The Scary Reason Pregnant Women Should Avoid Fish

All fish contain small amounts of methylmercury, the most toxic form of mercury, and “fish consumption represents the main source of methylmercury exposure.” In my videos Nerves of Mercury and Fish Fog, I discuss how 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, a shrunken brain disorder. But we didn’t know whether low exposure could also affect brain size until recently.

Autopsy studies suggest mercury preferentially affects the developing cerebellum, so researchers used ultrasound to measure cerebellum size in newborns of mothers who had high body levels of mercury.

Let’s put that into practical terms. In the above video, you can see the results of a study measuring mercury concentration in human hair. Just one can of tuna a week raises human hair mercury concentration to levels nearly three times as high as the “high” group in the ultrasound study. So the bodies of the women suffering high mercury contamination were considered heavily contaminated, but even just a little canned tuna once in a while could bump our levels even higher. So the high really wasn’t that high. But what did they find?

The researchers demonstrated that babies 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 methylmercury does indeed influence fetal brain development as evidenced “by decreased size of a newborn’s brain.”

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 video Mercury vs. Omega-3s for Brain Development.

For more on canned tuna in particular, check out:

In health,
Michael Greger, M.D.

PS: If you haven’t yet, you can subscribe to my free videos here and watch my live year-in-review presentations Uprooting the Leading Causes of Death and More Than an Apple a Day.

Fukushima and Radioactivity in Seafood
Mercury Testing Before Pregnancy
The Effects of Cow’s Milk on Babies


Janice Thompson
Janice Thompson4 years ago

Mercury was used in making hats. Hence, we had Mad Hatters.

Melania Padilla
Melania P5 years ago

I think all of us... The ocean is not the safe place it used to be...

Fi T.
Past Member 5 years ago

Love our mum

Nils Anders Lunde
PlsNoMessage s5 years ago


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Past Member 5 years ago

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Nicole Bergeron
Nicole Bergeron5 years ago

I was always told to avoid fish if pregnant because it could cause complications after birth for the child and could increase the risk of miscarriage before birth.

Marija Mohoric
Martija M5 years ago

thank you

Luna starr
luna starr5 years ago

ALL Doctors should warn women but will they;I doubt it

NO MORE FWD to Ana Marija
ANA MARIJA R5 years ago

Thank you.