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This study challenges a
previous Lancet study that suggest a mother’s consumption
of ocean fish contaminated with methyl mercury does not harm
development of her baby's brain.
In the previous study, researchers performed a series of
mental and motor tests on 779 children born on the Seychelles
Islands from birth to 9 years of age. Ocean fish eaten on
the Seychelles contain levels of methyl mercury that are comparable
to those in U.S. fish (about 0.3 µg/g). However, fish
consumption in the Seychelles is significantly higher than
in the United States, so Seychelles babies in the womb are
exposed to more methyl mercury than typical U.S. babies.
Researchers used hair analysis to determine mercury levels
in the mothers at the time of their babies’ birth. The
women ate fish an average of 12 times a week during pregnancy.
They found no link between higher methyl mercury exposures
and adverse neurocognitive scores among the infants.
If viewed in isolation, these results could be looked at
in a way that would ease concerns about low-level mercury
exposures associated with ocean-going fish consumption and
a potential adverse impact on fetal development.
According to researchers of the previous study, FDA recommendations
that pregnant women should avoid highly contaminated fish
such as swordfish and limit consumption of other species to
no more than 12 ounces per week are reasonable.
It could also be interpreted that the beneficial effects
of consuming fish oils may protect against the adverse effects
of mercury, a hypothesis that is being tested by researchers.
However, two other extensive studies
of mercury impacts on fetal development have shown mercury
to have deleterious effects. One study involved children
from the Faroe Islands whose mothers ate whale meat and blubber,
while the other study involved children from New Zealand whose
mothers ate fish and chips made with contaminated shark meat.
Following are several explanations that may explain the conflicting
results, along with rebuttals explaining why the explanations
may not be accurate:
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Shark muscle and whale meat/blubber on the Faroe Islands
and in New Zealand carry much higher methyl mercury concentrations
than does the fish eaten on the Seychelles. Therefore,
even if the Seychelle Islanders ate the same amount of
mercury as the other populations, the fish made up a more
consistent portion of their diet and would likely be transmitted
to fetal tissue in a low-level, continuous stream. Conversely,
mercury exposure in the Faroes and New Zealand would be
in higher, burst-like exposures, which may have different
effects on the developing fetus. However, according to
recent analysis, the Faroe Island exposures are actually
relatively continuous rather than burst-like.
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Whale meat consumed on the Faroe Islands contains mercury
persistent chlorinated compounds, including PCBs, along
with the mercury. The PCBs may either cause the effect
or interact with mercury to influence fetal neurological
development. However, the Faroe Island study separated
the effects of mercury from the effects of PCBs. Further,
this interpretation would not explain the New Zealand
result because the shark meat in the study does not contain
significant levels of PCBS.
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The Faroe Island study measured mercury in umbilical
cord blood and hair; the Seychelles study used hair samples.
Past research has suggested that hair samples may provide
a less accurate measure.
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Due to aspects of study design and execution, the Seychelles
study does not have the statistical ability to detect
small differences.
Combined, the studies do not provide clear evidence to determine
proper recommendations for consuming fish contaminated with
low-levels of mercury. While one study suggests that existing
recommendations are sufficient, other studies suggest they
should be stricter.
According to researchers, when issues of public health are
concerned and two well-designed studies yield conflicting
results, health regulations should be based on the study that
shows adverse effects, reflecting a "better safe than
sorry" mentality, until more conclusive results can be
determined.
Our
Stolen Future May 15, 2003
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