Please fill out the form below to get notified whenever telepk.com will be update.
|Researchers Cast About for Answers on Fish Benefits and Risks|
This is a tale of fish, its
demonstrable health benefits, and its less demonstrable health
The issue is not so much whether there are beneficial
heart effects from most fish, a clearly shown phenomenon, but
whether they are outweighed by the public's perception of risks of
mercury poisoning in some fish, an issue that is less well defined.
In particular, researchers looked at fish consumption among
women of childbearing age. It turns out, say researchers, that the
heart benefits are extremely important and the mercury risks are
less clear and easy to avoid.
But it also turns out that
this is a difficult and complex public health message, according to
a series of articles in the November issue of The American Journal
of Preventive Medicine.
Researchers at the Harvard Center
for Risk Analysis and other centers weighed the evidence for a
protective effect of fish consumption on heart disease and stroke
risk versus possible negative consequences on cognitive function of
methyl mercury in fish.
They looked askance at the
unintended impact of federal health warnings suggesting that women
of childbearing age limit fish consumption. Women who shun fish out
of fear of mercury-induced harm to fetuses may lose the
cardiovascular benefits of fish consumption, when they could instead
substitute fish with lower levels of mercury.
On a broader
scale, the papers explored the promises and pitfalls of
communicating health messages to the public. They looked into
whether the narrow mercury-risk message might have been absorbed by
the population at large to the detriment of the broader, more
important heart-healthy message.
Fish are an important
dietary source of n-3 polyunsaturated fatty acids (PUFAs), which
have been demonstrated to offer cardiovascular and cognitive
benefits, but some species also contain comparatively high levels of
methyl mercury (MeHg), a neurotoxin.
consumption confers both benefits and risks, the advisories issued
by the U.S. federal government raise the possibility of a classic
risk-risk trade-off," wrote Harvard's Joshua T. Cohen, Ph.D., and
colleagues in the main paper. "By avoiding one risk (exposure to
MeHg), consumers who follow these advisories may be incurring
another (adverse health consequences associated with lower n-3 PUFA
intake). Likewise, individuals who increase their consumption of
fish because of this food's nutritional benefits may incur risks
associated with MeHg exposure."
To try to get a handle on
whether possible shifts in fish consumption based on public health
recommendations could have unintended consequences, the Center for
Risk Analysis convened an expert panel to look at the effects of
fish consumption on prenatal cognitive development, coronary heat
disease mortality, and stroke.
On the plus side, the panel
found that consuming even small quantities of fish was associated
with a 17% reduction in coronary heart disease mortality risk, and
that each additional serving per week was associated with a further
reduction in this risk of 3.9%.
In addition, modest fish
consumption was associated with a 27% reduction in risk of nonfatal
myocardial infarction, but additional fish consumption per week did
not appear to offer any additional benefits.
investigators found that any fish consumption lowered the relative
risk of stroke by about 12%, and that each additional serving per
week appeared to offer an additional 2% risk reduction.
However, when they looked at whether PUFAs such as
docosahexaenoic acid (DHA) could boost brain power prenatally, they
found that a pregnant woman would have to take in 1 gram of DHA per
day to increase her child's IQ by 0.8 to 1.8 points.
Cast About for Answers on Fish Benefits and Risks
typical DHA intake associated with fish consumption is well under 1
g/day, changes in fish consumption will result in IQ effects
amounting to a fraction of a point," the authors wrote. "These
differences are not clinically detectable."
however, that "as with changes associated with exposure to
neurotoxins like lead, which are also typically undetectable at the
level of the individual, these changes can result in important
impacts when aggregated over a population."
On the negative
side, they reviewed evidence from three major prospective
epidemiology studies, and found that prenatal MeHg exposure
sufficient to increase the concentration of mercury in the mother's
hair at the time of birth by 1 microgram/gram would decrease the
infant's IQ by 0.7 points, although uncertainties about the estimate
mean that the actual effects could range from 0 to 1.5 IQ points,
the investigators wrote.
The risk of MeHg exposure to
children's cognitive abilities appears to be significantly lower
than the risk of lead exposure, they noted, but added that the risk
is not negligible, and could be cumulative.
What to make of
all of this? In their final analysis, the authors concluded that
"substitution of fish with high MeHg concentrations with fish
containing less MeHg among women of childbearing age yields
substantial developmental benefits and few negative impacts."
If, however, women of childbearing age and other adults were
to cut down on fish eating altogether out of concern for theoretical
mercury exposure, there would be an overall detrimental effect on
public health, they noted.
"Although high compliance with
recommended fish consumption patterns can improve public health,
unintended shifts in consumption can lead to public health losses,"
the investigators wrote. "Risk managers should investigate and
carefully consider how populations will respond to interventions,
how those responses will influence nutrient intake and contaminant
exposure, and how these changes will affect aggregate public
In an accompanying editorial, Walter C. Willett,
M.D., Dr.Ph., of the Harvard School of Public Health wrote, "This
analysis supports current guidelines that focus on changes in the
type of fish eaten by women in the reproductive age, but also
highlights concerns that educational messages and the implementation
of policies must be carefully crafted to avoid unintended