Researchers suggest that high prenatal exposure to fluoride - which is found in tap water and dental products - could hamper child intelligence.
A new study suggests that children exposed to high levels of fluoride in utero may be less intelligent than those exposed to lower levels.
Principal investigator Dr. Howard Hu, of the Dalla Lana School of Public Health at the University of Toronto in Canada, and colleagues recently reported their findings in the journal Environmental Health Perspectives.
Fluoride is a chemical compound frequently added to tap water and dental products, including toothpaste and mouthwash, as it helps to prevent oral cavities.
According to the Centers for Disease Control and Prevention (CDC), drinking fluoridated water can reduce tooth decay in children and adults by around 25 percent.
However, studies have suggested that fluoride may have a downside. Research published in 2014, for example, associated fluoride exposure with cognitive deficits in infant mice.
Dr. Hu and colleagues build on such research, after finding that prenatal exposure to higher fluoride levels could hamper a child's intelligence.
Fluoride exposure and child IQ
The study involved 299 women and their offspring, all of whom participated in the Early Life Exposures in Mexico to Environmental Toxicants project.
Urine samples were obtained from each mother during pregnancy, as well as from their children when they were aged 6 to 12 years, in order to determine their levels of fluoride exposure.
"This is significant," explains Dr. Hu, "because previous studies estimated exposures based on neighborhood measurements of drinking water fluoride levels, which are indirect and much less precise measures of exposure."
"They also looked at children's exposures instead of prenatal exposures or had much smaller sample sizes of subjects to study," he added.
The intelligence of each child was assessed at 4 years old using the General Cognitive Index (GCI) of the McCarthy Scales of Children's Abilities, as well as between the ages of 6 and 12 years using the Wechsler Abbreviated Scale of Intelligence (WASI).
The team then looked at how fluoride levels in urine might influence child intelligence.
Fluoride may impact fetal nervous system
The results revealed that women who had higher levels of fluoride in their urine during pregnancy were more likely to have children with lower intelligence.
Specifically, the researchers found that for every 0.5 milligram per liter increase in expectant mothers' fluoride levels, their offspring's GCI and WASI scores were reduced by 3.15 and 2.5 points, respectively.
Interestingly, the results revealed that levels of fluoride in children's urine between the ages of 6 and 12 years did not appear to influence their intelligence.
Taken together, the researchers say that their findings suggest that prenatal fluoride exposure may impact neurodevelopment in a way that reduces a child's intelligence.
"Our study shows that the growing fetal nervous system may be adversely affected by higher levels of fluoride exposure. It also suggests that the prenatal nervous system may be more sensitive to fluoride compared to that of school-aged children."
Dr. Howard Hu
The researchers note that their findings need to be confirmed in other populations before any firm conclusions can be made about the link between prenatal fluoride exposure and child intelligence.
As the study authors conclude, "[...] our findings, combined with evidence from existing animal and human 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."