Omega-3 In Arabian Gulf Fish (1)
Most of our cities in the Gulf Cooperation Council states (GCC or simply The Gulf), are on the seashore. Because fish is abundant in our sea, it protected the Gulf inhabitants from devastating famines that swept many parts of the world over the centuries. Fish is one of the most important sources of food for us. During my childhood, we ate fish almost daily and I rarely had a chance to eat meat. With one-quarter of the Indian Rupee, we used to buy four kilograms of fish, but with that money, we could not buy a quarter kilogram of meat. We had meat only when we had guests or on special occasions such as feasts of the festival. Therefore, I never miss eating meat but I cannot go for one week without having fish. Most Gulf citizens, especially those of my generation, do not need to be advised to eat fish.
During the time that I was undersecretary of health in Qatar and chairing the environment protection committee, I ordered the ministry of health food laboratory to analyze our local fish frequently for its fitness for human consumption, especially during oil spills. My main concern was seawater pollution. The laboratory did analyze the chemical content of several local fish and screened them for toxins.
In the next few issues of Heart Views, I will share with the readers my love for fish and enumerate the chemical composition of Qatar fish. The water environment in the whole Gulf is similar; therefore, I expect the content of fish found in the other Gulf States to be fairly similar to the fish of Qatar. I cannot say that they will be exactly the same because there are some differences in fish composition even in the same country where shores are but a few kilometers apart, depending on the feeding grounds. For example, I could tell the difference between Shari fish (Red Spot Emperor) caught in the east of Doha and Shari fish caught in the north of Qatar by the smell and taste. There are also some variations in the composition of fish caught in the same location in different seasons.
I will be starting one page devoted to fish in each issue of Heart Views, discussing one fish type at a time with the photographic illustration of the fish. The only hint I will give you here is that if you are fond of Hamoor (Grouper) you will be disappointed. Some unpopular cheap fish in the Gulf may have a higher fatty acid content than the expensive fish!
In this issue, I will summarize the cardiovascular effects of fish oil (omega-3) from the available studies I cited below as well as from my review of this topic in a recent electronic issue of Up-to-date [1] and Braunwald's Heart Disease Text Book [2].
Review of Cardiovascular Effects of Fish Oil
Early studies found low rates of coronary heart disease (CHD) death among Greenland Eskimos consuming large amounts of seafood[3]. Animal and human studies have identified the long-chain n-3 polyunsaturated fatty acids (n-3 PUFA) eicosapentaenoic acid (EPA, 20:5n-3), and docosahexaenoic acid (DHA, 22:6n-3) as the likely active constituents in fish oil.
EPA and DHA are absorbed from the gastrointestinal tract and are transported to the liver largely as triglycerides in chylomicron particles. From the liver, EPA and DHA are released into the circulation as triglycerides in lipoprotein particles such as LDL-cholesterol (LDL-C) and HDL-cholesterol (HDL-C) and plasma phospholipids. Smaller amounts circulate as free fatty acids, largely bound to albumin.
EPA and DHA are incorporated into cell membrane phospholipids throughout the body, particularly in the heart and brain, and stored in adipose tissue as triglycerides. Compared with EPA and DHA, other n-3 PUFA such as docosapentaenoic acid (DPA, 22:5n-3) are present in much smaller amounts in fish oil, but maybe biologically active and have important metabolites following consumption.
Effects on Cardiovascular Risk Factors
Fish oil influences several cardiovascular risk factors [4],[5],[6]. At typical dietary intakes, antiarrhythmic effects predominate, and such effects may reduce the risk of sudden cardiac death and CHD death within weeks. At higher doses, maximum antiarrhythmic effects have been achieved, but other physiologic effects may begin to modestly impact other clinical outcomes, although some of these physiologic effects (such as triglyceride-lowering) may require months to years of consumption before the lower risk of clinical outcomes is seen.
CHD Mortality
Although fish have a number of important nutritive qualities, their major cardiovascular benefit likely derives from their content of omega-3 fatty acids, eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA). Increased plasma levels of these fatty acids predicted a considerable reduction in sudden cardiac death, a result consistent with that of a report indicating that intake of 5.5 gm/month of EPA plus DHA (equivalent to one portion of fatty fish per week) was associated with a 50 percent lower incidence of primary cardiac arrest compared with individuals consuming no fish. This effect appears to be related to the enrichment of membrane phospholipids with omega-3 fatty acids and a resulting reduction in risk for abnormal cardiac electrical conductivity. Other properties of these fatty acids that may reduce the risk for CHD include antiplatelet and anti-inflammatory effects, as well as a reduction in plasma triglycerides at higher doses. On the basis of these studies, as well as results of intervention trials with omega-3 fatty acids described later, the AHA has recommended consumption of two portions of fish per week, particularly those fish rich in omega-3 fatty acids (e.g., salmon, mackerel, albacore tuna, swordfish, herring, sardines, lake trout) [2].
A recent analysis of the epidemiological data concluded that intake of small quantities of fish is associated with a 17 percent reduction in CHD mortality risk and a 27 percent reduction in risk for nonfatal myocardial infarction, whereas each additional serving per week is associated with a further reduction of 3.9 percent in CHD mortality but no further reduction in risk for myocardial infarction [2].
Blood lipids
Fish oil consumption lowers serum triglyceride concentrations by 25 to 30 percent, an effect within the range of efficacy of other triglyceride-lowering drugs. Fish oil doses required to lower triglycerides are several-fold higher than the doses that may reduce coronary mortality.
Fish oil supplementation also modestly raises HDL-C concentrations (+3 percent) and, particularly in patients with hypertriglyceridemia, raises LDL-C concentrations (+5 percent) and lowers the proportion of small dense LDL-C particles [7],[8] . This increase in LDL particle size may in part account for the higher LDL-C concentrations; that is, LDL-C concentration may slightly increase but without appreciable change in the number of circulating LDL particles. Given the frequently coexisting relationship of high triglycerides, low HDL-C, and small dense LDL particles in many individuals, the effects of fish oil to lower triglycerides, raise HDL-C and decrease the proportions of small dense LDL particles appear concordant.
These fatty acids (omega-3) lower plasma triglyceride levels and have antithrombotic properties. Although employed in the treatment of hypertriglyceridemia, their use is reserved in cases of severe hypertriglyceridemia refractory to conventional therapy [2] .
Blood Pressure and Systemic Vascular Resistance
Fish oil consumption lowers systolic BP by approximately 3 to 5 mm Hg and diastolic BP by approximately 2 to 3 mm Hg, due to reductions in systemic vascular resistance. Fish oil consumption increases biomarkers of nitric oxide production, mitigates peripheral vasoconstrictive responses to norepinephrine and angiotensin II, improves arterial wall compliance, and enhances vasodilatory responses [9]. These effects could account for the lowering of systemic vascular resistance.
Coagulation and Thrombosis
High doses of fish oil (3 to 15 g/d) increase bleeding time, but this has not been associated with higher rates of clinical bleeding. In a review of 9 randomized trials (n = 2,612), including people taking aspirin or warfarin, no consistent associations were seen between fish oil use or fish oil dose and bleeding risk [10]. Fish oil consumption lowers circulating markers of endothelial dysfunction, such as E-selectin, vascular cell adhesion molecule-1 (VCAM-1), and intercellular adhesion molecule-1 (ICAM-1) [11].
Coronary Stenosis
An observational study in 229 women found that after adjustment for other risk factors, during 3.2 years of follow-up, modest dietary consumption of n-3 PUFA was associated with less progression of coronary stenosis and fewer new lesions [12]. Overall there is currently no convincing evidence that fish oil supplementation decreases the risk of coronary restenosis. Increased consumption of n-3 PUFA from fish or fish oil supplements reduces rates of cardiac and sudden death [13].
Heart Failure
An observational study found an association between consumption of baked or broiled fish with a lower risk of incident heart failure (HF); consumption of fried fish was associated with an increased risk of HF [14].
Ekg
Besides the antiarrhythmic benefit of fish oil I mentioned above, dietary fish consumption may result in slowing of the resting heart rate, prolongation of the PR interval, and shortening of the QT interval [15] . Fish oil does not protect against ventricular tachycardia (VT) or death in patients with an ICD [16] .
Early Neurologic Development
DHA is preferentially incorporated into the rapidly developing brain during the last trimester of pregnancy and the first two years of infancy, concentrating in brain gray-matter and retinal membranes.
Stroke
Among elderly individuals, consumption of tuna or other broiled or baked fish is associated with a lower risk of ischemic stroke, while intake of fried fish or fish sandwiches is associated with a higher risk [17].
Summary
Modest fish oil consumption (approximately 250 mg/day EPA+DHA) reduces the risk of CHD death and sudden cardiac death. This is of particular importance in patients with established CHD or at high risk for CHD. There is limited evidence that long-term consumption of fish oil may reduce the risk of atherosclerosis and cardiovascular events other than CHD death and sudden cardiac death.
Accumulating epidemiological evidence indicates that alpha-linolenic acid, an omega-3 fatty acid precursor of longer chain EPA and DHA that is found in flaxseed, chia, and a variety of vegetable and nut oils, reduces risk for cardiovascular disease, although as with fish oils, the strongest evidence is for reduced cardiovascular mortality, specifically sudden cardiac death, suggesting the primary importance of antiarrhythmic effects [2] .
Recommendations
Healthy persons, patients with known CHD or patients who are at high risk for CHD, are urged to consume at least one to two servings per week of oily fish.
References:
1.Dariush Mozaffarian, MD. Fish oil and marine omega-3 fatty acids: Uptodate October 10, 2008.
2.Ronald M. Krauss. Chapter 44 - Nutrition and Cardiovascular Disease: Braunwald's Heart Disease, 8th Edition.
3.Bang, HO, Dyerberg, J. Lipid metabolism and ischemic heart disease in Greenland Eskimos. In: Advances in Nutrition Research, Draper, H (Ed), Plenum Press, New York 1980. p.1.
4.McLennan, PL. Myocardial membrane fatty acids and the antiarrhythmic actions of dietary fish oil in animal models. Lipids 2001; 36 Suppl:S111.
5.Leaf, A, Kang, JX, Xiao, YF, Billman, GE. Clinical prevention of sudden cardiac death by n-3 polyunsaturated fatty acids and mechanism of prevention of arrhythmias by n-3 fish oils. Circulation 2003; 107:2646.
6.Wang, C, Harris, WS, Chung, M, et al. n-3 Fatty acids from fish or fish-oil supplements, but not {alpha}-linolenic acid, benefit cardiovascular disease outcomes in primary- and secondary-prevention studies: a systematic review. Am J Clin Nutr 2006; 84:5.
7.Friedberg, CE, Janssen, MJ, Heine, RJ, Grobbee, DE. Fish oil and glycemic control in diabetes. A meta-analysis. Diabetes Care 1998; 21:494.
8.Minihane, AM, Khan, S, Leigh-Firbank, EC, et al. ApoE polymorphism and fish oil supplementation in subjects with an atherogenic lipoprotein phenotype. Arterioscler Thromb Vasc Biol 2000; 20:1990.
9.Kenny, D, Warltier, DC, Pleuss, JA, et al. Effect of omega-3 fatty acids on the vascular response to angiotensin in normotensive men. Am J Cardiol 1992; 70:1347.
10.Wang, C, Harris, WS, Chung, M, et al. n-3 Fatty acids from fish or fish-oil supplements, but not {alpha}-linolenic acid, benefit cardiovascular disease outcomes in primary and secondary-prevention studies: a systematic review. Am J Clin Nutr 2006; 84:5.
11.Robinson, JG, Stone, NJ. Antiatherosclerotic and antithrombotic effects of omega-3 fatty acids. Am J Cardiol 2006; 98:39i.
12.Erkkila, AT, Lichtenstein, AH, Mozaffarian, D, Herrington, DM. Fish intake is associated with a reduced progression of coronary artery atherosclerosis in postmenopausal women with coronary artery disease. Am J Clin Nutr 2004; 80:626.
13.Wang, C, Harris, WS, Chung, M, et al. n-3 Fatty acids from fish or fish-oil supplements, but not alpha-linolenic acid, benefit cardiovascular disease outcomes in primary- and secondary-prevention studies:a systematic review. Am J Clin Nutr 2006; 84:5.
14.Mozaffarian, D, Bryson, CL, Lemaitre, RN, et al. Fish intake and risk of incident heart failure. J Am Coll Cardiol 2005; 45:2015.
15.Mozaffarian D, et al. Dietary Fish and n-3 Fatty Acid Intake and Cardiac Electrocardiographic Parameters in Humans. J Am Coll Cardiol. 2006;48:478-484.
16.Brouwer IA, Zock PL, Camm AJ, et al. Effect of Fish Oil on Ventricular Tachyarrhythmia and Death in Patients With Implantable Cardioverter Defibrillators: The Study on Omega-3 Fatty Acids and Ventricular Arrhythmia (SOFA) Randomized Trial. JAMA. 2006;295:2613-2619.
17.Mozaffarian D, Longstreth WT Jr, Lemaitre RN, et al. Fish Consumption and Stroke Risk in Elderly Individuals: The Cardiovascular Health Study. Arch Intern Med. 2005;165:200-206.
