Measurement of Mercury Levels in Concentrated Over-the-Counter Fish Oil Preparations: Is Fish Oil Healthier Than Fish?

Archives of Pathology & Laboratory Medicine, Dec 2003 by Foran, Stacy E, Flood, James G, Lewandrowski, Kent B

Context.-Fish consumption has been associated with a decreased risk of coronary artery disease. Recent studies have illustrated that the high mercury content in cold-water fish may negate the cardiovascular benefits of fish meals. Fish oils have similar antiatherogenic properties to fish, and similar studies should be performed to determine the level of mercury in fish oils.

Objective.-To determine the concentration of mercury in 5 over-the-counter brands of fish oil.

Results.-The levels of mercury in the 5 different brands of fish oil ranged from nondetectable (

Conclusions.-Fish are rich in omega-3 fatty acids, and their consumption is recommended to decrease the risk of coronary artery disease. However, fish such as swordfish and shark are also a source of exposure to the heavy metal toxin, mercury. The fish oil brands examined in this manuscript have negligible amounts of mercury and may provide a safer alternative to fish consumption.

Epidemiologic studies have demonstrated that the Greenland Eskimos have a comparatively low incidence of coronary artery disease (CAD). This low incidence of heart disease is attributed to the consumption of greater than 400 g of fish per day. Presumably, this protection results from the high level of omega-3 polyunsaturated fatty acids (n-3 PUFAs) in oils derived from deep cold-water fish.1,2 This discovery underscores the important role of diet in the development of CAD and has prompted research on the potential benefits of fish consumption in the general population. For example, the Diet and Reinfarction Trial showed a 29% reduction in overall mortality rates in survivors of a first acute myocardial infarction who consumed fish rich in omega-3 fatty acids at least twice weekly for 2 years.3 Similar studies corroborate these results.2,4,5 Consequently, fish intake has been recommended to decrease the incidence of CAD.6 Although many studies have found that regular fish intake benefits cardiovascular function, some reports have not confirmed these conclusions and question the recommendations on fish intake.7

A potential issue arises from the fact that some fish may also contain relatively high levels of toxic heavy metals. For example, fish intake is a major source of exposure to mercury, primarily methylmercury. Large carnivorous fish that are high in the food chain, such as swordfish and shark, have the highest tissue concentration of mercury (1 �g/g), whereas tuna, trout, pike, and bass have intermediate concentrations (0.1-0.5 �g/g). In contrast, invertebrates, such as shellfish, have low concentrations of mercury.6-8 Mercury may promote atherosclerosis by increasing free radical production or by inactivating several antioxidant mechanisms. Recent studies show that toenail mercury levels are directly associated with the risk of an acute myocardial infarction.2,6,7 One study found no significant correlation between toenail mercury and CAD, but a trend did exist.9 The association between the amount of fish consumed and mercury levels has been documented. Data regarding the cardiovascular benefits of fish have been inconsistent. These conflicting results may be explained by the variable amounts of mercury contained in different fish, which may negate the beneficial effects of n-3 PUFAs.6,7

Fish oils contain concentrated forms of n-3 PUFAs. Regular consumption of fish oils also appears to reduce the risk of CAD. In one study, patients with CAD who ingested 1.5 g of omega-3 fatty acids per day for 2 years had less disease progression than did comparable patients who ingested placebo.10 The magnitude of effect of fish oil consumption on CAD is similar to the benefit of low-density lipoprotein cholesterol-lowering therapy, lifestyle change, and vigorous exercise.10 Studies also suggest that the effects of fish oil supplements are comparable to fish consumption. Fish oil supplements also permit the administration of large doses of n-3 PUFAs, which may produce a decrease in blood pressure in patients with hypertension and a stabilization of mood in bipolar disorder and depression.11-13 However, data concerning the level of mercury in commercial fish oil supplements are sparse. These data are critical if fish oil supplements are to be recommended in patients with CAD, bipolar and affective disorders, and for cardioprotective benefits in the general population. In this study, we measured the level of mercury in 5 commercial over-the-counter brands of fish oil to assess the risk of mercury toxicity from consumption of these dietary supplements.

METHODS

Five commercial over-the-counter brands of fish oil supplements were purchased from retail or Internet sources. The brands included Nordic Ultimate (San Dimas, Calif), Omega Brite (Waltham, Mass), Sundown (Boca Raton, Fla), Kirkland (Houston, Tex), and CVS (Woonsocker, RI). The capsules were punctured using a trace metal-free device, and the liquid contents were sent in trace metal-free containers to National Medical Services (Willow Grove, Pa) for mercury analysis. The mercury level was measured by cold vapor atomic absorption spectroscopy. The lower limit of detection of mercury for this assay is 6 �g/L.