Is higher fluoride intake in pregnancy affecting kids’ IQ?

By Dr. Liji Thomas, MDAug 20 2019

A new study suggests that fluoride consumption at higher levels in pregnancy could be linked to a decline in IQ by a few points in the children. Experts disagree on the acceptability of this finding, which has stirred up questions about fluoridation of public drinking water supplies.

Fluoride is a mineral found in nature, and is important in preventing dental caries, or tooth decay. Its addition to the drinking water supply has been consistently celebrated as among the Top Ten accomplishments in public health. About 66% of people in the US have fluoridated drinking water, compared to 38% in Canada and only 3% in Europe. In such communities, up to 80% of daily fluoride intake is from drinking water.

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The present study came into being after researcher Christine Till found a lack of good-quality studies to support the statement that fluoride consumption at approved water fluoride levels is safe in pregnancy.

Fluoride has been defended as a beneficial nutrient for all classes. However, several studies have shown an association between higher fluoride exposure from drinking water and reduced intelligence in children.  These studies have been criticized for being done in regions with abnormally high fluoride levels in water. A Mexican study has also shown a 6-point decline in IQ among school-age children for each 1 mg/L increase in maternal urinary fluoride levels. However,  few studies have been performed during pregnancy.

To address this, the current study looked at over 500 mother-child pairs in six Canadian cities. About 27% of this study population lived in areas where drinking water was fluoridated, and for the rest, it was not. The team then measured urinary fluoride levels during pregnancy, using archived samples. They also found the fluoride consumption during pregnancy from the levels in the public water supply and the recalled consumption of the participants in the study. The children born of these pregnancies were tested for IQ between 3 and 4 years of age, using the Wechsler Primary and Preschool Scale of Intelligence-III.

Urinary fluoride concentrations and total fluoride intakes were significantly greater in women living in areas with fluoridated drinking water, compared to the second group. Girls tested significantly higher for IQ compared to boys.

When they then analyzed this data, they found that the average IQ dropped by a couple of points over the whole spectrum of children. 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.

When it came to maternal urinary fluoride, an increase of 1 mg/mL was associated with a lowering of IQ in boys by about 4.5 points, but not in girls. To put this in perspective, the average maternal urinary fluoride concentration was 0.4 mg/L. However, the difference between the highest and lowest quartiles of urinary fluoride (0.33 mg/L) is roughly equal to that between women living in a fluoridated water vs non-fluoridated water community. This difference is linked to a reduction of 1.5 IQ points in boys.

When the maternal intake went up by 1 mg/day, both boys and girls showed a measurable decline in IQ of about 3.5 points overall. The median intake was 0.39 mg/day.

The researchers say the adverse effects of excessive fluoride exposure on the developing brain may show up differently in boys, as many neurodevelopmental conditions are found to develop at higher rates in boys.

The authors say, “We would feel an impact of this magnitude at a population level, because you would have millions of more children falling in the range of intellectual disability, or an IQ of under 70, and that many fewer kids in the gifted range.”

David Bellinger, a neurologist who wrote an editorial on the new study says the decline is not negligible, but is comparable in magnitude to that seen in children who were exposed to chronic lead poisoning. Moreover, he points out that fluoride during pregnancy was not primarily related to water intake, but to sources such as fluoride in black tea, toothpaste and food. He adds, “I think it's a mistake to focus too much on the water fluoridation piece here.”

The study appeared in the journal JAMA Pediatrics on August 19, 2019.Editor Dimitri Christakis admitted he was negatively biased about the finding before reading the article. He says the article was stringently vetted for its methodology and presentation style before it was published, due to the volatile nature of the debate about fluoridation of water.

Reactions to this finding varied, predictably. Many dental and pediatric practitioners disagree, saying they will continue to promote fluoridated water consumption in the absence of fresh evidence. The CDC’s official position is: “Community water fluoridation is one of the most practical, cost-effective, equitable, and safe measures communities can take to prevent tooth decay and improve their oral health, and is the best method of delivering fluoride to all members of the community, regardless of age, education, income level, or access to routine dental care.” Yet, in Europe with a measly 3% fluoridation rate, dental decay has declined just as much as in highly-fluoridated North America.

As Bellinger says, this single study is unlikely to shift the needle significantly. Nonetheless, the fact that such a finding survived the expert scrutiny of the editorial team should ensure its contribution to the evidence about fluoride.

The finding that children born to mothers with higher fluoride exposure during pregnancy at optimal fluoride levels show lower IQ scores should certainly stimulate thought.  Older studies have already suggested such a link. Moreover, the baby is not known to benefit in any way from maternal fluoride intake. Therefore, the conclusion would be, as Till says: “We recommend that women reduce their fluoride intake during pregnancy.”