Fluoride in the urine of pregnant women showed a correlation with lower measures of intelligence in their children, according to a new study that focused on women and children from Mexico (Environmental Health Perspectives, September 19, 2017). The researchers found that an increase in maternal urine fluoride of 0.5 mg/L predicted lower scores on two scales that measure intelligence. However, they cautioned that fluoride seems to have no effect on brain development after birth.
"Our study shows that the growing fetal nervous system may be adversely affected by higher levels of fluoride exposure," stated Howard Hu, MD, MPH, ScD, the study's principal investigator and a professor of environmental health, epidemiology, and global health at the Dalla Lana School of Public Health at the University of Toronto in Canada. "It also suggests that the prenatal nervous system may be more sensitive to fluoride compared to that of school-aged children."
While community water systems are not fluoridated in Mexico, people who live there are exposed to fluoride via fluoridated salt (250 parts per million [ppm] or mg/L), toothpaste, and fluoride that occurs naturally in drinking water.
The researchers wanted to see if prenatal exposure to fluoride was associated in any way with the neurocognitive development of children.
“Our study shows that the growing fetal nervous system may be adversely affected by higher levels of fluoride exposure.”
— Howard Hu, MD, MPH, ScD
Using data from the Early Life Exposures in Mexico to Environmental Toxicants (ELEMENT) project, they obtained complete data on 299 mother-child pairs. The study included data from 287 pairs with General Cognitive Index (GCI) of the McCarthy Scales of Children's Abilities at age 4 and 211 pairs with full-scale intelligence quotient (IQ) data.
They analyzed urine samples from these study participants and found that the mean fluoride levels measured in 299 mothers was 0.90 mg/L, while the children's fluoride level was 0.82 mg/L. As maternal urine fluoride levels increased 0.5 mg/L, this corresponded to lower GCI and IQ scores for their children, the study authors reported. The researchers also considered factors such as maternal education, tobacco use, age, and others.
"Higher prenatal exposure to fluoride was associated with lower GCI scores in children at approximately 4 years old and with lower full-scale IQ scores at 6 to 12 years old," the authors wrote. "Estimates from adjusted linear regression models suggest that mean GCI and IQ scores were about 3 and 2.5 points lower in association with a 0.5 mg/L increase in prenatal exposure, respectively."
Not apples to apples
The authors cautioned that their findings needed to be confirmed in other populations and additional research studies.
They noted that the urinary fluoride levels in pregnant women in their study were somewhat higher than urinary fluoride levels found in nonpregnant general populations in Canada and the U.S., but they were within the general range of such levels.
"However, 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," they concluded.
Pediatric dentist Johnny Johnson Jr., DMD, president of the American Fluoridation Society, said the study added to the knowledge of fluoride from other countries but was not a direct comparison to U.S. intentionally fluoridated water systems.
"This study adds to the knowledge base that we have on fluoride from other countries," Dr. Johnson wrote DrBicuspid.com in an email interview. "However, it is not an apples-to-apples comparison to intentionally fluoridated water as we have here in the U.S."
The community water fluoridation in the U.S. is set at 0.7 ppm, which is significantly lower than the levels of fluoride in fluoridated salt, he noted. The fluoride levels of fluoridated salt are set to provide a daily intake of fluoride that would be equivalent to if the water were fluoridated, according to Dr. Johnson. Intake from this salt cannot be controlled like it is with community water fluoridation, he stated.
"Intakes of fluoride in Mexico come from fluoridated salt (100 to 250 ppm), natural fluoride levels in the drinking water, toothpastes, and potentially from fluoride supplements, which are available over the counter in Mexico," Dr. Johnson wrote. "The level of fluoride in the water is not regularly monitored and has been shown to contain fluoride at low levels up to twice that of what is in fluoridated water in the U.S. (0.15 to 1.38 ppm)."
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