Controversial study links fluoride in water to lower IQ

Study claims fluoride exposure during pregnancy tied to low IQ scores in children

Study claims fluoride exposure during pregnancy tied to low IQ scores in children

512 pregnant women were recruited from 6 Canadian cities who were measured for exposure by analyzing fluoride levels in urine, examining how much tap water/tea they drank, and comparing fluoride concentration in their community drinking water.

"In my view, a strong case for a hypothesis is present when multiple studies conducted independently produce consistent results". Water fluoridation is supplied to approximately 66% of United States residents, 38% of Canadian residents, and 3% of European residents to prevent tooth decay. But Christine Till, an associate professor of psychology at York University in Toronto, also wondered about potential downsides. Prior research in lab animals also suggests males are more susceptible to damage from fluoride, and other research suggests they are at higher risk of neurodevelopmental disorders such as ADHD, so it's not entirely surprising that their IQ scores would be more closely linked to fluoride exposure, she adds.

The 2015 lowered the recommended amount of fluoride in drinking water supplies, from up to 1.2 milligrams per liter to 0.7 milligrams per liter, mainly to cut down on potential damage to teeth.

That mix gave her a sample of more than 500 women with a whole spectrum of fluoride exposure.

"Neither the method for collecting maternal fluoride exposure data nor the method for calculating total fluoride exposure have been validated, making the size and source of associations unreliable", Professor Davies said.

What the researchers discovered was that for each additional 1 milligram per liter in the concentration of fluoride that was found in the women's urine, their boys - not girls, so far - had a lower IQ by 4.5 points.

"Here's a single study that points a little in the other direction". In general, there was a small difference for any individual child.

"We welcome this and further scientific study of the issue to see if the findings can be replicated with methods that demonstrate more conclusive evidence", the ADA said.

The study was funded by the Canadian government and the U.S. National Institute of Environmental Health Science. These studies have been criticized for being done in regions with abnormally high fluoride levels in water.

Study coauthor Angeles Martinez-Mier, a fluoridation expert and a professor at the Indiana University School of Dentistry in Indianapolis, said that although pregnant women should reduce their fluoride intake, for everyone else, "we don't have enough information to make policy recommendations, so you should stick with what you have", including leaving fluoridation in place.

The journal's editorial team expected the controversial study to cause a few sparks and subjected it to additional scrutiny before publishing it. "It is the only editor's note I've ever written". "We tried to be as cautious and careful as possible", she says. A previous study in Mexico found a similar link, she says, so this is not the first to suggest a connection.

Several other experts agreed that while the latest research was interesting, it was important to interpret the findings with caution.

"We know that decisions need to be based on evidence, and we had no evidence on whether fluoride in pregnancy was safe, and regardless of the outcome, that knowledge was really critical".

'The gender difference in the results make it hard to interpret. When they compared children born to those with the highest fluoride exposure, to those born to women with the least, the difference was more marked.

First, the urinary fluoride samples collected could have been affected by behaviours that weren't controlled for in the study (e.g. consumption of fluoride-free bottled water or fluoride-containing toothpaste prior to sampling). And the other half like, Montreal and Vancouver, were cities that do not add fluoride to drinking water. Maternal urine samples, however, also captured fluoride from dietary sources and dental products, providing a fuller picture of prenatal risk factors, Till says.

However, experts say fluoride can be unsafe in high concentrations.

TILL: Only boys were affected when we looked at urinary fluoride.

"This is a major loss of IQ points that would have societal and economic impacts; it would definitely be felt at a population level", said Till. Bellinger reviewed the paper and also wrote an editorial about it.

"Dentists have a moral and ethical obligation to the community and its health and are effectively putting ourselves out of business by advocating water fluoridation".

Debate over fluoridation has simmered since cities began adding the mineral to public water supplies in the 1950s, Till said.

BELLINGER: So I think it's a mistake to focus too much on the water fluoridation piece here.

"A large body of empirical evidence across various types of study populations consistently points to parental social position, parental education, maternal intelligence, and (early) home environment as significant predictors of IQ". "You can live without your California roll, but this is an everyday thing, and we tell pregnant people to stay hydrated".