A few days ago, as part of a twitter conversation I was having with the basically anonymous @SafeWaterHfx, I was sent an article in support of their claims that fluoride shouldn’t be added to municipal tap water. The anti-fluoridation crowd make a lot of noise online (they’re not unlike the anti-wifi folk in that regard), but there doesn’t seem to be any evidence in support of their position. Moreover, all the evidence seems to say that adding fluoride to municipal drinking water is a win in every possible way: it has a large positive effect on the population, it’s cheap, and it’s effective.
The argument that SafeWaterHalifax is putting forward (and you have to read between the lines as they’re either unwilling or unable to make an explicit direct statement) is that the levels of fluoridation in the municipal water in the US and Canada is harmful. Sure, they might prefer to couch that as “could be harmful”, but that’s just hedging. Given that they are arguing for it to be removed, you can’t make that argument on the basis that something “could be” harmful, without some sort of belief that it actually is.
First the tweets that led up to this:
Being anti-fluoride goes against the science. If you’re not ignorant of it, then why are you lying about it @safewaterhfx? Only two options.
— Brian Lynchehaun (@blynchehaun) December 5, 2013
@blynchehaun We aren’t lying, Brian.You can get all the fluoride you like in Crest, Colgate, etc. It’s a fact: there is no fluoride RDA.
— SafeWaterHalifax (@SafeWaterHfx) December 5, 2013
.@SafeWaterHfx that is not an argument against putting fluoride in tap water.
— Brian Lynchehaun (@blynchehaun) December 7, 2013
@blynchehaun How much fluoride do you think you need, Brian? In mg/l or ppm per day? How much do you consume daily?
— SafeWaterHalifax (@SafeWaterHfx) December 10, 2013
.@SafeWaterHfx this is not, again, an argument against fluoridation. Do you actually have any science-based arguments?
— Brian Lynchehaun (@blynchehaun) December 12, 2013
— SafeWaterHalifax (@SafeWaterHfx) December 16, 2013
@SafeWaterHfx which article in the lancet says that? Your linked article is suspiciously short on references.
— Brian Lynchehaun (@blynchehaun) December 16, 2013
@blynchehaun “Fluoride,AnEmergingNeurotoxin”:A.Choi, G.Sun,Y.Zhang &P.Grandjean,Enviro.HealthPerspectives 1http://ehp.niehs.nih.gov/1104912/
— SafeWaterHalifax (@SafeWaterHfx) January 8, 2014
Notice that the article linked here isn’t actually the article that was supposedly found in The Lancet (although that was named a couple of days later: Grandjean P, Landrigan P. (2006). Developmental neurotoxicity of industrial chemicals. The Lancet 368: 2167-2178). This is a constant issue when trying to deal with the anti-stuff brigade: trying to get them to actually be clear about their points and where they’re getting their information from is like trying to nail smoke to the wall.
I really wish I was the first to write about this, but a buddy of mine (who apparently knows everything that has happened in the world of Skeptics, ever) was quick to point me to places this has been debunked already. I’d like to go into a little more depth than those places though.
To begin with, it’s important to note that this is a meta-analysis. This means that this paper does no new research itself, but it is collecting and amalgamating a bunch of different studies that were done, perhaps to see if there was a common effect that would otherwise be missed. The Achilles heel of a meta-study is that it can only be as good as the studies that go into it.
The studies that went into this were all conducted in China. The Neurologica post makes the point that:
First it should be noted that almost all of the studies reviewed were conducted in China (one was conducted in Iran) – not in the US. China had a limited fluoridation program for a time, and has had no fluoridation of drinking water since 2002. So why, then, are most of the studies from China?
I dislike this paragraph, and I think it has no real place in a review of the meta-analysis. The authors of the study note that their goal was to bring Chinese-language studies to the attention of those in the English-speaking world. This seems, to me, to be a laudable goal, thus criticising this strikes me as unreasonable. There are waaaaay more problems here that could be addressed, rather than merely Poisoning The Well.
The studies that went into this meta-analysis were all observational studies. This means that rather than directing the people in a particular area to ingest more or less water, they simply located populations that they were pretty sure had a low consumption of fluoride and a comparable population they were pretty sure had a high consumption of fluoride, and then ran IQ tests on both populations. Given the ethics of administering high levels of fluoride (a known neurotoxin), the only possible study that could be done here is observational. I think that the way these studies were set up was quite ingenious.
However. The shine rapidly goes off the rose. Of the studies reviewed, the sole source of fluoride was drinking water in only 9. Most of the others involved fluoride from coal-burning, or also included arsenic exposure, and other heavy metals. This means that, with regards to the relevancy of this meta-analysis, only those 9 studies are relevant to the situation in the US and Canada. If you scan through the exposure levels, many are simply “high” and “low”, without any documentation of what that actually means (this is something that was not collected in the initial observational study). More explicitly, the reviewers say:
Our review cannot be used to derive an exposure limit, because the actual exposures of the individual children are not known. Misclassification of children in both high- and low-exposure groups may have occurred if the children were drinking water from other sources (e.g., at school or in the field).
The setup was that there are people who are all living in the same area, but some live closer to a water source that has higher levels of fluoride than the other water sources in that area, so the people were grouped (it appears) according to whichever source they used. However, they can’t rule out kids going to their friends’ houses and getting water there, or someone bringing them water from another source, or any other useful piece of information which would help make a more solid argument.
Home life is known to have a profound effect on learning outcomes and intelligence in kids. The socioeconomic household of the parents absolutely cannot be ignored, as it will explain some differences in IQ scores in different populations. And yet:
Information on the child’s sex and parental education were not reported in > 80% of the studies, and only 7% of the studies reported household income.
There may well be a correlation between people in higher socioeconomic brackets and living in the low-fluoride-exposure areas. We have no way to rule out (i.e. control for) that possibility, because that (highly relevant) information was not collected.
Again, focusing on relevancy:
The exposed groups had access to drinking water with fluoride concentrations up to 11.5 mg/L (Wang SX et al. 2007); thus, in many cases concentrations were above the levels recommended (0.7–1.2 mg/L; DHHS) or allowed in public drinking water (4.0 mg/L; U.S. EPA) in the United States (U.S. EPA 2011).
So the groups with “high” exposure were, in many cases, consuming above the allowed US levels of fluoride (nevermind the recommended), which means that the “low” exposure groups are more akin to the current situation in the US. In short, this whole review has little to no relevance to the US or Canada, unless someone here was arguing for *increasing* the amount of fluoride in the water.
But for the sake of argument, let’s toss out all of these concerns. Let’s pretend that we had full socioeconomic backgrounds on all the families. Let’s pretend we had the precise exposure rates of every single child involved in these studies, and that we define “high” exposure as 0.7–1.2 mg/L, and “low” exposure as 0.1-0.2 mg/L (i.e. so the levels in the US and Canada fall into the “high” category). Let’s, in short, pretend that this study was near flawless and could not be rejected on the basis of methodology. What was the result of the meta-analysis? Buried (practically hidden) in one of the tables, the kids with the “high” exposure had an IQ that was, on average, 0.29 points lower than the kids with the low exposure (“–0.29 (–0.44, –0.14)”).
Yes, you’re reading that correctly: 0.29. If the average for the kids with the low exposure was 100, the average for the kids with the high exposure was 99.71.
The margin of error on most IQ tests is around 3 full points. The apparent “loss” that these kids were experiencing is 10% of the margin of error of a regular IQ test. Normally, if I score 98 on the test, and you score 102, given that our ‘real’ IQ is considered to be within +/-3 of the score we received on the test, then you and I (with a difference of 4 full points) are considered to have roughly the same IQ. A difference of 0.29 is, for all practical purposes, nothing.
Now I’m not saying that throwing out this study means that fluoride is entirely safe, and we should just start adding it to our lunch menu. But this study does not support the claims the anti-fluoride fear-mongers are making. At all.