Fluoride Could be the Cause of Hypothyroidism in Pregnant Women

Highlights:

Fluoride exposure has been associated with pregnancy-induced hypothyroidism
Thyroid function is critical for prenatal brain development
Fluoride exposure during pregnancy is linked to reduced IQ in boys

Fluoride in drinking water may raise the risk of hypothyroidism in pregnant women. The researchers discovered lower IQ scores in boys whose mothers had hypothyroidism compared to boys whose moms had normal thyroid levels in a smaller subset of subjects () .

According to York neuropsychology Ph.D. student Meaghan Hall, the main author of this current study, previous research done by the same lab at York indicated a link between maternal fluoride exposure during pregnancy and lower IQ in boys, and this new research may explain these earlier findings.

‘Fluoride in drinking water has been linked to an increased risk of hypothyroidism in pregnant women. It was also noted that there was a lower Intelligence Quotient score recorded in boys whose moms had hypothyroidism compared with boys whose mothers had normal thyroid levels.’

"We know from the literature that there is a link between high levels of fluoride exposure and thyroid disruption, and there is also an established link between untreated hypothyroidism in pregnancy and unfavorable childhood outcomes," Hall says. "Our latest study may provide a potential mechanism to explain correlations to lower IQs in boys born to moms with higher fluoride exposure. It is part of a growing body of evidence suggesting that prenatal fluoride exposure may be connected to poor cognitive outcomes in children."

About the Study

The study, which was published in Science of the Total Environment, followed more than 1,500 women who were part of the Maternal Infant Research on Environmental Chemicals (MIREC) study, an ongoing, multi-year study led by Health Canada to investigate the impact of environmental chemicals on vulnerable populations such as pregnant women and infants. Women were recruited from ten Canadian cities, seven of which have fluoridated water. The researchers only looked at pregnant women who reported consuming tap water. The mothers were tracked throughout their pregnancies, and their children were followed after birth and into early infancy.

A half-milligram-per-liter increase in drinking-water fluoride levels, which may not seem like much but is roughly the difference in exposure level between a fluoridated and non-fluoridated community, was associated with a 1.65-fold increase in the odds of having a diagnosis of or meeting criteria for hypothyroidism in pregnancy, according to the study.

"This translates into a 66% increase in risk," says Christine Till, Hall's supervising professor, senior author on the study, and clinical neuropsychologist who directs the Till Lab at the Faculty of Health, which analyzes how various environmental exposures affect children's health. "The findings are troubling because hypothyroidism is a known cause of brain abnormalities in youngsters," Till explains.

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Hall and Till hope that policymakers will take these new findings into account when assessing the safety of community water fluoridation.

How Exposure to Fluoride Results in Hypothyroidism

Previous research investigating the link between fluoride exposure and hypothyroidism has largely been done on lab animals, children, and people living in fluoride-rich areas of the world. Fluoride's capacity to inhibit the thyroid has been known since the 1930s, when it was used to treat hyperthyroidism, or an overactive thyroid.

According to Hall, the mechanism by which fluoride may interfere with thyroid function is not totally apparent, although it may interfere with specific enzymes and iodine absorption, which is necessary for thyroid hormone production.

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Women are more likely than men to develop hypothyroidism, a disorder in which the body does not synthesize enough thyroid hormones, resulting in symptoms such as fatigue, weight gain, and sadness. The demands placed on the thyroid system grow significantly during pregnancy, particularly during the first trimester when the fetus is entirely dependent on maternal thyroid hormones.

The researchers examined fluoride exposure from tap water as well as other dietary sources, including black tea, which is naturally high in fluoride. The researchers also tested urine fluoride levels and discovered no relationship between hypothyroidism and fluoride levels. According to the researchers, fluoride levels in tap water may be a more trustworthy measure of long-term fluoride exposure than urine levels, which may correspond better with short-term exposure.

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Fluoridated drinking water is available to approximately four in ten Canadians and seven in ten Americans who rely on public water systems. Fluoride compounds are added to tap water to minimize cavities in the population, which is a primary source of fluoride exposure.

Reference:

Fluoride exposure and hypothyroidism in a Canadian pregnancy cohort - (https://pubmed.ncbi.nlm.nih.gov/36764861/)

Source-Medindia