Harvard Study Confirms Fluoride Reduces Children's IQ (2013)
huffingtonpost.com
huffingtonpost.com
http://en.wikipedia.org/wiki/Joseph_Mercola
Of relevance :
> In 2005, 2006, and 2011, the U.S. Food and Drug Administration warned Mercola and his company to stop making illegal claims regarding his products' ability to detect, prevent and treat disease.[7] The medical watchdog site Quackwatch has criticized Mercola for making "unsubstantiated claims and clash with those of leading medical and public health organizations [and making] many unsubstantiated recommendations for dietary supplements."
In my opinion, everything with the exception of the cited study should be taken with a large grain of salt.
This was a meta-review of observational (non-randomized) trials. It's a classical case of correlation not equaling causation-- there was no randomized trial, and since education (of parents) and location are highly correlated, any non-randomized studies cannot be used to prove a causal relationship.
What would be _really_ interesting would be finding areas with basically no natural flouride in the drinking water.
My hypothesis is that you would observe an IQ deficit similar to that in areas with very high levels of flouride. However someone who believes flouride causes harm at low levels might expect IQs to be higher.
Except that they used models in many studies, likely with factors for wealth, area, etc. This attempts to control for those factors, meaning they no longer have their intuitive effect on outcomes. Now, I say "attempts", because it corrects for some measurement of wealth and area, not the full underlying structure.
You're basically left with an "empty" correlation between IQ and fluoride in the data, but useless for causation conclusions. By "empty" I mean that you have attempted to correct for all known factors like some measurement of wealth, but there are always still many unknown underlying factors that might cause issues. That's what randomization solves.
Also note that many of the source studies are from China. This might sound odd to people outside academics, but due to many factors you should generally judge studies from most Chinese universities as less trustworthy than from other countries.
> The actual findings of the study do not show that there is any risk to public water fluoridation (if anything, they show that it is safe), but the study was seized upon by antifluoridation activists and distorted for their propaganda purposes.
If fluoride lowers IQ in children, then it would be difficult to reconcile the widespread use of fluoride (put in the water in many developed nations since the mid 20th Century) with the Flynn Effect, so this really needs wide confirmation before anyone should take it seriously.
I don't agree with it, but felt it was worth discussing here. I am interested in what other HNers have to say.
The article says "Despite the evidence against it, fluoride is still added to 70 percent of U.S. public drinking water supplies." While the study reports a negative correlation with higher fluoride levels, "high" in the underlying studies usually mean above 2mg/L. The US recommended levels are (as the study says) between 0.7 and 1.2 mg/L. A city which adds fluoride to get to 0.7mg/L is in the "low" category for the study, where the IQ levels are higher.
As the study did not analyze negative effects of levels lower than about 1.0mg/L, it's impossible to use it to conclude that a level of 0.7mg/L, even if reached by adding fluoride, is bad for IQ.
But the HuffPo article makes that conclusion anyway.
Recommended upper levels of fluoride are <1.0 mg/L. Typical naturally occurring levels are 0.4 mg/L. In many areas that get water from mountains (India, China, western USA) naturally occurring fluoride can be anything from 1.5 mg/L to 50 mg/L.
If you are American living in the west coast and use water from your own well, you might want to check your fluoride levels. Excess fluoride is removed from tap water in US.
> Opportunities for epidemiological studies depend on the existence of comparable population groups exposed to different levels of fluoride from drinking water. Such circumstances are difficult to find in many industrialized countries, because fluoride concentrations in community water are usually no higher than 1 mg/L, even when fluoride is added to water supplies as a public health measure to reduce tooth decay. Multiple epidemiological studies of developmental fluoride neurotoxicity were conducted in China because of the high fluoride concentrations that are substantially above 1 mg/L.
Table 1 lists the results, and quantify more of what "high" and "low" mean. In all but one case, "high" is above 1mg/L (and mostly over 2mg/L) and "low" is under 1mg/L. (The one case, Xiang et al. 2003, uses "0.57–4.5 mg/L (high); 0.18–0.76 mg/L (reference)", so the high range is mostly above 1mg/L).
These results explain why the US is thinking to lower recommended fluoridation levels in the US:
> In response to the recommendation of the NRC (2006), the U.S. Department of Health and Human Services (DHHS) and the U.S. EPA recently announced that DHHS is proposing to change the recommended level of fluoride in drinking water to 0.7 mg/L from the currently recommended range of 0.7–1.2 mg/L, and the U.S. EPA is reviewing the maximum amount of fluoride allowed in drinking water, which currently is set at 4.0 mg/L (U.S. EPA 2011).
Therefore, while the HuffPo article implies that any fluoridation is harmful, the paper itself considers most US municipal water supplies - at least, those with <1mg/L - to be in the "low" category that is better for higher IQ.
What about lower fluoridation levels? From the paper:
> A recent cross-sectional study based on individual-level measure of exposures suggested that low levels of water fluoride (range, 0.24–2.84 mg/L) had significant negative associations with children’s intelligence (Ding et al. 2011).
However, that's a different type of study, so the authors excluded it from this metadata analysis.
The Flynn effect was much more marked in Europe than it was in the US and fluoridation is much less widespread in Europe than in the US.
Are we really meant to believe flouride is harmful like lead, or merely like vitamins in excess?