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Cardiovascular disease is the number one killer of men and women in the United States. In fact, heart disease is so pervasive that when statistics are broken down by ethnicity, CVD is the leading cause of death for Caucasians, African Americans, Latinos, Pacific Islanders, and Indian or Alaskan natives in this country. With an estimated 71.3 million Americans who have a form of CVD, the American Heart Association has projected that cardiovascular disease will cost the already overburdened American health care system 403.1 billion dollars in 2006. http://www.cdc.gov/nccdphp/publications/aag/cvh.htm
It is no mystery, then, that there exists a huge market of prescriptions, diet plans, and dietary supplements which are all aimed at improving heart health. Given that a huge money-making industry has capitalized on this great need, it is important that consumers sift through the products with a discerning eye. Fortunately, the extensiveness of this problem has prompted a multitude of research on the effectiveness of many such products.
What is Cardiovascular Disease?
Cardiovascular disease refers to the class of diseases that involve interruptions in the normal functioning of the heart, blood vessels, and veins. The term cardiovascular disease encompasses a number of more specific diseases including angina pectoris (pain in the chest resulting from restricted blood flow through the arteries), myocardial infarction (heart attack), and stroke. The two major contributing causes of cardiovascular disease are atherosclerosis and arteriosclerosis.
The majority of cases of CVD are caused by a disease in which the endothelial layer of arteries does not heal properly from tears, creating epithelial lesions. Lipoproteins, such as LDL cholesterol, leak into the lining of the blood vessel, attracting macrophages to the site. The macrophages then attack the LDL cholesterol, and collect over the damaged lining of the blood vessel. After continuous lesion repair situations over many years, the body’s macrophages lose their ability to digest lipoproteins. This condition leads to an accumulation of atherosclerotic plaque and a restriction of blood flow through the coronary arteries. As the individual ages, the plaque has the potential to become a serious threat to health.
Arteriosclerosis, on the other hand, is a condition in which the coronary arteries lose elasticity, or compliance. Referred to as “hardening of the arteries,” this condition makes it difficult for the arteries to efficiently pump the increased volume of blood that the body requires during physical exertion. Arteriosclerosis also increases the risk of blood clots in the inelastic arteries.
The two most common cardiovascular diseases are heart disease and stroke. According to the CDC (2006), heart disease and stroke account for the first and third leading causes of death for men and women in the United States combining for nearly 40% of all annual deaths http://www.cdc.gov/nccdphp/publications/aag/cvh.htm. Each year, more than 910,000 Americans die of cardiovascular diseases (CDC, 2006). This staggering statistic means that a person dies of CVD every 35 seconds in the U.S. (CDC, 2006). Although commonly considered a disease predominantly focused in elderly populations, the number of sudden deaths from heart disease among people between ages 15–34 is on the rise (CDC, 2006). The fact is, CVD is reaching an expanding portion of the American population at an alarming rate.
The Skinny on Fat
Considering all of the literature about the correlation between high fat diets and heart disease, it may seem strange to hear that the components of fish oils that appear to have a beneficial effect on the heart are fatty acids. However, research demonstrates that certain classes of essential fatty acids found in fish oils actually contribute to heart health. Why this apparent contradiction to common knowledge? The answer lies in the distinction between harmful saturated and trans fatty acids—which contribute to weight gain, heart disease, and forms of cancer when consumed in excess—and polyunsaturated fats which have a protective effect on the heart.
There are two major classes of polyunsaturated fatty acids, omega-6 and omega-3. Both omega-6 and omega-3 fatty acids are essential fatty acids, meaning that the body cannot produce them and, therefore, must obtain them through the diet. Omega-6 fatty acids are found mainly in grains and vegetable oils. Omega-3 fatty acids can be broken down into three important types: alpha-linolenic acid (ALA), eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA). While ALA can be obtained from flaxseed, soybean, and canola oils, EPA and DHA are found primarily in fatty, coldwater fish like salmon, mackerel, and sardines http://www.foodandhealth.com/cpecourses/omega3.php.
It is now believed that both omega-6 and omega-3 fatty acids are necessary for normal brain function, growth, and development http://www.umm.edu/altmed/ConsSupplements/Omega3FattyAcidscs.html. However, the two essential fatty acid families act very differently in the body, and therefore, it is critical that they each be obtained from the diet in an appropriate balance. The metabolic products of omega-6 acids “promote inflammation, blood clotting, and tumor growth” and the omega-3 acids have the opposite effect http://vvv.com/healthnews/fishoils.html.
Today, high incidences of heart disease, hypertension, diabetes, and obesity are blamed in part on the high ratio of omega-6 fatty acids to omega-3 fatty acids in the American diet. According to Kenney (2002), “the high intake of ALA and trans fatty acid in the Western diet could well be interfering with the production of EPA and DHA and altering normal cell lipid membrane function” http://www.foodandhealth.com/cpecourses/omega3.php. While experts claim that a healthy diet should consist of one to four times more omega-6 fatty acids than omega-3 fatty acids, the typical American diet contains 11 to 30 times more omega-6 fatty acids than omega-3 fatty acids http://www.umm.edu/altmed/ConsSupplements/Omega3FattyAcidscs.html. The American Heart Association and many individual physicians across the country have begun to encourage Americans to consume more omega-3 fatty acids in order to tip this dietary balance back in the healthy direction.
Why Fish Oil Supplements?
Scientists first became interested in the protective effects of omega-3 fatty acids in the 1970s when Danish physicians observed the remarkably low incidence of heart disease and arthritis among Greenland Eskimos. Although the Eskimos consumed a diet high in fat and cholesterol, they were found to have a low risk of ischemic heart disease http://qjmed.oxfordjournals.org/cgi/content/full/96/7/465. Numerous studies were conducted and the reduced risk in heart disease was soon attributed to the consumption of high levels of omega-3 fatty acids, and specifically, of EPA and DHA as found in fish—a staple of the Eskimo diet.
EPA and DHA are found in fatty, coldwater fish such as mackerel, salmon, herring, sardines, anchovies, and albacore tuna. Although experts differ on the amounts of fish oil needed to reap the alleged benefits of omega-3 fatty acids, the American Heart Association has published their own recommendations. The AHA advises people without a history of coronary heart disease to consume a variety of fish at least twice a week. For people who have had a “coronary event” the AHA recommends a dose of 1 gram of EPA and DHA a day. People who need to lower triglyceride levels are advised to consume 2 to 4 grams of EPA and DHA a day http://www.americanheart.org/presenter.jhtml?identifier=4632. This is where fish oil supplements enter the picture.
Generally, the dietary form of fish has more nutrients and is more satiating than supplementary sources and, therefore, is still considered preferable. Unfortunately, the inconvenience and cost associated with purchasing and preparing fish can be a significant deterrent for even the most health conscious Americans. For these individuals, fish oil supplements appear to be a healthy, available, and convenient alternative way to meeting the recommendations of the AHA. When produced by reputable companies who certify that they are low in heavy metals, fish oil supplements are an effective and easy way to ensure that individuals receive a healthy dose of omega-3 fatty acids.
What Claims Are Advertisers Making?
An internet search for “fish oil supplements” returns a long list of websites proclaiming the benefits of omega-3 fatty acids. These sites range from specific supplement manufacturers championing their particular brands to more reputable websites like the American Heart Association and PubMed. The websites are numerous and their claims are diverse but, as is to be expected in the cases of manufacturers with financial interests at stake, only some of the claims are supported by scientific evidence.
For example, the makers of OmegaBriteTM , an omega-3 formula, claim that their product is a “pharmaceutical quality…supplement promoting positive mood, cardiac and joint health, and overall well being” http://www.omegabrite.com/products/gelcaps_brochure/?source=google&gclid=CMrk3Yv6t4cCFSJvFQodyXDrTg. On a promotional website for XTend-Life’s Omega-3 and DHA Fish Oil Esters, site visitors read that not only does this particular supplement contain the “purest fish oil on the planet,” but that “overwhelming evidence from thousands of clinical studies” demonstrates its benefits including “lowering triglycerides, general heart benefits, improving brain functioning, as well as helping with diabetes, strokes, depression, arthritis, allergies, circulation problems, ADHD, Alzheimer's, skin disorders, gout, and many others” http://www.truthaboutomega3.com/omega.html?pg=g01-001-1000D. Wonder Laboratories makes similar claims about their omega-3 fatty acid supplement adding the support of the eyes and maintaining good vision to the list http://www.wonderlabs.com/omega-3/index.html.
How Does Fish Oil Work?
Despite the copious amounts of research on the effects of omega-3 fatty acids and their ability to reduce risk of cardiovascular disease, the mechanisms through which this is accomplished are not clear. Possible mechanisms suggest that CVD incidence may be reduced through:
· A decrease in the risk for arrhythmias (abnormal heart rhythms)
· A decrease in the risk for thrombosis (which could lead to heart attack and stroke)
· A decrease in triglyceride levels
· Diminished growth rate of atherosclerotic plaque
· Improved endothelial function
· Lowering blood pressure
· Reducing inflammatory responses
The Evidence: Studies and Clinical Trials
The numerous claims about fish oil sound impressive, but unfortunately not all are backed by conclusive evidence. Extensive studies have been conducted, some reputable and many not, to assess the real benefits of omega-3 fatty acids and fish oil. Although they are not all in agreement, a few noteworthy studies and results will be discussed.
First, based on a review of over 70 clinical trials, it appears that fatty acids from fish or fish oil supplements significantly reduce triglyceride levels http://www.mayoclinic.com/health/fish-oil/NS_patient-fishoil#B2F9D79E-E7FF-0DBD-1B0C78F42D912A69. This is especially significant as high levels of triglycerides have been recognized as an independent risk factor for coronary heart disease and, consequently, have contributed greatly to the deaths in this country.
According to an analysis of the research on fatty acids and cardiovascular disease published by Kris-Etherton, Harris, and Appel (2003), a regular diet of fish oils increases levels of high density lipoprotein (“good cholesterol”) but also increases the concentration of low density lipoprotein, or “bad cholesterol” http://atvb.ahajournals.org/cgi/content/full/23/2/e20. Individuals with high LDL concentrations should seek out another form of treatment besides fish oil supplementation to lower their risk factors for coronary heart disease.
In addition, fish oil has been shown to play a role in the secondary prevention of cardiovascular disease. Based on clinical trials, regular consumption of 500-800 mg of omega-3 fatty acids reduces the risk of non-fatal heart attack, fatal heart attack, sudden death, and all-cause mortality (Kris-Etherton et al., 2003). Kris-Etherton et al. (2003) conducted a review of randomized controlled trials to assess the role of fish oil and omega 3 fatty acids in secondary prevention of heart disease. In the GISSI-Prevention Study, the largest prospective RCT conducted to test the efficacy of omega-3 acids for secondary prevention, 11,324 patients with coronary heart disease were randomly assigned to one of four study groups. Based on their group assignment, subjects received 300 mg of Vitamin E, 850 mg of EPA + DHA, both, or neither. After 42 months of follow-up, the group receiving the 850 mg of omega-3 fatty acids (the EPA +DHA) experienced a 15% reduction in the primary end point of death, nonfatal heart attack, and nonfatal stroke. In addition, experimenters observed a 20% reduction in all-cause mortality and a 45% reduction in sudden death http://atvb.ahajournals.org/cgi/content/full/23/2/e20.
Meta-analysis of several human clinical trials suggests that the omega-3 fatty acids found in fish oil reduce blood pressure (Morris, Sacks, Rosner, 1993). Morris and his colleagues (1993) observed this through analysis of data from 31 placebo controlled trials on 1,356 subjects on the efficacy of fish oils in the reduction of blood pressure. After extensive analysis, they concluded that omega-3 fatty acids can cause an average reduction in blood pressure of -3.0/1.5 mm Hg. This effect was particularly significant in individuals with higher than average blood pressure http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=pubmed&cmd=Retrieve&dopt=AbstractPlus&list_uids=8339414&query_hl=39&itool=pubmed_docsum.
When consumed in recommended amounts, fish oils are also credited with improved endothelial function and better arterial elasticity as Nestel (2000) observes http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=pubmed&cmd=Retrieve&dopt=AbstractPlus&list_uids=10617976&itool=iconfft&query_hl=33&itool=pubmed_docsum. Diabetic patients suffer from poor arterial elasticity as arteries stiffen—a condition which greatly increases their risk of cardiovascular disease. Remarkably, adding fish oil supplements to the regimens of diabetics improves their arterial compliance (elasticity) within just a few weeks (Nestel, 2000).
As Simopoulos (1999) notes, the anti-inflammatory effects of omega-3 fatty acids have also been shown in the secondary prevention of type 2 diabetes, rheumatoid arthritis, ulcerative colitis, and chronic obstructive pulmonary disease http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=pubmed&cmd=Retrieve&dopt=AbstractPlus&list_uids=10479232&itool=iconfft&query_hl=41&itool=pubmed_docsum. However, not all clinical trials exhibit such impressive health preserving effects of omega-3 fatty acids. For example, a systematic review conducted by Hooper et al. (2006) analyzed 48 randomized control trials and 41 cohort studies to find evidence for claims that omega-3 acids reduce risk of total mortality or combined cardiovascular events. After extensive meta-analysis, Hooper et al. (2006) concluded that it cannot be determined whether or not omega 3 fatty acids help reduce total mortality, cardiovascular events, or strokes. These differences among clinical trials may be a result of differences in the backgrounds of cardiovascular risk, fish oil intake levels, or lifestyle behaviors of study populations http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=pubmed&cmd=Retrieve&dopt=AbstractPlus&list_uids=16565093&itool=iconpmc&query_hl=45&itool=pubmed_docsum.
Like the Hooper et al. (2006) study, there are a handful of recent studies that do not conclusively suggest that omega-3 fatty acids possess protective effects for heart health. However, for the most part, experts agree that diets that contain adequate amounts of EPA and DHA help prevent cardiovascular disease. In fact, in September 2004, the Food and Drug Administration announced the approval of the health claim for reduced risk of coronary heart disease on foods that contain EPA and DHA omega-3 fatty acids. http://www.fda.gov/bbs/topics/news/2004/NEW01115.html
It is important to include a note about the potential risks involved in consuming diets rich in fish oil and omega-3 fatty acids. Noteworthy risks include:
1. High levels of mercury, PCBs, and other environmental contaminants can be found in some fish
2. Children and pregnant and nursing women may be at especially high risk of mercury poisoning when consuming such fish
3. The effect of fish oil on LDL levels vary from person to person but it has been shown to raise LDL levels in some people
4. Cod liver oil, if used as a fish oil supplement, may cause toxicity if taken in an excess amount due to high levels of Vitamins A and D
What Does it All Mean?
Through my research I have found an enormous amount of medical literature proclaiming that fish oils, taken in the natural dietary form or the convenient supplementary form, help reduce the risk factors for cardiovascular disease. They have been shown to prevent, ameliorate, and possibly to repair damage from atheriosclerosis, angina, heart attack, and stroke. Considering the havoc that cardiovascular disease wreaks on the American population each year, these results are quite significant. Health care professionals and researchers must continue to seek out similar cost-effective and simple ways for people to better their health and lessen the devastation of cardiovascular disease. Our lives and the future of our already over-burdened health care system may very well be dependent on it.
Hooper L, Thompson RL, Harrison RA, Summerbell CD, Ness AR, Moore HJ, Worthington HV, Durrington PN, Higgins JP, Capps NE, Riemersma RA, Ebrahim SB, Davey Smith G. Risks and benefits of omega 3 fats for mortality, cardiovascular disease, and cancer: systematic review. BMJ. 2006 Apr 1;332(7544):752-60.
Kris-Etherton PM, Harris WS, Appel LJ. Fish consumption, fish oil, omega-3 fatty acids, and cardiovascular disease. Arterioscler Thromb Vasc Biol 2003;23(2):e20-e30. http://atvb.ahajournals.org/cgi/content/full/23/2/e20
Larsen, H. Fish Oils: The Essential Nutrients. International Health News 2000; Issue 103. http://vvv.com/healthnews/fishoils.html
Morris MC, Sacks F, Rosner B. Does fish oil lower blood pressure? A meta-analysis of controlled trials. Circulation 1993;88(2):523-533. http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=pubmed&cmd=Retrieve&dopt=AbstractPlus&list_uids=8339414&query_hl=39&itool=pubmed_docsum
Sanders TA, Oakley FR, Miller GJ, et al. Influence of n-6 versus n-3 polyunsaturated fatty acids in diets low in saturated fatty acids on plasma lipoproteins and hemostatic factors. Arterioscler Thromb Vasc Biol 1997;17(12):3449-3460. http://atvb.ahajournals.org/cgi/content/full/17/12/3449
Simopoulos, A. “Essential Fatty Acids in Health and Chronic Disease.” American Journal of Clinical Nutrition, 70(3 Suppl):560S-569S, September 1999. http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=pubmed&cmd=Retrieve&dopt=AbstractPlus&list_uids=10479232&itool=iconfft&query_hl=41&itool=pubmed_docsum
FDA Announces Qualified Health Claims for Omega-3 Fatty Acids (2004) Retrieved on September 18, 2006. http://www.fda.gov/bbs/topics/news/2004/NEW01115.html
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