The Fluoride IQ studies

There are now 78 out of 87 IQ studies reporting lowered IQ from exposure to elevated levels of fluoride. Since 2017 we learned that the fluoride level of 0.7 mg/L, the "optimal" level used in U.S. and Canadian drinking water fluoridation projects, can create neurodevelopmental harm to the fetus, bottle-fed infant, and child. The fetus and bottle-fed infant were never considered in any risk assessment for water fluoridation by any regulatory agency in any fluoridating country.

The Mother-Offspring Fluoride Studies

There are now 9 Mother-Offspring fluoride studies. Eight of the studies revealed that the fetus and the formula-fed infant (Till 2020) are the most vulnerable to fluoride’s neurotoxicity. Seven of the nine studies measured the urinary levels of pregnant women for fluoride as it is the most accurate indicator of daily total fluoride intake. The urinary fluoride levels taken from the pregnant mothers were compared to the IQ of their offspring (up to 12 years of age) in blinded tests where the examiners were unaware of the subject’s fluoride exposure status at the time of the neurodevelopmental exams.  Certain high levels of fluoride in the pregnant women’s urine were found to significantly impact the IQ, or neurodevelopment, of the offspring. These high urinary fluoride levels are found in pregnant women living in fluoridated cities as well as in naturally-occurring high fluoride areas. The first study on urinary fluoride levels in pregnant women in the U.S. was published in April 2020. The U.S. and Canada have the same “optimum” level for fluoridation schemes: 0.7 mg/L fluoride. Lastly, no government agency has performed a risk assessment on the effects of water fluoridation on the pregnant woman, the fetus, or the bottle-fed infant.

The studies are:

1. Li et al. (2004) reported significant differences in the behavioral neurological assessment score in 1 to 3 day-old offspring

This Chinese study, Effects of high fluoride level on neonatal neurobehavioral development, was first published in 2004, translated into English and re-published in 2008 in the journal Fluoride 41(2):165–170.

  • Ninety-one full-term, normal neonates were randomly selected for observation, 46 were male and 45 female.
  • A urine sample was collected after the pregnant women were hospitalized but before labor began
  • The standard neonatal behavioral neurological assessment (NBNA) method was used for measurements, which were carried out by professionals (pediatric department physicians working in neonatal section trained in national NBNA training program)
  • In the high fluoride group the urinary fluoride level averaged 3.58±1.47 mg/L, significantly higher than the normal range of 0.18–2.6 mg/L and was significantly different from the fluoride level in urine samples from the control group. When compared with the fluoride result in urine samples from the control group (1.74±0.96 mg/L), the difference is statistically very significant (p<0.01).
  • The two study groups are located in the same area with similar climate, living habits, economic and nutritional conditions, and cultural backgrounds. There is no industrial fluoride contamination in the endemic fluoride or the non-endemic control area. As can be seen in Table 1, there was no statistically significant difference in the delivery mode, birth weight, infant length, and sex.
  • As seen in Table 2, neonatal neurobehavioural assessment of the neonates from the high fluoride group and the control group indicated that the neurobehavioural capability and agonistic muscle tension from the high fluoride group were impaired, resulting in a statistically significant lower overall (total) assessment score than in the control group (p<0.05).
  • Table 3 shows that the various neurobehavioral capabilities, such as non-biological visual, biological visual, and auditory directional reactions of the neonates from the high fluoride group lagged behind those of the control group with differences that are statistically significant (p<0.05).

2. Chang et al. (2017) reported significant differences in the mental development index and psychomotor development index of the offspring at 3, 6, 9, and 12 months of age.

This study,  Analysis on the Effect of Coal-Burning Fluorosis on the Physical Development and Intelligence Development of Newborns Delivered by Pregnant Women with Coal-Burning Fluorosis, was conducted in China and published in the  Chinese Journal of Control of Endemic Diseases 32(8):872-873.

  • • 118 newbors in this study: The Observation Group: 68 newborns from coal-burning high-fluoride areas (called endemic fluorosis areas). The Control Group: 50 full-term newborns delivered by healthy pregnant women.
  • The type of test used: Mental development index (MDI) and psychomotor development index (PDI) (assessed using the Standardized Scale for the Intelligence Development of Children formulated by the Children Development Center of China [CDCC]).
  • The body weight, body length, head circumference, chest circumference, upper arm circumference and top arm length of newborns in the observation group were all significantly lower than those in the control group, and their differences were statistically significant (P < 0.05).
  • At 3, 6, 9 and 12 months after birth, the grades of body weight development and body-length development of infants in the control group were significantly higher than those in the observation group (P < 0.05);
  • Both the Mental development index and the psychomotor development index of infants in the observation group were significantly lower than those in the control group (P < 0.05).
  • The socioeconomic status of all the three villages were the same in both endemic and control areas.
  • The results suggest that maternal exposure to high levels of fluoride have a significant impact on the intelligence development of newborns.

3. Valdez Jiménez et al. (2017) reported lower IQ in children between the ages of 3 to 15 months.

This was the first mother-infant pair study performed by a team from three universities in Mexico. The study is titled In utero exposure to fluoride and cognitive development delay in infants by Valdez Jiménez et al. and was published in the journal Neurotoxicology on March 1, 2017. This study differs from the other two studies discussed above inasmuch as the pregnant women in the study lived in areas of high naturally occurring fluoride in the drinking water. The authors noted that “cognitive alterations in children born from exposed mothers to F could start in early prenatal stages of life.”

• this study had 65 mother-baby pairs
• the IQ testing took place between the ages of 3 to 15 months
• this study took place in an area with high naturally occurring levels of fluoride in the drinking water (called endemic hydrofluorosis areas).
• Over 81.5% of the samples of tap water were above 1.5 mg/l with the highest value of 12.5 mg/.
• 33.8% of the births were pre-term. The authors stated, “We found higher levels of F in urine across trimester in premature compared with full term.”
• The authors state, “In this study near to 60% of the children consumed contaminated water and the prevalence of children with IQ below 90 points was 25% in the control group (F urine 1.5 mg/g creatinine) in comparison with the 58% of children in the exposed group (F urine >5 mg/g creatinine)… Our data suggests that cognitive alterations in children born from exposed mothers to F could start in early prenatal stages of life.”

4. Bashash et al. (2017) reported lower IQ in children at 4 years of age and between 6 to 12 years of age.

This study by Bashash et al., titled Prenatal Fluoride Exposure and Cognitive Outcomes in Children at 4 and 6–12 Years of Age in Mexico, was published in September 2017 in the prestigious journal Environmental Health Perspectives

The researchers followed up to 299 women-offspring pairs in Mexico during a 12-year period and reported that the fluoride levels in the urine of the pregnant women was the factor for a loss of 5 to 6 IQ points in the offspring at ages 4 and 6-12 years of age. The fluoride levels in the urine of the pregnant women are similar to what is found in adults in fluoridated communities in the U.S. This study, as well as the following one by Thomas et al., was funded by the U.S. National Institutes of Health, the U.S. Environmental Protection Agency, and the U.S. NIEHS.

5. Thomas et al. (2018) reported lower IQ in children between 1 to 3 years of age.

This study by Thomas et al., titled, OPV – 2 Prenatal fluoride exposure and neurobehavior among children 1–3 years of age in Mexico, was presented at a conference on epidemiology in Germany in March 2018. Only the abstract of the study has been published in the journal Occupational & Environmental Medicine. This abstract reports pregnant women’s fluoride exposure is linked to lower IQ in their children at one- to three-years-old at levels commonly found in U.S. women. The authors of this study said that their findings “suggest higher in utero exposure to fluoride has an adverse impact on offspring cognitive development that can be detected earlier, in the first three years of life.”

6. Bashash et al. (2018) on Attention Deficit Hyperactivity Disorder:

This paper, Prenatal fluoride exposure and attention deficit hyperactivity disorder (ADHD) symptoms in children at 6–12 years of age in Mexico City, was also funded by NIEHS. The authors reported:

  • Higher concentration of maternal urinary fluoride was associated with more ADHD-like symptoms in school-age children.
  • Prenatal exposure to fluoride was most strongly associated with behavioral ratings of inattention, but not hyperactivity and impulse control.
  • Findings are consistent with the growing body of evidence suggesting neurotoxicity of early-life exposure to fluoride

7. Green et al. (2019) reported lower IQ in children between 3 – 4 years of age.

Titled Association Between Maternal Fluoride ExposureDuring Pregnancy and IQ Scores in Offspring in Canada, and published in JAMA Pediatrics, this study took place in 6 Canadian cities with 512 mother-child pairs. Women living in areas with fluoridated tap water compared with nonfluoridated water had significantly higher mean urinary fluoride concentrations. A 1-mg/L increase in urinary fluoride levels was associated with a 4.49-point lower IQ score in boys, but there was no statistically significant association with IQ scores in girls. A 1-mg higher daily intake of fluoride among pregnant women was associated with a 3.66 lower IQ score in boys and girls. According to the authors, the urinary fluoride levels observed in this study are “typically found in white North American women.” This study was also funded by the U.S. NIEHS.

8. Till et al. (2020) reported lower IQ in children at 3 – 4 years of age.

Titled, Fluoride exposure from infant formula and child IQ in a Canadian birth cohort and funded by the U.S. National Institute of Environmental Health Sciences (NIEHS), it was published in Environment International. The authors “examined whether feeding status (breast-fed versus formula-fed) modified the impact of water fluoride and if fluoride exposure during fetal development attenuated this effect.” The mothers urinary fluoride (MUF) levels were used as a proxy of fetal fluoride exposure. A second model estimated the association between fluoride intake from formula and child IQ. According to the authors:

  • Consumption of formula reconstituted with fluoridated water can lead to excessive fluoride intake.
  • Breastfed infants receive very low intake of fluoride.
  • We compared IQ scores in 398 children who were formula-fed versus breastfed during infancy.
  • IQ scores were lower with higher levels of fluoride in tap water.
  • The effect was more pronounced among formula-fed children, especially for nonverbal skills

9. Cantoral et al. (2021) reported lower IQ in children at 24 months of age.

This study, Dietary fluoride intake during pregnancy and neurodevelopment in toddlers: a prospective study in the Progress Cohort, included 103 mother-infant pairs. It was performed in Mexico where salt is fluoridated. ‘The practice of adding salt to a meal was reported by 27% of the participants.” According to the authors,

“To our knowledge, this is the first prospective and longitudinal study to examine associations between maternal fluoride intake from food and beverages during pregnancy and offspring neurodevelopment. Our findings are consistent with two other prospective cohort studies from Mexico that measured urinary fluoride levels in pregnancy…

“In the mixed-effects longitudinal model, we observed a statistically significant negative association between dietary fluoride intake in pregnancy and cognitive score (averaged across both time points) in boys, but not girls (interaction p value = 0.07) (Table 4). Specifically, a 0.5 mg increase in dietary fluoride intake during the third trimester and across pregnancy (i.e. trimesters 2 and 3) was associated with a 3.10-point (95% CI: -5.67, -0.53) and 3.46-point (95% CI: -6.23, -0.70) lower cognitive score in boys, respectively…

“In this prospective cohort study, higher exposure to fluoride from food and beverage consumption in pregnancy was associated with reduced cognitive outcome, but not with language and motor outcome in male offspring over the first two years of life. Given the ubiquity of fluoride in food and beverages, it will be important to develop recommendations for how vulnerable populations, such as pregnant women, may limit dietary fluoride intake to minimize potential adverse health risks of the unborn fetus.”

What were the fluoride levels that caused the harm?

Urine tests are a better indicator of daily total fluoride intake than is the concentration of fluoride in the drinking water. Testing urine for fluoride provides one of the best indicators for all exposures to fluoride whether its through ingestion of water and food or through inhalation.

The Bashash et al. (2017) study found a very large effect. An increase in urine fluoride of 1 mg/L was associated with a drop in IQ of 5 to 6 points. To put this into perspective with the fluoride levels ingested by the Mexican mothers and the levels ingested in fluoridated parts of the U.S., the average fluoride intake in the Mexican mothers was about the same as that in women in the U.S. It was not substantially higher. The range of fluoride levels in Mexico also corresponded closely to the range found in most of the U.S. The higher levels were similar to what is found in areas in the U.S. with fluoridated water, and the lower levels were similar to what is found in most unfluoridated parts of the U.S.

Most of the Mexican women had urine fluoride between 0.5 and 1.5 mg/L. Studies have found that adults in the U.S. have between about 0.6 and 1.5 mg/L, almost exactly the same range. From the low end of that range to the high end is a difference of 1 mg/L which is what caused the 5 to 6 IQ point difference in the children of the study.

In the latest Green et al. (2019) study, an increase in urine fluoride of 1 mg/L was associated with a drop in IQ of 4.49 points in boys. The authors noted that women living in areas with fluoridated tap water compared with nonfluoridated water had significantly higher mean urinary fluoride levels.

A 2018 national survey of urinary fluoride levels in pregnant women in Canada

This study by Till et al., published on October 11, 2018, found that pregnant women in “optimally” fluoridated Canada have significantly higher levels of fluoride in their urine than women living in non-fluoridated communities. This study also showed that pregnant Canadians had fluoride urinary levels similar to those that reduced IQ in offspring in the study by Bashash et al. (2017). The U.S. NIH-funded Bashash study reported a lowering of 5 to 6 IQ points in the offspring. These findings suggest that the results from Bashash’s Mexico City study may be appliicable to Canada and the U.S. as both countries use 0.7 mg/L fluoride in their fluoridation schemes.

The study: Till C, Green R, Grundy JG, Hornung R, Neufeld R, Martinez-Mier A, Ayotte P, Muckle G, Lanphear. 2018. Community Water Fluoridation and Urinary Fluoride Concentrations in a National Sample of Pregnant Women in Canada, Environmental Health Perspectives.


See short EPA paper

Building a Database of Developmental Neurotoxicants: Evidence from Human and Animal Studies, by Mundy et al. Note: Fluoride is listed among “Chemicals with Substantial Evidence of Developmental Neurotoxicity (n=100)”

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