The study was funded by the Canadian fishing industry, which supplies much of the farmed salmon eaten in the United States.
In recent years, concerns have been raised about the safety of farmed salmon vs. wild, and there have also been suggestions that Canadian and other Atlantic-farmed salmon contains more contaminants than farm-raised fish from other areas, such as Chile. The newly published study was conducted in an attempt to address these concerns.
Researchers measured mercury levels as well as levels of 18 other trace metals in commercial salmon feed and farmed and wild salmon from British Columbia fisheries and waters.
They found that levels of all the metals tested were well below recommended consumption guidelines.
"(These findings) further validate the relative safety of farmed and wild British Columbia salmon," write Barry C. Kelly and colleagues from Canada's Institute of Ocean Sciences. "The current scientific evidence therefore supports the weekly consumption of oily fish species as recommended by the American Heart Association."
Concerns About PCBs
But the new study did not examine levels of polychlorinated biphenyls (PCB) in the fish, a chemical compound once widely used in manufacturing.
In a widely reported 2004 study, researchers examined PCB levels in farmed and wild salmon from around the world, concluding that farmed salmon contained significantly higher levels of the chemical than wild varieties of the fish.
The study found the greatest PCB levels in salmon from farms in northern Europe and the lowest levels in fish farmed in Chile. They concluded that eating farmed Atlantic salmon, "may pose health risks that detract from the beneficial effects of fish consumption."
That same year, the FDA and EPA issued a recommendation that pregnant women and young children eat no more than two servings, or 12 ounces, of salmon and other low-mercury fish each week.
Harvard Medical School nutritionist George Blackburn, MD, PhD, tells WebMD that although the risks associated with contaminants in farmed or wild salmon have yet to be proven, the health benefits of eating salmon are well established.
Great Source of Omega-3s
Salmon is one of the best food sources of omega-3 fatty acids, which have been shown to lower heart disease risk.
"In 2008, we know much more about the health benefits of omega-3 fatty acids than we did even a few years ago, but people are confused about the mixed messages they are getting," he says.
He adds that the benefits associated with eating two to four servings of salmon a week -- whether wild or farm raised -- clearly outweigh the risks for most people.
American Heart Association nutrition expert Barbara Howard, PhD agrees.
AHA recommends eating salmon or other omega-3 packed fatty fish at least two times a week, but Howard says unproven concerns about the safety of salmon have confused the public and health care professionals alike.
Howard chairs the AHA's Nutrition, Physical Activity and Metabolism Council and is a professor of medicine at Georgetown University.
"The result is that people may be eating less fish and more less-healthy forms of protein that have a lot more saturated fat," she says.