Fluoride Exposure and Children's IQ Scores a Systematic Review and Meta-Analysis | Hacker News Reader

Fluoride Exposure and Children's IQ Scores a Systematic Review and Meta-Analysis

jamanetwork.com

30 pointslogicchains17 comments

It's very interesting that the group level results (table 1) of this analysis seem entirely opposite when comparing western and non-western countries.

As noted by table 1, all the group level results indicating that fluoride has a negative impact on IQ come from China, India and Iran.

When you look at the studies done in western countries, in particular Canada, New Zealand, Taiwan, Australia, Sweden, Denmark or Spain, you do not see negative IQ effects (Australia, Sweden, Denmark and Spain studies were not included in this meta analysis, but you can find links to studies from those countries in https://www.statnews.com/2025/01/06/fluoride-iq-jama-pediatr...).

>As noted by this meta-analysis itself, all the results indicating that fluoride has a negative impact on IQ come from China, India and Iran.

That's not accurate. Table 3 shows negative impact from data collected in Canada and Mexico as well.

The Canadian and Mexican studies are invalid because they use spot urine to measure fetal fluoride exposure. Spot urine of the pregnant woman can't measure her chronic fluoride exposure. It can't tell us anything about what the fetus was exposed to. These are studies, regretfully, that might as well not have been written. They are not useful because they are invalid.

I think you're referring to the Canadian and Mexican studies that were excluded from the meta-analysis.

If you read the paper, two Canadian studies and three Mexican studies were excluded, but not all of them were. Table 3 only shows results from studies that were judged to be robust.

This feels a lot like the "blue-zone problem" in that it turned out blue zones were only prevalent in areas where they kept birth records poorly.

I dont know much, but are less wealthy countries more statistically likely to create unreliable research or is that not a vector that seems to affect deep science?

China and India are countries with highly trained good scientists, who work in a bad system. They have to make results constantly to keep officials happy. So there is a lot of research fraud. I don't know about Iran but it's probably similar. A lot depends on the field and institution but it's possible. (The West is really bad for research fraud too, but not as bad.)

This meta analysis tries to look for high "risk of bias" based on methodology. But it doesn't look like they consider the possibility of fraud, only bad methodology and statistics.

> They have to make results constantly to keep officials happy. So there is a lot of research fraud.

What's surprising is that if there was fraud one would expect the results to go in the other direction since fluoridation is the official policy.

there may also be political pressure, but mainly there is just a strong demand for more papers, which means getting results that are publishable. "fluoridation has no effect on IQ" would be less publishable. same as in the west, but the western bureaucrats are more realistic and more focused on quality so the pressure is not as strong.

> have to make results constantly to keep officials happy

Ironically, there is probably some public pressure in the West to publish findings that make fluoride look bad. Why solve actual problems when you can defeat imaginary ones?

Thats the funny thing, Its hard to tell which side has more motivation for fraud.

I doubt it’s that coördinated. More likely: researchers respond to funders who really want to see a particular outcome. Nobody goes in aiming to be corrupt. But as a system it winds up being.

The study does seem to have some problems: https://arstechnica.com/health/2025/01/controversial-fluorid...

Seems like SES could be a confounder since it looks at individuals from various countries, and fluoridation policy is probably related dental health found in a population. Yet I see no attempt to control for SES.

Takeaways:

-Higher fluoride exposure may negatively affect children’s IQ.

-At lower levels, particularly in water, this effect seems weaker or non-existent.

-More careful studies still show a potential risk, even at relatively low exposure levels.

Growing body of science for what some people have been saying for years now.

A good science based take on this issue: https://sciencebasedmedicine.org/fluoride-and-iq/

TLDR; children who got higher fluoride exposure tended to have slightly lower IQ. Lower amounts in drinking water <1.5 mg/L were inconclusive on IQ impact and requires additional study.

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