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Comment by culi | Hacker News Reader

The IQ link is very heavily lacking in evidence.

In the actual research the main "risk" posed by flouridated water is actually fluorosis. This causes minerals in your enamel to be replaced with flouride which can cause them to be brittle in the long term. It's pretty uncommon but the thought is that now that flouride toothpaste are commonplace, the benefit of flouridated water is also way less. Which changes the calculus.

A not insignificant number of researchers are advocating for the view that flouridating water just isn't worth it anymore and the (slight) risk of flourosis is more significant than the (slight) benefit of decreased dental caries.

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Children are the main group that benefits from fluoride in water because the fluoride helps strengthen teeth as they form. Lack of fluoride increases childhood cavities, leading to decreased academic performance.

This was a real problem in the San Jose school district until recently. They started fluoridation of water in the last ten years, and were the biggest US city that didn’t fluoridate. The evidence of the above is clear according to SJ dentists I have talked to.

The National Toxicology Program recently completed a fairly substantial meta study and concluded that "for every 1 mg/L increase in urinary fluoride, there is a decrease of 1.63 IQ points in children.". [1] This is also relevant to OP since it's not just pregnant women at risk from excessive fluoridation but also children. For now it seems that adults are, somewhat oddly, unaffected.

[1] - https://ntp.niehs.nih.gov/whatwestudy/assessments/noncancer/...

In bold from your source:

> It is important to note that there were insufficient data to determine if the low fluoride level of 0.7 mg/L currently recommended for U.S. community water supplies has a negative effect on children’s IQ.

Yeah, note the measurement is in urine. So there are two separate issues. Determining whether fluoride is damaging to IQ, and then whether the levels in water can drive this. The former is way easier to evaluate than the latter. The reason comes from that study's intro pargraphs:

---

"Since 1945, the use of fluoride has been a successful public health initiative for reducing dental cavities and improving general oral health of adults and children. There is a concern, however, that some pregnant women and children may be getting more fluoride than they need because they now get fluoride from many sources including treated public water, water-added foods and beverages, teas, toothpaste, floss, and mouthwash, and the combined total intake of fluoride may exceed safe amounts."

---

So the issue is trying to isolate the exact amount and source of fluoride people are getting. And that probably has no answer because it's going to vary dependent on how much fluoridated water somebody drinks, the rest of their diet, their other dental hygiene composition, and more. So levels that would be safe for one percent of the population, will be dangerous for another percent of it.

Here is a concise detailed analysis of the concerns with the metaanalysis provided by the NTP:

https://theunbiasedscipod.substack.com/p/the-well-runs-deep-...

The NTP report is flawed and likely biased.

Says the substack paper which takes everything it can and spins and misrepresents it to the point of absurdity, for clicks.

Which changes the calculus

Was that intentional? (https://en.wiktionary.org/wiki/dental_calculus for those who didn't get the reference.)

The canonical form is "I see what you did there".

Fluorosis is very common afaik. My dentist told me I have it: slightly whiter patches on my teeth. Then he showed me his own fluorosis. It actually is stronger than the old enamel.

> The IQ link is very heavily lacking in evidence.

Not really: https://jamanetwork.com/journals/jamapediatrics/fullarticle/...

your study has been heavily criticized where you already posted it:

https://news.ycombinator.com/item?id=43523900

I can only assume once you see those very valid criticisms, you will update your references

Does the study not literally refute the claim that fluoride's negative impact on IQ is lacking in evidence, contrary to the original claim? What exactly do you think needs to be updated?

the original refutation was "fluoride in the drinking water concentrations is proven safe and it doesn't affect brains". Your study does not show that IQ is effected at concentrations that are being added to water supplies. Just because X can result from Y levels of some substance does't mean X results from Y-n concentrations.

> the original refutation was "fluoride in the drinking water concentrations is proven safe and it doesn't affect brains".

No, this is the original claim:

> but it turns out that there are a decent amount of good studies showing a link between fluoride in water and (slightly) lower IQ when pregnant mothers ingest the fluoride.

Then the parent replied that this IQ link is lacking evidence, which it's not, per the meta-analysis I cited.

The meta analysis you linked ( https://jamanetwork.com/journals/jamapediatrics/fullarticle/... ) specifically denies any noticable associations with fluoride at the levels recommended in countries that add fluoride to water.

  For fluoride measured in water, associations remained inverse when exposed groups were restricted to less than 4 mg/L or less than 2 mg/L but not when restricted to less than 1.5 mg/L

  There were limited data and uncertainty in the dose-response association between fluoride exposure and children’s IQ when fluoride exposure was estimated by drinking water alone at concentrations less than 1.5 mg/L.

The meta analysis you linked gets the strongest results in areas of the world with outstandingly high levels of fluoride and other elements in the ground water .. water with so many additives it rings like a bell when tapped with a hammer (okay, that's an embellishment).

> specifically denies any noticable associations with fluoride at the levels recommended in countries that add fluoride to water. (Emphasis added)

Which is not a claim that was being discussed in this subthread, since the original claim being refuted specify any such qualification.

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