[Global Assessment of Organic Contaminants in Farmed Salmon - Science v.303, 9jan04]
If you have eaten salmon recently, chances are it was raised in a "farm" - a giant cage floating in the ocean.
Chances are, the fish was tainted with chemicals believed to cause cancer.
Yet chances are, you will be perfectly fine. And because fish is good for the heart and brain, you might be better off eating more salmon rather than less - unless you end up as one of a very small fraction of the population to get cancer from it.
That's the statistical reality that got lost in the headlines and sound bites this month when the journal Science published a study on contaminated salmon.
The authors recommended that people eat no more than one eight-ounce serving a month of farmed salmon, which accounts for more than 90 percent of salmon sold in the United States. For some European varieties, the recommendation was just one serving every four months, based on U.S. Environmental Protection Agency guidelines.
Eating those amounts of tainted fish would cause an estimated one additional case of liver cancer for every 100,000 people - a theoretical number derived from studies on lab animals. So, if a person ate twice the maximum recommendation - two servings a month for most farmed salmon - their added lifetime risk of liver cancer would theoretically be 2 in 100,000.
Statistically speaking, that risk from the tainted fish is a relative drop in the bucket. Liver cancer is a common disease, afflicting 1 in 116 U.S. men and 1 in 238 women during their lifetimes. So if the typical woman ate twice as much salmon as recommended, her risk of liver cancer would be 0.0042 (1 in 238) plus 0.00002 (2 in 100,000), which equals 0.00422 - a total risk of about 1 in 237.*
"The benefits [of salmon] in my opinion are way over the risks of having cancer," said Martha Daviglus, an associate professor of preventive medicine at Northwestern University, who has studied the effects of eating fish on cardiovascular health and was not involved with the study.
Toxicologist Jeffery Foran, one of the study's authors, conceded that the cancer risks in question are small.
But he urged against paying too much attention to specific numbers, and said the relative risks are large enough that, given the choice, people should eat fish with less contamination. That includes wild salmon or other kinds of fish.
"The whole point is, you're trying to minimize or eliminate, in a statistical sense, cancer risk," Foran said. "We're not saying if you eat a lot of fish, that you're going to get cancer tomorrow. What we are saying is you can reduce your risk and get all the health benefits of eating fish by changing some of your consumption behaviors."
Moreover, the 14 contaminants measured, known as organochlorines, can cause other types of cancer, though none of these were included in the analysis.
And the chemicals can cause health problems other than cancer, noted Foran, who is president of Citizens for a Better Environment, a Milwaukee-based nonprofit group.
Some of the substances are thought to interfere with fetal brain development, while others have been linked to problems with the immune and endocrine systems. But little work has been done to quantify what level of these substances is risky.
On the flip side, the omega-3 fatty acids in fish are thought to be very beneficial, if not critical, for fetal brain development. Pregnant women are told to eat 12 ounces of fish per week.
Salmon has more of these beneficial fatty acids than most fish, plus it has relatively low amounts of mercury, another harmful contaminant, said Carol Lammi-Keefe, a nutrition professor at the University of Connecticut who has studied the impact of fish during pregnancy.
"There's no one amongst us who would say we shouldn't be concerned about pollution, but there has to be medium ground there someplace," said Lammi-Keefe, who was not involved with the study. "You have to weigh the benefits against the risks. It's not an easy thing to do."
Most of the chemicals studied are pesticides. All 14 have been banned in the United States for years, but all are "persistent," meaning they do not break down readily in the environment. They also accumulate in the fatty tissues of fish and people, where they remain for years.
Many also are present in other foods, including beef. The chemicals are generally less concentrated in beef than in salmon, but Americans also tend to eat more beef than they do fish.
So what is a health-conscious person to do?
Lammi-Keefe recommended halibut as one fish that is rich in fatty acids but low in contaminants.
Wild salmon, though harder to find and typically three times more expensive than the farmed variety, is another option. The wild fish have much lower contaminant levels because they eat smaller, less contaminated sea creatures such as shrimp and krill.
Farmed salmon are given fish feed made from larger "forage" fish, which generally have accumulated higher levels of contaminants.
Even critics of fish farms say the farms will be a vital source of food for a growing world population. The farmed salmon industry said it already has taken steps to reduce the amounts of contaminants in fish feed.
One more wrinkle:
The relative benefits and dangers of eating farmed salmon change with a person's age, said David O. Carpenter, another of the study's authors.
The cardiovascular benefits of eating salmon and other fish rich in omega-3 acids, such as reducing arrhythmias after a heart attack, are more important later in life, said Carpenter, director of the Institute for Health and the Environment at the University at Albany.
"Heart attacks are an old person's disease," Carpenter said. And cancer generally takes many years to develop, so the risk of getting that disease from some new exposure, such as eating salmon, is not as great for older people, he said.
Women of childbearing age, on the other hand, would be wise to limit their intake of contaminated food, he said.
Perhaps inevitably, the salmon headlines have resulted in some concerned, and confused, consumers.
Joe Lasprogata, purchasing director at Samuels & Son Seafood, a seafood wholesaler in South Philadelphia, said his phone has been ringing frequently.
Some customers have insisted on wild salmon even though it's out of season. Lasprogata tells them if they absolutely have to have it, he will sell them wild salmon that has been frozen.
But with a former career as a marine biologist under his belt, he also tries to educate them.
"The big headline was 'Salmon causes cancer,' " Lasprogata said. "But it'll probably keep you alive longer."
source: http://www.philly.com/mld/inquirer/7743101.htm?template=contentModules/printstory.jsp 19jan04
* Mindfully.org Note: Author revised 29jan2007 by email. Original statement was "So if the typical woman ate twice as much salmon as recommended, her risk of liver cancer would be 1 in 238.00002."