Tag Archives: rats

Not just another rat study

A new high-quality study of the effect of fluoride on the memory and learning behaviour of rats has produced definitive results. Anti-fluoride campaigners had great hopes this study would bring an end to community water fluoridation (CWF) – but their hopes have been dashed.

The study showed no effect of fluoride on the memory, learning and motor skills of rats thus reinforcing the consensus that CWF is safe

Animal experiments are commonly used to investigate possible health effects of chemicals like fluoride. This enables strict research protocols without the ethical problems faced by human studies. Consequently, there have been a large number of investigations of the effect of fluoride on animals. Some of these have suggested harmful effects. The US anti-fluoride activist organisation, the Fluoride Action Network (FAN) lists 45 studies “where mice or rats treated with fluoride were found to suffer impairments in their learning and/or memory abilities” (see FLUORIDE AFFECTS LEARNING & MEMORY IN ANIMALS).

FAN claims these and similar studies as irrefutable evidence that CWF is harmful – particularly in their major campaign claiming CWF lowers IQ and should be stopped. However, a more scientific assessment is far less dogmatic.

The US National Toxicity Program (NTP) examined published research of potential neurological effects from fluoride exposures in experimental rodent animals in a systematic review published in 2016 (see Systematic literature review on the effects of fluoride on learning and memory in animal studies). They found many of the studies had limitations due to confounding in the learning and memory assessments and there was a lack of discrimination between motor and learning skills. Very few of the studies were made at drinking water concentrations relevant to CWF and the evidence for adverse effects was “low to moderate,” and weakest for animals during their developmental phase.

The NTP concluded further research was needed and undertook laboratory studies with rodents to fill the research gaps it had identified. Those studies are now complete and have been published in a research paper:

McPherson, C. A., Zhang, G., Gilliam, R., Brar, S. S., Wilson, R., Brix, A., … Harry, G. J. (2018). An Evaluation of Neurotoxicity Following Fluoride Exposure from Gestational Through Adult Ages in Long-Evans Hooded Rats. Neurotoxicity Research. Neurotoxicity Research.

The laboratory experiment

The authors used four treatments for the rats:

  • G1: Fed standard rodent chow;
  • G2: Fed low-fluoride chow;
  • G3: Fed low-fluoride chow + drinking water with 10 ppm F;
  • G4 Fed low-fluoride chow + drinking water with 20 ppm F.

Effects of drinking water F were determined by comparing results for G3 and G4 with G2.

The drinking water fluoride concentrations still seem high (compared with the recommended level of 0.75 ppm for CWF) but are lower than used in most earlier studies (often around 100 ppm). However, the basis for these choices was the use of the US secondary drinking water standard (2 ppm) and US UPA maximum contaminant level (4 ppm) and “the conventional wisdom that a 5-fold increase in dose is required to achieve comparable human serum levels.” However, this “wisdom” is debated as blood serum levels fluctuate.

These drinking water concentrations are still far higher than the recommended optimum level for CWF (0.75 ppm) so the results should be seen as more related to the defined upper limits than to CWF itself.

Behavioural assessments

A range of behavioural assessments was made. These included:

“motor, sensory, or learning and memory performance on running wheel, open-field activity, light/dark place preference, elevated plus maze, pre-pulse startle inhibition, passive avoidance, hot-plate latency, Morris water maze acquisition, probe test, reversal learning, and Y-maze.”

The purpose of using such a wide range was to overcome deficiencies of the measurements made in earlier studies and to fill in gaps. Animals at the developmental stage were included as most earlier studies had been made with adult rats.

“No significant differences observed”

One of the most commonly used phrases in this paper as the results are presented and discussed is that there were “no significant differences observed across groups.”

The authors note in their abstract that they “observed no exposure-related differences” in any of the behavioural tests listed above.

This result is important. The study is authoritative. The chosen experimental protocols resulted from an extensive systematic review of the earlier work which identified gaps and deficiencies. A very wide range of behavioural tests was used. And the experimental plans were discussed very widely before the experiments began.

We can conclude, therefore, that rodent experiments are unlikely to show behavioural effects related to fluoride exposure at the concentrations which, the authors argue, are relevant to the recommended maximum drinking water standard (2 ppm) and maximum contaminant level (4 ppm) for humans. The argument that this result is relevant to humans is strengthened by the possibility that ““the conventional wisdom that a 5-fold increase in dose is required” to make results relevant for humans may be inflated.

The argument is further strengthened for humans as the recommended drinking water fluoride concentrations for humans is even lower than the maximum drinking water standard and the maximum contaminant level.

Other assessments

The researchers also analysed thyroid hormones and examined collected tissues. They reported:

“No exposure-related pathology was observed in the heart, liver, kidney, testes, seminal vesicles, or epididymides.”


No evidence of neuronal death or glial activation was observed in the hippocampus at 20 ppm F.”

In fact, the only statistically significant effects they found were a “mild inflammation in the prostate gland” and “evidence of mild fluorosis in adults” at 20 ppm F (treatment G4). Remember this level corresponds to the maximum contaminant level for humans and dental fluorosis has also been reported for humans at that concentration.

The anti-fluoride spin

Several years ago I discussed the planned NTP work and the reaction of anti-fluoride campaigners to it in my article Fluoride and IQ – another study coming up.

These campaigners seemed ecstatic about the planned NTP work, although I did comment:

“You wouldn’t think the anti-fluoride crowd would welcome such a careful analysis of the poor-quality articles they promote”

However, Fluoride Free NZ revealed the spin they placed on the NTP document describing the systematic review and the planned work in their press release at the time (see Fluoride-Brain Studies Set to Expose Fluoridation Damage):

“Results could mean the end to fluoridation world-wide, and definitely should put a halt to any plans to start fluoridation in places not currently fluoridated.

Because it is now well established that fluoride affects the brain, the NTP plans to conduct new animal studies to determine the lowest dose at which this damage occurs. They also plan to do a systematic review of all the existing scientific literature. To date, there have been 314 studies that have investigated fluoride’s effects on the brain and nervous system. These include 181 animal studies, 112 human studies, and 21 cell studies.”

I commented on this:

“The confirmation bias and dogmatic agenda stick out like a sore thumb – don’t expect these people to accurately report this study’s findings.”

Well, it seems that these campaigners are still stuck in dumb shock of the denial phase as they have yet to make any comment on these research results. When they do get around to overcoming their speechlessness they are going to be hard put to reconcile this denial with their earlier hopes for the research findings.

There is no way this study can be used to argue for “the end to fluoridation worldwide” or that there “definitely should” be “a halt to any plans to start fluoridation in places not currently fluoridated.

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Local anti-fluoride activists tell porkies yet again

FFNZ confuses lack of low fluoride studies on rats with human studies

Well, I suppose that’s not news. A bit surprising, though, because they are claiming the absence of research on fluoridation and IQ – which sort of conflicts with the previous attempts to actually condemn and misrepresent the actual research on fluoridation and IQ.

Fluoride Free NZ’s (FFNZ) face book page is claiming:

Would you be interested to know that no studies have been conducted on fluoridated water at 0.7ppm to determine whether there is IQ reduction? The National Toxicology Program are currently completing research to fill this gap. You would have thought that they would have done this in the 1950s before starting the fluoridation program wouldn’t you?

There have actually been three recent studies from three different countries which have specifically investigated the claim of an effect of fluoridation on IQ – and, unsurprisingly, all threes studies showed there was no effect.

Here are those studies:

New Zealand

Broadbent, J. M., Thomson, W. M., Ramrakha, S., Moffitt, T. E., Zeng, J., Foster Page, L. A., & Poulton, R. (2014). Community Water Fluoridation and Intelligence: Prospective Study in New Zealand. American Journal of Public Health, 105(1), 72–76.

In fact, anti-fluoride activists in the US, as well as New Zealand, have campaigned against this study. Their major criticism is that the study also included the effect of fluoride tablet use. They argue that this makes the unfluoridated control group useless because many participants will have consumed fluoride tablets. However, they ignore the fact that the statistical analysis corrected for this but still found no statistically significant difference in IQ of children and adults from fluoridated and unfluoridated areas.


Other critics of the Broadbent et al. (2014) study have raised the issue of experimental power because of the numbers of people in the study. This could be a valid issue as it would determine the minimum effect size capable of being detected. Aggeborn & Öhman (2016) made that criticism of Broadbent et al., (2016) and all other fluoride-IQ studies. Their study is reported at:

Aggeborn L, Öhman M. (2016) The Effects of Fluoride in the Drinking Water. 2016.

Aggeborn & Öhman (2016) used much larger sample size than any of the other studies – over 81,000 observations compared with around 1000 or less for the commonly cited studies. It was also made on continually varying fluoride concentrations using the natural fluoride levels in Swedish drinking waters (the concentrations are similar to those in fluoridated communities), rather than the less effective approach of simply comparing two villages or fluoridated and unfluoridated regions. The confidence intervals were much smaller than those of other cited fluoride-IQ studies. This makes their conclusion that there was no effect of fluoride on cognitive measurements much more definitive. Incidentally, their study also indicated no effect of fluoride on the diagnosis of ADHD or muscular and skeleton diseases.


Another recent fluoridation-IQ study is that of Barbario (2016) made in Canada:

Barberio, AM. (2016). A Canadian Population-based Study of the Relationship between Fluoride Exposure and Indicators of Cognitive and Thyroid Functioning; Implications for Community Water Fluoridation. M. Sc. Thesis; Community Health Sciences, University of Calgary.

This study also had a large sample size – over 2,500 observations. This reported no statistically significant relationship of cognitive deficits to water fluoride.

Incidentally, Barberio (2016) also found there was no evidence of any relationship between fluoride exposure and thyroid functioning. That puts another pet claim of anti-fluoride campaigners to rest.

Animal studies

So much for NZFF’s claim that “no studies have been conducted on fluoridated water at 0.7ppm to determine whether there is IQ reduction.” But, just a minute, they are quoting the National Toxicology Program (NTP):

“No studies evaluated developmental exposure to fluoride at levels as low as 0.7 parts per million, the recommended level for community water fluoridation in the United States. Additional research is needed.”

But they omit the next sentence from the quote:

“NTP is conducting laboratory studies in rodents to fill data gaps identified in the systematic review of the animal studies.”

The NTP is discussing the research with animals, mainly rats, where effects of fluoride on the cognitive behaviour of the test animals have been reported but the fluoride concentrations are very high. And NTP’s assessment base on the review of the literature found only “a low to moderate level of evidence that the studies support adverse effects on learning and memory in animals exposed to fluoride in the diet or drinking water.” Hence the need for more research.

As part of the NTP’s research, which is currently underway, there are plans to extend studies to low fluoride concentrations more typical of that used in community water fluoridation.

The high concentrations used in animal studies is a major flaw in the anti-fluoride activist use of them to oppose community water fluoridation. For example, Mullinex et al (1995) (very commonly cited by anti-fluoride campaigners) fed test animals drinking water with up to 125 mg/L of fluoride (concentrations near 0.8 mg/L of fluoride are used in community water fluoridation).

While it is unlikely that the NTP research will find any significant effects of fluoride on the cognitive behaviour of rats at the low concentrations used in community water fluoridation the anti-fluoride campaigners have their fingers (and probably toes as well) crossed.

NTP will begin publishing the results of their new research next year (see Fluoride and IQ – another study coming up).

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