Prenatal exposure to higher levels of fluoride not only impairs cognitive development but also significantly increases the incidence of attention-deficit/hyperactivity disorder (ADHD) in children, new research shows.
"Our current study suggests that fluoride not only interferes with overall IQ or overall cognitive development but may also contribute to symptoms of ADHD," lead investigator Morteza Bashash, PhD, Dalla Lana School of Public Health, University of Toronto, Canada, told Medscape Medical News.
This isn't the first study linking fluoride to childhood ADHD or cognitive impairment. But, said Bashash, it is the first to find an increased incidence of ADHD with prenatal fluoride exposure.
"This work builds off of previous research I and my team published on this population demonstrating that higher levels of urine fluoride during pregnancy are associated with lower scores on tests of cognition and IQ in these school-age children," he said.
The study was published online October 10, 2018 inEnvironment International.
Previous animal studies as well as clinical studies have raised concerns over potential effects of fluoride exposure on neurobehavioral development, such as lower IQ and attention deficits, the investigators note.
To examine the association between prenatal exposure and symptoms associated with ADHD, the researchers analyzed data on 213 mother-child pairs from the Early Life Exposures to Environmental Toxicants (ELEMENT) birth cohort study. The study recruited pregnant women from 1994 to 2005 and continues to follow these women and children.
The research team used maternal urinary samples and child assessments of ADHD-like behaviors at ages 6 to 12 years.
They measured urinary fluoride levels adjusted for creatinine (MUFcr) in spot urine samples collected during pregnancy.
Child assessments consisted of both the Conners' Rating Scales–Revised (CRS-R), which was completed by mothers, and the Conners' Continuous Performance Test (CPT-II), which was administered to the children.
Data were adjusted for factors known to affect neurodevelopment, including lead exposure, smoking history, gestational age at birth, maternal marital status, age at delivery, and socioeconomic status.
The investigators found that the mean MUFcr was 0.85 mg/L (SD = 0.33). The difference between the first and third quartiles, or interquartile range (IQR), was 0.46 mg/L.
Using gamma regression in multivariable adjusted models, the researchers found that a 0.5-mg/L higher MUFcr (about one IQR higher) corresponded with significantly higher scores on the CRS-R for DSM-IV Inattention (2.84 points; 95% confidence interval [CI], 0.84 - 4.84) and DSM-IV ADHD Total Index (2.38 points; 95% CI, 0.42 - 4.34).
Participants also scored higher on the symptom scales, including the Cognitive Problems and Inattention (2.54 points' 95% CI, 0.44 - 4.63) and the ADHD Index (2.47 points; 95% CI, 0.43 - 4.50).
"We observed a positive association between higher prenatal fluoride exposure and more behavioral symptoms of inattention, which provide further evidence suggesting neurotoxicity of early-life exposure to fluoride," said Bashash.
The investigators found no significant associations with outcomes on the CPT-II or on symptom scales assessing hyperactivity.
Sources of Fluoride
In addition to water fluoridation, fluoride is also added to dental products, and a range of foods contain it in varying quantities. One consequence of excess fluoride consumption is dental fluorosis, discoloration or pitting of teeth.
The Centers of Disease Control and Prevention (CDC) notes that from 1999 to 2004, about 33% of 6- to 11-year-olds had experienced some form of dental fluorosis.
The CDC has suggested measures to protect children.It has recommended that families with children younger than 8 years consider using alternate sources of drinking water or, if they live in an area where fluoride levels are higher than 2 ppm, filtering their water.
"Our findings, combined with evidence from other studies, reinforce the need for additional research on potential adverse effects of fluoride, particularly in pregnant women and children, and to ensure that the benefits of population-level fluoride supplementation outweigh any potential risks," said Bashash.
"Early-life exposures can play a critical role in disease susceptibility later in life, with increasing recognition of the link between disturbance of central nervous system development and neuropsychiatric and neurological disorders later in life," he added.
For the past 50 years, the medical establishment has claimed that fluoride is safe and effective; should the official position on fluoridation change?
"I do not believe our study alone can be used to answer this question," said Bashash.
More Research Needed
Commenting on the findings for Medscape Medical News, Alex Dimitriu, MD, who has board certification in psychiatry and sleep medicine and is founder of Menlo Park Psychiatry and Sleep Medicine,said it's worth noting that many mental health problems, ranging from depression to dementia and likely including ADHD, may be a consequence of numerous factors that together result in illness.
Dimitriu, who was not involved in this research, said that although the researchers may have identified one of many environmental factors that contribute to ADHD, he would like to see their findings replicated in a larger study "before taking a general position of advising against fluoridated water or products.
"Fluoridation is not all bad, and indeed there are health benefits, dental at least, which we benefit from. But if it's associated with increased ADHD, some pregnant mothers may wish to avoid fluoridated products, including toothpaste," said Dimitriu.
"Genetics," he said, "also play a role in ADHD, and numerous twin adoption studies support a strong genetic role. Sleep is also a major player. Any child with ADHD should be screened for sleep apnea and dentition. I cannot emphasize enough how many 'cures' I've seen for childhood ADHD which resulted from correcting sleep," Dimitriu said
The study was funded by the National Institute of Environmental Health Sciences, which is part of the National Institutes of Health. The study authors and Dr Dimitriu report no relevant financial relationships.