[Mercury, fish, fish oil and the risk of cardiovascular disease]

Several clinical studies have documented that intake of fish may reduce mortality from coronary heart disease, and two epidemiological investigations have shown a 50% reduction in the incidence of sudden death and of "primary cardiac arrest" in subjects eating fish. However, in some studies no beneficial effects of fish intake on coronary heart disease could be found; one Finnish study even found a positive correlation between intake of freshwater fish and coronary heart disease. One possible explanation for this paradox could be a high content of mercury in fish.

We have studied the relevant literature describing beneficial, less beneficial and negative effects of fish intake on the development of coronary heart disease. Furthermore, we have studied reports that mercury may have properties that enhance the development of coronary heart disease.

Several studies have shown an inverse correlation between omega-3 fatty acids from fish in serum/adipose tissue and coronary heart disease. However, a high content of mercury in hair/toe nail had a negative effect, and in one study the odds ratio for myocardial infarction in those with the highest content of mercury was 2.16. A positive correlation between mercury in hair and the progression of carotid atherosclerosis has been found. Intake of fish is a major source of exposure to mercury, and a high content of mercury probably inhibits the beneficial effects of omega-3 fatty acids on the development of coronary artery disease.