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Great Lakes
Article:
Small fish for healthy babies
Science News
Published June 10, 2004
Japanese researchers have shown for the first time that
when pregnant women
eat fish, they can increase their fetuses' exposure to
harmful methylmercury
as well as beneficial omega-3 fatty acids. As a result,
the authors of
research recently posted to ES&T's Research ASAP website
(es034983m)
recommend that mothers-to-be eat small fish to maximize
their uptake of
beneficial fatty acids while minimizing the detrimental
methylmercury.
Small fish generally contain less methylmercury than large
fish because the
toxin bioaccumulates through food webs. As a result, top
predators like
swordfish have the highest methylmercury concentrations.
Fish are also the
primary source of docosahexaenoic acid-an omega-3 fatty
acid that plays an
important role in development of the brain and visual
system.
Mineshi Sakamoto of the Japanese environmental agency's
Minamata Institute, in Minamata, and colleagues measured
the concentrations of mercury and docosahexaenoic acid
in the blood of 63 Japanese mothers and their newborns'
umbilical cord blood. The mothers reported eating about
50 grams of fish and shellfish each day. Minamata, on
the west coast of Kyushu, Japan's
southernmost island, gained worldwide notoriety in the
1950s. Residents
became severely ill and died and their children were born
with severe
abnormalities from eating seafood contaminated by mercury,
which! a local
company had dumped into the bay (www.einap.org/envdis/Minamata.html).
Methylmercury primarily binds to hemoglobin. So, by measuring
only the
mercury in red blood cells, Sakamoto's group ensured that
the measured
contaminant levels would not be artificially low because
of confounding
factors, such as anemia, says Harvard School of Public
Health epidemiologist
Philippe Grandjean. The researchers measured the amount
of docosahexaenoic acid in whole blood plasma.
Sakamoto found a good correlation between the level of
mercury in a mother's
blood and in her baby's cord blood. In keeping with previous
studies, they
also found that mercury levels were higher in the baby's
blood than in the
mother's-as much as 2-fold greater. Fatty acid concentrations
also
correlated between mother's and baby's cord blood. In
addition, the
concentrations of the fatty acid and mercury were also
correlated in the
babies' umbilical cord blood.
"This pa! per provides documentation that Japanese
fish-eaters get both toxic
mercury and essential fatty acids from seafood. However,
the correlation
will depend on the types of fish eaten and may not hold
for other
populations," says Grandjean, who leads the Faroe
Islands study, one of two
ongoing, long-term studies of the effects of mercury on
children's
neurodevelopment (Environ. Sci. Technol. 2000, 34, 410A-411A).
Grandjean's team looked for, but didn't find, a good correlation
between
fatty acids and mercury exposure in the Faroes. He says
that the lack of
apparent correlation is probably because people who live
on these North
Atlantic islands are primarily exposed to methylmercury
by eating whale meat
that is very lean.
The Japanese researchers suggest that their findings might
explain the
discrepancy between the Faroe Islands study and the other
large study of
mercury's effect on the neurodevelopment of children,
which is taking place
in ! the Seychelles Islands in the Indian Ocean off the
coast of eastern
Africa. The Faroe Islands study found harmful developmental
effects from low
levels of exposure to mercury in fish and sea mammals,
whereas the
Seychelles study did not find an adverse effect. Although
the data on fatty
acid levels are not available for both groups, the Japanese
researchers
speculate that the Seychelles Islanders, with their diet
of some 12 fish
meals a week, should be exposed to much higher levels
of fatty acids than
the Faroe Islanders. The results of this latest study
hint that the fatty
acids may help protect children.
Grandjean agrees that people should eat fish with high
essential fatty acid
levels and the lowest possible mercury concentrations,
but he cautions that
the two characteristics probably act in different ways.
"You can't
compensate for a high mercury exposure by taking fish
oil supplements," he
says. -REBECCA RENNER
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