| The
issue of mercury contamination in fish remains in the news.
New studies are being published that give significant new
information on both the mechanisms of mercury contamination
and the human health implications of current mercury standards.
Unfortunately, it appears that all the subsequent media
attention has resulted in a generalized backlash against
seafood consumption, with negative health implications for
some.
Numerous
health benefits from seafood consumption have been documented
over the past ten years or so. Consumption of omega-3-rich
fish is proven to lower risks of cardiac, cardiovascular
and eye diseases, and to mediate mood, attention and dementia
disorders. Pregnancy diets rich in omega-3 fatty acids help
to prevent pre-term births, and a study appearing in the
March 2008 American Journal of Epidemiology demonstrated
that children of women who consumed the most low-mercury,
omega-3-rich fish while pregnant — specifically canned
tuna — scored the highest on intelligence and motor-skills
tests. Additionally, a 2007 study published in The Lancet,
a leading British medical journal, concluded that avoiding
dietary omega-3s during pregnancy has a measurable detrimental
health effect: Children whose mothers eat no fish during
pregnancy are 29 percent more likely to have abnormally
low IQs.
This
latter effect may be occurring as an unfortunate result
of over-reaction about the threat of mercury contamination
by some environmental organizations and then by people who
read the resulting headlines. In fact, there are questions
about the validity of the EPA and FDA mercury criteria.
The EPA included a 1,000-percent safety cushion during the
formulation of its methylmercury “Reference Dose”
— the maximum level of continuous lifetime exposure
believed to be without risk of harm. The FDA set its minimum
action level for mercury in commercially available fish
to limit consumers’ exposure “to levels 10 times
lower than the lowest levels associated with adverse effects,”
which is, in effect, a ten-fold safety factor that is not
based on actual scientific data. Many researchers and medical
professionals believe that new information supports revision
(upward) of U.S. mercury criteria, or at least co-consideration
of other critical factors involved, such as the health benefits
of seafood and problems with some early mercury studies.
Recent work has shown that a mineral nutrient that is prevalent
in fish, selenium, reduces the uptake of mercury in consumers.
One study stated that “measuring the amount of mercury
present in the environment or food sources may provide an
inadequate reflection of the potential for health risks
if the protective effects of selenium are not also considered.”
In the
meantime, some people have stopped eating fish. One seafood
promotion group has developed information on canned tuna,
in particular. Canned tuna is the cheapest and most readily
available source of omega-3 fatty acids in the United States.
For many low-income families, canned tuna is the only consistently
affordable source of dietary omega-3 fatty acids. Survey
data show that in 1999, 80 percent of low-income American
households were buying canned tuna. By 2006, and after much
news about mercury in tuna, that number had dropped to 69
percent — a decline of about 4.4 million households.
During those years, women in those households gave birth
to nearly 260,000 children who were put at risk of developmental
problems due to lack of dietary omega-3s in their mothers’
diets. The seafood group noted that cost was probably not
a primary factor in the move away from canned tuna, since
its price rose only about 1 percent during that period.
To put
this in perspective, some average mercury concentrations
of several well known seafoods are:
- Chunk
light tuna, canned 0.118 ppm (parts per million)
- Albacore
tuna, canned 0.353 ppm
- Shrimp
not detectable
- Seatrout
0.256 ppm
- Snapper
0.189 ppm
- Shark
(falls under the “avoid” category) 0.988 ppm
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