Fish Oil and Mercury

Fish Intake and Omega 3 & 6

MONTREAL, CANADA. The American Heart Association and similar organizations have long extolled the virtue of consuming fish once or preferably twice a week as a powerful preventive measure against cardiovascular disease. Although there is increasing evidence that most fish now contain mercury (especially methylmercury), it is still felt that regular fish consumption is beneficial overall.

University of Quebec researchers now question the assumption that fish consumption is universally beneficial. They do not question whether an increased intake of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) is beneficial; however, they do question whether all fish actually ends up contributing to the body’s stores of DHA and EPA when consumed.

Their study involved 243 moderate consumers of fish living in the areas surrounding four lakes in the province of Quebec. The participants were interviewed to determine their consumption of 12 freshwater and 30 marine (saltwater) fish over the preceding three months and then had blood samples drawn for the determination of fatty acid (especially EPA and DHA), mercury, and selenium content. The age of the participants ranged between 18 and 74 years, 53% were men and 26% were considered obese (BMI >30). No relation was observed between fish intake and BMI, or between fish intake and alcohol intake. The 243 participants were divided into 4 groups according to daily consumption (occasional – < 24 grams/day, low – 24-41 grams/day, moderate – 41-66 grams/day, and high – > 66 grams/day). The average (mean) estimated intake of DHA and EPA from fish was 223 mg/day and that of omega 6 fatty acid (from fish) was 95 mg/day giving a very healthy ratio of omega 6 to omega 3 of 0.32. Much to their surprise, the researchers found no correlation between the total intake of fish or the intake of locally caught fish and serum levels of DHA and EPA. They did, however, find a strong correlation between the intake of salmon and trout and serum levels of these omega 3s.

Saltwater Fish Consumption Raises Omega 3 Serum Levels

They concluded that, even though food tables may show that some lean fish do contain DHA and EPA, for some reason consuming these fish does not increase serum levels of these omega 3s. Thus, the advice to eat fish on a regular basis needs to be revised to apply to only saltwater fish consumption (especially salmon, mackerel, trout, sardines, and herring). The researchers also noted an increased blood methylmercury concentration in frequent fish eaters. They conclude that no matter how many locally caught freshwater fish are eaten, serum DHA and EPA levels are not affected.
Philibert, A, et al. Fish intake and serum fatty acid profiles from freshwater fish. American Journal of Clinical Nutrition, Vol. 84, December 2006, pp. 1299-1307

Share this post