While some research relates to the neurotoxic effects of fluoride in adults, recent focus has been on fluoride’s neurotoxicity to the developing brain, in infancy and even in utero.

The most recent, and most important so far, is a study published in JAMA Pediatrics August 2019, Association Between Maternal Fluoride Exposure During Pregnancy and IQ Scores in Offspring in Canada. This is a landmark study that looked at the fluoride urine levels and the fluoride level in the water of Canadian pregnant women and found children exposed to fluoride in utero has significantly lowered IQ. The mean level of fluoride in the Canadian mothers (0.59mg/l) was greater than the mean level found in the New Zealand mothers (0.82 mg/l) in the only New Zealand study to measure this. Their water fluoridation levels are also lower (0.7ppm compared to 0.85ppm).

In September 2017 a US Government funded study was published in the US Government’s Environmental Health Perspectives. This is another landmark study that found children exposed to fluoride in utero has significantly lowered IQ. The level of fluoride the Mexican mothers were exposed to is the same as the New Zealand women. See here for more information.

As at July 2019 there are 60 human studies that have looked at fluoride exposure and effects on brain function. 53 of these show fluoride’s damaging effect: lowered IQ, behavioral deficits, nervous disorders, and memory disruption. There are also hundreds of animal studies showing fluoride’s adverse effects on the brain.

The US Government Review 2006

In 2006 the US Government’s National Research Council produced a Report Fluorides in Drinking Water p 222. This was a 12-member, three-year review and is still the most comprehensive review of fluorides in water to date.

This panel concluded that “it is apparent that fluorides have the ability to interfere with the functions of the brain”. At this stage there were only five published studies.

The Meta Analaysis

By 2012 there were 27 studies. A team of researchers from Harvard then published a meta-analysis of these in Environmental Health Perspectives. Twenty-five of the studies were from China and two from Iran. The Harvard team acknowledged that there were weaknesses in many of the studies. However, they stressed that the results were remarkably consistent. In 26 of the 27 studies average IQ in the “high fluoride” village was lower than the “low fluoride village “. The average loss was 7 IQ points.

New Zealand Report

In 2014, a review commissioned by the Prime Minister of NZ’s Chief Science Advisor Sir Peter Gluckman and the Royal Society of New Zealand’s president Sir David Skegg, Health Effects of Water Fluoridation: a Review of the Scientific Evidence, concluded:

“Recently there have been a number of reports from China and other areas …that have claimed an association between high water fluoride levels and minimally reduced intelligence (measured as IQ) in children.…the claimed shift of less than one IQ point suggests that this is likely to be a measurement or statistical artifact of no functional significance”

However, they had incorrectly interpreted the figure of 0.45 as less than one IQ point, whereas, it was less than one standard deviation. See Table 1 below. When this error was pointed out to the authors, they changed the premise but did not change the conclusion.

“Recently there have been a number of reports from China and other areas …that have claimed an association between high water fluoride levels and minimally reduced intelligence (measured as IQ) in children.…the claimed shift of less than one standard deviation suggests that this is likely to be a measurement or statistical artifact of no functional significance”.

This will no doubt have led many people in New Zealand to believe there was no reported drop in IQ, when in actual fact these studies did show an average drop of 7 IQ points. A drop of 5 IQ points across society will halve the number of geniuses and increase by 50% the number of mentally impaired. This is not a “minimal reduction” and it is definitely of “functional significance”.

Table 1

The Lancet
In 2014 a study Neurobehavioural effects of developmental toxicity identified fluoride as “an emerging developmental neurotoxin”. The authors say “In 2006, we did a systematic review and identified five industrial chemicals as developmental neurotoxicants: lead, methylmercury, polychlorinated biphenyls, arsenic, and toluene. Since 2006, epidemiological studies have documented six additional developmental neurotoxicants—manganese, fluoride, chlorpyrifos, dichlorodiphenyltrichloroethane, tetrachloroethylene, and the polybrominated diphenyl ethers.”

Broadbent et al

By 2016 there were 55 human studies with 49 showing a lowering of IQ in high fluoride villages. One of the six studies that did not find an association was the Broadbent study from Dunedin. However this study reported very few controls: 891 lived in fluoridated area, and only 99 in non-fluoridated. In an article for the Government’s National Fluoridation Information Service, Broadbent admitted that 46 of the children in the nonfluoridated area were taking fluoride supplements, bringing their control down to only 53 compared to over 900 (taking fluoride supplements results in the same level of fluoride as drinking fluoridated water). This study did not allow for maternal IQ, the biggest known predictor of IQ, nor maternal exposure to fluoride, as we will see may be the most important aspect. Note also that this study was conducted by dentists, not neuroscientists. Dr Broadbent was fluoridation spokesperson for the NZ Dental Association at the time.

Bashash 2017

In September 2017, a landmark IQ study, Prenatal Fluoride Exposure and Cognitive Outcomes in Children at 4 and 6–12 Years of Age in Mexico, was published in Environmental Health Perspectives, the world’s leading environmental health science journal.

The funding agencies for this study were U.S. National Institutes of Health (NIH), U.S. National Institute of Environmental Health Sciences (NIEHS), U.S. Environmental Protection Agency (EPA), National Institute of Public Health, and the Ministry of Health of Mexico.

This study was completed by a team of distinguished neurotoxicity researchers who have produced over 50 papers on the cognitive health of children as related to environmental exposure to other toxins like lead and mercury. The researchers were from highly respected Universities in North America such as Harvard, Toronto, McGill and Michigan and Public Health in Mexico.

The study reported that for every 0.5 mg/L increase of fluoride in the urine of the mothers there was a statistically significant decrease in average IQ of the children of about 3 IQ points.

Therefore, a fluoride level increase in urine of 1 mg/L could result in a loss of 5 – 6 IQ points. This is particularly relevant to the New Zealand situation where fluoride urine levels have been found to be in exactly the same range as the Mexican women.

The lead investigator had this to say: “This is a very rigorous epidemiology study. You just can’t deny it. It’s directly related to whether fluoride is a risk for the neurodevelopment of children. So, to say it has no relevance to the folks in the U.S. seems disingenuous…” – Dr. Howard Hu, Dean of the Dalla Lana School of Public Health at the University of Toronto on Bashash et al. (Sept 2017).

Relating Bashash to NZ

The range of urinary fluoride levels in the Mexico City pregnant women are almost identical to the range found in Palmerston North by Brough et al, 2015

The exact median and quartile values for Bashash are 0.82 (0.64, 1.07) mg/L urine F.

Brough found a median concentration of 0.82 (0.62, 1.03) mg/L urine F.

Note the numbers in parenthesis are the 25th and 75th Inter-Quartile percentile values

The exposures in the Bashash study are about as similar to those in New Zealand as you could get.

Canadian study has confirmed Bashash

On the 28th of August 2018, a study was presented at the ISES – ISEE Joint Annual Meeting in Ottawa, Canada. This study was carried out using data from pregnant women in Canadian towns and cities both fluoridated and not. They have found the same results as the Bashash study.

It is expected that this study will be published in the the latter half of 2019.

Concentration vs dose vs blood levels

As much research is conducted on laboratory rats, it is important to understand the irrelevance of the water-concentration of fluoride and the relevance of the final blood plasma levels of fluoride. rats drink very little water in relation to body weight compared with humans. They also absorb less through the intestine. So rats have to be given water with much higher concentrations of fluoride to result in the same levels of fluoride in the blood as humans, and it is this level that is critical. This is important, as fluoride promoters falsely claim that the higher water concentrations of fluoride used invalidate the rat studies’ relevance to water fluoridation. Be assured, they DO NOT. This is just spin.

It should also be noted that rats are less susceptible to nervous system damage than humans at the same blood-fluoride levels.

Older research

In 1995, Phyllis Mullinex et a (Neurotoxicity of sodium fluoride in rats), quite unexpectedly, that fluoride fed to mother rats resulted in offspring that suffered from either malaise or ADHD-like symptoms. depending on whether the mother was given fluoride before or after birth. Males were most sensitive to pre-natal exposure, whereas females were most sensitive to post-natal and adult exposure.

In 2007 a Scientific Consensus Statement identified that the developing brain is much more susceptible to neurotoxins than the adult brain. This is particularly so before 6 months of age, as the blood-brain barrier is not fully formed until that age. This places bottle-fed infants at particular risk of their formula is made with fluoridated water.

Also in 2007 the prestigious medical journal Lancet described fluoride as “an emerging neurotoxin” in this context, and as being “an obvious candidate” for being so.

Numerous IQ studies from China and elsewhere identified a lowering of IQ with increasing fluoride exposure in children. Fluoride promoters tried to dismiss these studies as unsound. However, a review led by the Harvard School of Public Health in 2012 confirmed that they raised valid concerns. This is a summary of their findings. The full Harvard IQ report can be viewed here.

Fluoride readily crosses the placenta. (ATSDR 2003) Fluoride exposure to the developing brain, which is much more susceptible to injury caused by toxicants than is the mature brain, may possibly lead to damage of a permanent nature (US EPA 2011).

The review more systematically addresses study selection and exclusion information, and is overall more comprehensive than previous reviews.

As noted by the NRC 2006, assessments of fluoride safety have relied on incomplete information on potential risks. In regard to developmental neurotoxicity, much information has been published but these have not been available to most expert committees.

“The results suggest that fluoride may be a developmental neurotoxicant that affects brain development at exposures much below those that can cause toxicity in adults.”

“In conclusion, our results support the possibility of adverse effects of fluoride exposures on children’s neurodevelopment. Future research should formally evaluate dose-response relations based on individual-level measures of exposure over time, including more precise prenatal exposure assessment and more extensive standardised measures of neurobehavioural performance.”

“The estimated decrease in average IQ associated with fluoride … may seem small and may be within the measurement error of IQ testing. However, as research on other neurotoxicants has shown, a shift to the left of IQ distributions in a population will have substantial impacts, especially among those in the high and low ranges (Bellinger 2007)”

The review found a correlation between fluoride exposure and lowered IQ independent of other potential causes such as arsenic and low iodine. It further found that, from the geographical distribution of the studies and the local mineral content, it was unlikely that the effect was due to neurotoxicants other than fluoride.

“Although the studies were generally of insufficient quality, the consistency of their findings adds support to existing evidence of fluoride-associated cognitive deficits, and suggests that potential developmental neurotoxicity of fluoride should be a high priority for research.”

These findings are supported by US Government data published by the Centers for Disease Control and Prevention in 1993. These data show a clear correlation between the rate of mental retardation per capita in children, and the percentage of the population exposed to water fluoridation (0.7 to 1.2 ppm in the US).

Adult and general neutotoxicity

In 2004, Guan et al showed that fluoride inhibited nicotinic acetylcholine receptors (nAChRs) in the brain (in laboratory rats) – a crucial part of the nervous system. The association with Central Nervous System disorders has been researched by Dr. Agneta Nordberg, a Swedish neurotoxicologist and expert on nAChRs: “The [nAChRs] in the brain are important for functional processes, including cognitive and memory functions… The nAChRs are found to be involved in a complex range of central nervous system disorders including Alzheimer’s disease (AD), Parkinson’s disease, schizophrenia, Tourette’s syndrome, anxiety, depression, and epilepsy.”

Alzheimers’ Dementia

The link with Alzheimers’ was reported by Varner et al in 1998, and Nordberg (Ref: Nordberg. Biological Psychiatry 2001; vol. 49; pp. 200-10.)

Review –  Effects of Fluoride on the Central Nervous System – Valdez-Jiménez et al[1]

This is a literature review. The review is helpful in canvassing literature on fluoride’s neurotoxicity. The review’s focus is on water fluoride levels higher than that used in water fluoridation. However the issue with fluoride toxicity is not the level in water but the total daily intake. Levels at which fluoride neurotoxicity is shown by the research canvassed in this review are reached by some members of communities fluoridated at 0.7 to 1 ppm. The studies do not address the proportion of the population with heightened sensitivity to fluoride toxicity.

The review identifies the following research findings:

  • “Various studies, both clinical and experimental, have reported that Fluoride causes alterations on the morphology and biochemistry brain, affecting neurological development of individuals and, therefore, functions related to cognitive processes, such as learning and memory. “
  • “Fluoride is capable of crossing the blood-brain barrier, which may cause biochemical and functional changes in the nervous system during pregnancy. Since the Fluoride accumulates in brain tissue before birth it has been reported that exposure of the embryo to Fluoride during pregnancy is associated with impaired learning.”
  • Research results suggest that the accumulation of Fluoride in the tissue can disrupt brain neurotransmitters synthesis and nerve cell receptors, have a specific effect on protein synthesis in the brain, leading degenerative changes in neurons and changes in the cerebellar cortex. These changes indicate that Fluoride can slow growth and cell division in the cortex, and that the smaller number of mitochondria, microtubules and synaptic vesicles in the terminal may decrease efficacy between the neural connections, produce abnormal operation, and influence synaptic development during postnatal life.

The study recommends that people in communities with more than 0.7ppm fluoride in the water avoid all other sources of fluoride, including toothpasteof safety on the (false) claim that dental fluorosis is only cosmetic. That argument cannot apply in the case of neurotoxicity, hence the usual safety margin of 10 would be appropriate (i.e. less than 0.1ppm).

[1] Valdez-Jiménez L, Soria Fregozo C, Miranda Beltrán ML, Gutiérrez Coronado O, Pérez Vega MI. “Effects of the fluoride on the central nervous system” Neurologia 2011 Jun; 26(5):297-300. Epub 2011 Jan 20.