of the WAIS-IV test (verbal comprehension, perceptual reasoning, working memory, and processing speed) and found no link between fluoride exposure and performance on any of these specific cognitive abilities.
The findings are in line with previous research conducted by Do and his colleagues, which found no evidence that fluoride exposure was associated with altered measures of behavioral development and executive functioning.
“The two studies using different primary outcomes of child development have provided strong evidence that early life exposure to fluoride as observed in Australia does not have negative impacts on child development,” Do told PsyPost. “That means that the current levels of fluoride are safe for Australian children.”
Looking forward, Do said he is interested in working with other researchers to address issues related to this topic. “I would seek opportunities to collaborate in researching the topic in populations with higher natural fluoride levels,” he said. “It is much harder to have quality data in those populations.”
“It is important to prevent mis- and disinformation surrounding this topic,” Do added. “I am concerned that a public health program has been politicized. The current scientific evidence indicates that community water fluoridation is effective and safe. Fluoridation cessation would negatively affect those in disadvantaged socioeconomic groups.”
The study, “Early Childhood Exposures to Fluorides and Cognitive Neurodevelopment: A Population-Based Longitudinal Study,” was authored by L.G. Do, A. Sawyer, A. John Spencer, S. Leary, J.K. Kuring, A.L. Jones, T. Le, C.E. Reece, and D.H. Ha.
