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.
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 concentartions 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.
In 1995, Phyllis Mullinex and others showed, 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.
In 2007 a Scientific Consensus Statement identified that the developing brain is much more susceptible to neurotoxins than the adult brain. This is partiocularly 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 formul;a 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 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.”
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
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).
 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.