New findings from research in the Seychelles
provide further evidence that the benefits of fish consumption on prenatal
development may offset the risks associated with mercury exposure. In fact, the
new study, which appeared January 20, 2015 in the American Journal of
Clinical Nutrition, suggests that the nutrients found in fish have
properties that protect the brain from the potential toxic effects of the
chemical.
Three decades of research in the Seychelles
have consistently shown that high levels of fish consumption by pregnant mothers
- an average of 12 meals per week - do not produce developmental problems in
their children. Researchers have previously equated this phenomenon to a kind
of biological horse race, with the developmental benefits of nutrients in fish
outpacing the possible harmful effects of mercury also found in fish. However,
the new research indicates that this relation is far more complex and that
compounds present in fish - specifically polyunsaturated fatty acids (PUFA) -
may also actively counteract the damage that mercury causes in the brain.
"These findings show no overall
association between prenatal exposure to mercury through fish consumption and
neurodevelopmental outcomes," said Edwin van Wijngaarden, Ph.D., and
associate professor in the University of Rochester Department of Public Health
Sciences and a co-author of the study. "It is also becoming increasingly
clear that the benefits of fish consumption may outweigh, or even mask, any
potentially adverse effects of mercury."
"This research provided us the
opportunity to study the role of polyunsaturated fatty acids on development and
their potential to augment or counteract the toxic properties of mercury,"
said Sean Strain, Ph.D., a professor of Human Nutrition at the Ulster
University in Northern Ireland and lead author of the study. "The findings
indicate that the type of fatty acids a mother consumes during pregnancy may
make a difference in terms of their child's future neurological
development."
The new study comes as the U.S. Food and Drug
Administration and international agencies are in the process of revisiting fish
consumption advisories to better reflect the health benefits of nutrients found
in fish. The FDA's current guidance - which recommends that pregnant women
limit their consumption of certain fish to twice a week - was established
because of the known risk of high level mercury exposure on childhood
development.
Mercury is found in the environment as a
result of both natural and human (e.g. coal plant emissions) activity. Much of
it ends up being deposited in the world's oceans and, as a result, fish harbor
the chemical in very small amounts.
This has given rise to concerns that the
cumulative impact of prenatal exposure to mercury through fish consumption may
have negative health outcomes, despite the fact that that a link between
low-level exposure and developmental consequences in children has never been
definitively established.
At the same time, fish are rich in a host of
beneficial nutrients, including fatty acids, which are essential to brain
development, leading to a long-standing exchange among scientists,
environmentalists, and policymakers over the risk vs. benefit of fish
consumption. This debate has significant consequences for global health, as
billions of people across the world rely on fish as their primary source of
protein.
The Seychelles Child Development Study - a
partnership between the University of Rochester Ulster University, and the
Republic of Seychelles Ministry of Health and Education - is one of the longest
and largest population studies of its kind. The Seychelles, a cluster of
islands in the Indian Ocean, has proven to be the ideal location to examine the
potential health impact of persistent low-level mercury exposure. The nation's
89,000 residents consume fish at a rate 10 times greater than the populations
of the U.S. and Europe.
The study published today followed more than
1,500 mothers and their children. At 20 months after birth, the children
underwent a battery of tests designed to measure their communication skills,
behavior, and motor skills. The researchers also collected hair samples from
the mothers at the time of their pregnancy to measure the levels of prenatal
mercury exposure.
The researchers found that mercury exposure
did not correlate with lower test scores. This finding tracked with the results
of previous studies by the group - some of which have followed children in the
Seychelles into their 20s - that have also shown no association between fish
consumption and subsequent neurological development.
The researchers also measured the PUFA levels
present in the pregnant women and found that the children of mothers with
higher levels of fatty acids known as n3 - the kind found in fish - performed
better on certain tests. Another common form of PUFA, called n6, comes from
other meats and cooking oils and is found in greater abundance in the diets of
residents of developed countries.
The fatty acids in fish (n3) are known to
have anti-inflammatory properties, compared to n6, which can promote inflammation.
One of the mechanisms by which mercury inflicts its damage is through oxidation
and inflammation and this has led the researchers to speculate that not only
does n3 provide more benefit in terms of brain development, but that these
compounds may also counteract the negative effects of mercury.
This was reflected in the study's findings,
which showed that the children of mothers with relatively higher levels of n6
did poorer on tests designed to measure motor skills.
"It appears that relationship between
fish nutrients and mercury may be far more complex than previously
appreciated," said Philip Davidson, Ph.D., the principal investigator of
the Seychelles Child Development Study, a professor emeritus at the University
of Rochester, and senior author of the study. "These findings indicate
that there may be an optimal balance between the different inflammatory
properties of fatty acids that promote fetal development and that these
mechanisms warrant further study."
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