Public health guidance on cardiovascular benefits and risks related to fish consumption
Alan H Stern
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Department of Environmental and Occupational Health, University of Medicine and Dentistry of New Jersey - School of Public Health
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683 Hoes Lane West, P.O. Box 9, Piscataway, NJ 08854
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USA
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Division of Science, Research and Technology, New Jersey Department of Environmental Protection
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401 E. State St., Trenton, NJ 08625
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USA
Historically, concerns with fish consumption have addressed risks from contaminants (e.g., methylmercury (MeHg), and PCBs). More recently public health concerns have widened in appreciation of the specific benefits of fish consumption such as those arising from polyunsaturated fatty acids (PUFAs) in fish oil. Fish contains varying levels of PUFAs and MeHg. Since both address the same health outcomes (in opposite directions) and occur together in fish, great care must be exercised in providing public health guidance. Mozaffarian and Rimm in a recent article (JAMA. 2006, 296:1885-99) have made a strong case for the beneficial effects of PUFAs in reducing the risk of coronary heart disease, but at the same time, have also broadly discounted the increased risks of coronary heart disease posed by MeHg in fish, stating that "... among adults... the benefits of fish intake exceed the potential risks." This conclusion appears to be based on an inaccurate and insufficiently critical analysis of the literature. This literature is re-examined in light of their conclusions, and the available and appropriate public health options are considered.
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Background
During the past 15 years or so, public health concerns
regarding fish consumption have tended to focus mostly
on the risks associated with contaminants such as
methylmercury (MeHg) and PCBs in fish. More recently,
recognition of the general and specific nutritional benefits
provided by fish, particularly polyunsaturated fatty acids
(PUFA, omega-3 fatty acids (n-3 fatty acids) has
appropriately widened the public health focus to include the
public health benefits of fish consumption. The potential for
both risks and benefits arising from the same food source
begs for an overall assessment and ultimately a balancing
of risks and benefits in public health guidance. This is all
the more so because the major potential health risks of
concern, neurodevelopmental effects and cardiovascular
effects are precisely the areas where the potential benefits
may also occur. This unusual state of affairs means that
great care must be exercised in providing public health
guidance. It also places a considerable burden on those
who would advocate significant changes in existing
guidance. In their relatively recent review paper in JAMA [1],
Mozaffarian and Rimm make a strong case for beneficial
effects of fish-based polyunsaturated fatty acids (PUFA)
per se, particularly with respect to their apparent reduction
in the risk of coronary heart disease. However, I believe
that they did not give adequate consideration to the
increased risks of coronary heart disease posed by the
MeHg in fish, and their broad conclusion that "... among
adults... the benefits of fish intake exceed the potential
risks" therefore constitutes inappropriate and potentially
misleading public health guidance.
Discussion
The case that Mozaffarian and Rimm present for the
beneficial effects of PUFAs in providing protection against
coronary heart disease is seen most strongly in the studies
represented in Figs. 1 and 2 of their paper. However, their
analysis addresses only part of the public health issues
connected with fish consumption. A closer analysis of
their data raises serious questions about whether their
analysis of the cardiovascular risks and benefits of fish
consumption take both PUFAs and methylmercury into
account as opposed to merely addressing PUFA intake in
isolation. Many of the data in the studies they analyze
reflect studies in which subjects consumed purified fish
oil. To the extent that some of these studies, in fact, reflect
fish intake, it is not clear that they also reflect significant
MeHg intake. Higher levels of PUFA intake (in studies of
fish consumption) do not necessarily reflect increased fish
intake and, by extension, do not necessarily imply higher
levels of MeHg intake, but may simply reflect, instead,
intake of fish species with higher PUFA content. Oily fish
(i.e., those high in PUFAs) are not characteristically also
high in Hg. This can be seen in the data for commonly
consumed species of fish presented in Table 2 of the
Mozaffarian and Rimm paper and shown here (minus
catfish and trout, which are not ocean fish) in Figure 1
(author's rendition).
This figure shows that fish with high PUFA content are not
particularly high in Hg, and the fish with the highest Hg
concentration (shark, swordfish, tilefish) do not have
particularly high levels of PUFA. It is also worth noting that
these particular species of fish do not account for a
significant portion of national fish consumption [2]. Thus, it is
likely that for studies analyzed by M (...truncated)