I've recently learned about alleged dangers to drinking fluoridated water. Amongst them is increased rate of cancer and lowering of IQ. Interestingly enough, wiki doesn't mention this at all, but searching for it brings up a decent amount of (what look like) reasonable results. I am really curious about this, and want to learn more about this. I was wondering if anyone on LW has already conducted a research literature investigation on this topic, or if you just have tips/advice on what to pay attention to when I read the literature.


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wiki doesn't mention this at all

Yes it does. In fact it has a whole article dedicated to it.

This quote seems especially relevant:

A major Australian study found no clear association between fluoridation and cancer or deaths due to cancer, both for cancer in general and also specifically for bone cancer and osteosarcoma,[7] and other adverse effects lack sufficient evidence to reach a confident conclusion.[13]

Thanks! Can't believe I missed that.

I notice neither that Wikipedia page nor the general water fluoridation page cover water fluoridation's alleged effect on IQ, although that's the main recent claim I've seen conspiracy theorists make about it. (My impression, based on a desultory skim through a few of the studies they refer to: they're wrongly inferring causality from fairly weak observational studies that compare people in different regions with different levels of fluoride in the drinking water. These studies normally take place in less developed nations like India & China where the water is more likely to have naturally high levels of fluoride — often more than is added in the US — and other toxic chemicals that could readily confound the results.)

There's very good evidence that Fluoridation reduces dental cavities. Bad teeth are costly, painful, distracting, and probably unhealthy, too. I don't know how to weigh those factors against hypothetical and ill-documented but scary-sounding health risks, so I figure I should invest my scarce mental resources in a decision where I think there are bigger gains as a result of research.

Bad teeth are costly, painful, distracting, and probably unhealthy, too.


Periodontitis has been linked to increased inflammation in the body such as indicated by raised levels of C-reactive protein and Interleukin-6.[4][5][6][7] It is through this linked to increased risk of stroke,[8][9] myocardial infarction,[10] and atherosclerosis.[11][12][13][14][15][16][17] It also linked in those over 60 years of age to impairments in delayed memory and calculation abilities.[18][19] Individuals with impaired fasting glucose and diabetes mellitus have higher degree of periodontal inflammation, and often have difficulties with balancing their blood glucose level owing to the constant systemic inflammatory state, caused by the periodontal inflammation.[20][21]

And now I'm going to brush my teeth....

I am really curious about this, and want to learn more about this.

What is the value of this information, remembering that you are an adult, trace elements are hard to remove from water, and non-tap water is way more expensive than tap water?

Some of us have kids.

If it actually affects my brain in a negative way, I would really like to know about it, so VOI is high.

If it actually affects my brain in a negative way, I would really like to know about it, so VOI is high.

In order to determine the VOI, you need a path from the information to a change in action, with a probability that you'll act differently and an expected value if you do. Both of these are small; the evidence seems to indicate that fluoride is okay, and even if fluoride does affect your brain negatively, the effect size would have to be very small to have escaped detection, and it would have to be weighed against the additional expense of drinking bottled water. (And yes, very-minor brain damage and money are fungible, since you money can buy books and classes and free time and intelligence-enhancing drugs.)

Most people in the Bay Area rationalist community are not financially limited on classes, books, and intelligence-enhancing drugs.

I’ve never met someone who told me they didn’t take modafinil because they couldn’t afford it.

A quick Google search suggests that reverse osmosis will take fluoride levels down by an order of magnitude, and although under-sink reverse osmosis filter output is indeed "way more expensive" than tap water, the difference is negligible as long as you only use the filtered stuff for drinking, while still bathing, cleaning, landscaping etc. with unfiltered.

This all assumes you actually want to remove fluoride from your water, though; I still haven't seen any decent evidence suggesting you would.

You would have to do more than that; for example, you would have to avoid any toothpastes, obviously, but less obviously you would have to completely cut out tea and some other plants which naturally contain high levels of fluoride. (Tea would be a real sacrifice for me.)

There exists non-flourinated toothpaste.

Ah. I wondered whether it was a big enough market to support a non-flouridated toothpaste, but I didn't have enough energy to look it up. (Head cold.)

I suspect the largest market is for very young children. My son's pediatrician recommended we brush his teeth, but all the children's toothpaste I've bought has been non-flourinated. I assume that this is based on some sort of medical advice to the manufacturers, but I've never actually checked.

At a guess, it's a precaution: very young children may eat it down as a kind of candy. (Don't all flouridated toothpastes come with warnings against swallowing?)

Not just the very young - my 5 year old son was consuming toothpaste at such a rate that we have had to cut off his formerly unfettered access to it.

No amount of telling him 'eating a tubeful every few days is probably unhealthy' had any effect - he just loves the stuff.

Amongst them is increased rate of cancer and lowering of IQ. Interestingly enough, wiki doesn't mention this at all, but searching for it brings up a decent amount of (what look like) reasonable results

Show us the goods.

I just did a basic google search, nothing fancy.

Well as far as I know the only real danger is that fluoride impairs absorption of iodine, which is only an issue if you are borderline iodine deficient in the first place. Furthermore, the fluoridated water is within the range of fluoride content of natural water.

The low dose negative effects are a special property of radiation and other carcinogens (radiation doesn't dilute below 1 particle track through cell nucleus, and 1 particle track has been shown to be mutagenic); in general (e.g. for fluoride)this no threshold biological response should not be taken as a prior.

Also i can't resist linking this particular danger of fluoridation.

The appeal to nature here isn't just a logical fallacy, it's a particularly bad heuristic in this case: if you ever find yourself actually stuck with nothing but "natural water", then for the sake of your life make sure not to drink it until after you hit it with iodine tablets, give it days of UV exposure, pass it through a microfilter, or do something to make it safe first.

That's all about microorganisms, though; I hadn't heard of any real dangers from tap-water levels of fluoride. Even potential inhibition of iodine uptake is news to me. It's always possible there are extremely subtle effects; look at the correlations between groundwater lithium (in tiny tiny concentrations!) and suicide/violence/addiction rates in those Japan and Texas studies. But AFAIK the only likely effect we know of is still the strong correlation between drinking fluoridated water and not having your teeth rot away.

Yep. One simple way to make water safe from micro-organisms is to boil it. The few that survive are no big deal, and it's no worse than all the food you eat anyway.

With regards to natural, the thing is that we didn't just decide to add fluorine to water everywhere. It's added to water where natural level is too low, and removed where natural level is too high. And the worst that is happening from the level that is considered to be optimal is some instances of minor cosmetic effect on the teeth, which correlates with even fewer cavities. So there is actually a chance we are not adding enough, due to some stupid appearance concerns driven by fake teeth and photoshopped advertising.

I'm not even sure any more that fluorine even could have any effect on iodine uptake. There's chlorine and bromine between iodine and fluorine, and we got a lot of chlorine in our bodies.

The cancer issues, well, studying cancer rate empirically is a popular topic for nonsense because there's a lot of co-founding factors yet the highly dubious results that you obtain sound like 'true evidence' to be put against 'theories', whereby the theories are good reasoning based on our knowledge.

For example of one such controversy, small doses of ionizing radiation can be reasonably expected to cause cancer at a rate linearly proportional to doses, due to well understood mechanisms and the radiation not actually diluting at the cellular level. Yet, the folks who are punched in their wallets by this reasoning are funding various nonsense statistical 'studies' (which don't control for co-founding factors as significant as age and smoking) that find positive effects of low doses of radiation, never mind complete lack of any remotely plausible mechanism beyond some non-specific stupidity about some anti-cancer defence responses that are presumed to be asleep when you live normal life having lifetime cancer rate of ~40% with mortality rate 20%, primarily from mutations entirely unrelated to radiation. But which would turn on when radiation several times over background would increase the mutation rate by some tiny fraction of a percent (effect of which is not statistically significant unless you got sample sizes in the tens millions, which you never will have).

You're wise to turn your attention to this disturbing matter. To me, it feels obvious that the whole thing stinks of Communist infiltration, Communist indoctrination, Communist subversion and the international Communist conspiracy to sap and impurify all of our precious bodily fluids.

"Why do you never hear the conspiracy theory that fluoridation is a Communist plot, but the Communists were wrong and it's not actually bad?"

-- Nick Tarleton

Because that's a strictly more complicated hypothesis? Also it runs into cognitive dissonance and issues of belief overkill/confirmation bias?

Given that the only point of the above comment appears to be to remind people that the OP topic is associated with a low status conspiracy theory and is therefore low status, would one of the people who upvoted it care to explain why?


A truly brilliant movie, with many insightful comments on decision theory and Cold War politics. Absolutely everyone should watch it.