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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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