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Fish Oils and Blood Coagulation
Summaries of the latest research concerning fish oils and blood coagulation
Fish oils recommended for diabetes and hypertension
TROMSO, NORWAY. Fish and fish oils help protect against the development of atherosclerosis and heart disease. It is believed that fish oils exert their protective effect by lowering blood pressure and the levels of triglycerides and very-low-density lipoprotein (VLDL). Fish oils are also believed to reduce platelet aggregation and to suppress the growth of smooth-muscle cells in the arterial walls. Many people with hypertension also suffer from diabetes and there has been concern that fish oil supplementation may aggravate problems with glucose intolerance. Researchers at the University of Tromso now report that fish oil supplementation lowers blood pressure significantly in people with hypertension and has no effect on glucose control even in people with mild diabetes. The study involved 78 obese volunteers with essential hypertension. The participants were randomly assigned to one of two equal-sized gr! oups. The fish oil group received four fish oil capsules a day (containing a total of 3.4 grams of a mixture of eicosapentaenoic acid and docosahexaenoic acid) for a period of 16 weeks. The control group received four corn oil capsules a day.
At the end of the test period the average (mean) systolic blood pressure had dropped by 4.4 mm Hg and the diastolic pressure by 3.2 mm Hg in the fish oil group. The average blood pressure in the control group did not change. The researchers also found that plasma triglyceride and VLDL levels in the fish oil group decreased significantly (by about 9 per cent) while they increased significantly (by about 12 per cent) in the control group. There were no changes in total or low-density-lipoprotein levels in either group. Extensive tests (oral glucose tolerance, hyperglycemic and hyperinsulemic clamps) were done to evaluate the effect of fish oil supplementation on glucose control. No adverse effects were found. An editorial accompanying the research report concludes that fish or fish oil is useful in the prevention of vascular disease in diabetics. Patients with diabetes should eat fish two to three times a week or, as an alternative, supplement with two to three one gram cap! sules of fish oil per day.
Toft, Ingrid, et al. Effects of n-3 polyunsaturated fatty acids on glucose homeostasis and blood pressure in essential hypertension. Annals of Internal Medicine, Vol. 123, No. 12, December 15, 1995, pp. 911- 18
Connor, William E. Diabetes, fish oil, and vascular disease. Annals of Internal Medicine, Vol. 123, No. 12, December 15, 1995, pp. 950-52
Fish oils help prevent cardiac arrest
SEATTLE, WASHINGTON. Cardiac arrest is a serious, usually fatal condition in which the heart stops pumping. Cardiac arrest most commonly occurs in connection with ventricular fibrillation and its primary cause is a heart attack. Researchers at the University of Washington now report that the risk of cardiac arrest can be significantly lowered by an increased intake of seafood rich in eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). Their study involved 334 patients who had suffered cardiac arrest during the period 1988 to 1994 and 493 controls matched for age and sex. None of the study participants had had any indication of heart disease prior to the beginning of the study. Interviews with survivors or their spouses were used to determine the participant's fish intake in the month preceding the cardiac arrest. The researchers found that the intake of just one portion of fatty fish per week lowered the risk of card! iac arrest by an impressive 50 per cent after adjusting for age, smoking, family history of heart attacks, hypertension, diabetes, obesity, physical activity, education, and cholesterol level.
The researchers believe that consumption of fish increases the level of EPA and DHA in the membranes of the red blood cells which in turn reduces platelet aggregation and coronary spasm. This belief was confirmed by finding that blood samples taken from 95 cardiac arrest patients and 133 controls showed that a high blood content of EPA and DHA (five per cent of total fatty acids) corresponded to a 70 per cent reduction in the risk of cardiac arrest when compared to study participants with a low EPA and DHA content in their blood (3.3 per cent of total fatty acids). Other studies have shown that patients who have already suffered a heart attack can reduce their risk of future life-threatening arrhythmias and sudden cardiac death by increasing their intake of fish, fish oils or linolenic acid (flax seed oil). The researchers conclude that a modest intake of EPA and DHA from seafood may reduce the risk of ventricular fibrillation and death from coronary heart disease.! NOTE: Fresh salmon is one of the best sources of fish oils; it contains twice as much per serving as does albacore tuna and six times more EPA and DHA than a serving of cod.
Siscovick, David S., et al. Dietary intake and cell membrane levels of long-chain n-3 polyunsaturated fatty acids and the risk of primary cardiac arrest. Journal of the American Medical Association, Vol. 274, No. 17, November 1, 1995, pp. 1363-67
Fish oil supplementation does not increase bleeding tendency
OSLO, NORWAY. A group of Norwegian medical researchers reports that fish oil supplementation does not increase the bleeding tendency in heart disease patients receiving aspirin or warfarin. The study involved 511 patients who had undergone coronary artery bypass surgery. On the second day after the operation half the patients were assigned in a random fashion to receive 4 grams of fish oil per day (providing 2 g/day of eicosapentaenoic acid, 1.3 g/day of docosahexaenoic acid, and 14.8 mg/day of vitamin E). At the same time the patients were also randomized to receive either 300 mg of aspirin per day or warfarin aimed at achieving an INR of 2.5-4.2. The patients were evaluated every 3 months and questioned about bleeding episodes for the duration of the 9-month study.
The researchers concluded that fish oil supplementation did not result in a statistically significant increase in bleeding episodes in either the aspirin group or in the warfarin group. They also found no significant long-term effects of fish oil on common parameters of coagulation and fibrinolysis. They noted that the blood levels (serum phospholipid levels) of eicosapentaenoic acid and docosahexaenoic acid increased by 140% and 14% respectively in the patients taking fish oil. The serum triglyceride levels decreased by 19.1% in the fish oil group while no significant change was observed in the remainder of the patients. NOTE: This study was partially funded by Pronova Biocare AS (a fish oil manufacturer) and Nycomed Pharma AS.
Eritsland, J., et al. Long-term effects of n-3 polyunsaturated fatty acids on haemostatic variables and bleeding episodes in patients with coronary artery disease. Blood Coagulation and Fibrinolysis, Vol. 6, 1995, pp. 17-22
Fish oils reduce cardiovascular risk factors
OSLO, NORWAY. High blood levels of triglycerides and fibrinogen are known risk factors for cardiovascular disease. Fibrinogen is a large protein molecule which is a key factor in blood coagulation. High levels of fibrinogen aggravate the symptoms of intermittent claudication and speeds up the progression of atherosclerosis. Recent research has shown that fibrinogen level is a more reliable indicator of heart disease risk than is total cholesterol level.
Researchers at the University of Oslo now report that fish oil supplementation is effective in lowering both triglyceride and fibrinogen levels. Their study involved 64 healthy men between the ages of 35 and 45 years. The participants were randomly assigned to receive either 14 1-gram capsules of fish oils or 14 1- gram capsules of olive oil every day for six weeks. The fish oil capsules contained 25.7% eicosapentaenoic acid (EPA) and 20.5% docosahexaenoic acid (DHA) and the olive oil capsules contained about 80% oleic acid. Blood samples were taken and analyzed at the start of the study, 3 and 6 weeks into the study, and 3 weeks after stopping supplementation. The red blood cell (phospholipid phase) content of EPA increased markedly after supplementation; DHA level increased slightly and the level of both linoleic acid and arachidonic acid decreased significantly. Blood level of fibrinogen dropped an average of 13% (from 2.73g/L to 2.37 g/L) after 3 weeks, but returned t! o baseline 3 weeks after stopping fish oil supplementation. There were no changes in fibrinogen levels in the olive oil group. Triglyceride levels decreased by an average of 22% (from 1.58 mmol/L to 1.23 mmol/L) after 6 weeks in the fish oil group, but increased by about 19% in the olive oil group. Values in both groups reverted to baseline 3 weeks after ceasing supplementation. Total cholesterol level and the level of LDL cholesterol (low-density lipoprotein) did not change with supplementation in either group, but a small transient decrease in the level of HDL (high-density lipoprotein) cholesterol was noted in the fish oil group. Blood pressure fell slightly in both groups after 3 and 6 weeks of supplementation, but reverted to baseline once supplementation was discontinued.
The researchers conclude that the antithrombotic (blood clot preventing) effect of fish oils may be due to their ability to lower fibrinogen levels.
Flaten, Hugo, et al. Fish-oil concentrate: effects of variables related to cardiovascular disease. American Journal of Clinical Nutrition, Vol. 52, 1990, pp. 300-06
Consuming freshwater fish may lower risk of heart disease
KUOPIO, FINLAND. A 15-week experiment involving 62 students was carried out to determine if a regular diet of freshwater fish affects coronary heart disease risk factors. The students were divided into three groups: a fish eating group who made no other changes to their diet, a fish eating group who also decreased their overall fat intake and a control group (19 students) who ate a typical western diet. The special diet consisted of one fish meal a day (in addition to the regular diet) and provided about 0.25 g/day of eicosapentaenoic acid and 0.55 g/day of docosahexaenoic acid. Serum cholesterol was found to decrease in fish eaters who also decreased their lipid intake but not in the other groups. Blood triglyceride levels decreased significantly in the fish eating groups, but not in the control group. Levels of apolipoproteins A1 and B were lowered in both fish eating groups as was the formation of t! hromboxane B2 during incubation of whole blood. In the fish eating groups, the proportion of omega-3 fatty acids increased significantly in erythrocyte ghosts and platelets at the expense of omega-6 fatty acids. The results of the study support the contention that moderate fish consumption has a protective effect against coronary heart disease.
Agren, J.J., et al. Boreal freshwater fish diet modifies the plasma lipids and prostanoids and membrane fatty acids in man. LIPIDS, Vol. 23, No.10, October 1988, pp. 924-929