Fluoride in tap water is associated with attention deficit hyperactivity disorder (ADHD) in children and adolescents, according to new research out of York University that looked at exposure to fluoridated water and rates of ADHD in the United States.
“Our findings showed that artificial fluoridation prevalence in 1992 predicted ADHD prevalence in 2003, 2007 and 2011 among children and adolescents in the United States, and that was after controlling for median household income,” says Ashley Malin, a York clinical psychology doctoral student. Fluoride also can occur naturally in the water.
Malin is first author on the paper “Exposure to fluoridated water and attention deficit hyperactivity disorder prevalence among children and adolescents in the United States: an ecological association,” with psychology Professor Christine Till, published in the journal Environmental Health.
ADHD is one of the most common neurodevelopmental disorders of childhood, say the authors. And, it can persist into adulthood. Till says the high prevalence of the disorder is a public health concern as it can seriously affect learning and social skills and have long-term consequences.
The researchers looked at state-based ADHD prevalence in children from four to 17 years of age that was collected as part of the National Survey of Children’s Health in 2003, 2007 and 2011, as well as the prevalence of fluoride in tap water between 1992 and 2008 from the Centers for Disease Control and Prevention (CDC) in the U.S.
What they found was that the prevalence of artificial fluoride in tap water was significant in predicting the prevalence of ADHD even after they controlled for socioeconomic status. Each one per cent increase in artificial water fluoridation prevalence in 1992 was associated with an additional 67,000 to 131,000 cases of ADHD depending on the year examined.
“In states where a greater proportion of people received artificially fluoridated water from public water systems, there tended to be a greater proportion of children and adolescents who were diagnosed with ADHD, according to parent-reported, health-care provider diagnoses,” says Malin.
They also looked at other years and found the correlation with fluoride, whether artificial or naturally occurring, and ADHD continued. A greater proportion of parents reported their children had ADHD in those states where a greater proportion of people were exposed to fluoridated public water.
“We found significant positive associations again with fluoridation prevalence in all subsequent years examined, so 2000, 2002, 2004, 2006 and 2008, and ADHD prevalence in 2003, 2007 and 2011,” says Malin. “I think the magnitude and consistency of these relationships over time is pretty compelling and it suggests that exposure to fluoridated water may be an environmental risk factor for ADHD.”
Although many parts of Canada don’t add fluoridation chemicals to water, Toronto and Mississauga, two of the largest cities in Canada, do. Most developed countries and 97 per cent of the western European population do not fluoridate drinking water.
“The study provides a compelling addition to the current debate about the safety of water fluoridation,” says Till. “We should be asking whether it is safe for many cities in Canada, including Toronto, to continue to fluoridate the water we consume. It is especially important to consider the impact of fluoride on the developing brain and we should be examining sensitive endpoints, like behaviour, for determining fluoride toxicity. ”
As Malin says, “As citizens of Toronto, living in an artificially fluoridated community, I think we need to ask ourselves whether this is still a worthwhile practice.”
Fluoride is considered a developmental neurotoxin. Artificial fluoride, a byproduct of fertilizer production, is supplied in the form of one of three chemicals, hydrofluorosilicic acid being the most common, followed by sodium fluorosilicate and sodium fluoride. These chemicals have been found to cross the placenta and end up in the infant brain.
“Several mechanisms can explain how fluoridated water can contribute to the disorder,” says Malin. “These include hydrofluorosilicic acid and its sodium salt’s ability to leach lead from water delivery pipes, and fluoride’s effect on increasing risk of hypothyroidism, both of which are pathways linked with ADHD.”
There are not many studies conducted in humans related to the effects of low-level fluoride in water on neurodevelopmental outcomes. Studies that examine the more subtle effects of a neurotoxin are often the more sensitive studies. “The current study is important for informing water fluoridation policy, though additional studies examining this relationship are needed,” says Till. “This study serves an important first step in evaluating one potential risk of water fluoridation.”
By Sandra McLean, YFile deputy editor