Earlier this week, Newsweek published an article about a possible link between fluoride in water supplies and ADHD. It seems to have caused quite a stir. Just three weeks ago, Newsweek published another article (by the same author) about a potential link between water fluoridation and thyroid disease. If you read the comment threads–which I wouldn’t recommend, you’ll see fluoride implicated in arthritis, intellectual disability, kidney disease, hip fractures, and a multitude of other maladies. (You may also notice that the vast majority of the hundreds of comments are written by the same handful of people…or that some of the comments are directly copied and pasted onto over 600 other sites–not very creative.) By the time you get to the end, you’ll probably be thinking that “fluoridation is the most monstrously-conceived and dangerous Communist plot we have ever had to face.” But don’t knock that glass of water out of your kid’s hand just yet.
Just like those who oppose vaccines or promote homeopathy, anti-fluoride activists are a very vocal minority, and they are intent on banning this “toxin” from our water supplies. Leading the way is the Fluoride Action Network. When I visited their website (I cringed a little before I clicked), I noticed a few things right away. There are lots of underlined words in red capital letters: ALERT, POISON, TOXIC, GOVT FAILED TO WARN. There’s a large picture of a stamp reading BANNED. They use a time-honored tactic—the appeal to a celebrity (because what film star doesn’t have an in-depth understanding of dental pathophysiology?). And, of course, they include several links to make it easy for you to make a one-time or recurring donation.
Opponents of water fluoridation cite numerous studies that show adverse health outcomes supposedly attributable to fluoride. But if you examine the studies closely, to see what they really say (or if they’re even capable of saying anything at all), the claims just don’t hold up. Take the ones I mentioned above, for example:
The ADHD article cites a study recently published in the journal Environmental Health. The Newsweek headline reads: “Water Fluoridation Linked to Higher ADHD Rates.” But linked is a strong word. The authors are somewhat more conservative in their conclusion and mention that there may have been some other confounding factors. I’d take it a step further and say the study is largely worthless and doesn’t really say anything at all about ADHD except that it might be more prevalent in the South. Here’s why:
- The authors gather data about the prevalence of ADHD and water fluoridation in each state. But when they report it (see the table below), they report it by region. Maybe that was just for convenience, but the skeptic in me wonders if compiling the states into regions made them average out to show a better correlation and support their hypothesis.
- There’s no analysis of the dosage of fluoride per state or region–only whether or not they contained fluoride. The fluoride concentration in one location may be 6 mg/L, but only 0.9 mg/L somewhere else. If fluoride were, in fact, a neurotoxin that could cause ADHD, this would certainly be important information. The concept of a dose-response relationship isn’t a secret, and it should be familiar to the editors of Environmental Health. It would make much more sense to compare the concentration in different locations instead of the percentage of people receiving fluoridated water (you know, unless it doesn’t support your hypothesis).
- While there was a positive association overall between fluoridated water and ADHD, there were also times where those two things didn’t match up at all–and times when the exact opposite was true. The statistical analysis gets complicated, but to keep it simple, it’s really not a very consistent relationship.
- There are lots of confounding factors that go unaddressed. Besides fluoride, what other things could affect the prevalence of ADHD in different regions? The authors account for one: that children in poor families are more likely to have ADHD. But there are so many more for which they don’t account: genetics, race, gender, access to healthcare (and thus diagnosis), school systems, premature birth rates…the list goes on. And in the statistical analysis, they are all ignored.
- A study with this design can never prove that one thing caused another; only that two things are “associated.” For instance, there’s a strong association between organic food consumption and autism. But eating organic foods doesn’t cause autism. The two trends just happened at the same time (or, if anything, autism played a role in increasing organic food consumption). To show “causation,” you’d need to start with two groups of otherwise similar people, give some of them fluoridated water and the rest water with no fluoride (without telling them which group they are in), and then watch them over time to see if one group developed ADHD at a higher rate.
I could keep going, but my point isn’t to rip this article apart; it’s to emphasize that studies like this should never be interpreted as “linking” one thing to another. To be fair, the authors of the study identify some of these limitations, which are also briefly mentioned in the Newsweek article. But there seems to be a lot more attention given to the rather meaningless correlation between ADHD and fluoridated water, while a number of weaknesses go unaddressed. Given the significantly higher prevalence of ADHD in Southern states, the researchers probably could have shown an even stronger correlation between ADHD and consumption of sweet tea.
As far as the thyroid study goes, a group of researchers looked at different areas in England and compared the prevalence of people with hypothyroidism (underactive thyroid) with the fluoride content of their water. Brits who drank fluoridated water were more likely to have hypothyroidism. But it’s pretty much the same story as the one above–those two things could very feasibly be entirely unrelated.
There are so many others. Some involve injecting large doses of fluoride into pregnant rats (whose offspring apparently exhibit “ADHD-like symptoms”–whatever that means for rats). But people aren’t rats, and nobody’s talking about injecting pregnant women with ridiculous doses of fluoride. Another article, often cited as “proof” that fluoride is a neurotoxin, was a review of studies performed in China that looked at children in regions with fluoride concentrations much higher than those recommended in the US, comparing their IQs to those of children in areas with lower fluoride concentrations. Again…only a correlation, higher doses than we recommend, a totally different population, doesn’t address confounding factors, etc. In short, there hasn’t been a methodologically-sound study showing that fluoride concentrations in the recommended range cause any harm at all.