
Harvard Study Confirms Fluoride Reduces Children's IQ (2013) - deevus
http://www.huffingtonpost.com/dr-mercola/fluoride_b_2479833.html
======
doktrin
This is the author of the op-ed :

[http://en.wikipedia.org/wiki/Joseph_Mercola](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.

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computer
The title is wrong (i.e. not supported by the data).

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.

~~~
xyzzy123
Yes, so there will be a strong correlation between tight control over flouride
in drinking water (e.g. clamping it to 1mg/L or so versus not deflouridating
at 10mg/L levels) and a wealthier environment with good infrastructure. I
think it's just so hard to "weight" for the differences here.

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.

~~~
computer
> Yes, so there will be a strong correlation between tight control over
> flouride in drinking water (e.g. clamping it to 1mg/L or so versus not
> deflouridating at 10mg/L levels) and a wealthier environment with good
> infrastructure. I think it's just so hard to "weight" for the differences
> here.

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.

~~~
xyzzy123
Right, I understand your logic. Thanks.

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gus_massa
There is a 2012 post in Science Based Medicine about the same Harvard study:
“Antifluoridation Bad Science”
[http://www.sciencebasedmedicine.org/antifluoridation-bad-
sci...](http://www.sciencebasedmedicine.org/antifluoridation-bad-science/)

~~~
dalke
Nice find. I think the key quote is:

> 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.

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lkrubner
Please do not upvote this.

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.

[http://en.wikipedia.org/wiki/Flynn_effect](http://en.wikipedia.org/wiki/Flynn_effect)

~~~
nabla9
high levels of fluoride <> fluoride added to water.

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.

~~~
dalke
While the Huffington Post article is fully of scary alarmism, the actual
referenced paper, at
[http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3491930/pdf/ehp....](http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3491930/pdf/ehp.1104912.pdf)
, is in complete agreement with what you just wrote. Some relevant quotes:

> 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.

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judk
Headline is irresponsible. Is the effect monotonic with dose, from 0? Or is
it, like most substances, excessive concentration is harmful?

Are we really meant to believe flouride is harmful like lead, or merely like
vitamins in excess?

