New Studies Link Fluoride to Reduced IQ and ADHD in Children

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In this series, we explore the contentious findings surrounding fluoridation of the U.S. public water supply and answer the question of whether water fluoridation poses a risk and what we should do about it.

Previously: Decades of research have raised concerns about the safety of water fluoridation. In 2006, the National Research Council urged further investigation into fluoride exposure’s impact on endocrine function and brain health, resulting in recent NIH-funded studies addressing these issues.

In 2006, concerns about fluoride exposure in sensitive subpopulations arose when the National Research Council’s (NRC) Committee on Fluoride in Drinking Water conducted a scientific review of the Environmental Protection Agency’s (EPA) fluoridation standards.

The review mentioned particular concerns regarding infants and young children after it looked at the estimated aggregated total fluoride exposures from pesticides, background food, air, toothpaste, and drinking water.

The NRC committee warned that “on a per-body-weight basis, infants and young children have approximately three to four times greater exposure than do adults.”

Due to the NRC’s subsequent concerns, several peer-reviewed studies funded by the U.S. National Institutes of Health (NIH) followed, investigating the effects of pre- and postnatal fluoride exposure on neurodevelopment.

An ongoing federal lawsuit that began in 2017, brought against the EPA by the Fluoride Action Network (FAN) to remove fluoride from public drinking water, has also brought attention to significant research on health issues associated with drinking fluoride. 

Two principal scientists leading NIH-funded studies, Dr. Howard Hu and Dr. Bruce Lanphear, have testified as expert witnesses for FAN.

New Studies on Prenatal, Postnatal Risks of Fluoride Exposure

Hu and Lanphear are known for their seminal research on the impact and neurotoxicity of lead exposure, and both have worked with the EPA in expert advisory roles.

Their NIH-funded multi-year studies from Mexico and Canada have shown that early-life fluoride exposures were negatively associated with children’s performance on cognitive tests.


The Maternal-Infant Research on Environmental Chemicals (MIREC) Study is a multi-year research study led by Health Canada. “The study was designed to produce new knowledge on Canadians’ exposure to environmental chemicals and address data gaps on vulnerable populations in Canada, including infants, children, and pregnant women,” Health Canada’s website states.

The original study was the basis for a platform for various follow-up studies that looked at multiple chemical exposures. Multiple MIREC-based studies have looked at fluoride exposures.

MIREC’s cohort study of fluoride and IQ was funded by a grant from the NIH. Lanphear has been involved with the study for more than 10 years and is one of the principal investigators for the study’s neurobehavioral assessments. He oversaw the neurodevelopmental assessments.

The study, “Association Between Maternal Fluoride Exposure During Pregnancy and IQ Scores in Offspring in Canada,” was published in JAMA Pediatrics in 2019. It examined mother-child pairs from six major cities comparing fluoridated and non-fluoridated areas in Canada.

Data was collected over a five-year period and children’s IQs were assessed at ages 3 to 4 years using the Wechsler Primary and Preschool Scale of Intelligence-III.

The analysis showed several outcomes:

  • Every 1 milligram per liter (mg/L) increase in fluoride levels in maternal urine was associated with a statistically significant loss of 4.49 IQ points in boys, but not in girls.
  • Every 1 mg higher daily intake of fluoride from beverages was associated with a loss of 3.66 IQ points in girls and boys.
  • Every 1 mg/L higher concentration of fluoride in water was associated with a loss of 5.29 IQ points in girls and boys.

The research team concluded that findings indicated “the possible need to reduce fluoride intake during pregnancy.”

The study triggered a backlash, with an international cohort of scientists calling for a probe of the study. York University and JAMA Pediatrics have stood behind the work.

Because of concerns that infant consumption of formula reconstituted with fluoridated water may lead to excessive fluoride intake, a second MIRECS-based study was published in January 2020 in the journal Environment International. That study, “Fluoride Exposure from Infant Formula and Child IQ in a Canadian Birth Cohort” looked into the formula-fluoride issue.

The study examined two criteria. First, it investigated the association between water fluoride concentration and the intellectual abilities of Canadian children who were formula-fed versus breastfed.

Second, it tested the postnatal effects of fluoride exposure on child IQ after controlling for fetal exposure.

The study found a decrease of 4.4 full-scale intelligence quotient (FSIQ) points among preschool children who were formula-fed in the first six months of life for each 0.5 mg/L increase in water fluoride concentration.

The authors noted that 0.5 mg/L is roughly the difference between a fluoridated (0.59 mg/L) and non-fluoridated (0.13 mg/L) community.

The authors also state that they “did not find a significant association between water fluoride concentration and FSIQ among exclusively breastfed children.”

The findings also suggest that both prenatal and early childhood fluoride exposure affect the development of nonverbal intelligence to a greater extent than verbal intelligence.

A 0.5 mg/L increase in water fluoride level predicted a decrease in performance intelligence quotient (PIQ) in both the formula-fed (-9.3 points) and the breastfed groups (-6.2 points).

The research team concluded that fluoride intake among infants younger than 6 months may exceed the tolerable upper limits if they are fed exclusively with formula reconstituted with fluoridated tap water.

“It is prudent to limit fluoride exposure by using non-fluoridated water or water with lower fluoride content as a formula diluent,” the researchers noted.

One of the most recent MIREC studies, “Fluoride Exposure and Hypothyroidism in a Canadian Pregnancy Cohort” published in Science of the Total Environment in April, was led by York University researchers.

It found that fluoride affects thyroid function and increases the risk of hypothyroidism in pregnant women, which is a known cause of brain-based disorders in children that may affect their learning ability.

”The safety of fluoride intake in pregnancy has not been well studied. We conducted our study to address the gaps in our knowledge about the potential health effects of fluoride in pregnant women living in cities with optimally fluoridated water,” lead author, Meaghan Hall, a doctoral student at York University in Toronto, wrote in an email to The Epoch Times.

She added that because we are exposed to fluoride from a variety of sources, with the largest source being fluoridated tap water, the public should be aware of both the benefits and health risks of fluoride.

A February York University press release reported that a 0.5 mg/L increase in drinking water fluoride level—roughly the difference between a fluoridated and non-fluoridated community —was associated with a 65 percent increase in clinical hypothyroidism among pregnant women.

“Our research on pregnant women suggests that fluoride, even at low levels of ingestion, may have a deleterious effect on fetal development, Hall said.

Their press release noted that studies have revealed, children born to mothers with hypothyroidism tend to have lower IQ scores, particularly among boys, compared to children born to mothers with normal thyroid levels.

“We found that higher concentrations of fluoride in drinking water during pregnancy was strongly associated with increased odds of hypothyroidism. This is important because insufficient thyroid hormone in pregnancy may adversely impact fetal development and future learning ability of the child,” Hall said.


In 1993, Howard Hu, the scientist mentioned above, co-founded the Early Life Exposures in Mexico to Environmental Toxicants (ELEMENT) project, a pregnancy and birth cohort study funded by EPA and NIH, studying how environmental toxicants impact children’s health. His award-winning project has involved collaborators at top institutions, generating 80-plus publications influencing global environmental health policies.

In 2012, Hu’s team successfully competed for a peer-reviewed NIH RO1 grant to study fluoride’s neurodevelopmental effects of pre- and postnatal fluoride exposures, which included looking at a possible link between fluoride exposure and attention deficit hyperactivity disorder (ADHD).

“This research was funded with an understanding that it would provide a major contribution to fluoride risk assessment and policy decision-making on the neurotoxicity concerns identified by the NRC,” Hu said in his May 2020 expert witness declaration in the fluoride lawsuit against the EPA.

Their September 2017 study, “Prenatal Fluoride Exposure and Cognitive Outcomes in Children at 4 and 6–12 Years of Age in Mexico,” published in Environmental Health Perspectives, resulted in similar outcomes as Lanphear’s cohort studies.

The research team found that each 0.5 mg/L increase in prenatal fluoride exposure was significantly associated with a loss of 3.15 General Cognitive Index (GCI) points among the 4-year-olds, and a loss of 2.5 IQ points among the 6-to-12-year-olds.

“These are substantial reductions in intelligence that rival the effect sizes associated with lead exposure,” Hu said in his witness declaration.

Hu notes that in contrast with prenatal exposures, they didn’t find statistically significant associations between IQ and childhood urinary fluoride levels at ages 6 to 12, although there was some suggestion of an adverse effect.

“This suggests that the timing of fluoride exposure is an important determinant of fluoride’s neurodevelopmental effects, and is consistent with exposures occurring prenatally being more detrimental than those occurring during school-aged years,” he said

In their December 2018 study, “Prenatal Fluoride Exposure and Attention Deficit Hyperactivity Disorder (ADHD) Symptoms in Children at 6–12 Years of Age in Mexico City,” published in Environment International, the team investigated 213 mother-offspring pairs, with the ADHD assessment conducted between ages 6 and 12.

“The effect sizes between prenatal fluoride and ADHD behaviors in our cohort were substantial,” Hu said in his 2020 declaration.

The study found that increases of 0.5 mg/L in maternal urinary fluoride were associated with 2.4-to-2.8-point higher scores (higher scores reflect indicate poorer performance on the ADHD behavior scale).

“It is my opinion, to a reasonable degree of scientific certainty, that the results of the ELEMENT studies support the conclusion that fluoride is a developmental neurotoxicant at levels of internalized exposure seen in water fluoridated communities,” Hu said.

The Debate Continues

Despite Hu and Lanphear’s studies, there is still significant debate around the prenatal and postnatal toxicity of fluoride in the scientific community.

The Infancia y Medio Ambiente (INMA) Project, a network of birth cohorts in Spain that aim to study the role of environmental pollutants in air, water, and diet during pregnancy, recently studied fluoride effects on prenatal exposure.

The study, “Prenatal Exposure to Fluoride and Neuropsychological Development in Early Childhood: 1-to 4 Years Old Children” published in May 2022 in Environmental Research, examined 248 mother-child pairs in both fluoridated and non-fluoridated areas.

The highest levels of fluoride in community drinking water that pregnant mothers were exposed to in the study were slightly above 0.8 mg/L and the lowest levels were below 0.10 mg/l.

Researchers said that the results of their study could support the view that fluoride has a detrimental effect with exposure through community drinking water at levels above 0.8 mg/l as previously suggested in the ELEMENTAL studies but they say that fluoride may have a positive effect at lower levels although they don’t specify what those levels may be.

“The positive associations between the maternal urinary fluoride level adjusted for creatinine (MUFcr) and cognitive functions seemed to be more evident in children of mothers who lived their pregnancy in the non-fluoridated zones,” the research team noted.

They suggest that fluoride could have a dose-response effect like those of other chemical elements essential for life, showing a different behavior at levels in the range of or lower than those recommended by agencies such as the World Health Organization.

The researchers concluded that “further studies should be carried out before ruling out a potential beneficial effect of F [fluoride] at low levels in natural or FCDW [fluoridated community drinking water].”

Currently, the CDC says it’s safe to use fluoridated water for preparing infant formula but warns that if a child is only consuming infant formula mixed with fluoridated water, there may be an increased chance for mild dental fluorosis.

They recommend alternating with bottled water without any fluoride, which is labeled as de-ionized, purified, demineralized, or distilled.

There is still limited knowledge on the toxicity of fluoride for sensitive subpopulations.

In a 2020 deposition clip provided to The Epoch Times by the Fluoride Action Network, when asked by plaintiff attorney Micheal Connett whether the CDC has any data from the published literature that would define the tolerable upper fluoride intake for neurotoxic effects on children, Casey Hannan, CDC oral health director responded, “As a rep of CDC, to my knowledge, we don’t have any knowledge about that. ”

Next: Your lifetime dose of fluoride depends on how much fluoridated water you drink and how much fluoride you get from other sources like tea, food, dental products, air, and pesticide residue. Dose can define the harm, and different bodies respond to different amounts.

Read Part 1 – The Renewed Scientific Opposition to Water Fluoridation

Read Part 2 – Uncovering the Differences: Why Natural Fluoride and Synthetic Fluoride Are Not Created Equal

Read Part 3 – Fluoride: A Miracle Cure for Cavities, a Poison, or Both

Read Part 4 – Health Effects of Fluoride: The Science

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