Study of fluoride during pregnancy and children’s IQ raises questions but draws criticism

A new study links fluoride consumption during pregnancy to lower IQ in children, but experts are saying it’s not time to rush out and filter your H2O just yet.

Researchers in Canada found women who drank fluoridated tap water while pregnant had children with slightly lower IQ scores than women who lived in non-fluoridated cities.

The message from public health experts, however, is “don’t panic”.

While the authors of the study claim the research “raises possible concern”, other researchers say the findings don’t move the needle much — if at all — on the question of fluoride safety.

“The overwhelming body of evidence is still supporting water fluoridation,” said Matt Hopcraft, associate professor of dental public health at the University of Melbourne.

“Here’s a single study that points a little in the other direction. I think we just need to be cautious.”

Water fluoridation began in Australia in the 1960s as a way to help prevent dental decay. It’s been heralded as one of the greatest public health achievements of the 20th century.

But it’s also been marred by controversy, from unfounded claims that it’s a government conspiracy to more legitimate concerns about dental fluorosis (when too much fluoride at an early age causes teeth to stain).

In 2017, the National Health and Medical Research Council undertook a review of the latest scientific evidence and found no indication that water fluoridated at current Australian levels causes health problems.

“Our recommendation would still be that … water fluoridation is safe and effective, and that you wouldn’t change [public policy] on the basis of this one study,” Dr Hopcraft said.

So, what should we make of these latest findings?

What the study found

The observational study published in JAMA Paediatrics looked at 512 mother-child pairs across six Canadian cities. About 40 per cent of the mothers lived in communities with fluoridated water.

To determine the children’s pre-natal exposure to fluoride, the researchers analysed the average fluoride concentration in the mothers’ urine during pregnancy, and assessed the mothers’ fluoride intake based on self-reported water and beverage (e.g. tea and coffee) consumption.

The children’s IQ was then assessed at ages three and four.

After accounting for factors like maternal education and the quality of the home environment, the researchers found a one milligram-per-litre (mg/L) increase in reported fluoride intake by mothers was associated with a 3.7-point drop in the children’s IQ.

They also found a 1 mg/L increase in maternal urinary fluoride was associated with a 4.5 lower IQ score in boys, but not girls.

The authors and an accompanying editorial acknowledged that while the study wasn’t conclusive, it added to an important discussion around the safety of community fluoridation for expectant mothers.

“No single observational study provides a definitive test of a hypothesis,” wrote editorial author David Bellinger, a professor of neurology at Harvard University.

“These considerations notwithstanding, the hypothesises that fluoride is a neurodevelopmental toxicant must now be given serious consideration.”

But others aren’t so sure.

Study has its limitations

The authors acknowledged that the study had several limitations.

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). The samples may also not precisely reflect foetal exposure to fluoride throughout pregnancy.

Second, the fluoride intake data did not measure actual fluoride concentration in tap water in the participants’ homes. Rather, it was an estimate of fluoride intake based on self-reported beverage consumption, and did not include fluoride from other sources, such as dental products and food.

Reproductive epidemiologist Michael Davies from the University of Adelaide said the study was not appropriately designed.

“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.

Several independent experts also noted that the overall effect on IQ scores was relatively small.

“I would be very cautious about over interpreting this data. Statistical significance does not equal ‘importance’,” said Grainne McAlonan, professor of translational neuroscience at King’s College London.

“This is a large sample and although a statistically significant relationship is reported, any shift in IQ said to be elicited by exposure to more fluoride is not very dramatic.

“If you look at the figures, it’s only the individuals which have the very highest levels of fluoride whose children have any IQ lowering, and it’s a pretty small drop.”

While the authors report a 1 mg/L increase in maternal urinary fluoride is associated with a 4.5 lower IQ score in boys, Professor McAlonan said the average difference in fluoride levels between people living in low- and high-fluoride areas is about 0.3 mg/L.

“Also, if you look at average IQ in the children from fluoridated and non-fluoridated groups, these are virtually the same: 108.07 vs. 108.21 respectively,” he said.

Other experts pointed to the inconsistent results when it came to sex differences (one measure of fluoride exposure showed an effect in boys and girls, the other in just boys), and the lack of “theoretical reason” behind this.

“It seems strange that for foetal brains developing, male ones are going to be affected by fluoride in the water, but female brains aren’t,” Dr Hopcraft said.

“That’s a little more suggestive that it’s a methodological anomaly rather than a true finding.”

Dr Hopcraft said the fact the children’s fluoride consumption after birth was not measured also limited what meaning we could draw from the findings.

“[The researchers] didn’t look at fluoride exposure after the babies had been born, so it’s just purely on what happened from a maternal perspective.”

Treat findings with caution

The study authors say the latest findings were consistent with previous research that had found higher fluoride exposure from drinking water is associated with lower children’s intelligence.

“Collectively, these findings support that fluoride exposure during pregnancy may be associated with neurocognitive deficits,” they wrote.

“This indicates the possible need to reduce fluoride intake during pregnancy.”

But equally, Dr Hopcraft said there were multiple studies that showed no effect whatsoever.

“There’s a really good study that came out of New Zealand that’s been following a birth cohort since 1972 in fluoridated and non-fluoridated areas, and they haven’t been able to show a link between IQ and water fluoridation,” he said.

“And there’s other studies around the world that are the same.

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

Anticipating the study’s findings may stir some controversy, JAMA Paediatrics took the unusual step of publishing an editor’s note alongside the paper, stating that the decision to publish the study “was not easy”.

“Given the nature of the findings and their potential implications, we subjected [the paper] to additional scrutiny for its methods and the presentation of its findings,” journal editor Dimitri Christakis wrote.

“That said, scientific inquiry is an iterative process. It is rare that a single study provides definitive evidence.

“This study is neither the first, nor will it be the last, to test the association between prenatal fluoride exposure and cognitive development.”