The Institute of Medicine, an arm of the National Academies, released a report providing recommendations for consumers to make choices about seafood consumption, per a request by the National Oceanic and Atmospheric Administration.
In addition, a Harvard study, to be published Wednesday in the Journal of the American Medical Association, also reviewed existing studies on the benefits and risks of seafood.
The studies, which drew their conclusions from relevant, available data, agreed the benefits of eating fish are greater than the health risks from contaminants.
"Both studies came to the same conclusion: Seafood is safe and nutritious, and Americans should incorporate a variety of seafood in their diet," William T. Hogarth, director of NOAA, said at a news briefing.
"This was based on scientific evidence, rather than ... fear and speculation," he added.
The reports evaluated the best scientific information available to date on consumption of fish, which includes finfish and shellfish. The IOM report also reviewed studies including mollusks.
Fish diets have been associated with a reduced cardiovascular risk, as well as better vision and cognitive development in fetuses.
Dr. Dariush Mozaffarian, lead author of the Harvard study and cardiologist at the university's schools of public health and medicine, and colleagues concluded eating one or two servings a week of fish rich with omega-3 fatty acids reduces the risk of dying from a heart attack by 36 percent; it cuts the rate of death overall by 17 percent.
Since heart attacks are the leading cause of death for men and women in the United States, the role of fish consumption could be a "huge health benefit," he said.
Seafood is a good source of protein, vitamins such as selenium, and omega-3 fatty acids such as EPA and DHA. Fish consumption has increased in recent decades, prompting a shift from catching seafood in the oceans to raising the animals in aquaculture. Among the most commonly consumed seafood species in the United States are shrimp, canned tuna, salmon, pollock and catfish, according to 2004 data from the National Marine Fisheries Service.
Taking supplements of fish oil seem to produce the same effects as eating fish, Mozaffarian said, although the consumer would miss out on the protein and vitamins.
A number of contaminants can be found in seafood, such as chemicals, metals and harmful microbes. These contaminants are present in different geographical regions and species. Methylmercury is of particular concern, as the heavy metal can cause possible permanent damage to the brains of children in the womb. Inconclusive studies have also linked the metal, which is emitted by industrial processes, to cardiovascular disease in adults.
Also potentially dangerous are dioxins and PCBs, industrial pollutants that may cause cancer after a lifetime of exposure.
In the past few decades a surge in media attention surrounding these contaminants has muddied the public health messages about seafood's benefits, the reports said.
For instance, the government has issued just one public health warning for mercury in fish, which recommends pregnant women -- whose developing fetuses are more sensitive to the metal -- reduce their consumption of certain species of fish.
Yet the general American population, mistakenly, has also taken this warning to heart, Mozaffarian said.
"Somehow the message has gotten lost in the public," Mozaffarian told United Press International.
Mozaffarian was also surprised at how little evidence existed for some of the purported harms from eating mercury-ridden fish.
He also found low potential cancer risks from PCBs and dioxins relative to the benefits of fish. Each time scientists evaluate risks, they also need to consider benefits, and vice versa, he said.
Nine percent of the PCBs and dioxins Americans are exposed to come from seafood, according to Hogarth.
However, the health effects of mercury are unknown at low levels, such as those found in fish. Previous research involving mercury spills, for example, has shown mercury in large amounts is severely toxic to the brain.
Overall, more research needs to be done on the health benefits and risks of seafood, since much of the research thus far is still preliminary.
For instance, there is inconclusive evidence that eating fish prevents stroke, dementia and overall cognitive decline, so Mozaffarian did not examine these studies.
Mozaffarian's research differed from the IOM report in one major point: He asserted stronger evidence for a fish diet protecting against heart attack. The IOM report claims the evidence of fish oil protecting against heart attacks after an initial event is weaker than previously thought.
However, Mozaffarian believes the additional quantitative analyses performed by his research team -- including metanalyses -- are more definitive evidence of a preventive factor against heart attack.
The IOM report also issued recommendations to specific population groups.
-- Women who are or may become pregnant, or are breastfeeding, can reasonably consume two 3-ounce cooked servings of fish per week, and should avoid eating large predatory fish such as shark, swordfish, tilefish or king mackerel, which can contain higher levels of mercury.
-- Children under 12 can consume two 3-ounce servings a week, including up to 6 ounces of white (albacore) tuna per week. They should also avoid the same large predatory fish as pregnant women.
-- Healthy adolescents and adult males and females (who will not get pregnant) can reduce their risk for cardiovascular disease by consuming seafood regularly. If they eat more than two servings a week, a variety of fish should be selected to reduce risk of exposure to contaminants from a single source.
-- Adult men and women at risk for coronary heart disease may also reduce their risk by eating seafood regularly, and may additionally benefit from including more omega-3 fatty acids in their diet. They should also ensure a variety of seafood is consumed.
Such tailored messages are clear and much-needed, said Michael Dourson, director of the Toxicology Excellence for Risk Assessment, a group that develops and communicates risk assessment information to the public.
"As a public health guy, I'm glad to see this emphasis from the National Academies," Dourson told UPI.
The IOM also issued several recommendations centered around communicating health messages effectively to the public.
For instance, federal agencies should advise the public about the benefits of seafood, particularly as a substitute for protein sources that are higher in saturated fat, such as beef.
In addition, state and federal agencies should develop an interagency task force to coordinate data and communications on seafood consumption benefits and risks, the report said.
For more information: iom.edu/Object.File/Master/37/683/11762_Seafood%20Choices%20Report%20Brief.pdf