Exposure to mercury during pregnancy appears to influence fetal brain development as detected by decreased size of a newborn’s brain.
All fish contain small amounts of methylmercury, the most toxic form of mercury, and fish consumption represents the main source. We’ve seen that mercury exposure through fish consumption, even within the government’s safety limits, can have adverse neurological and behavioral effects on child development. Severe exposure can cause overt structural brain abnormalities like microcephaly, which is a shrunken brain disorder. But we didn't know whether low exposure could also affect brain size until this new study.
Autopsy studies suggest mercury preferentially affects the developing cerebellum, and so researchers used ultrasound to measure its size in newborns of mothers who had high body levels of mercury compared to a control group of women who had low levels. Let’s put that into practical terms.
Compared to the low level control group… here’s where the high-level mercury women were. How much canned tuna consumption is that equivalent to? Here’s what your bodily mercury burden is if you eat one serving of canned tuna a day, about half a can. Here’s what two cans a week will do to you, and this is just one can a week. So the bodies of the women suffering high mercury contamination in the ultrasound brain study were considered heavily contaminated, but even just a little canned tuna once in a while could bump your levels even higher. So the high really wasn't that high, but what did they find?
They demonstrated that newborns born to mothers with higher hair mercury levels had cerebellums up to 14% shorter than those born to mothers with lower hair mercury levels. They conclude that prenatal exposure to what may be considered low-levels of methyl-mercury does indeed influence fetal brain development as detected by decreased size of a newborn’s brain.
To see any graphs, charts, graphics, images, and quotes to which Dr. Greger may be referring, watch the above video. This is just an approximation of the audio contributed by Ariel Levitsky.
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I’ve covered mercury in fish before in videos such as Nerves of Mercury, Hair Testing for Mercury Before Considering Pregnancy, and Fish Fog. For more on canned tuna in particular, check out:
What else can we do to protect our newborns? See:
But what about the long chain omega-3 DHA in fish—isn’t that necessary for healthy brain development? That’s the topic of my next video, Mercury vs. Omega-3s for Brain Development.
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