Millions of Americans eat fish or take fish oil supplements to boost their levels of heart-protective essential fatty acids (EFAs) like EPA, DHA and DPA. And by all accounts, it has worked. Essential fatty acids from fish and fish oil have been shown to reduce heart disease and blood pressure, and prevent various other diseases and conditions.
However, there is one downside to the consumption of fish and fish products — the potential exposure to methylmercury, an environmental contaminant found to some degree in most seafood.
Mercury exposure has been linked to an increased risk of cardiovascular disease and higher blood pressure in those who have been highly exposed to it.  So, ironically, the very foods that are rich in heart-protective essential fatty acids are often also high in a toxin that has been linked to cardiovascular problems — completely offsetting the amazing benefits of essential fatty acids.
Fortunately, most of us are only minimally exposed to mercury, but still, not much research has been done on the relationship between mercury and blood pressure in people with low to moderate exposure. Are those of us who have had minimal to moderate mercury exposure at higher risk of cardiovascular problems, especially high blood pressure? Researchers in Finland set out to get an answer.
The participants in this study were part of Kuopio Ischaemic Heart Disease Risk Factor Study, an ongoing population-based study investigating risk factors for cardiovascular disease in middle-aged and older people in eastern Finland. For purposes of their study, the researchers followed 396 men and 372 women who met all of their specific inclusion criteria.
In addition to having their blood pressure measured and providing blood samples to determine serum concentrations of essential fatty acids, participants provided hair samples to test for mercury exposure.
The mean concentrations of essential fatty acids in the study participants were:
- 1.63% for EPA
- 0.77% for DPA
- 2.73% for DHA
After adjusting for factors like age and gender, higher serum concentration levels of these three polyunsaturated fatty acids were significantly associated with a lower systolic (top number) blood pressure and lower pulse pressure, but not with diastolic (bottom number) blood pressure.
The participants’ mean hair mercury concentration was 1.42 μg g, which is considered moderate exposure. Researchers found that this moderate exposure was not associated with increased blood pressure. So, while high levels of exposure to mercury have been found to cause increased blood pressure, low to moderate levels of exposure seem to have no effect. As a result, the researchers suggest that continuing to eat fish may help in controlling blood pressure.
Controlling Your Mercury Exposure
While there’s little doubt that occasional fatty fish consumption is good for your heart and health, it is important to choose seafood that tends to be lower in mercury. You can (and should) continue eating fish twice a week. Just make sure you avoid or drastically limit your intake of the types that tend to be high in mercury. These include marlin, orange roughy, tilefish, swordfish, shark, sea bass, grouper and tuna (the ahi, yellowfin and albacore varieties).
Lower mercury seafood that you can enjoy more often includes carp, cod, halibut, lobster, mahi mahi, snapper, sea trout and canned chunk light tuna.
The seafood with the lowest mercury levels, which you can feel confident eating twice a week, includes anchovies, butterfish, catfish, clam, flounder, haddock, herring, oysters, sardines, scallops, shrimp, sole, squid, freshwater trout, whitefish, and probably the healthiest and most robust source of essential fatty acids — wild salmon. (Just be sure to avoid farm-raised fish, particularly salmon, which are raised in unsanitary conditions, fed commercial feed, and aren’t nearly as healthy for you as wild-caught fish.)
Of course, fish oil is also an option if you want to get sufficient levels of essential fatty acids without eating fish. If you prefer to take fish oil supplements, make sure the packaging says that the product has been tested to be free of contaminants like mercury, heavy metals and dioxins. If you are looking for a high-quality fish oil supplement, click here.
 Ueshima H et al. Good omega-3 fatty acid intake of individuals (total, linolenic acid, long chain) and their blood pressure: INTERMAP study. Hypertension. 2007 Aug;50(2):313-19.
 Virtanen JK et al. Mercury, fish oils, and risk of acute coronary events and cardiovascular disease, coronary heart disease, and all-cause mortality in men in eastern Finland. Arterioscler Thromb Vasc Biol. 2005 Jan;25(1):228-33.
 Pedersen EB et al. Relationship between mercury in blood and 24-h ambulatory blood pressure in Greenlanders and Danes. Am J Hypertens. 2005 May;18:612-18.
 Valera B et al. Environmental mercury exposure and blood pressure among Nunavik inuit adults. Hyptertension. 2009 Nov;54(5):981-6.
 Virtanen J et al. Serum long-chain n-3 polyunsaturated fatty acids, methylmercury and blood pressure in an older population. Hypertens Res. 2012 Oct;35(10):1000-4.