Summary: A new analysis links higher maternal urinary fluoride during pregnancy with increased ADHD-like symptoms in school-age children, especially inattentive behaviors and cognitive difficulties.
Source: University of Toronto.
Higher maternal urinary fluoride during pregnancy is associated with more ADHD-related symptoms in school-age children, according to a new study involving researchers from the University of Toronto and partner institutions.
The study, published in Environment International, analyzed data from 213 mother–child pairs enrolled in the Early Life Exposures in Mexico to Environmental Toxicants (ELEMENT) project in Mexico City. The cohort recruited pregnant women between 1994 and 2005 and has followed the mothers and their children for years to examine how early-life environmental exposures affect development.
“Our findings add to growing evidence that the developing fetal nervous system may be sensitive to higher levels of fluoride exposure,” said Morteza Bashash, the study’s lead author and a researcher at the Dalla Lana School of Public Health, University of Toronto.
For decades, communities in Canada and the United States have supplemented tap water and dental products with fluoride to prevent tooth decay; other countries have used fluoridated milk or table salt. In recent years, however, debate about the safety of fluoridation—particularly its effects on the developing brain—has intensified. This has prompted further research to inform public health guidance and drinking water standards.
The research team, which includes experts from the University of Toronto, York University, the National Institute of Public Health of Mexico, the University of Michigan, Indiana University, the University of Washington and Harvard University, measured fluoride in urine samples collected from mothers during pregnancy and from their children between ages six and 12. These biomarker measurements were used to estimate personal fluoride exposure in both mother and child.
Researchers then examined how maternal urinary fluoride related to children’s behavior, using standardized tests and questionnaires that assess inattention, hyperactivity, and overall ADHD-related symptoms. Analyses controlled for many factors that can affect neurodevelopment, including gestational age at birth, birthweight, birth order, sex, maternal marital status, smoking history, maternal age at delivery, education, socioeconomic status and lead exposure.
“Children with higher prenatal fluoride exposure were more likely to show ADHD-like symptoms reported by their parents,” Bashash said. “The association was strongest for inattentive behaviors and cognitive problems; we did not observe a clear association with hyperactivity.”
This study builds on earlier work by the same research group showing that higher maternal urinary fluoride during pregnancy was linked to lower IQ and reduced cognitive performance in school-age children in the same cohort.
Attention-deficit/hyperactivity disorder (ADHD) is one of the most common childhood psychiatric conditions, affecting an estimated five to nine percent of school-age children. Symptoms often continue into adolescence and adulthood and can interfere with daily functioning.
“If we can better understand the factors that contribute to these associations, it may be possible to develop strategies to reduce risk,” said Christine Till, associate professor of psychology at York University and a study co-author. Till also leads a related National Institutes of Health-funded study examining fluoride exposure during pregnancy in a large Canadian cohort.
Funding: The research was supported by the National Institute of Environmental Health Sciences, part of the National Institutes of Health (NIH).
Source: Nicole Bodnar, University of Toronto
Publisher: NeuroscienceNews.com (organized reporting)
Image Source: Image adapted from the University of Toronto news release.
Original Research: Bashash M., Marchand M., Hu H., Till C., Martinez-Mier E. A., Sanchez B. N., Basu N., Peterson K. E., Green R., Schnaas L., Mercado-García A., Hernández-Avila M., Téllez-Rojo M. M. “Prenatal fluoride exposure and attention deficit hyperactivity disorder (ADHD) symptoms in children at 6–12 years of age in Mexico City.” Environment International. Published October 10, 2018. doi: 10.1016/j.envint.2018.09.017
University of Toronto. “Link Between ADHD and High Fluoride Levels in Pregnancy.” NeuroscienceNews. October 14, 2018.
Abstract
Prenatal fluoride exposure and attention deficit hyperactivity disorder (ADHD) symptoms in children at 6–12 years of age in Mexico City
Background
Epidemiological and animal studies have raised concerns that fluoride exposure may affect neurobehavioral development, including lower IQ and attention deficits. Until now, few prospective human studies have examined prenatal fluoride exposure using biomarkers alongside sensitive measures of attention.
Objective
This study evaluated the association between prenatal fluoride exposure and symptoms related to attention-deficit/hyperactivity disorder (ADHD) in school-age children.
Method
The analysis included 213 mother–child pairs from the ELEMENT birth cohort with available maternal urinary fluoride during pregnancy and child behavioral assessments at ages 6–12. Maternal urinary fluoride adjusted for creatinine (MUFcr) was measured in spot urine samples collected during pregnancy. Mothers completed the Conners’ Rating Scales–Revised (CRS-R), and children completed the Conners’ Continuous Performance Test (CPT-II).
Results
Average MUFcr was 0.85 mg/L (SD = 0.33) with an interquartile range of 0.46 mg/L. In adjusted models, a 0.5 mg/L higher MUFcr (about one IQR) was associated with higher parent-reported scores on measures of inattention and overall ADHD symptoms. Specifically, higher MUFcr correlated with increases on the CRS-R DSM-IV Inattention scale and the DSM-IV ADHD Total Index, as well as scales reflecting cognitive problems and inattention. The pattern suggested a possible ceiling effect at higher exposures. There were no significant associations between prenatal fluoride and outcomes on the CPT-II or with hyperactivity symptom scales.
Conclusion
Higher prenatal fluoride exposure was associated with more ADHD-related symptoms—particularly inattention and cognitive problems—on parent reports in this cohort.