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Comment by mlyle | Hacker News Reader

> It is IMO both very reasonable to fund more research into this to know conclusively if 0.7mg/L is indeed safe

How exactly do you propose we do this? It's tough to prove absence of harm.

The meta-analysis put together tons of research under different situations, and found a weak and relatively small dose-response relationship above 1.0 mg/L and failed to find a relationship below. The evidence between 1.0mg/L and 1.5mg/L is particularly weak. And, of course, most dose-response curves are sigmoidal, so the failure to find a response under 1.0 mg/L is most easily explained by the inflection point being above that level.

If you're not satisfied when combining 74 studies fails to find a relationship, will you be happy with 75? 76? 100?

(Sure, a big proportion of the studies and study power focused on higher levels of fluorination-- and I always support filling gaps in research; but it's not like we have an absence of research below 1.5 mg/L).

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Well I mean the flip side is... does community water fluorination at its current levels actually help?

https://www.cochranelibrary.com/cdsr/doi/10.1002/14651858.CD...

The Cochrane Collaboration's research is near the gold standard, and yet they find surprisingly limited evidence of benefit for CWF in the modern research:

"These low‐certainty findings (a 4 percentage point difference and 3 percentage point difference for primary and permanent dentition, respectively) favoured CWF."

3-4% reduction in cavities is not nothing, but it's a far cry from the 60% drop observed in the 1940s and certainly much less than what I think most strong proponents of water fluoridation would have you believe. The ongoing discussion I find quite legitimate given we're no longer living in the 1940s and CWF seems to have a substantially lower benefit than it once did, and likewise we do notice a concerning trend with fluorine neurotoxicity that has only emerged in the last few decades of research.

Public health policy is all about a risk/benefit analysis, and CWF is one of those topics that I feel legitimately should be discussed because much has changed over the many decades since the US first introduced it and since then the risks seemingly have gone up and the benefit has astronomically gone down.

Again, I do not think there'd be much discussion if current water fluorination was at 0.15mg/L, and we started seeing a negative trend at 1.5mg/L. But I don't think its actually at all unreasonable for public health officials to be worried and possibly start considering alternatives to CWF out of an abundance of caution.

3-4% of your teeth is an entire tooth.

> but it's not like we have an absence of research below 1.5 mg/L).

But it is?

>> "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"

Yes you would need a higher powered study to rule out the potentially smaller effect, but when your treatment can affect tens of millions of children, it doesn't seem crazy to ask for more funding.

> > but it's not like we have an absence of research below 1.5 mg/L).

> But it is?

But it isn't. There's 7 studies included in that meta-analysis looking at levels below 1.5mg/L, covering 2832 children. The effect measured so far across all of the studies is a statistically insignificant increase in IQ.

I'm in favor of additional research; I just don't think getting to n=10,000 showing little or no effect is going to convince anyone. I also don't think that these possible modest effects are going to be in the top 5 most important environmental stressors to measure the effects of.

I agree, the effects of fluoride probably aren't in the top 5 things to be concerned about (although perhaps they are from a political perspective, with it becoming such a strong topic of debate for a variety of reasons). But do you assume that getting to n=10,000 is going to show little or no effect (e.g. having a level you define as little effect)? I'm not convinced the NTP data is extremely high quality and can't make much conclusion from it on the effects.

Also, for other commenters: the 2832 children number I believe comes from the supplemental content from the supplemental material for the NTP Fluoride Monograph: https://cdn.jamanetwork.com/ama/content_public/journal/peds/... (this url is very long because of some hashing measure, sorry: if it is no longer accessible, it is the supplemental content for doi:10.1001/jamapediatrics.2024.5542), on page 51 of the PDF. I have a small summary table of data I view relevant here:

The columns are:

* Studies used; Fluoride Exposure; Number of Studies / Number of Observations (number of Children)

* Estimate for slope in linear Model, given as increase in IQ points per mg/L increase (95% CI) (p value)

All studies; < 2mg/L; 8 / 10 (N = 3682); -0.18 (-0.40, 0.03) (p = 0.096)

All studies; < 1.5mg/L; 7 / 7 (N = 2832); 0.05 (-0.36, 0.45) (p = 0.816)

Low risk of bias studies; < 2mg/L; 4 / 5 (N = 1632); -0.33 (-0.53, -0.13) (p = 0.001)

Low risk of bias studies; < 1.5mg/L; 3 / 3 (N = 879); -0.32 (-0.91, 0.26) (p = 0.276)

> But do you assume that getting to n=10,000 is going to show little or no effect (e.g. having a level you define as little effect)?

I don't necessarily assume this, but even if you assume linearity, 0.7 * -0.32 is pretty dang small at baseline. I think if you generate n=10000 showing MLE=-.32 or +.05, few people are going to change their minds. I might, but I don't think it does much to shape the debate.

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