good for expectant mums if mercury level is low
Women's Health News
Published June 20, 2005
For years medical experts have argued, as fish can be
harmful as well as healthy, and what advice to give people,
particularly pregnant women, about how much is safe to
Now a new study by Harvard University doctors has to some
extent settled the debate by concluding that pregnant
women can boost their baby's intelligence by eating fish
a couple of times a week, but only if they avoid varieties
with large concentrations of mercury.
Fish which is full of omega-3 fatty acids, helps young
brains develop and seems to protect against heart disease.
But some of it is tainted by mercury, a potent neurotoxin
that interferes with the building of brains.
Almost all fish contain traces of mercury, but larger
marine species such as swordfish, shark and albacore tuna
accumulate the highest levels.
Although mercury can harm adults by affecting the memory,
causing the hair to fall out and possibly increasing the
risk of heart disease, fetuses are the most vulnerable
because neurological effects have been found at low levels.
This new study of 135 Boston-area babies is important
because it quantifies and compares the risks and benefits
of a fish diet.
The researchers concluded that pregnant women should
eat fish because their babies are likely to score higher
on intelligence tests, but the benefits of the nutrients
disappear and the babies' intelligence scores drop substantially
if the fish contains high levels of mercury.
The U.S. Environmental Protection Agency (EPA) estimates
that about 630,000 babies a year are born with mercury
exposure that could reduce their mental abilities.
Dr. Philippe Grandjean, an environmental epidemiologist
at the Syddansk Universitet (University of Southern Denmark)
and Harvard University who has studied the effects of
mercury on children for 20 years, says the study adds
to the mounting evidence that women should eat fish but
follow warnings to limit the types and amounts they consume.
Grandjean and others have previously presented similar
findings for school-age children, he says the study suggests
that the effects on infants are quite strong.
According to the report, the women in the study ate fish
on average once a week during the second trimester of
their pregnancy. The highest intelligence scores were
among the babies whose mothers had consumed more than
two helpings of fish per week but whose mercury levels
remained under 1.2 parts per million.
Dr. Emily Oken of Harvard Medical School, the study's
lead researcher, Oken, who specializes in pregnancy and
nutrition, says that for each additional weekly serving
of fish, the babies' intelligence scores increased by
4 points, or an average of almost 7%. But for every increase
of 1 part per million of mercury, the babies' intelligence
scores dropped by 7.5 points, or 12.5%. A woman could
raise her mercury level by 1 ppm if she ate an average-sized
serving of swordfish once a week.
The study findings support the U.S. Food and Drug Administration's
guidelines, issued in 2004, which recommend that pregnant
and nursing women and those who might become pregnant
eat up to two meals, or 12 ounces, of fish a week and
that they avoid certain types of fish entirely.
Young children are advised to follow the same guidelines
because their brains are still developing.
In it's guidelines the FDA entirely rules out swordfish
and shark as well as king mackerel and tilefish, found
on the Atlantic Coast and Gulf of Mexico, for pregnant
and nursing women and young children. Some white and albacore
tuna, canned and fresh, also have high mercury levels.
The darker the fish meat, the higher the mercury content.
Sardines, herring, canned light tuna, cod, haddock, tilapia,
sea bass and shrimp are considered good, low-mercury choices.
Small fatty fishes such as sardines and herring are especially
beneficial to babies because they contain a lot of fatty
Salmon is generally low in mercury and high in fatty
acids, but some farmed salmon contains high concentrations
of other contaminants, PCBs, which are also risky for
In California, grocery stores and restaurants selling
fish are required to post mercury warnings for women and
young children. The EPA also has issued localized advisories
for some species caught by recreational fishermen, particularly
in the Great Lakes and the San Francisco Bay.
Oken, who practices medicine at Harvard Pilgrim Health
Care in Boston, say that many doctors are as confused
as patients about this issue.
Many are women are unaware they should avoid swordfish
and limit tuna and other fish. Others stop eating all
fish during pregnancy, which means their babies do not
get its brain-enhancing effects.
To add to the confusion, scientists disagree on how much
mercury is safe.
In the study the babies were subjected to tests designed
by neuropsychologists to study early signs of intelligence
and memory. The babies were shown photographs of new faces
and ones they had been shown before, and the researchers
recorded how much time they spent studying each one. Babies
score higher on the test if they move quickly from the
familiar face, indicating recognition, to exploring the
Dr. Jane Hightower, a San Francisco internist says consumers
might have to resort to omega-3 supplements to get the
benefits of fish without the risks, she has apparently
detected excessive mercury levels in many of her patients,
particularly those who eat swordfish.
Mercury, a natural element found in the Earth's crust,
when released into the air through smokestacks, spreads
globally and accumulates in tissues of animals, particularly
fish. The largest sources of man-made mercury emissions
are coal-fired power plants, mainly in Asia.
The report is published online in the journal Environmental