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Nutrition: Patients may come to you with salmon worries
Recent study shows PCB levels high, but experts say questions remain
By Karen Richardson
TORONTO ? Patients, particularly expectant mothers, may be concerned about the health risks associated with eating salmon following a well-publicized study on farmed and wild salmon.
The study, which appeared in a January issue of Science, showed that farm-raised salmon contains substantially higher levels of PCBs and other potentially cancer-causing industrial pollutants than their wild counterparts, and study researchers recommended it not be eaten more than once or twice a month.
While the risk/benefit computation of eating salmon is complicated, results of a Canadian Food Inspection Agency (CFIA) and Health Canada investigation indicate the levels of PCBs are well below Health Canada's current guidelines for both farmed and wild salmon.
"Based on Health Canada's risk assessment, consuming farmed salmon does not pose a health risk to consumers," Health Canada spokeswoman Margot Geduld told the Medical Post.
Physicians should bear in mind, however, for pregnant patients, young children or women of childbearing age, Health Canada has issued an advisory for other types of fish as a result of mercury levels. The last statement, issued on May 29, 2002, limits shark, swordfish and fresh and frozen tuna to no more than one meal per month. This advisory does not apply to canned tuna.
The salmon study, however, showed several of the contaminants found in farmed and wild salmon "pose reproductive and developmental risks," according to study author Dr. Jeffery Foran (PhD), adjunct professor in the school of natural resources and environment at the University of Michigan. They based their conclusions on previous laboratory and epidemiologic studies of PCBs.
However, the team did not look at reproduction and development as an endpoint in this particular study, therefore they are unable to advise on consumption rates in pregnant women, said Dr. Foran.
"Removal of skin and fat prior to cooking and preparing fish so fats drip off during cooking may reduce contaminant concentrations to some extent, although there are relatively few data available to help us understand how much, if any, benefit accrues from cooking and cleaning procedures," he said.
Dr. Gideon Koren, director of the Motherisk program at The Hospital for Sick Children (SickKids), said the Toronto organization is now looking into the implications of the new data for pregnant women.
"The key word is moderation," said Dr. Koren, also a professor at the University of Toronto and senior scientist in the SickKids' Research Institute.
He advised women who consume more than a few servings of salmon a month to inquire more carefully about the source of the fish and its possible contaminants. While the new studies on salmon need to be evaluated carefully, he said: "We should all be careful before scaring thousands of pregnant Canadian women every year, causing them not to consume a healthy source of essential nutrients."
Whether the consumption of farmed Atlantic salmon poses risks that outweigh its beneficial effects seems to be the important question.
Salmon remains an important source of valuable nutrients, particularly heart-healthy omega-3 fats. Recent research out of Laval University in Quebec City, which studied the health of Inuit residents in Nunavik, Quebec's Arctic region, suggests the traditional Inuit diet?rich in the omega-3s that lower blood cholesterol levels?actually has cardiovascular protective effects.
Researchers found half the rate of cardiovascular disease there compared with the general Quebec population, despite mercury contamination. Some nutrition experts question the strong recommendations about potential risks of eating farmed salmon put forth in the Science study.
For one thing, the study was not funded by a peer-reviewed agency, said gastroenterologist Dr. Khursheed Jeejeebhoy, a professor of medicine at the University of Toronto, in an e-mail interview.
"Unfortunately, there are several problems with these types of studies. First, the levels are well within the WHO (World Health Organization) recommended levels.
"Second, higher levels have been recorded in several animal products consumed daily in our diet. In short, if we have to avoid these toxins we will have to stop eating entirely.
"Third, all the data showing harm of these 'toxins' is based on large doses (several hundred-fold) given to experimental animals. Direct human data showing harm from the small amounts (nanograms) is totally lacking."
While physicians and patients must assess the risks proposed by the study, Dr. Jeejeebhoy said it is important not to lose perspective.
"We have to be careful not to make recommendations which may avoid a potential for cancer (little data) but may certainly increase the risk of coronary artery disease which is the number one killer in North America. My family and I eat fish of all kinds regularly and will continue to do so."
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