Thursday, November 21, 2019
Everybody knows to avoid tuna when pregnant, right? Not so fast. Eating tuna might actually yield better results, says a large new study.
Eating ocean fish is good for you, but some fish
have significant levels of methylmercury which is bad for you, so you should
avoid those fish, right? Wrong, says a new study.
Mothers who ate seafood, even when it contained
high levels of methyl mercury, had smarter kids than those who didnʻt eat
seafood, says the comprehensive, peer-reviewed study.
"Moderate and consistent evidence indicates
that consumption of a wide range of amounts and types of commercially available
seafood during pregnancy is associated with improved neurocognitive development
of offspring as compared to eating no seafood," it said.
This flies in the face of conventional wisdom,
and some medical wisdom. Both the U.S. Environmental Protection Agency and the
U.S. Food and Drug Administration recommend against pregnant women eating ahi,
over concerns about methyl mercury exposure.
There is no question that thereʻs methylmercury
in yellowfin, bigeye and bluefin tuna, and that the amount has been increasing
in recent years. There are also significant amounts of mercury in blue marlin
and other species.
The Hawai`i Department of Health warns against
pregnant women eating any blue marlin, swordfish and shark and recommends
severe limits on consumption of tunas.
Yet the new study suggests women who eat some ocean fish,
even when mercury levels are high, actually have kids who have
better mental outcomes. The authors wrote: " No net adverse neurocognitive
outcomes were reported among offspring at the highest ranges of seafood intakes
despite associated increases in mercury exposures."
The paper is entitled, "Relationships
between seafood consumption during pregnancy and childhood and neurocognitive
development: Two systematic reviews." It is published in the journal, Prostaglandins,
Leukotrienes and Essential Fatty Acids. Its authors come from some of the
most prestigious medical and scholarly institutions in three countries,
including the Center for Food Safety and Applied Nutrition, American Society
for Nutrition, National Institutes of Health and others.
So whatʻs going on? The authors say thereʻs
something in seafood that counteracts the impacts of mercury, and makes it even
healthier for kids to eat seafood than not to eat
it.
Here is the technical way they say that:
"This evaluation of seafood consumption inherently integrates any adverse
effects from neurotoxicants, and benefits to neurocognition from omega-3 fats,
as well as other nutrients critical to optimal neurological development."
Even small amounts of seafood have a beneficial
effect, and the study found no downside to large amounts:
"Benefits to
neurocognitive development began at the lowest amounts of seafood consumed in
pregnancy (∼4 oz/wk) and up to >100 oz/wk, with benefits
to age appropriate measures of neurocognitive development including an average
increase of 7.7 IQ points, in evaluating 44 publications reporting on 102, 944
mother-offspring pairs, no adverse effects on neurocognitive development were
found."
It is not that the mothers and children arenʻt
exposed to methyl mercury. They are, but there appear to be no negative impacts
from that exposure from seafood, the paper says: "No net adverse neurocognitive
outcomes were reported in offspring at the
highest ranges of seafood intakes despite associated increases in mercury
exposures."
The authors are aware that this is controversial
stuff, and they urge the scientific community to do more research. There needs
to be work, they say, that follows the children into older age, research into
whether fatty or oily fish like tuna are healthier than white-fleshed fish, on
making sure the IQ tests in studies are comparable, and research on differences
based on species of fish and of how it is prepared.
But how is it possible that mercury
exposure in kids is dangerous, except when it comes from fish?
The authors of
this paper donʻt say in the publication, but others have suggested that seafood
contains something else that protects against mercury- namely, selenium.
This study from 2010 argues that selenium
protects against mercury poisoning, and it cites studies indicating selenium
can actually reverse some of the effects of methylmercury toxicity.
"Studies of populations exposed to MeHg (methyl mercury) by eating
Se-(selenium) rich ocean fish observe improved child IQs instead of harm."
Tuna and most billfish tend to have high levels
of selenium, which may help explain things. Hereʻs a useful report from NOAA
and other agencies.
© Jan
TenBruggencate 2019
Posted by Jan T at 11:31 AM
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