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By April Forristall, SeafoodSource assistant
editor — 6/25/2009 3:17:19 PM
In 2002, Nick Ralston took a position at the University
of North Dakota working with the Environmental Protection
Agency-funded Center for Air Toxic Metals Health Effects
program. Last week, Ralston and his colleagues published
the results of their seven-year-long study, which shows
that current U.S. Food and Drug Administration methods
for developing seafood consumption guidelines may not
provide an accurate assessment of seafood safety. The
study's results led them to develop the Selenium Health
Benefit Value criterion, which predicts risks or benefits
of seafood species based on methylmercury and selenium
content. Ralston recently talked to SeafoodSource about
the study's implications and what it could mean for
the future of FDA's seafood-consumption recommendations.
Forristall: What led to the study?
Ralston: The bulk of the studies (at the University
of North Dakota's Energy and Environmental Research
Center) have involved studying mercury issues how to
capture it, clean it up out of the air. The part that
got added when I joined was looking at human health
effects. We figured we should get into the biochemistry
of mercury, too.
The mercury issue got my attention because I understood
the importance of selenium physiology and knew high
mercury exposures would cause harm to the brain if it
knocked out selenium metabolism. Since I initially though
there was far more mercury than selenium in seafood,
I thought seafood consumption was causing a lot of harm
to children. But after months of full-time research,
it became clear that ocean fish contain lots of selenium
and relatively little mercury, so I was perplexed about
how harmful effects could ever occur. It wasn't until
I learned that the studies that had found harm had involved
eating whale meat and large sharks that did contain
far more mercury than selenium that the story started
to become clear.
Why hasn't there been research like this before?
Actually, in 1967, the first study of mercury-selenium
interactions showed essentially the same thing that
our work shows today. We understand selenium physiology
better and can interpret the results better, but some
of the early work in the '60s and '70s is hard to beat.
Since that time, work on this subject has been largely
overlooked or ignored. I am currently writing a manuscript
with three of the selenium scientists that did work
in this area (they are mostly retired) to get them some
of the credit they deserve.
Why hasn't the selenium-mercury issue been more
publicized?
For at least the last couple of decades, many have had
the problem of dogmatically thinking they knew certain
things about the mercury issue for sure. Donmatic thinking
always causes trouble and it certainly did in this case.
That is why dogmatic thinking is never supposed to be
permitted in scientific research. However, politics
and policy makers have different agendas and their attitudes
toward dogma is quite different than that of scientists.
Not wanting to be confused by facts, there has been
a long-term tendency to ignore any and all scientific
data that got in the way of policy.
Is the FDA taking the research into consideration?
In February, the FDA presented an examination of the
data from all the human studies that does a great job
of connection all the dots for seafood consumers to
consider. Basically, since all the biggest studies show
substantial benefits when mothers eat increasing amounts
of ocean fish, it's pretty clear the dots are pointing
toward encouraging women to increase fish consumption
during pregnancy instead of limiting it. They came to
the same conclusion as us, but in a different way.
What effect will this study have on the public's perception
of the dangers of mercury in seafood?
A lot of people have gotten a completely wrong assumption
about what the EPA-FDA advisory actually sys. The current
advisory suggests that pregnant women should avoid shark,
swordfish, king mackerel and titefish because they contain
high levels of mercury. Since we know shark meat can
contain more mercury than selenium, I can completely
endorse that suggestion. The mercury and selenium levels
in the other three varieties on the do-not-eat list
need to be examined further before I could comment.
However, most people don't understand that the FDA-EPA
advisory encourages women to eat up to 12 ounces (two
average meals) of ocean fish a week. If the selenium-health
benefit values (Se-HBVs) for the various seafood become
more widely known, this will make it much easier for
women to select ocean fish that are the most beneficial
to their children's health. Omega-3 health benefit values
(O3-HBV's) calculated in a fashion that is very similar
to the Se-HBV's are currently being discussed. And if
properly done, these HBVs can be combined to create
an overall health benefit value for each of the various
varieties of ocean fish.
We developed a way of simplifying how to understand
the mercury-selenium issue. If (a species) is not good
to eat it will have a negative value. The better it
is, the more positive the value; the worse (it is),
the more negative. There is a real big contrast to normal
types of ocean fish, between 20 and 200. Whales are
-100. Seafood with negative values are kind of rare.
New Study Provides Reliable Seafood Consumption Guidelines
Understanding the benefits and safety of eating
ocean fish
Grand Forks, North Dakota (9 June, 2009) - A study
released this week by the University of North Dakota
show that current Food and Drug, Administration methods
for formulating seafood consumption guidelines may not
provide a reliably accurate assessment of seafood safety.
Results of the study; Selenium-Health Benefit Values
as Seafood Safety Criteria, reported in the journal,
EcoHealth, (volume 5, number R, pages 442-455) indicate
that when mercury levels are measured in fish, the levels
of the essential dietary mineral selenium also need
to be considered. Since only mercury levels in fish
are presently being overstated, and conversely, risks
from eating fresh water fish from some locations may
be much greater than is currently assumed.
Selenium is an essential nutrient that is required
for health of the brain and hormone producing tissues.
Mercury binds to selenium with an incredibly high affinity,
preventing it from doing its essential functions in
the body, especially the brain.
The research team lead by Dr. Nicholas Ralston has
previously demonstrated that laboratory animals fed
diets with selenium levels approximately equal to those
present in ocean fish are more than are many times greater
than those that actually occur in ocean fish.
"Since selenium and mercury occur together in
seafood but affect health outcomes in opposing directions,
it is essential to look at the balance of these elements
present in fish," says Ralston.
The study examined a new seafood safety criterion known
as the Selenium-Health Benefit Value (or Se-HBV) that
predicts risks or benefits of seafoods based on their
relative mercury and selenium contents. Foods that contain
disproportionately high amounts of mercury have negative
Se-HBV's and need to be completely avoided during pregnancy.
However, foods with positive Se-HBV's provide mothers
with the selenium their babies need in order to develop
healthy brains. Fortunately, only a few seafoods have
negative Se-HBV's. For example, among mothers that eat
meats of pilot whaled; -85, and larger sharks estimated
between -11 and -100, increasing exposures have been
found to harm their unborn children. However, most other
varieties of ocean fish have highly positive Se-HBV's
that are expected to promote child health.
Predictions based on Se-HBV's coincide with findings
that children of mothers that eat ocean fish enjoy substantial
IQ benefits of up to 10 IQ points, Previous warnings
regarding fish consumption have been Based on worst
case scenarios projected based on adverse effects of
mothers eating foods with negative Se-HBV's.
"Seafood safety criteria based on the Se-HBV will
improve protection of public health by properly restricting
consumption of hazardous seafoods such as pilot what
and shark meats while improving public health by encouraging
mothers to eat types of ocean fish that optimize their
nutritional status and enhance the IQs of their children,"
says Ralston.
Proponents of the study, which was funded by the National
Oceanic and Atmospheric Administration (NOAA) and the
Environmental Protection Agency (EPA), hope the findings
will lead to a more balanced approach to seafood consumption
guidelines. Particularly those pertaining to pregnant
and nursing women.
About the Selenium-Health Benefit Value Study
The Selenium-Health Benefit Value Study (Se-HBV) was
proposed by Dr. John Kanelkp and Dr. Nicholas Ralston
(Biol. Trace Elem. Res. 2007, 119,242-54) to provide
a reliably accurate and easily understood assessment
of seafood safety for consumers.
Because it considers both the health benefits of selenium
as well as risks of methylmercury, the Se-HBV index
provides far more accurate predictions of seafood benefits
and safety than current criteria which are based on
mercury alone.
Pilot whale meats that were eaten by mothers in the
Faroes study that form the basis of current U.S. Environmental
Protection Agency advisories regarding seafood safety.
However, studies of the effects of maternal ocean consumption
are finding IQ benefits of up to 10 points in children
of mothers that eat increasing amounts of ocean fish.
What is Selenium?
Selenium is an essential mineral nutrient required
for vital bodily processes that are especially important
in the brain and hormone producing tissues. Once in
the body, selenium becomes incorporated in enzymes (selenoenzymers)
that provide vital antioxidant protection in the brain
in addition to aiding thyroid and immune system function.
Ocean fish are particularly rich in selenium. Out of
1,100 foods that have been analyzed for selenium by
the U.S.D.A., oceans fish comprised 17 of the 25 best
dietary selenium sources.
What is Mercury?
Mercury is a naturally occurring element that originates
form geothermal sources, but once released into the
air, it is rapidly distributed around the world until
it falls to the ground where it accumulates in plants
and animal materials, Mercury present in these materials
is released back into the air when these materials are
burned in grass or forest fires, or become retired from
circulation if they become buried. Large amounts of
mercury released from volcanic activities during prehistoric
times became retained in fossilized materials that turned
into coal.
When coal is burned, the mercury that had been fossilized
in these materials for millennia is released back into
the air and becomes actively distributed throughout
the environment once more. Airborne mercury that deposits
and accumulates in plants and animals becomes more concentrated
in the food web, especially in aquatic environments.
As a result, nearly all fish and shellfish contain traces
of methylmercury. However, larger and older predatory
fish have the highest levels of methylmercury.
Available for Interview
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Dr. Nicholas Ralston
Energy and Environmental Research Center
University of North Dakota
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Wayne Heikkila - Executive Director
Western Fishboat Owners Association |
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