fish, mercury, omega 3s, and heart disease

An intriguing new study published in the American Journal of Clinical Nutrition, took a look at fish consumption, mercury levels, and blood levels of long chain omega 3 fatty acids from fish, in relationship to heart disease in Scandanavian men. You can read the abstract (and the full paper) here . Basically what they found was that eating more fish raised both blood levels of EPA and DHA, but also increased measured mercury levels. Those with the highest levels of omega-3s and the lowest levels of mercury, compared with those with the highest mercury levels and lowest levels of omega-3s had a greater than 3 fold difference in diagnosis of heart and vascular disease. The authors noted: “Our model indicated that even a small change in fish consumption (ie, by increasing S-PUFA by 1%–blood levels of EPA+DHA–) would prevent 7% of MIs (heart attacks), despite a small increase in mercury exposure. However, at a high hair-mercury content, the modeled beneficial effect of PUFA on MI risk was counteracted by methylmercury.”

Although not stated in the paper, it still seems to me like the safest way to get your EPA and DHA is from high quality fish oils–those that have been molecularly distilled to remove environmental contaminants, such as PCBs and dioxins–mercury is never an issue, even in low quality fish oils, as it stays in the fish protein, and does not come out in the oil. But many low quality fish oils are also oxidized (rancid), which can increase oxidative stress in the body significantly. As noted in a recent post about the meta-analysis (desk research) which stated that fish oils supplements were of ‘no value’–see that post for all the reasons that this was a very poor ‘study of studies’–not the least of which reasons is that many of those studies used over the counter fish oils and didn’t analyze them for content, rancidity, or toxins. Not all fish oils are created equal. When you do eat fish, choose small fish, like sardines, herring (pickled is fine if you like them), anchovies, mackerel. And NEVER farmed fish–unless the are certified organic, with a natural food chain established, rather then feeding them pellets of grain (which are often GMO corn and soy). Virtually all tilapia (a marketing term for perch) are farm raised, and their fatty acid profile is closer to that of bacon than to that of fish. Caveat Emptor!