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Omega-3 Fatty Acids & Cardiovascular Disease: Smells Fishy?
September 24, 2007
According to the United States Department for Health and Human Services, “cardiovascular disease (CVD) causes more deaths in Americans of both genders and all racial and ethnic groups than any other disease” (http://www.cdc.gov/omh/AMH/factsheets/cardio.htm). Cardiovascular disease is also once of the leading causes of disability in the United States. Additionally, every year CVD costs Americans approximately 300 billion dollars, including everything from treatments, prescriptions, and even deaths. Also every year in the United States about 700,000 people die a year from heart disease (http://www.cdc.gov/HeartDisease/facts.htm). From these few statistics it is clear that CVD is a widespread and significant disease in America, let alone the world.
Cardiovascular disease is an encompassing term for “disorders of the heart and blood vessel system, including stroke and coronary heart disease (CHD)” (Straub, 2007, p. G-3). While stroke and heart disease are the most common cardiovascular disorders, other diseases such as myocardial infarction (heart attack), arrhythmia (irregular heartbeat), and angina (chest pain due to insufficient blood reaching the heart) are also categorized as CVD (http://www.cdc.gov/HeartDisease/about.htm).
There are many risk factors that are associated with this prevalent disease. A few of these risk factors, people have no control over, such as their heredity. Several of these risk factors are conditions in themselves, such as diabetes or high blood pressure. Yet, the majority of these factors are behavioral factors, such as smoking, diet, physical inactivity, obesity, and alcohol. Overall, these risk factors increase one’s blood pressure, cholesterol, and level of triglycerides, all of which explain why people develop cardiovascular disease (http://www.cdc.gov/HeartDisease/risk_factors.htm).
Background on Omega-3 Fatty Acid Research
Ever since the 1970s, after Bang and Dyerberg’s study on Greenlandic Eskimos was published, omega-3 fatty acids and their relation to the cardiovascular system has been extensively researched (Harris, 1997). Bang and Dyerberg (1975) discovered that coronary atherosclerosis was basically unheard of among the population when living in their native environment. Coronary atherosclerosis is the building up of plaque in arteries, which cause these arteries to thicken and loose their elasticity (http://heart-disease.health-cares.net/atherosclerosis.php). The reason that this study was so important is because atherosclerosis is the main cause behind most cardiovascular diseases. The reason that the Greenlandic Eskimos had barely any cases of coronary atherosclerosis was mainly due to their “significantly lower plasma concentrations of cholesterol, triglycerides, β -lipoproteins, and pre-β-lipoproteins, as compared to a Danish reference population” (Bang & Dyerberg, 1975, p. 958). Even though both groups of Eskimos’ diets consisted of higher saturated fats than polyunsaturated fats, there was still a lower incidence of heart disease in the Greenlandic Eskimos when compared their Eskimo relatives living in Denmark. Overall, this study began the scientific world to question the benefits of these long-chained fatty acids largely present in the Greenlandic Eskimo’s diet.
Omega-3 Fatty Acids
“Fish and other marine life are rich sources of a special class of polyunsaturated fatty acids called omega-3 or n-3 fatty acids” (Stone, 1996, p. 1083). The 1975 study done by Bang and Dyerberg raised the question of the dietary benefits of fish and other marine life because this type of meat was central to these Eskimos’ diet. In the past thirty years, countless research studies have been done on these fatty acids to confirm whether as supplements they can reduce or prevent cardiovascular disease. The main omega-3 fatty acids that are present in marine life are eicosapentaenoic acid (EPA) and docosahexaneioic acid (DHA) (Harris, 1997). There is also an omega-3 fatty acid that is derived from plants called α-linolenic acid. Another interesting discovery about these fatty acids is their affect on what we call good (HDL) and bad (LDL) cholesterol. Harris showed in his that the omega-3 fatty acids actually slightly increased both of these types of cholesterol (1997). This result of omega-3 fatty acids presents a confounding variable in most of the studies of these fatty acids because high cholesterol is a risk factor of CVD.
There are several possible mechanisms that the American Heart Association (AHA) presents as an explanation to the seemingly preventive effects of omega-3 fatty acids (Kris-Etherton et al, 2002). The first mechanism presented is that there is a “dose-response relationship between omega-3 fatty acid intake and triglyceride lowering” (Kris-Etherton et al, 2002, p.2750). The one limitation with this mechanism is that only the right dosage of EPA and DHA from supplements will possibly have the desired effect. The recommended dosage is 3 g/d. There may be detrimental effects on the patient if more than this dosage is taken, while there will most likely be no changes at all if there is less than this amount taken.
The second mechanism discussed in the AHA’s statement is fatty acid’s effect on blood pressure. In a study done by M.C. Morris and other scientists in 1993, it was revealed through meta-analysis that blood pressure in hypertensive subjects was significantly reduced when these subjects consumed omega-3 fatty acids. Yet Kris-Etherton et al adds that, “in view of the high dose required to lower blood pressure and the proven efficacy of other nutritional factors and of antihypertensive medications, an increased intake of omega-3 fatty acids has a limited role in the management of hypertension” (2002, p. 2750).
A third mechanism that is presented this AHA journal is the possibility that omega-3 fatty acids may reduce sudden death from heart attacks because it reduced the likelihood of arrhythmia. The reason that arrhythmia might be reduced in some people is due to the fact that omega-3 fatty acids are “potent inhibitors of voltage-gated sodium channels in cultured neonatal cardiac myocytes” (Kris-Etherton et al, 2002, p.2750). (One drawback of the possible mechanisms listed above, is that they are presented by the AHA, which is surely a biased entity because this organization wants to show the scientific community that they are actually making progress in the prevention of CVD. Therefore, a list of other possible mechanisms not already mentioned above from Din et al is included in the following list).
Other possible mechanisms:
Where’s the evidence?
There are over 100 journal articles referenced in the summary article by the AHA. There is much research on these omega-3 fatty acids, so only a few of these many articles will be reviewed in the following section. The majority of the research found was in favor of small amounts of omega-3 fatty acids in order to prevent cardiovascular disease, while only a few found negative or no results.
In a clinical review by several scientists in 2004, summarizes four successful research studies that show the reduced risk of myocardial infarction through the consumption of fish or fish oil more than once a week. The four research studies discussed in this article were the “Diet and reinfarction trial”, “Indian experiment of infarct survival”, “GISSI- Prevenszione trial” and “Nilsen et al” (Din et al, 2004, p. 32). In the research reviewed the relative risk reduction of heart attacks were between 29.7 and 48.2 percent among these studies. All of these studies showed significant results for the effectiveness in the omega-3 fatty acids (present in fish and fish oil) for reducing one type of CVD.
Another positive review for omega-3 fatty acids is a research review by Gerry Schwalfenberg in 2006. One strong study that Schwalfenberg (2006) uses as evidence is the Lyon Diet Heart Study done which was published in 1999. In this study followed 605 men for 4 years after they had heart attacks. Half of the men in this study were given a Mediterranean diet rich is omega-3 fatty acids, while the other half were given a diet similar to the American Heart Association diet. The study focused on heart attacks, hospital visits due to cardiovascular problems, and cardiac death. The subjects following the Mediterranean diet had the least occurrence of these events in all areas of the study.
One research study that did not find positive results, but in fact an increased risk of cardiovascular disease was the Alpha Tocopherol Beta-Carotene Cancer Prevention Study done in 1997 (Pietinen et al). This study found “that estimated omega-3 fatty acid intake from fish was associated with a trend toward increased relative risk of coronary death after adjustment for trans, saturated, and cis-monounsaturated fatty acids.
Overall most of the research shows that supplementing one’s diet with omega-3 fatty acids in the form of marine animals or fish oil could reduce or prevent the likelihood of developing a cardiovascular disease. While many of the research studies found results that confirm this result from omega-3 fatty acids, there are many other risk factors that contribute to CVD that sometimes present themselves as confounding variables in these reports. Hopefully, in the future, we will know whether these “healthy fats” are actually increasing our cardiovascular health. Until then, especially if you have a history of heart disease in your family, you might want to supplement your diet with a little more fish…just in case.
Bang, H.O. & Dyerberg, J. (1975). Fatty acid composition of the plasma lipids in Greenland Eskimos. American Journal of Clinical Nutrition, 28, 958-66.
Din, J.N., Newby, D.E. & Flapan, A.D. (2004). Omega-3 fatty acids and cardiovascular disease—fishing for a natural treatment. BMJ, 328, 30-5.
Harris, W.S. (1997). n-3 Fatty Acids and serum lipoproteins: human studies. American Journal of Clinical Nutrition, 65, 1645-51.
Kris-Etherton, P.M., Harris, W.S. & Appel, L.J. (2002) Fish consumption, fish oil, omega-3 fatty acids, and cardiovascular disease. Circulation, 2747-57.
Morris, M.C., Sacks, F. & Rosner, B. (1993). Does fish oil lower blood pressure? Circulation, 88, 523-33.
Pietinen, P., Ascherio, A., Korhoenen, P., et al. (1997). Intake of Fatty Acids and risk of coronary heart disease in a cohort of Finnish men: the Alpha-Tocopherol Beta-Carotene Cancer Prevention Study. American Journal of Epidemiology, 145, 876-87.
Schwalfenberg, G. (2006). Omega-3 Fatty Acids: Their beneficial role in cardiovascular health. Canadian Family Physician, 52, 734-40.
Stone, N.J. (1996). Fish Consumption, Fish Oil, Lipids, and Coronary Heart Disease. American Journal of Clinical Nutrition, 65, 1083-6.
Straub, R.O. (2007). Health Psychology: A Biopsychosocial Approach (2nd ed.) New York: Worth Publishers.
“About Heart Disease.” Centers for Disease Control and Prevention. (2007). Retrieved September 20, 2007 from: http://www.cdc.gov/HeartDisease/about.htm.
“Eliminate Disparities in Cardiovascular Disease.” Centers for Disease Control and Prevention. (2007). Retrieved September 20, 2007 from: http://www.cdc.gov/omh/AMH/factsheets/cardio.htm.
“Heart Disease Facts and Statistics.” Centers for Disease Control and Prevention. (2007). Retrieved September 20, 2007 from: http://www.cdc.gov/HeartDisease/facts.htm.
“Heart Disease Risk Factors.” Centers for Disease Control and Prevention. (2007). Retrieved September 20, 2007 from: http://www.cdc.gov/HeartDisease/risk_factors.htm.
“What is coronary atherosclerosis?” Health-Cares.net. (2007). Retrieved September 21, 2007 from: http://heart-disease.health-cares.net/atherosclerosis.php.
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