Study raises questions about fluoride and children's IQ
A study of young children in Canada suggests those whose mothers drank fluoridated tap water while pregnant had slightly lower IQ scores than children whose mothers lived in non-fluoridated cities. But don't dash for the nearest bottled water yet. Health experts at the American Academy of Pediatrics and the American Dental Association cautioned that public policy and drinking water consumption should not change on the basis of this study.
"I still stand by the weight of the best available evidence, from 70 years of study, that community water fluoridation is safe and effective," said Brittany Seymour, a dentist and spokeswoman for the American Dental Association. "If we're able to replicate findings and continue to see outcomes, that would compel us to revisit our recommendation. We're just not there yet."
The American Academy of Pediatrics, likewise, recommends fluoride in toothpastes and tooth varnishes for children because the mineral prevents tooth decay. In drinking water, "fluoridation has been incredibly protective," said Aparna Bole, a pediatrician who chairs the Council on Environmental Health at the American Academy of Pediatrics. Fluoridation reduces the prevalence of cavities by about one-fourth, according to the Centers for Disease Control and Prevention. The CDC considers water fluoridation one of the 10 top health achievements of the past century, on par with vaccines and antismoking campaigns.
Bole called the new study, published Monday in JAMA Pediatrics, "an important addition to our body of knowledge. It supports the public health community's ongoing reevaluation of optimal fluoridation levels in drinking water."
In January 1945, researchers added fluoride to municipal water in Grand Rapids, Michigan, the first program to enlist fluoride to protect a city's teeth. Opponents of fluoridation have since raised concerns both ludicrous - fluoridation is not a communist plot - and legitimate, such as fluorosis. In the mild form of fluorosis, faint white streaks appear on the teeth of young children. Severe fluorosis, which is much rarer, damages bones.
Dozens of cities in the United States and Canada, such as Portland, Oregon, and Vancouver, do not add fluoride to city water. Elsewhere in the United States, fluoridation is the norm. As of 2014, per CDC data, two-thirds of people in the United States had fluoride in their drinking water. In 2015, to reduce the risk of mild fluorosis, the Department of Health and Human Services cut its fluoride recommendations almost in half, from 1.2 milligrams per liter to 0.7 milligrams per liter.
Few older studies addressed potential risks, or the lack thereof, associated with fluoride exposure during pregnancy, said study author Christine Till, a neuropsychologist at Canada's York University. She added that "whether we found an effect or not, the data would be really relevant because we would then address that gap in our knowledge."
Till and her colleagues acquired data and frozen urine samples previously collected by Maternal-Infant Research on Environmental Chemicals, or MIREC. That project, run by Canada's public health department, studied thousands of mothers who gave birth between 2008 and 2012. MIREC researchers measured the toddlers' IQ after the children turned 3.
Pregnant women reported their consumption of tap water and black tea, which is high in fluoride, in questionnaires. The authors of the new study also calculated the amount of fluoride in municipal water, based on the levels at wastewater treatment plants linked to the women's postal codes. The researches estimated the women's fluoride intake based on a combination of those measures.
The researchers compared the fluoride intake of 400 women, some who lived in fluoridated cities and some who did not. They controlled for factors such as household income and the women's education. A 1 milligram increase in fluoride intake was associated with a 3.7-point drop in children's IQ, they found.
As an additional step, Till and her colleagues measured fluoride biomarkers in urine from 500 pregnant women, collected during each trimester. Fluoride content in urine was only moderately related to the estimates of the mothers' fluoride intake, suggesting that neither was a perfect measure of how much fluoride a pregnant woman drank.
The scientists observed that a 1 milligram-per-liter increase in urine fluoride predicted a drop in IQ of 4.5 points in young boys. When the researchers examined the urine of mothers who had daughters, however, fluoride had no association with IQ.
Previous observational studies claimed to find relationships between fluoride and IQ, but most were "of poorer quality due to various weaknesses in study design," said David Bellinger, an expert in neuroepidemiology at Boston Children's Hospital who was not associated with this study. The methods in this report, he said, are "very similar" to studies that showed low-dose lead and pesticide toxicities.