By Maria Kippler
Fluoride occurs naturally in drinking water, especially well water, but the concentrations are generally low in public water supplies. In some countries, such as the US, Canada, UK, Australia and Ireland, fluoride is commonly added to the public water supply at around 0.7mg per litre to prevent tooth decay. The World Health Organization guideline for fluoride in drinking water is 1.5mg per litre.
Given the concern that fluoride in drinking water might affect children’s intelligence, the addition of this mineral to drinking water has become controversial. Consensus among researchers about the precise nature of the link between fluoridation and intelligence is lacking and the existing evidence is widely debated.
The US National Toxicology Program’s, part of the Department of Health and Human Services, most recent evaluation states with moderate confidence that higher fluoride exposure (above the World Health Organization guideline) is consistently associated with decreased child intelligence, while they conclude that more research is needed to understand the effects at lower fluoride exposure levels.
A new study my colleagues and I conducted found that relatively low exposure to fluoride during the foetal stage (as a result of the mother’s exposure to fluoride) or in the child’s early years may affect their intelligence.
For the study, which was published in Environmental Health Perspectives, we followed 500 mothers and their children in rural Bangladesh, where fluoride occurs naturally in the drinking water, to investigate the link between early life exposure to fluoride and children’s intelligence.
Psychologists evaluated the children’s cognitive abilities at five and ten years of age, using standard IQ tests. The exposure to fluoride in the mothers during pregnancy and children at five and ten years of age was determined by measuring the concentrations in urine samples. Urine samples reflect the continuing exposure from all sources, such as drinking water, food and dental products (such as toothpaste and mouthwash). Urine samples are the most accurate way of determining fluoride exposure in people.
Increasing urinary concentrations of fluoride in pregnant women were linked to decreasing intelligence in their children at five and ten. Even the lowest fluoride concentrations were associated with decreases in the children’s cognition. The average maternal urinary fluoride concentration was 0.63mg per litre, with the vast majority of concentrations falling between 0.26 and 1.4mg per litre.
The children’s average urinary fluoride concentrations at five and ten years of age (0.62 and 0.66mg per litre, respectively) were similar to those of their mothers during pregnancy.
Among children who had more than 0.72mg per litre of fluoride in their urine by age ten, increasing urinary fluoride concentrations were associated with lower intelligence. In children with less fluoride in their urine, there were no consistent associations with their intelligence. So childhood exposure seemed to be less detrimental than the exposure during early foetal development.
Out of the cognitive abilities measured, associations of both maternal and child urinary fluoride concentrations were most pronounced with nonverbal reasoning and verbal abilities. There were no consistent differences between boys and girls.
We didn’t find a link between fluoride concentrations in the urine of the five-year-olds and their intelligence. This could be due to the shorter exposure time or that urinary fluoride concentrations aren’t as reliable in younger children owing to greater variations in how much fluoride is taken up and stored in the body, particularly in the bones.
As well as the children’s urinary fluoride concentration, the fluoride concentrations in drinking water were measured at the age of ten for a random subset of the studied children. The average was 0.20mg per litre, which is well below the WHO guideline value for fluoride in drinking water.
The concentrations in drinking water tracked with the concentrations in urine, confirming that water is a main source of exposure. Still, we couldn’t exclude the possibility that there were contributions from other sources. Fluoride in toothpaste is important for preventing tooth decay, but it’s important to encourage small children not to swallow the toothpaste during brushing.
Limitations
A limitation of our study is that we measured fluoride only in one urine sample at each time point. As a large fraction of the absorbed fluoride is excreted in some hours, one measurement may give uncertain levels for the individual. However, as the exposure largely comes from water it can be assumed that the intake is rather constant over time.
Another limitation is that the intelligence tests that were used have not been standardised for the Bangladeshi population. As a result, we did not convert the results to IQ scores (with an average of 100) that can be compared across populations.
Our findings support previous well-designed studies from Canada and Mexico, where exposure levels obtained below the existing WHO guideline for fluoride in drinking water were associated with impaired cognitive development.
Similar findings were recently provided when combining multiple studies from several countries. It was noted that at low exposure levels, findings with cognitive development were more conclusive among studies estimating fluoride exposure via urine than among studies that relied on concentrations in drinking water only. This highlights that imprecise estimation of the exposure can lead to difficulties in assessing the true impact on cognitive development.
Taken together, the concern about the effect of fluoride on children’s intelligence at low exposure levels is further strengthened by our study. In particular exposure during foetal development, but also prolonged childhood exposure seems to be of concern.
Still, as this is an observational study, no firm conclusions can be drawn about causalities. There is still a need for more well-designed research studies on low-level fluoride exposure and cognitive development, in combination with experimental studies to determine the possible molecular mechanisms driving it. Collectively, this will create a robust basis for reviewing fluoride health risks and thresholds for drinking water, foods, and dental care products, especially for children.
Maria Kippler is Associate Professor, Institute of Environmental Medicine, Karolinska Institutet.
Engin Ruslpostur says
I am not a medical researcher but the gaping holes of logic in this study make this far too unreliable to draw any conclusions. As usual, I am disappointed in the poor reporting by Flagler Live, whose editor Pierre Tristram uses what could be a valuable local news source into a platform for his gripes and grievances. The study falls into the statistical axioms…
Correlation DOES NOT demonstrate causation. Meaning thispngs that happen at the same time aren’t necessarily causes
The study is 500 people. The author indicates that no standard test for intelligence exists in Bangladesh. The author stipulates that urine samples were only taken once and there is no assurance that it was the same time, so actual Flouride levels may not be done consistently. Most importantly, the study was run in RURAL Bangladesh. There is NO WAY to isolate, in this preposterous study, the impact of nutrition, food supply, ability of the study participants to have obtained proper diet during pregnancy in this financially poor country. There are so many issues with this study that it is a real disservice to print this and muddy up already confused water surrounding Flouride.
But this is typical of Tristam. He will print rubbish but I guarantee no one will ever see the other side of the discussion . It’s a shame to waste the opportunity, but he is expert at that,
Samuel L. Bronkowitz says
I’m not going to assassinate Pierre over this article because it’s a “the conversation” piece and they’re consistently packed with bad takes, probably to generate whatever passes for conversation these days.
As Engin correctly points out, the researchers used a population size of 500 mother-infant pairs from rural Bangladesh and attempts to draw a line from fluoridation to mental delays. There is no control group. The authors do not address other things that can cause developmental issues – for example, India is rife with hookworm (see for example https://pmc.ncbi.nlm.nih.gov/articles/PMC8184002/) and for the unaware hookworm as a reputation that Floridians should be intimately familiar with, e.g. https://www.pbs.org/wgbh/nova/article/how-a-worm-gave-the-south-a-bad-name/ let alone the many and varied issues that socioeconomic problems lend to child development and rearing. I would also be very, very, very suspect of anything published in Environmental Health Perspectives since it’s an extension of the US National Institute of Environmental Health.
Jake from state farm says
Unlike Egin, I have to tip my hat to Mr. Tristam. For once, he’s published something that, not too long ago, would have been immediately dismissed—and even ridiculed—as nothing more than a “conspiracy theory.” I can vividly recall local articles in FlaglerLive that mocked and belittled concerned citizens at public meetings, labeling them as “conspiracy theorists” for bringing up the very same issues that are now being openly discussed. To see this kind of shift is a significant step forward. Pierre, credit where it’s due—you should be proud of yourself.
Now, here’s hoping this marks the beginning of a more nuanced and balanced approach to your reporting. Maybe it’s time to start broadening the scope of your coverage and entertain perspectives that challenge the usual narrative. The hiding of Biden’s cognitive decline by the media (except for your 2 minutes on the radio). We can’t ignore the fact that, while he publicly claimed he needed Congress to curb the flood of illegal immigration at the southern border, he had the power to address it himself—and simply chose not to. The same goes for the origins of COVID-19: it came from a lab, and the U.S. government may have been involved in funding that research. Dr. Fauci’s role in all of this is something that deserves more than a passing glance; he should be held accountable for his actions. Don’t wear a mask wear a mask, 6 ft, shut down of our schools, boys in girls locker rooms,,,,,
This article you printed shows that you have the ability to think outside your usual narrative and step beyond the comfort zone of one-sided reporting. Keep pushing in that direction. True, fair, and honest journalism isn’t just about championing one side—it’s about presenting all sides, even the ones that make you uncomfortable or that you might disagree with. You’ve taken an important step here, and I hope it’s just the beginning of a more open-minded approach
c says
Headline : “Relatively Low Fluoride Levels May Affect Intelligence in Children”
As ‘Engin Ruslpostur’ posted –
A) a study done of 500 people (significantly insignificant :) ;
B) In Bangladesh ?? And what controls were placed on the ‘naturally occurring fluorides’
c) And, as the Author posted – ‘Still, as this is an observational study, no firm conclusions can be drawn about causalities. ‘
* But we’re gonna go ahead and make exaggerated claims to get attention –
And Finally D) – The author notes : ‘That the intelligence tests that were used have not been standardised for the Bangladeshi population’- BUT … This Is Florida, Not Bangladesh and if fluorides affect intelligence levels … Who Will Notice?
DaleL says
There was recently published a meta-analysis of fluoride studies. https://jamanetwork.com/journals/jamapediatrics/fullarticle/2828425 The researchers reviewed and included 74 individual studies. They found that no (null) association of lower IQ at a level less than 1.5 mg/L. (At present the recommended drinking water fluoridation level is 0.7 mg/L.) Among low risk-of-bias studies (The best studies), there was an IQ score decrease of 1.14 points per 1.0 mg/L increase in fluoride.
Fluoride is found naturally in ground water (water from wells) and food. Fluoride and fluoridation has been associated with heavy metals such as lead and arsenic. Both lead and arsenic are known to reduce IQ levels.
Fluoride, at low levels, is proven to dramatically improve dental health by making teeth resistant to decay.
In summary, well designed studies do not show an association with fluoride and IQ at or even near the recommended drinking water fluoridation level. That level of fluoridation has definite health benefits.
Deborah Coffey says
Do more research. So far, this isn’t convincing many people. At 76, I’ve only seen the positive side of fluoride. And, do the benefits outweigh the negatives? Every drug can have side effects.
Ray says
In Texas, there are many counties that put too much fluoride in the potable water. I worked with people that had white spots on their teeth. I can’t recall the term for that. This was years ago, but it happened.
Look it up I am too lazy, but it is a Fack.
Sherry says
@engin. . . While I agree that a much better study and analysis is needed before drawing any negative conclusions on the use of fluoride in drinking water, your characterization “Award Winning” Flaglerlive and its publisher smacks loudly of your very own biased opinion. Don’t like Flaglerlive, read something else!
BillC says
Poll question- does RFK Jr. seem like a healthy and well adjusted person to you?