Fluid had been found to be a developmental neurotoxin in
rats and mice leading to learning and memory deficits which
led to an interest in studying human populations. Starting
in the 19 eighties, reports started appearing in Chinese
medical journals that found correlations between areas naturally containing higher
fluoride levels in water with lower intelligence among Children,
dental fluorosis. The fluoride induced tooth modeling is widespread
in China with more than 90 million residents affected often
in small pockets surrounding particular small springs or mountain sources
. Researchers took advantage of the fact that even adjoining
neighborhoods could have widely different fluoride exposure setting up a
kind of natural experiment due to limited access to Chinese
journals at the time, these studies largely escaped the
attention of scientists in the West until a meta analysis
of 16 such studies was published in English in 2008
fluoride and children's intelligence. A meta analysis found that
Children living in areas prone to fluorosis had five times
higher odds of developing low IQ than those living in
areas with little or no fluorosis. So here we
were thinking dental fluorosis was just a cosmetic blemish,
but it may instead be a visual indicator of intellectual
deficits. A subsequent meta analysis in 2012, including
about 10 more studies found that the average intelligence gap
between high and low fluoride exposure areas was about seven
IQ points. By far, the largest study involving
thousands of Children found that even if fluoride levels below
one P PM, higher fluoride levels were associated with
a large drop in the chances of developing excellent intelligence
uh defined as an IQ of 130 or higher.
Even very mild sclerosis was associated with less than half
the odds of reaching such a high IQ. By
now, there have been more than 50 studies showing
an association between higher fluoride exposure and lower IQ.
In the latest systematic review meta analysis, 90% of
the studies published in the last 10 years reported the
link between high fluoride exposure and reduced intelligence. However
, serious caveats are in order first, the fluoride
concentrations in most of these studies were well above Fluoridation
levels. In the 2012 meta analysis. For example
, one study clocked concentrations as high as 11.5 P
PM, far exceeding the US target of 0.7 parts
per million as well as the average concentration in the
United States which is around 0.8 P PM in municipal
water and 0.3 P pm in well water. Now
to be fair, I mean the 11 P PM
and the meta analysis that that was an outlier,
I mean the average elevated level was only about two
parts per million and most found associated IQ detriments below
the EPA S upper limit. It's it's maximum contaminant
level goal of four P PM, which is supposed
to represent the level below which there is no known
or expected risk to health. Some studies showed lower
intelligence with fluoride concentrations even down at 1 to 2
P PM. With one estimate suggesting the smallest harmful
concentration, potentially shaving off a single IQ point would
be down around 0.3 P PM, assuming you drink
four cups of water a day. While others suggest
it's too early to be able to calculate a threshold
for human neurotoxicity due to insufficient available data. The
second major caveat is confounding and nearly all the studies
to date have been performed in rural communities in countries
like China, Iran Mongolia areas within these countries with
unusually high fluoride levels may be particularly poor and underdeveloped
. Since relatively rich communities may be more likely to
invest in a higher quality drinking water that filters out
fluoride if only to reduce dental fluorosis, high fluoride
water may also be more likely to be contaminated with
other neurotoxins. Uh fluoride exists in water as a
negatively charged particle to maintain electro neutrality. This may
pull into the groundwater positively charged particles such as aluminum
arsenic lead or mercury. This doesn't happen in water
Fluoridation since the negative fluoride ions are balanced out in
the water treatment process. Finally, most of the
older studies were cross sectional and ecological. Meaning they
looked at a snapshot in time of group level data
rather than individual exposures over time. Uh Just because
a child with low IQ lives in a high fluoride
area doesn't necessarily mean they or their mom actually drank
the water. For example, ideally, we'd be
able to measure individual exposure levels and th the kids
over time to see if those with higher exposure really
do grow up with stunted intellect. And that's exactly
what we'll cover in my next video entitled why I
changed my mind on water Fluoridation.