OMEGA-3 FATTY ACIDS AND HEART DISEASE PREVENTION: THE MYTHS AND THE TRUTH
As heart disease continues to be one of the leading causes of death for Americans each year, scientists and the society as a whole strive to find effective ways of preventing this sometimes stoppable killer. Every thirty-two seconds a person in the United States dies from cardiovascular disease. That is over 900,000 Americans die each year from this killer. Coronary heart disease is one of the diseases grouped with cerebrovascular disease and peripheral artery disease under the group heading, cardiovascular disease. Coronary heart disease kills thousands of Americans every year and is mostly preventable. 1.5 million Americans have heart attacks each year. (Kaplan, Sal1lis, Patterson, 1993) There are many risk factors for coronary heart disease including being overweight, high blood pressure, high cholesterol levels in the blood, genetic history of the disease, a high fat diet, a high stress lifestyle, and smoking. The main cause of coronary heart disease is a buildup of plaque in the artery walls called atherosclerosis. Once the buildup causes an obstruction in the artery where the blood cant flow normally, the patient has a myocardial infarction, commonly referred to as a heart attack.
The best proven way to prevent the onset of heart disease is through behavioral measures. The risk of developing heart disease can be prevented in many ways. People have to form habits in their lifestyle which conform to preventing it. The goals of these preventive behaviors are to lower blood pressure , control the level of low density lipoproteins (LDLs) and cholesterol in the blood , reduce the percentage of fat in body tissue and in the blood, have a strong and healthy heart, and to increase the levels of high density lipoproteins (HDLs) in the blood. Exercising regularly, eating foods low in fat and salt, not smoking, and deleting stress from our lives are some of the primary ways of keeping a healthy heart and circulatory system. However, genetics also plays a large role in the incidence of heart disease which some of the time cannot be overcome by adhering to prevention methods. As with many of the illnesses that plague our society, several drugs and treatments have been discovered in order to address the problem once it is already implanted in a person. Some of these treatments are drugs that help lower cholesterol levels in the blood while others are nutritional treatments that naturally help reduce the risk of getting heart disease. One such treatment involves the increased intake of Omega-3 fatty acids in the diet.
The Claims Being Made About Omega-3 Fatty Acids and Their Effect on Heart Disease Prevention
Omega-3 fatty acids, also known as linolenic acids, include eicosapentaenoic acid(EPA) and decosahexaenoic acid (DHA) which are found in fish oils. These long-chain unsaturated fatty acids are usually found together in cold-water fish such as salmon, sardines, mackerel, butter fish, pompano, eel, trout, bonita, and bluefish. (http:/206.135.37.254/library/books/haas/medtreat/heart.htm) These fatty acids can also be ingested by taking fish oil supplements. Capsules containing 300mg of the fatty acids,such as MaxEPA, are commonly found and it is recommended to take two to four capsules per day. Because they are prone to going rancid, Vitamin E is usually added to keep the oil from oxidizing. Except for slight nausea experienced by some people, there are no side effects from using these supplements. (http://206.135.37.254/library/books/haas/medtreat/heart.htm)
There are several ways in which these Omega-3 fatty acids help to prevent heart disease. They seem to reduce cholesterol, blood pressure, and triglyceride levels, as well as platelet aggregation. Also, they raise the levels of HDLs in the blood which are the good cholesterols. By reducing platelet aggregation, they also decrease the risk of vascular thrombosis. Taking just 1 gram of Omega-3 per week which is equivalent to eating oily fish twice a week will help to prevent the formation of blood clots in the arteries, and the thickening of the artery walls in the heart. It also will improve the blood flow in the heart. Levels of LDLs , which are the bad cholesterols are lowered while enlarging of the arteries tends to occur. By decreasing the tendency of platelets to clump together, fish oil impedes the development of atherosclerosis which leads to heart attacks. Also the platelets become less sticky and therefore less able to adhere to the artery walls. Lower fat levels and reduced blood viscosity in the blood help to prevent the onset of coronary heart disease. (http://www.amhrt.org/heartg/fishoil.html)
The support of these claims is mixed with evidence present but not in tremendous abundance. Bryant Stamford , director of the Health Promotion and Wellness Center at University of Louisville, says Recent research provides modest support for fish oil. It might lower blood pressure, but only slightly-three to five points. It might help lower cholesterol and triglycerides in the blood, but not to a great extent. It might reduce clot formation, and it might help keep cholesterol from being deposited in artery walls- the first step in atherosclerosis. But these effects have yet to be established. However, eating fish is a healthy thing to do, regardless of whether you are getting a hefty dose of omega-3 fatty acids.
Recent research suggests that eating fish helps prevent heart attacks, possibly because if you are eating fish you are not eating red meat, which is high in saturated fat. (University of Louisville Medical School) However the American Heart Association claims that current studies show that people who eat fish regularly have lower rates of heart disease and that some benefits come from the fat content of fish. They also warn that excess fish oil in the body could be potentially harmful.(http://www.amhrt.org/heartg/fish oil.html) Fish oil supplements can lower cholesterol levels in the blood, help to lower blood pressure, and reduce excessive blood clotting (platelet activity). (http://206.135.37.254/library/books/haas/medtreat/heart.htm)
Studies in populations such as the Netherlands and the US with low but regular fish intake show more significant associations between fish consumption and lower rate of heart disease than studies done in places such as Norway and Hawaii where fish intake is very high.
Eating oily fish twice a week may help to prevent heart attacks in people with angina. This is because the fatty acids present in fish oil are thought both to prevent the thickening of arteries and to improve blood flow to the heart. Dr. Martijn Katan, of the New England Journal of Medicine states that A little fish may do some good, but more fish is not necessarily better. (http://tirpitz.ibg.uit.no/www/faq/omega3/story.html)
Yet another source claims that scientists have confirmed that populations with higher fish intake have a lower incidence of heart disease. Of the six main ways to prevent cardiovascular disease, eating more cold water fish for the Omega-3 fatty acid content is on the list. Consumption of cold water fish once or twice weekly seems to have a positive effect on cholesterol levels. (http://206.135.37.254/library/books/haas/medtreat/heart.htm)
The beneficial effects of omega-3 fat ty acids have been noted in both clinical trials and population studies and were recently confirmed at an American Heart Association conference by two leading researchers in the field. These same researchers stress however that moderate fish intake is beneficial but that eating fish eight times a week or taking heavy doses of fish oil capsules can surely be detrimental. (http://tirpitz.ibg.uit.no/www/faq/omega3/story.html)
A merchant of fish oil concentrate capsules claims that the incidence of coronary heart disease in Greenlandic Eskimos is extremely low with only 3 cases reported from 1963 to 1967. This is because,they claim, that their diet consists mainly of meat from whales, salmon, seals , and halibut. The Eskimos and other societies with diets rich yin fish are known to have a greatly reduced incidence of heart and circularory disease and it is thought that supplementing with high quality EPA and DHA like that found in Life Plus EPA Plus can help prevent heart disease. They also claim that the natural marine lipids contained in their fish oil supplement product, EPA Plus, will improve overall health by helping to nutritionally support the natural control of blood lipids, such as cholesterol. This helps to protect against heart disease. (http://www.mindspring.com/%7Ecjus1/epa-plus.htm)
As we seek to find ways of preventing coronary disease in our population, the use of omega-3 fatty acids in the diet is surely an interesting study. There is concrete evidence to support that eating moderate amounts of fish on a weekly basis is beneficial to your health. However the exact ways in which these fatty acids prevent tmhe onset of heart disease and how much of them should be ingested is still under investigation. Intense research is still under way as scientists strive to find precise answers to this prevention question.
The Evidence
Because heart disease is so preventable, researchers have been trying for years to find the best ways to reduce the prevalence of it in our society. Besides lifestyle changes, research has been and is being done on both nutritional and drug treatments and therapies. One of these nutritional treatments being studied is omega-3 fatty acids. These long chain polyunsaturated fatty acids are found in high concentrations in fish and fish oil and are thought to have preventive effects on heart disease. Studies are therefore being done on omega-3 fatty acid supplements, fish, and fish oil and their possible relations to heart disease.
Do Omegka-3 Fatty Acids Prevent Heart Disease?
For years, scientists have studied the strong relation between the low incidence of coronary heart disease among the Eskimo population despite high overall fat in their diet. Dyerberg and Bang (1976)have surmised that the link is the high intake of omega-3 fatty acids in their diet coming from marine vertebrates, especially fish.
The Multiple Risk Factor Intervention Trial done by Dolcek (1992) divided 6,000 subjects according to their average intake of omega-3 fatty acids ranging from 0 to 0.66 grams per day. A significant inverse relationship was found between the ingestion of these fatty acids and the incidence of coronary heart disease in the group.
Alexander Leaf of Harvard Medical School deduces that omega-3 fatty acids don't completely prevent the development of atherosclerosis especially when accompanied by many risk factors; however, when added as a supplement to a low-fat diet, they certainly may reduce the risk of coronary heart disease. He also states that in general they enhance the effects of preventive measures while lessening the negative effects of some risk factors. (Leaf, 1994)
Ascherio et al.(1995) in the New England Journal of Medicine reports no benefits from fish intake on development of coronary heart disease as found in the Health Professionals follow-up study. In this study 44,895 male health professionals were followed and their average fish intake was calculated. They report that fish oil slightly reduces blood pressure and triglyceride levels but do not lower levels of LDLs in the blood and may even increase them. (Ascherio et al., 1995)
Omega-3 Fatty Acids - Reduced Risk of Mortality Due to Heart Disease
In the DART trial, people who were given advice to eat~ oily fish experienced a 29% reduction in mortality in the first two years after a heart attack, where people in the fish advice group ingested about 0.3 grams per day and the control group only ingested 0.1 grams per day . (Burr et al., 1989) In the same study , patients who were told to increase consumption of fish or take fish oil supplements decreased their risk of mortality from coronary heart disease but didnt reduce their risk of developing heart disease. (Burr et.al ,1989)
Similarly, McLennan et al.(1989) demonstrated that high levels of tuna fish oil in the diet help to prevent fatal effects after experimentally induced heart attacks in rats. Large amounts of fatty fish and fish oil do help to reduce mortality after heart attacks. (Burr et al., 1989) A small amount of fish compared to no fish reduces mortality in heart attack patients. These results are from studies done with Western Electric workers in Chicago (Shekelle et al. 1985), the control group from the Multiple Risk Factor Intervention Trial (Dolecek ,1991), and among an elderly population in the Netherlands(Kromhout, 1995).
Ascherio et al.(1995) reports a 25% reduction in death due to heart disease among men who consume at least some fish in comparison to those who eat none. A small amount of fish may help to reduce your risk of dying from a heart attack but increasing your intake of fish to more than two servings per week is not likely to prevent heart disease. A little fish may still do some good, but more fish is not necessarily better. (Katan, 1995)
Another study examined the effect of a small amount of fish in the diet on mortality due to coronary heart disease in the elderly. 137 men and 135 women with an average age of 71.2 were followed in a retrospective cohort study. Sixty percent of the cohort consumed an average of twenty-four grams of fish a day. The researchers found no correlation between fish consumption and total cholesterol, triglyceride levels, systolic blood pressure, or body mass index. In men, the prevalence of heart attacks was one-third lower in those who ate fish regularly while no relation was found in the women. Fifty-eight people died from coronary heart disease. Only twenty-five of the 162 fish eaters died from coronary heart disease while thirty three of the 110 no- fish eaters died from it. The risk ratio for fish eaters compared with no-fish eaters was 0.47, meaning that .47 fish eaters die from heart disease for every 1 non-fish eater who dies from it. This study showed that the inverse relationship betweenc moderate fish intake and coronary heart disease mortality also holds true in the elderly. (Kromhout, Daan, Feskens, Edith JM, Bowles, Carel H, 1995)
Fish Oil and Restenosis Following Angioplasty
The hypothesis that a dietary supplement of fish oil given before and after angioplasty will help to reduce the frequency of restenosis was tested in a prospective, randomized, placebo-controlled, double-blind, clinical trial. Restenosis is defined as a greater than 30% narrowing at the site where the angioplasty successfully got rid of the blockage. All of the patients were given the same therapy following the angioplasty for six months including oil capsules, aspirin, and other indicated therapy. A total of 474 patients who had undergone successful angioplasty were used. The placebo group of 230 received an oil capsule containing corn oil while the experimental group received a fish oil capsule containing the omega-3 fatty acids. Leaf et al. (1994) report that only a 6% reduction in the risk of restenosis was due to fish oil. They find this to not be a significant relation and therefore conclude that fish oil does not prevent restenosis following successful angioplasty. Patients in the experimental group did however experience a large decrease in their triglyceride levels, a small decrease in their total and LDL cholesterol levels and a slight increase in HDL levels. (Leaf, 1994)
The Bottom Line on Omega-3 Fatty Acids and Heart Disease
Although many claim that omega-3 fatty acids and fish oil are magic cures for preventing heart disease, this has little truth. The common thread of all the above studies is that moderate amounts of fish in the diet or modest supplements of omega-3R fatty acids helps to prevent mortality after a heart attack. The method of omega-3 fatty acid intake, whether it be fatty fish in the diet or fish oil capsules, does not seem to change the benefits of the omega-3 fatty acids. In most of the preceding studies , similar effects were reported for both fish in the diet and moderate consumption of fish oil capsules. This means that fish eaters or people who take fish oil capsules compared with non-fish eaters or those with no omega-3 fatty acid intake are less likely to die following a cardiac event, not that they are less likely to develop heart disease.
The results the studies done on the effects of omega-3 fatty acids on lowering cholesterol and triglyceride levels in the blood are mixed but most studies find a significant positive relationship between the two. However, fish consumptvion along with a low-fat diet, smoke-free lifestyle, a lifestyle low in stress, and regular exercise certainly can protect you from the number one killer in America.
It is not necessary to ingest as many fish oil capsules as possible because incorporating fish into the diet will offer all the benefits the omega-3 fatty acids have to offer. Fish and omega-3 fatty acids in particular certainly don't have negative effects when consumed in moderation and certainly do have some protective benefits in relation to mortality due to heart disease.
REFERENCES
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Bang HO, Dyerberg J, Horne N: The composition of food consumed by Greenland Eskimos. Acta Med Scand 19ç76;200:69-73
Burr ML, Fehily AM, Gilbert Jf, et al. Effects of changes in fat, fish and fibre intakes on death and myocardial reinfarction:diet and reinfaction trial (DART). Lancet 1989; ii: 757-61.
Dolecek T A, Grandits G. Dietary polyunsaturated fatty acids and mortality in the Multiple Risk Factor Intervention Trial. World Rev Nutr Diet 1991; 66:205-16.
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Kromhout, Daan, Feskens, Edith JM, Bowles, Carel H. (1995). The protective effect of a small amount of fish on coronaråy heart disease mortality in an elderly population. International Journal of Epidemiology, 24(2), 340-5.
Leaf, Alexander.(1994). Some effects of omega 3 fatty acids on coronary heart disease. World Review of Nutrition and Dietetics, 76, 1-8.
Leaf, Alexander. (1994) Angioplasty and Interventional Cardiology: Do Fish Oils Prevent Restenosis After Coronary Angioplasty? Circulation, 90(5), 2248-255.
McKeigue, Paul. (1994) Diets for secondary prevention of coronary heart disease: can linolenic acid substitute for oily fish? The Lancet, 393(8911), 1445.
McLennan PL, Abeywardena MY, Charnock JS: The influence of age and dietary fat in an animal model of sudden cardiac death. Aust NZ J Med 1989;19:1-5.
Shekelle R, Missell L, Paul O, MacMillan-Shyrock A, Stamler. Fish consumption and mortality from coronary heart diseases. (Letter) New England Journal of Medicine 1985;313:820.
http://www.vanderbilt.edu/AnS/psychology/health_psychology/omega3.htm
