F.A.N. Newsletter

Low Iodine In Pregnancy Worsens IQ Loss From Fluoride

A new study from Canada published this week in the journal Nutrients, found that pregnant women who had low iodine levels and elevated fluoride had boys who suffered an average IQ loss that was 58% greater than the already significant IQ loss from elevated fluoride alone [Goodman 2022].  Artificially fluoridated drinking water was the main source of the fluoride. The boys of women with low iodine levels lost, on average, 9.3 IQ points, while those of mothers with adequate iodine lost 5.9 IQ points, for every 1 mg/g increase in mother’s urine fluoride concentration.*  In previous work in the same group of pregnant mothers, drinking water fluoridated at 0.7 mg/L was associated with an increase of roughly 1 mg/g in urine fluoride [Till 2018].

23% of the Canadian women who took part in the new study were classified as having “low iodine”.  The iodine status of pregnant women in the USA is much worse than in Canada, with well over 50% currently meeting the criteria for “low iodine” used in this study [Watson 2020].

The authors point out that theirs was the first mother-child cohort study “to estimate the interplay between prenatal fluoride exposure and maternal iodine status in relation to child IQ”.  They also warned that “even mildly reduced iodine levels may have biological significance when interacting with fluoride.”

The study was spurred by the well-established link between low iodine during pregnancy and lowered intelligence in children, as well as previous studies finding fluoride can exacerbate the problem.  Iodine is essential for thyroid function, and the developing brain in utero critically depends on the mother’s thyroid activity.  Studies dating back to the 1930s found that fluoride can interfere with thyroid function.  More recently, there have been studies in England and Canada that have shown associations between fluoridated water and increased risk of hypothyroidism [Peckham 2015, Malin 2018].

The degree of intelligence lost from the combination of low iodine and elevated fluoride is large, at 9 IQ points from just drinking fluoridated water.  This loss of IQ can be put in context by comparing it to EPA policy that considers an average loss of just 1 to 2 IQ points as an “unacceptable risk” for public health and -1 IQ point as a standard in risk assessments of neurotoxins, including a 2021 assessment of fluoride [EFSA 2010, Budtz-Jørgensen 2013, Grandjean 2021].

The Goodman 2022 study follows up on a series of fluoride-IQ studies in Canadian and US cohorts by a team lead by Christine Till, PhD and funded by the National Institutes of Health (NIH) through the National Institutes for Environmental Health Sciences (NIEHS). 

Click here to see the following studies for example:
Goodman 2022
Till 2020
Green 2019
Cantoral 2021
Grandjean 2021

Their most prominent study was Green 2019, published in the Journal of the American Medical Association Pediatrics, and which garnered amongst the highest attention scores of any scientific article published in recent years [Altmetric score].  The Green 2019 study included an alternative measure of fluoride, which was the estimated milligrams per day (mg/d) intake based on tap water fluoride concentration and consumption plus fluoride from tea.  Using that measure of fluoride intake, loss of IQ was found not just for boys, but also for girls.  The authors offered several explanations for why, in their analysis with urine fluoride as the exposure measure, only the boys lost IQ.  The same explanations may apply to the Goodman 2022 study, which found lowered IQ in boys but not girls, associated with mother’s urine fluoride.

FAN Senior Advisor Paul Connett PhD, said of this newest study linking fluoride to IQ loss: “With over half of pregnant American women meeting this study’s criteria for low iodine, and with 2/3rds of the United States fluoridated, this results in a huge number of children at increased vulnerability to fluoride’s neurotoxic effects.  The arguments now being voiced by fluoridation’s defenders that fluoride’s benefits against tooth decay need to be balanced against its neurotoxicity ring hollow.  Permanently damaged brains far outweigh a saving of no more than about 1 cavity per child.”

Chris Neurath
Research Director
Fluoride Action Network

* Urine fluoride was adjusted for dilution by dividing by the concentration of creatinine.  This gives fluoride exposure in units of mg/g or milligrams of fluoride per gram of creatinine.