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[dupe] Maternal fluoride exposure during pregnancy and IQ scores in offspring (jamanetwork.com)
48 points by bookofjoe 59 days ago | hide | past | web | favorite | 30 comments

The previous thread was very critical of this article's statistics.

Reposting my comment:

When I see a headline like this my instinct is to jump to "overfitting". In a study like this they use P=0.05 as their cut off for significance. One in 20 such studies would be expected to give meaningless results. But they had the choice of cohort (all kids or boys and girls separately), so 1 in 10. They measured urine concentrations of fluorine at three time points during pregnancy, which makes for 7 different potential combinations of input variables, for a total of 14 different potential analyses, where 1 in 20 is expected to be significant. Of course, they didn't preregister, so who knows whether their analysis changed on the fly..

Those multiple comparisons are quite obvious from the text, so a rigorous reviewer may have asked them to do a Bonferroni correction. Not sure if this was the case though.

You're right, and one would hope that happened. But not knowing the field or journal norms, all I could do was search the text for "Bonferroni" and "regist". In my lab if additional analysis was requested by the reviewer and we did it, we would have added a sentence to the manuscript.

But not having published in this field or journal, I have no idea what their norms are.

There is always a lot of skepticism around studies that show fluoridation is bad for health. Question though, shouldn't we need strong evidence that adding fluoride to the water is safe, rather than the other way around? Even if it has some (questionably) positive effects, that doesn't make it right to add an arbitrary chemical to a fundamental substance needed for life. While we are at it, why don't we add iodine, vitamin D, magnesium, etc?

What kind of safety threshold do you require?

Acute, chronic, cancer studies, Alzheimer's links? Comparison vs bad dental hygiene in the above? What is the reference group you propose?

How much would you pay for this relatively superb level of detail? (Which is on par with 50+ years of longitudinal and cross sectional studies. About 1 billion USD.)

No need to pay a cent if you don't add it to the water. Anecdotally it appears difficult to find a toothpaste than doesn't contain fluoride sufficient to strengthen tooth enamel & bone via its incorporation over time and there are other sources in food and drink (tea). Fluoride has no other role in human metabolism.

1 billion dollars is negligble when considering dumping industrial chemicals into the water of those who have no choice in a country of 350 million with a GDP of 20 trillion.

If you're water conscious like me that doesn't want anything "added" to the water, consider buying a home distiller. Just search for distiller in amazon for some ideas of what you get. It takes 3-5 hours for about a gallon. If you just queue them up during your work day. Just store the water in large glass mason jars and throw them in the fridge. Kick the plastic bottled water habits. It's not just BPA but tons of plasticizers that leech into your fav. bottled waters. My wife and I switched to this after we drank some Fiji from a gas station, after it had warmed up - all you can taste is plastic - even with the BPA free stickers. In the end we decided you can't really trust the companies distributing plastic bottled water because you never know which crate is left out in 105 degree summer heat during its various transitions. That's pretty disgusting if you think about it.

Do you add back in salts and minerals so you don't leech your teeth?

That sounds like a horrible waste of electricity.

If you do go down this track you need to re-mineralise the water as pure water is damaging to the body as pure water will leach all the electrolytes from your body.

Not if you're also eating food.

Most people are already deficient in salt and magnesium, I think more is likely better.

Why did you go with a water distiller and not a reverse osmosis filter?

All the tap water in Australia is fluoridated. You would be considered a bit odd if you drink filtered water instead of tap water (bar say SA where the water tastes bad). All other things equal, we should expect 3&4 yearolds to have a 3.66 higher IQ than those, say, in NSW, where the water is treated and tastes good enough to drink?

Surely there are some population effects or something else going on here, or the effect, especially later on in life, evens out between the groups.

Particularly with the nationwide school test scoring, there should be statistically significant score differences in QLD (only recently fluoridated).

Could look at Warrnambool (VIC) as an example, as I believe they only started fluoridating in 2008.[0]

Likewise, I understand several council areas in Queensland stopped fluoridating in around 2016.[1]

[0]: https://hnb.dhs.vic.gov.au/web/pubaff/medrel.nsf/LinkView/08... [1]: https://www.abc.net.au/news/2016-09-28/mackay-council-vote-s...

SA (really, Adelaide) is very region specific, though. I grew up drinking tap water here, though I've had some strange tasting water in other suburbs


"If the work holds up—a big “if,” as the paper’s findings are already coming under heavy scrutiny—it could hold serious implications for public policy."

Why should scientific data be doubted simply because its implications, if taken seriously, would be to cause more inconvenience or less money-making in our lives?

Because it would be too easy to influence public policy by any interested parties. We already know corporations sponsor papers for their PR, this just means it would become a simple tool to influence policy.

Thats not what your quote says.

Barely significant results like this are suspect. See https://www.vox.com/science-and-health/2017/7/31/16021654/p-... for a good overview. TLDR: the smart money is on this result failing to reproduce.

Reposting a more skeptical comment to provide some balanced responses: https://old.reddit.com/r/slatestarcodex/comments/cslscx/is_f...

>Sci-Hub Link: https://sci-hub.se/10.1001/jamapediatrics.2019.1728

>Study itself: https://sci-hub.se/10.1001/jamapediatrics.2019.1729

>A decent amount of this is focused on Black Tea consumption during pregnancy which is apparently a problem: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4808922/

>Collected skeptical commentary at the Science Media Centre: https://www.sciencemediacentre.org/expert-reaction-to-study-...

>First, the claim that maternal fluoride exposure is associated with a decrease in IQ of children is false. This finding was non-significant (but not reported in the abstract). They did observe a decrease for male children and a slight increase in IQ (but non-significant) for girls. This is an example of subgroup analysis – which is frowned upon in these kinds of studies because it is nearly always possible to identify some subgroup which shows an effect if the data are noisy. Here the data are very noisy. A further issue is that the estimate of the decrease in IQ for male offspring is unfeasibility large – at 4-5 IQ points. This level of average deficit would be readily detectable in previous studies and is likely a reflection of bias or very noisy data (the interval estimate here is very wide). As high fluoride areas are not randomly assigned there are also countless uncontrolled confounders. While they did correct for a limited set of covariates, the overall effect was non-significant with and without covariates. In summary it is not correct to imply that the data here show evidence of a link between maternal fluoride exposure and IQ. The average change in IQ is not statistically significant.

Estimated Fluoride Intake and IQ A 1-mg increase in fluoride intake was associated with a 3.66 (95% CI, −7.16 to −0.15; P = .04) lower FSIQ score among boys and girls

Yup; it's absolutely terrifying.

The scales chosen in the study make it sound a lot more scary, though, given the unfluoridated mean intake was 0.3 mg and the fluoridated mean intake was 0.93mg. Still, this is an estimated difference of two whole IQ points between the populations.

I'm on Detroit water and just checked the latest water test I could find -- .57ppm fluoride. If I did the math right, there is 1mg fluoride in every .46 gallons of water.

Additionally, the maximum level allowed in my city is 16mg per gallon, and has been since I was born. However, in the year I was born(1992) the maximum measured level per the city test was 48mg per gallon.

Compare with average ingestion of fluoride salts from toothpaste. (Nobody precisely rinses teeth after applying it.)

P=.04 is barely significant. What it means is that further research may be worth pursuing, not that we found conclusive evidence.

I am personally a bit spectical, sounds too big to be true. Here is an illustration of what I am saying https://xkcd.com/882/

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