Myocardial membrane fatty acids and the antiarrhythmic actions of dietary fish oil in animal models

Omacor (prescription omega-3-acid ethyl esters 90): From severe rhythm disorders to hypertriglyceridemia

Despite progress made in post-myocardial infarction (MI) revascularization and background therapy for the failing heart, the prevention of adverse cardiac remodeling associated with severe rhythm disorders remains an important drug target. Part of the remodeling can be counteracted by modulating the activity of ion channels and exchangers by omega-3 acids eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). In the GISSI-Prevenzione and GISSI-HF trials, omega-3 fatty acids were administered as ethyl esters (Omacor Solvay Pharmaceuticals) and not as triglycerides present in fish oil. Ethyl esters result in a sustained intestinal absorption of EPA and DHA and require various purification steps during production, thereby minimizing the content of environmental toxins. Also the rather high (38%) DHA content of Omacor should not be ignored since in rats with low dose intake of omega-3 acids, DHA but not EPA inhibited ischemia-induced arrhythmias. In patients on multiple tablets, 840 mg EPA+DHA in one capsule is preferred to increase compliance. It is not justified to refer to Omacor as "n-3 polyunsaturated fatty acid supplementation" or even "fish oil" and, based on controlled clinical trials, there is no evidence that fish oil could be a substitute of Omacor. To avoid further confusion, guidelines should be precise and refer to the medication, eg, as in NICE guideline CG48: "Omega-3-acid ethyl esters treatment licensed for secondary prevention post-MI." The anti-arrhythmogenic action of Omacor should be seen in the context of implantable cardioverter-defibrillator trials (DINAMIT, IRIS) where non-sudden death was increased and total mortality unaltered. However, Omacor administered in the GISSI-HF trial reduced the incidence of severe arrhythmic events and mortality. Also in the GISSI-Prevenzione trial, arrhythmic death and mortality were reduced. At higher dosages (daily, 3-4 g) Omacor exhibits more pronounced cardiovascular benefits and, as a licensed indication, improves hypertriglyceridemia and related lipid parameters.

Fish, mercury, selenium and cardiovascular risk: current evidence and unanswered questions

Controversy has arisen among the public and in the media regarding the health effects of fish intake in adults. Substantial evidence indicates that fish consumption reduces coronary heart disease mortality, the leading cause of death in developed and most developing nations. Conversely, concerns have grown regarding potential effects of exposure to mercury found in some fish. Seafood species are also rich in selenium, an essential trace element that may protect against both cardiovascular disease and toxic effects of mercury. Such protective effects would have direct implications for recommendations regarding optimal selenium intake and for assessing the potential impact of mercury exposure from fish intake in different populations. Because fish consumption appears to have important health benefits in adults, elucidating the relationships between fish intake, mercury and selenium exposure, and health risk is of considerable scientific and public health relevance. The evidence for health effects of fish consumption in adults is reviewed, focusing on the strength and consistency of evidence and relative magnitudes of effects of omega-3 fatty acids, mercury, and selenium. Given the preponderance of evidence, the focus is on cardiovascular effects, but other potential health effects, as well as potential effects of polychlorinated biphenyls and dioxins in fish, are also briefly reviewed. The relevant current unanswered questions and directions of further research are summarized.

omega-3 polyunsaturated fatty acid supplementation for the treatment of heart failure: mechanisms and clinical potential

Heart failure (HF) is a complex clinical syndrome with multiple aetiologies. Current treatment options can slow the progression to HF, but overall the prognosis remains poor. Clinical studies suggest that high dietary intake of the omega-3 polyunsaturated fatty acids (omega-3PUFA) found in fish oils (eicosapentaenoic and docosahexaenoic acids) may lower the incidence of HF, and that supplementation with pharmacological doses prolongs event-free survival in patients with established HF. The mechanisms for these potential benefits are complex and not well defined. It is well established that fish oil supplementation lowers plasma triglyceride levels, and more recent work demonstrates anti-inflammatory effects, including reduced circulating levels of inflammatory cytokines and arachidonic acid-derived eicosanoids, and elevated plasma adiponectin. In animal studies, fish oil favourably alters cardiac mitochondrial function. All of these effects may work to prevent the development and progression of HF. The omega-3PUFA found in plant sources, alpha-linolenic acid, may also be protective in HF; however, the evidence is not as compelling as for fish oil. This review summarizes the evidence related to use of omega-3PUFA supplementation as a potential treatment for HF and discusses possible mechanisms of action. In general, there is growing evidence that supplementation with omega-3PUFA positively impacts established pathophysiological targets in HF and has potential therapeutic utility for HF patients.

Towards establishing dietary reference intakes for eicosapentaenoic and docosahexaenoic acids

There is considerable interest in the impact of (n-3) long-chain PUFA in mitigating the morbidity and mortality caused by chronic diseases. In 2002, the Institute of Medicine concluded that insufficient data were available to define Dietary Reference Intakes (DRI) for eicosapentaenoic acid (EPA) or docosahexaenoic acid (DHA), noting only that EPA and DHA could contribute up to 10% toward meeting the Adequate Intake for alpha-linolenic acid. Since then, substantial new evidence has emerged supporting the need to reassess this recommendation. Therefore, the Technical Committee on Dietary Lipids of the International Life Sciences Institute North America sponsored a workshop on 4-5 June 2008 to consider whether the body of evidence specific to the major chronic diseases in the United States--coronary heart disease (CHD), cancer, and cognitive decline--had evolved sufficiently to justify reconsideration of DRI for EPA+DHA. The workshop participants arrived at these conclusions: 1) consistent evidence from multiple research paradigms demonstrates a clear, inverse relation between EPA+DHA intake and risk of fatal (and possibly nonfatal) CHD, providing evidence that supports a nutritionally achievable DRI for EPA+DHA between 250 and 500 mg/d; 2) because of the demonstrated low conversion from dietary ALA, protective tissue levels of EPA+DHA can be achieved only through direct consumption of these fatty acids; 3) evidence of beneficial effects of EPA+DHA on cognitive decline are emerging but are not yet sufficient to support an intake level different from that needed to achieve CHD risk reduction; 4) EPA+DHA do not appear to reduce risk for cancer; and 5) there is no evidence that intakes of EPA+DHA in these recommended ranges are harmful.

Effect of fish oil on ventricular tachyarrhythmia in three studies in patients with implantable cardioverter defibrillators

AIMS

To determine the effects of omega-3 polyunsaturated fatty acids (omega-3 PUFAs) from fish on the incidence of recurrent ventricular arrhythmia in implantable cardioverter defibrillator (ICD) patients by combining results from published trials.

METHODS AND RESULTS

We searched in the Medline, EMBASE, and Cochrane databases and performed a meta-analysis on all three available trials on fish oil and ventricular arrhythmia. Furthermore, we pooled individual data of two of these randomized, double-blind, placebo-controlled trials (Raitt et al. Fish oil supplementation and risk of ventricular tachycardia and ventricular fibrillation in patients with implantable defibrillators: a randomized controlled trial. JAMA 2005;293:2884-2891 and Brouwer 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). The main outcome was time to first confirmed ventricular fibrillation (VF) or ventricular tachycardia (VT) combined with death for the meta-analysis, and time to first spontaneous confirmed VF or VT for the pooled analysis. The meta-analysis (n = 1148) showed no convincing protective effect of fish oil (RR 0.90; 95% CI 0.67-1.22). The hazard ratio for the subgroup of patients with coronary artery disease at baseline (0.79; 0.60-1.06) tended towards a protective effect. The pooled analysis (n = 722) showed that time to appropriate ICD intervention was similar for fish oil and placebo treatment (log-rank P = 0.79).

CONCLUSION

These findings do not support a protective effect of omega-3 PUFAs from fish oil on cardiac arrhythmia in all patients with an ICD. Current data neither prove nor disprove a beneficial or a detrimental effect for subgroups of patients with specific underlying pathologies.

Effect of fish oil on arrhythmias and mortality: systematic review

OBJECTIVE

To synthesise the literature on the effects of fish oil-docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA)-on mortality and arrhythmias and to explore dose response and formulation effects.

DESIGN

Systematic review and meta-analysis.

DATA SOURCES

Medline, Embase, the Cochrane Library, PubMed, CINAHL, IPA, Web of Science, Scopus, Pascal, Allied and Complementary Medicine, Academic OneFile, ProQuest Dissertations and Theses, Evidence-Based Complementary Medicine, and LILACS. Studies reviewed Randomised controlled trials of fish oil as dietary supplements in humans.

DATA EXTRACTION

The primary outcomes of interest were the arrhythmic end points of appropriate implantable cardiac defibrillator intervention and sudden cardiac death. The secondary outcomes were all cause mortality and death from cardiac causes. Subgroup analyses included the effect of formulations of EPA and DHA on death from cardiac causes and effects of fish oil in patients with coronary artery disease or myocardial infarction.

DATA SYNTHESIS

12 studies totalling 32 779 patients met the inclusion criteria. A neutral effect was reported in three studies (n=1148) for appropriate implantable cardiac defibrillator intervention (odds ratio 0.90, 95% confidence interval 0.55 to 1.46) and in six studies (n=31 111) for sudden cardiac death (0.81, 0.52 to 1.25). 11 studies (n=32 439 and n=32 519) provided data on the effects of fish oil on all cause mortality (0.92, 0.82 to 1.03) and a reduction in deaths from cardiac causes (0.80, 0.69 to 0.92). The dose-response relation for DHA and EPA on reduction in deaths from cardiac causes was not significant.

CONCLUSIONS

Fish oil supplementation was associated with a significant reduction in deaths from cardiac causes but had no effect on arrhythmias or all cause mortality. Evidence to recommend an optimal formulation of EPA or DHA to reduce these outcomes is insufficient. Fish oils are a heterogeneous product, and the optimal formulations for DHA and EPA remain unclear.

Aqueous fish extract increases survival in the mouse model of cytostatic toxicity

Background

Treatment of cancer patients with anthracycline antibiotic doxorubicin (DOX) may be complicated by development of acute and chronic congestive heart failure (CHF), malignant arrhythmias and death. The aim of this study was to test whether an aqueous low molecular weight (LMW) extract from cod muscle decreases acute mortality in the mouse model of acute CHF caused by DOX.

Methods

A LMW fraction (<500 Da) of the aqueous phase of cod light muscle (AOX) was used for treatment of male BALB/c mice (~25 g, n = 70). The animals were divided into four groups, DOX + AOX (n = 20), DOX + saline (NaCl) (n = 30), NaCl + AOX (n = 10) and NaCl only (n = 10). Echocardiography was performed in the separate subgroups (DOX treated n = 6 and controls n = 6) to verify the presence and the grade of acute CHF. The cod extract was delivered by subcutaneously implanted osmotic minipumps over the period of 2 weeks. High-dose injection of DOX was administered to randomly selected animals. The animals received single intraperitoneal injection of DOX (25 mg/kg) and were followed over two weeks for mortality.

Results

Mortality rate was 68% lower (p < 0.05) in the mice treated with the extract. The analyses of cod extract have shown strong antioxidative effect in vitro.

Conclusion

The aqueous LMW cod muscles extract decreases mortality in the mouse model of DOX induced acute CHF. This effect may be mediated by cardioprotection through antioxidative mechanisms.

Fish and n-3 fatty acids for the prevention of fatal coronary heart disease and sudden cardiac death

Large observational studies, randomized clinical trials, and experimental studies have evaluated the effects of fish and n-3 fatty acid consumption on fatal coronary heart disease (CHD) and sudden cardiac death (SCD), clinically defined events that most often share the final common pathway of fatal ventricular arrhythmia. These different study designs, each having complementary strengths and limitations, provide strong concordant evidence that modest consumption of fish or fish oil (1-2 servings/wk of oily fish, or approximately 250 mg/d of EPA+DHA) substantially reduces the risk of CHD death and SCD. Pooled analysis of prospective cohort studies and randomized clinical trials demonstrates the magnitude and dose-response of this effect, with 36% lower risk of CHD death comparing 0 and 250 mg/d of EPA+DHA consumption (P < 0.001), but then little additional benefit with higher intakes. Reductions in risk are even larger in observational studies utilizing tissue biomarkers of n-3 fatty acids that more accurately measure dietary consumption. The concordance of findings from different studies also suggests that effects of fish or fish oil on CHD death and SCD do not vary depending on presence or absence of established CHD. The strength and consistency of the evidence, and the magnitude of this effect are each notable. Because more than one-half of all CHD deaths and two-thirds of SCD occur among individuals without recognized heart disease, modest consumption of fish or fish oil, together with smoking cessation and regular moderate physical activity, should be among the first-line treatments for prevention of CHD death and SCD.

Dietary fish and omega-3 fatty acid consumption and heart rate variability in US adults

BACKGROUND

Fish and omega-3 fatty acid consumption reduce risk of cardiac death, but mechanisms are not well established. Heart rate variability (HRV) predicts cardiac death and reflects specific electrophysiological pathways and influences. We hypothesized that habitual consumption of fish and marine omega-3 fatty acids would be associated with more favorable HRV, elucidating electrophysiological influences and supporting effects on clinical risk.

METHODS AND RESULTS

In a population-based cohort of older US adults, we evaluated cross-sectional associations of usual dietary fish and omega-3 consumption during the prior year and ECG-derived (n=4263) and 24-hour Holter monitor-derived (n=1152) HRV. After multivariable adjustment, consumption of tuna or other broiled/baked fish was associated with specific HRV components, including indices suggesting greater vagal predominance and moderated baroreceptor responses (eg, higher root mean square successive differences of normal-to-normal intervals [P=0.001]; higher normalized high-frequency power [P=0.008]; and lower low-frequency/high-frequency ratio [P=0.03]) and less erratic sinoatrial node firing (eg, lower Poincaré ratio [P=0.02] and higher short-term fractal scaling exponent [P=0.005]) but not measures of circadian fluctuations (eg, 24-hour standard deviation of normal-to-normal intervals). Findings were similar for estimated dietary consumption of marine omega-3 fatty acids. For magnitudes of observed differences in HRV comparing the highest to lowest category of fish intake, differences in relative risk of cardiac death during 10.8 years of follow-up ranged from 1.1% (for difference in standard deviation of normal-to-normal intervals) to 5.9% and 8.4% (for differences in Poincaré ratio and short-term fractal scaling exponent) lower risk.

CONCLUSIONS

Habitual tuna/other fish and marine omega-3 consumption are associated with specific HRV components in older adults, particularly indices of vagal activity, baroreceptor responses, and sinoatrial node function. Cellular mechanisms and implications for clinical risk deserve further investigation.

Contaminants in fish: risk-benefit considerations

Fish provide a healthful source of dietary protein and are high in nutrients such as omega-3 fatty acids. There is evidence of beneficial effects of fish consumption in coronary heart disease, stroke, age-related macular degeneration, and growth and development. Yet, benefits may be offset by the presence of contaminants, such as methylmercury (MeHg), dioxins, polychlorinated biphenyls (PCBs) and several other halogenated persistent organic pollutants. MeHg is a known developmental neurotoxicant, as evidenced by several animal studies and episodes of human intoxication in Japan and Iraq. Fish represent the main source of exposure to MeHg for the general population, and large predatory fish (swordfish, tuna) have the highest levels of MeHg contamination. Provisional tolerable weekly intakes of 0.7 microg kg(-1) to 1.6 microg kg(-1) have been set by regulatory agencies. Concern for contamination of fish with dioxins and dioxin-like PCBs stems from their reported carcinogenicity, immunotoxicity, and reproductive and developmental toxicities. Farmed and wild-caught fish appear to have similar levels of contaminants. Advisories are in place that recommend limited consumption of certain fish in children, pregnant women and women of childbearing age. Careful risk-benefit considerations should foster fish consumption while minimizing exposure to toxic contaminants.

Myocardial function, ischaemia and n-3 polyunsaturated fatty acids: a membrane basis

Long-chain n-3 polyunsaturated fatty acids (PUFAs) are selectively incorporated into cardiac cell membranes from the diet in a dose-related manner. Regular intake can slow the heart rate, reduce myocardial oxygen consumption, and increase coronary reserve. These properties contribute to preconditioning-like effects of resistance to myocardial ischaemic damage and improved post-ischaemic recovery. These effects can be demonstrated in isolated hearts independently of the effects of n-3 PUFAs on neural or blood parameters. The enrichment of myocardial membranes with n-3 PUFA also reduces vulnerability to cardiac arrhythmias, particularly ventricular fibrillation during myocardial ischaemia and reperfusion, and attenuates heart failure and cardiac hypertrophy. n-3 PUFA concentrations can increase from 7% to 15% in the myocardial membranes of rats (mainly in the form of docosahexaenoic acid [22: 6 n-3]) with dietary intakes of only 0.3% fish oil, equivalent to two meals of salmon per week in the human diet. Dietary fish oil produces changes in cardiac function that might contribute to cardiovascular health benefits in humans and does so by modifying cardiac membranes within a dose range achievable in the human diet.

n-3 Fatty acids and cardiovascular disease: actions and molecular mechanisms

Cardiovascular disease and atherosclerosis are a leading cause of morbidity and mortality worldwide. Epidemiological studies and randomized control intervention trials have reported that n-3 fatty acids reduce cardiovascular events. A variety of biologic and molecular effects of n-3 fatty acids can modulate the mechanisms of development and progression of atherosclerosis. These include n-3 fatty acid effects on inflammation, cardiac excitability, platelet function, triglyceride blood levels, blood pressure and the stability of atheroma plaques. The molecular mechanisms are still not fully defined; but might involve changes in membrane fluidity, receptor responses and binding to intracellular receptors regulating gene transcription. Understanding and elucidating these mechanisms is important to development of future strategies for prevention and treatment of cardiovascular disease.

Fish, n-3 fatty acids, and cardiovascular haemodynamics

Consistent evidence indicates that modest consumption of fish or fish oil supplementation lowers the incidence of cardiac death and possibly other cardiovascular events. Precise physiologic mechanisms accounting for such reduced clinical risk are not well understood. Animal-experimental studies, randomized trials, and large observational studies indicate that consumption of fish and marine n-3 polyunsaturated fatty acids (PUFAs) affects cardiac haemodynamics. Independent effects include lowering of systemic vascular resistance (reducing systolic blood pressure by approximately 3-5 mmHg and diastolic blood pressure by approximately 2-3 mmHg); reduction of resting heart rate (by approximately 3 bpm); and improvement of cardiac diastolic filling (by means of potential improvement in both active relaxation and passive compliance). Stroke volume increases, apparently a secondary effect of lower vascular resistance, slower heart rate, and improved filling; direct effects on resting contractility or cardiac output are not evident. These haemodynamic effects could in part account for clinical benefits of fish or fish oil intake, including lower risk of cardiac death and possibly ischaemic stroke, heart failure, cognitive decline, and nonfatal coronary events.

Analysis of long-chain ω-3 fatty acid content in fish-oil supplements

BACKGROUND

Omega-3 polyunsaturated fatty acids (long-chain omega-3 PUFA) have proved to be beneficial in atherosclerosis, arrhythmia and hypertriglyceridemia in several studies, which has led national and international societies to recommend an intake of 1 g/d long-chain omega-3 PUFA for anti-atherosclerotic and antiarrhythmic purposes or 2-4 g/d for a lipid lowering effect. Numerous preparations are marketed for supplementing western diet, which is low in long-chain omega-3 PUFA. Since these preparations vary in their long-chain omega-3 PUFA content, we tested nine commercially available products for their fatty acid composition.

METHODS

Nine commercially available omega-3 fatty acid supplements were analyzed using capillary gas chromatography to determine their fatty acid content.

RESULTS

The nine preparations showed huge differences, up to 63.7 +/- 1.58 mol% (P = 0.002), in their longchain omega-3 fatty acid content. Most of them failed to achieve the daily recommended dose of 1 g, even when administered at the highest dosage according to the manufacturer's recommendations. Eight of the preparations contained either equal or significantly greater amounts of long-chain omega-3 PUFA than denoted by the manufacturer; one preparation did not provide any information. The highest percentage of DHA and EPA was detected in Omacor(95.80 +/- 0.63%) and Percucor (76.8 +/- 7.109%).

CONCLUSION

Administering long-chain omega-3 fatty acid preparations may result in huge differences in terms of the actual amount ingested. It is therefore advisable to use the most standardized and purified products available.

Fish, marine n-3 polyunsaturated fatty acids and coronary heart disease: a minireview with focus on clinical trial data

In this paper, we will briefly deal with the background for the possible effects of long-chain marine n-3 (also called omega-3) polyunsaturated fatty acids (PUFA) in coronary heart disease (CHD) and then focus on findings from clinical trials in humans. We will not deal with effects of alpha-linolenic acid, the non-marine type of n-3 PUFA derived from plant oils.

Dietary fish and n-3 fatty acid intake and cardiac electrocardiographic parameters in humans

OBJECTIVES

We evaluated the association between dietary fish intake and several cardiac electrocardiographic parameters in humans relevant to arrhythmic risk.

BACKGROUND

Fish consumption may reduce the incidence of sudden death and atrial fibrillation, possibly related to anti-arrhythmic effects.

METHODS

In a population-based study of 5,096 men and women, we evaluated cross-sectional associations between usual dietary fish intake and electrocardiographic measures of heart rate, atrioventricular conduction (PR interval), ventricular repolarization (QT interval), and ventricular conduction (QRS interval). Multivariate models were adjusted for age, gender, race, education, smoking, body mass index, diabetes, coronary heart disease, physical activity, and intakes of beef or pork, fried fish, fruits, vegetables, alcohol, and total calories.

RESULTS

Consumption of tuna or other broiled or baked fish (comparing the highest to the lowest category of intake) was associated with lower heart rate (-3.2 beats/min, 95% confidence interval [CI] = 1.3 to 5.1; p trend <0.001), slower atrioventricular conduction (PR interval +7.2 ms, 95% CI = 1.4 to 12.9; p trend = 0.03), and substantially lower likelihood of prolonged QT (relative risk = 0.50, 95% CI = 0.27 to 0.95; p trend = 0.03). Tuna/other fish intake was not associated with ventricular conduction (p = 0.60). Findings were similar for estimated intake of marine n-3 fatty acids: a 1 g/day higher intake was associated with 2.3 beats/min lower heart rate (95% CI = 0.9 to 3.7), 7.6 ms longer PR interval (95% CI = 3.3 to 11.9), and 46% lower likelihood of prolonged QT (relative risk = 0.54, 95% CI = 0.33 to 0.88).

CONCLUSIONS

These findings in this large, population-based study suggest that dietary fish intake is associated with cardiac electrophysiology in humans, including heart rate, atrioventricular conduction, and ventricular repolarization, with potential implications for arrhythmic risk.

n−3 Fatty acids, cardiac arrhythmia and fatal coronary heart disease

n-3 Polyunsaturated fatty acids (n-3 PUFA) are suggested to prevent cardiac death via inhibition of cardiac arrhythmia. In this review we discuss the results of human studies on intake of n-3 PUFAs and heart disease and, more specifically, on cardiac arrhythmia. Observational studies indicate that intake of fish is associated with a lower incidence of fatal coronary heart disease in several populations. These studies are fairly consistent, but people that have a high intake of fatty fish might have a healthier lifestyle in general, and such confounding is difficult to remove completely with statistical adjustments and corrections. Evidence from trials is less clear. In two open label trials in patients with a previous myocardial infarction intake of fish or fish oil prevented fatal coronary heart disease. In contrast, a trial in patients with angina suggested a higher risk of sudden cardiac death in patients taking fish oil. Furthermore, results of trials in patients with an implantable cardioverter defibrillator (ICD) that investigated effects of fish oil on arrhythmia in patients already suffering from ventricular tachycardia are not consistent. Also, studies on relationships between intake of n-3 PUFA from fish and less life-threatening forms of arrhythmia, such as atrial fibrillation and premature ventricular complexes (PVCs) are equivocal. Thus, after 35 years of research the question whether fish prevents heart disease remains unanswered, and an anti-arrhythmic effect of fish oil remains unproven although the idea is still viable and is being actively tested in further trials.

Peroxisome proliferator-activated receptor alpha agonist, clofibrate, has profound influence on myocardial fatty acid composition

The hypolipidemic fibrates have been identified as agonists of the peroxisome proliferator-activated receptor alpha (PPARalpha), which plays a critical role in the regulation of cardiac fatty acid metabolism. Despite the widespread clinical use of fibrates, their role in myocardial oxidative stress and fatty acid composition is less known. In this study, male Sprague-Dawley rats were treated with either vehicle (olive oil, 1 ml/kg) or clofibrate (300 mg/kgday i.p.) for 1-14 days. Lipid peroxidation in heart homogenate was determined by thiobarbituric acid reactive substance (TBARS) assay. Results show that hearts from clofibrate-treated rats are more susceptible to FeSO(4)-induced TBARS production. The antioxidants including catalase and glutathione-related enzymes were marginally affected. We demonstrated that myocardial fatty acid composition was dramatically altered by clofibrate treatment. In hearts from clofibrate-treated rats, the principal n-6 polyunsaturated fatty acids (PUFAs), linoleic acid (C18:2 n-6) and arachidonic acid (C20:4 n-6), was significantly reduced, while the content of the principal n-3 PUFA, docosahexaenoic acid (C22:6 n-3), was markedly increased. The overall effect was to reduce n-6/n-3 ratio and increase the unsaturation extent of myocardial fatty acids. Functional study showed that hearts from clofibrate-treated rats had an improved recovery of post-ischemic contractile function and reduced ischemia/reperfusion (I/R)-induced infarct size. The data shows that clofibrate has a profound impact on cardiac fatty acid composition, which may contribute to its cardioprotective effect.

Membrane basis for fish oil effects on the heart: linking natural hibernators to prevention of human sudden cardiac death

The concept that diet-induced changes in membrane lipids could modify heart function partly arose from observations that membrane composition and physical properties were closely associated with the capacity of the heart to respond appropriately to torpor and hibernation. Observations of natural hibernators further revealed that behavior of key membrane-bound enzymes could be influenced through the lipid composition of the cell membrane, either by changing the surrounding fatty acids through reconstitution into a foreign lipid milieu of different composition, or by alteration through diet. Myocardial responsiveness to beta-adrenoceptor stimulation, including initiation of spontaneous dysrhythmic contractions, was altered by both hibernation and dietary modulation of membrane fatty acids, suggesting modified vulnerability to cardiac arrhythmia. Subsequent studies using whole-animal models recognized that vulnerability to ventricular fibrillation decreased as the polyunsaturated: saturated fat (P:S) ratio of the diet increased. However, dietary fish oils, which typically contain at least 30% saturated fatty acids and only 30% long-chain n-3 (omega-3) polyunsaturated fatty acids (PUFA), exhibit antiarrhythmic effects that exceed the predicted influence of the P:S ratio, suggesting properties unique to the long-chain n-3 PUFA. Large-scale clinical trials and epidemiology have confirmed the arrhythmia prevention observed in vitro in myocytes, papillary muscles, and isolated hearts and in whole-animal models of sudden cardiac death. Some progress has been made towards a biologically plausible mechanism. These developments highlight nature's ability to provide guidance for the most unexpected applications.

Intake of tuna or other broiled or baked fish versus fried fish and cardiac structure, function, and hemodynamics

Fish intake is associated with improved cardiovascular health, including a lower risk of arrhythmic death, atrial fibrillation, and heart failure. However, the physiologic effects that may produce these cardiovascular benefits are not well-established. We investigated the cross-sectional associations between a usual dietary intake of fish during the previous year and cardiac structure, function, and hemodynamics as determined by physical examination and 2-dimensional, Doppler, and M-mode transthoracic echocardiography among 5,073 older adults enrolled in the Cardiovascular Health Study. On multivariate-adjusted analyses, consumption of tuna or other broiled or baked fish was associated with a lower heart rate (p < 0.001), lower systemic vascular resistance (p = 0.002), and greater stroke volume (p < 0.001). Tuna/other fish intake was also associated with a higher E/A ratio (p = 0.004), a measure of more normal diastolic function. In contrast, fried fish or fish sandwich (fish burger) intake was associated with left ventricular wall motion abnormalities (p = 0.02), a reduced ejection fraction (p < 0.001), lower cardiac output (p = 0.04), a trend toward a larger left ventricular diastolic dimension (p = 0.07), and higher systemic vascular resistance (p = 0.003). In conclusion, in this large population-based study, the intake of tuna or other broiled or baked fish was associated with improved cardiac hemodynamics, but fried fish intake was associated with structural abnormalities indicative of systolic dysfunction and potential coronary atherosclerosis. These findings suggest potential specific physiologic mechanisms that may, in part, account for the effects of fish intake on cardiovascular health.

A systematic review and meta-analysis of the impact of omega-3 fatty acids on selected arrhythmia outcomes in animal models

Epidemiological studies and clinical trials report the beneficial effects of fish or fish oil consumption on cardiovascular disease outcomes including sudden death. We performed a systematic review of the literature on controlled animal studies that assessed the effects of omega-3 fatty acids on selected arrhythmia outcomes. On the basis of predetermined criteria, 27 relevant animal studies were identified; 23 of these were feeding studies, and 4 were infusion studies. Across species, fish oil, eicosapentaenoic acid, and/or docosahexaenoic acid appear to have beneficial effects on ventricular tachycardia (VT) and fibrillation (VF) in ischemia- but not reperfusion-induced arrhythmia models; no effect on the incidence of death and infarct size; and inconsistent results with regard to arrhythmia score, VF threshold, ventricular premature beats or length of time in normal sinus rhythm, compared to omega-6, monounsaturated, or saturated fatty acids, and no treatment controls. In a meta-analysis of 13 studies using rat models, fish oil but not alpha-linolenic acid supplementation showed a significant protective effect for ischemia- and reperfusion-induced arrhythmias by reducing the incidence of VT and VF. It is not known whether omega-3 fatty-acid supplementation has antiarrhythmic effects in other disease settings not related to ischemia.

Effects of dietary fats versus carbohydrates on coronary heart disease: A review of the evidence

Recommendations arising from the traditional diet-coronary heart disease (CHD) paradigm, which focuses on effects of total and saturated fat on serum total and low-density lipoprotein cholesterol, may have failed to reduce CHD risk and inadvertently exacerbated dyslipidemia, insulin resistance, and weight gain, particularly among individuals who are older, female, sedentary, or obese. A suitable dietary paradigm must consider types and qualities of fats and carbohydrates consumed, their effects on a range of intermediary risk factors, and characteristics that may modify individual susceptibility. Based on current evidence, replacement of total, unsaturated, and even possibly saturated fats with refined, high-glycemic index carbohydrates is unlikely to reduce CHD risk and may increase risk in persons predisposed to insulin resistance. In contrast, a diet that is 1) rich in whole grains and other minimally processed carbohydrates; 2) includes moderate amounts of fats (approximately 30%-40% of total energy), particularly unsaturated fats and omega-3 polyunsaturated fats from seafood and plant sources; 3) is lower in refined grains and carbohydrates; and 4) eliminates packaged foods, baked goods, and fast foods containing trans fatty acids, will likely reduce the risk of CHD.

Paradoxical effect of n−3-containing vegetable oils on long-chain n−3 fatty acids in rat heart

Flaxseed, echium, and canola oils contain alpha-linolenic acid (18:3n-3, ALA) in a range of concentrations. To examine their effect on elevating cardiac levels of long-chain n-3 FA, diets based on these n-3-containing vegetable oils were fed to rats for 4 wk. Sunflower oil, which contains little ALA, was a comparator. Despite canola oil having the lowest ALA content of the three n-3-containing vegetable oils, it was the most potent for elevating DHA (22:6n-3) levels in rat hearts and plasma. However, the relative potencies of the dietary oils for elevation of EPA (20:5n-3) in heart and plasma followed the same rank order as their ALA content, i.e., flaxseed > echium > canola > sunflower oil. This paradox may be explained by lower ALA intake leading to decreased competition for Delta6 desaturase activity between ALA and the 24:5n-3 FA precursor to DHA formation.

Effect of Fish Oil on Heart Rate in Humans

Background— The effect of fish oil on heart rate (HR), a major risk factor for sudden death, is not well established. We calculated this effect in a meta-analysis of randomized, double-blind, placebo-controlled trials in humans.

Methods and Results— Randomized trials of fish oil that evaluated HR were identified through MEDLINE (1966 through January 2005), hand-searching of references, and contact with investigators for unpublished results. Two investigators independently extracted trial data. A pooled estimate was calculated from random-effects meta-analysis. Predefined stratified meta-analyses and meta-regression were used to explore potential heterogeneity. Of 197 identified articles, 30 met inclusion criteria. Evidence for publication bias was not present. In the overall pooled estimate, fish oil decreased HR by 1.6 bpm (95% CI, 0.6 to 2.5; P =0.002) compared with placebo. Between-trial heterogeneity was evident (Q test, P <0.001). Fish oil reduced HR by 2.5 bpm ( P <0.001) in trials with baseline HR ≥69 bpm (median) but had little effect (0.04-bpm reduction; P =0.56) in trials with baseline HR <69 bpm ( P for interaction=0.03). Fish oil reduced HR by 2.5 bpm ( P <0.001) in trials with duration ≥12 weeks but had less effect (0.7-bpm reduction; P =0.27) in trials with duration <12 weeks ( P for interaction=0.07). HR reduction with fish oil intake did not significantly vary by fish oil dose (range, 0.81 to 15 g/d), type of HR measure, population age, population health, parallel versus crossover design, type of control oil, or study quality by Delphi criteria ( P for interaction >0.25 for each).

Conclusions— In randomized controlled trials in humans, fish oil reduces HR, particularly in those with higher baseline HR or longer treatment duration. These findings provide firm evidence that fish oil consumption directly or indirectly affects cardiac electrophysiology in humans. Potential mechanisms such as effects on the sinus node, ventricular efficiency, or autonomic function deserve further investigation.

N-3 Fatty acids for the prevention of atrial fibrillation after coronary artery bypass surgery: a randomized, controlled trial

OBJECTIVES

The aim of this study was to assess the efficacy of preoperative and postoperative treatment with n-3 polyunsaturated fatty acids (PUFAs) in preventing the occurrence of atrial fibrillation (AF) after coronary artery bypass graft surgery (CABG).

BACKGROUND

Postoperative AF is a common complication of CABG. There is growing clinical evidence that PUFAs have cardiac antiarrhythmic effects.

METHODS

A total of 160 patients were prospectively randomized to a control group (81 patients, 13 female, 64.9 +/- 9.1 years) or PUFAs 2 g/day (79 patients, 11 female, 66.2 +/- 8.0 years) for at least 5 days before elective CABG and until the day of discharge from the hospital. The primary end point was the development of AF in the postoperative period. The secondary end point was the hospital length of stay after surgery. All end points were independently adjudicated by two cardiologists blinded to treatment assignment.

RESULTS

The clinical and surgical characteristics of the patients in the two groups were similar. Postoperative AF developed in 27 patients of the control group (33.3%) and in 12 patients of the PUFA group (15.2%) (p = 0.013). There was no significant difference in the incidence of nonfatal postoperative complications, and postoperative mortality was similar in the PUFA-treated patients (1.3%) versus controls (2.5%). After CABG, the PUFA patients were hospitalized for significantly fewer days than controls (7.3 +/- 2.1 days vs. 8.2 +/- 2.6 days, p = 0.017).

CONCLUSIONS

This study first demonstrates that PUFA administration during hospitalization in patients undergoing CABG substantially reduced the incidence of postoperative AF (54.4%) and was associated with a shorter hospital stay.

Interplay between different polyunsaturated fatty acids and risk of coronary heart disease in men

BACKGROUND

Consumption of polyunsaturated fatty acids (PUFAs) may reduce coronary heart disease (CHD) risk, but n-6 PUFAs may compete with n-3 PUFA metabolism and attenuate benefits. Additionally, seafood-based, long-chain n-3 PUFAs may modify the effects of plant-based, intermediate-chain n-3 PUFAs. However, the interactions of these PUFAs in relation to CHD risk are not well established.

METHODS AND RESULTS

Among 45,722 men free of known cardiovascular disease in 1986, usual dietary intake was assessed at baseline and every 4 years by using validated food-frequency questionnaires. CHD incidence was prospectively ascertained. Over 14 years of follow-up, participants experienced 218 sudden deaths, 1521 nonfatal myocardial infarctions (MIs), and 2306 total CHD events (combined sudden death, other CHD deaths, and nonfatal MI). In multivariate-adjusted analyses, both long-chain and intermediate-chain n-3 PUFA intakes were associated with lower CHD risk, without modification by n-6 PUFA intake. For example, men with > or = median long-chain n-3 PUFA intake (> or =250 mg/d) had a reduced risk of sudden death whether n-6 PUFA intake was below (<11.2 g/d; hazard ratio [HR]=0.52; 95% confidence interval [CI]=0.34 to 0.79) or above (> or =11.2 g/d; HR=0.60; 95% CI=0.39 to 0.93) the median compared with men with a < median intake of both. In similar analyses, > or = median intake of intermediate-chain n-3 PUFAs (> or =1080 mg/d) was associated with a reduced total CHD risk whether n-6 PUFA intake was lower (HR=0.88; 95% CI=0.78 to 0.99) or higher (HR=0.89; 95% CI=0.79 to 0.99) compared with a < median intake of both. Intermediate-chain n-3 PUFAs were particularly associated with CHD risk when long-chain n-3 PUFA intake was very low (<100 mg/d); among these men, each 1 g/d of intermediate-chain n-3 PUFA intake was associated with an approximately 50% lower risk of nonfatal MI (HR=0.42; 95% CI=0.23 to 0.75) and total CHD (HR=0.53; 95% CI=0.34 to 0.83).

CONCLUSIONS

n-3 PUFAs from both seafood and plant sources may reduce CHD risk, with little apparent influence from background n-6 PUFA intake. Plant-based n-3 PUFAs may particularly reduce CHD risk when seafood-based n-3 PUFA intake is low, which has implications for populations with low consumption or availability of fatty fish.

Marine n-3 polyunsaturated fatty acids and coronary heart disease

In this paper, we will give an overview of the background for the possible effects of long-chain marine n-3 (synonymously called omega-3) polyunsaturated fatty acids (PUFA) in coronary heart disease (CHD) with focus on recent findings. In a forthcoming paper, we will focus on the clinical trial data, current recommendations and suggest trials to further study the role of marine n-3 PUFA in the prevention and treatment of CHD.

Omega-3 (n-3) Fatty Acids in Health and Disease: Part 1—Cardiovascular Disease and Cancer

The omega-3 (n-3) polyunsaturated fatty acids have a wide range of beneficial effects in several human health conditions. Animal and in vitro studies have indicated that omega-3 fatty acids affect blood lipid profiles, cardiovascular health, membrane lipid composition, eicosanoid biosynthesis, cell signaling cascades, and gene expression. Findings from epidemiological studies suggest that intake of omega-3 fatty acids from natural sources or supplements may influence the onset and progression of several disease states, including cardiovascular disease and cancer. This review highlights some recent research findings that help advance our understanding of how omega-3 fatty acids influence cardiovascular disease and cancer.

Lifestyles of older adults: can we influence cardiovascular risk in older adults?

Influences of lifestyle habits on cardiovascular disease risk among older adults are not well established. The authors present evidence from the Cardiovascular Health Study that dietary, physical activity, and smoking habits assessed late in life are associated with cardiovascular disease risk among adults aged 65 years or older. Persons consuming fatty fish twice per week had a 47% lower risk of coronary death compared with those who consumed fatty fish less than once per month, while cereal fiber intake (about two whole-grain bread slices per day) was associated with a 14% lower risk of myocardial infarction or stroke. Modest alcohol intake (1-6 drinks per week) predicted the fewest subclinical cerebrovascular abnormalities. Compared with little activity, moderate and high leisure-time activity predicted 28% and 44% lower mortality, respectively, while compared with nonexercisers, low, moderate, and high exercise intensity predicted 30%, 37%, and 53% more years of healthy life, respectively. Former and current smokers had 25% and 44% fewer years of healthy life than those who never smoked; lifetime smoking (pack-years) predicted higher mortality. Clinical practice and public health implications, gaps in knowledge, and future research directions are summarized.

Effects of dietary fat intake in sudden death: Reduction of death with omega-3 fatty acids

Sudden death is one of the most common modes of death in those who survive a myocardial infarction. A recent study of 11,324 patients showed a marked decrease in risk of sudden cardiac death as well as a reduction in all-cause mortality in the post-myocardial infarction group taking a highly purified form of omega-3 fatty acids, added to the use of other secondary prevention drugs, including b-blockers and lipid-lowering therapy. There is now amounting evidence indicating that the clinical benefits of highly purified omega-3 fatty acids may be attributed to their anti-arrhythmogenic properties. Evidence for this mechanism of benefit is reviewed here.

Fish intake and risk of incident atrial fibrillation

BACKGROUND

Atrial fibrillation (AF) is the most common arrhythmia in clinical practice and is particularly common in the elderly. Although effects of fish intake, including potential antiarrhythmic effects, may favorably influence risk of AF, relationships between fish intake and AF incidence have not been evaluated.

METHODS AND RESULTS

In a prospective, population-based cohort of 4815 adults > or =age 65 years, usual dietary intake was assessed at baseline in 1989 and 1990. Consumption of tuna and other broiled or baked fish correlated with plasma phospholipid long-chain n-3 fatty acids, whereas consumption of fried fish or fish sandwiches (fish burgers) did not. AF incidence was prospectively ascertained on the basis of hospital discharge records and annual electrocardiograms. During 12 years' follow-up, 980 cases of incident AF were diagnosed. In multivariate analyses, consumption of tuna or other broiled or baked fish was inversely associated with incidence of AF, with 28% lower risk with intake 1 to 4 times per week (HR=0.72, 95% CI=0.58 to 0.91, P=0.005), and 31% lower risk with intake > or =5 times per week (HR=0.69, 95% CI=0.52 to 0.91, P=0.008), compared with <1 time per month (P trend=0.004). Results were not materially different after adjustment for preceding myocardial infarction or congestive heart failure. In similar analyses, fried fish/fish sandwich consumption was not associated with lower risk of AF.

CONCLUSIONS

Among elderly adults, consumption of tuna or other broiled or baked fish, but not fried fish or fish sandwiches, is associated with lower incidence of AF. Fish intake may influence risk of this common cardiac arrhythmia.

Alpha-linolenic acid and the risk of prostate cancer. What is the evidence?

PURPOSE

Several studies have examined the association between polyunsaturated fatty acids and prostate cancer risk. We evaluated the evidence on the association between the essential polyunsaturated fatty acid, known as alpha-linolenic acid, and the risk of prostate cancer in humans.

MATERIALS AND METHODS

We comprehensively reviewed published studies on the association between alpha-linolenic acid and the risk of prostate cancer using MEDLINE.

RESULTS

A number of studies have shown a positive association between dietary, plasma or red blood cell levels of alpha-linolenic acid and prostate cancer. Other studies have demonstrated either no association or a negative association. The limitations of these studies include the assumption that dietary or plasma alpha-linolenic acid levels are positively associated with prostate tissue alpha-linolenic acid levels, and measurement errors of dietary, plasma and red blood cell alpha-linolenic acid levels.

CONCLUSIONS

More research is needed in this area before it can be concluded that there is an association between alpha-linolenic acid and prostate cancer.

The role of fish oil/omega-3 fatty acids in the treatment of IgA nephropathy

Beneficial effects of omega-3 polyunsaturated fatty acids (n-3 PUFA) have been reported in recent epidemiologic studies and randomized clinical trials in a variety of cardiovascular and autoimmune diseases. Fish and marine oils are the most abundant and convenient sources of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), the two major n-3 fatty acids that serve as substrates for cyclooxygenase and lipoxygenase pathways leading to less potent inflammatory mediators than those produced through the n-6 PUFA substrate, arachidonic acid. N-3 PUFA can also suppress inflammatory and/or immunologic responses through eicosanoid-independent mechanisms. Although the pathophysiology of IgA nephropathy is incompletely understood, it is likely that n-3 PUFA prevents renal disease progression by interfering with a number of effector pathways triggered by mesangial immune-complex deposition. In addition, potential targets of n-3 PUFA relevant to renal disease progression could be similar to those involved in preventing the development and progression of cardiovascular disease by lowering blood pressure, reducing serum lipid levels, decreasing vascular resistance, or preventing thrombosis. In IgA nephropathy, efficacy of n-3 PUFA contained in fish oil supplements has been tested with varying results. The largest randomized clinical trial performed by our collaborative group provided strong evidence that treatment for 2 years with a daily dose of 1.8 g of EPA and 1.2 g of DHA slowed the progression of renal disease in high-risk patients. These benefits persisted after 6.4 years of follow up. With safety, composition, and dosing convenience in mind, we can recommend two products that are available as pharmaceutical-grade fish-oil concentrates, Omacor (Pronova Biocare, Oslo, Norway) and Coromega (European Reference Botanical Laboratories, Carlsbad, CA).

Differential eicosapentaenoic acid elevations and altered cardiovascular disease risk factor responses after supplementation with docosahexaenoic acid in postmenopausal women receiving and not receiving hormone replacement therapy

BACKGROUND

Dietary docosahexaenoic acid (DHA) has triacylglycerol-lowering potential and undergoes in vivo retroconversion to eicosapentaenoic acid (EPA) in humans. Hormone replacement therapy (HRT) influences circulating lipid concentrations and fatty acid metabolism. DHA supplementation has not been studied in postmenopausal women.

OBJECTIVE

We studied the effects of supplementation with DHA (free of EPA) on the resulting elevation in EPA and on selected cardiovascular disease risk factors in postmenopausal women.

DESIGN

Women receiving (n = 18) and not receiving (n = 14) HRT completed a randomized, double-blind, placebo-controlled crossover trial with a DHA supplement (2.8 g DHA/d). A washout period of > or =6 wk divided the two 28-d intervention periods. Fasting blood samples were collected for analysis.

RESULTS

In all women, DHA supplementation was associated with significant changes (P < 0.05), including 20% lower serum triacylglycerol concentrations, 8% higher HDL-cholesterol concentrations, a 28% lower overall ratio of serum triacylglycerol to HDL cholesterol, and a 7% decrease in resting heart rate. DHA supplementation resulted in a 45% lower net increase (P = 0.02) in EPA and a 42% lower (P = 0.0028) estimated percentage retroconversion of DHA to EPA [DeltaEPA/(DeltaEPA + DeltaDHA) x 100] in women receiving than in those not receiving HRT.

CONCLUSION

With DHA supplementation, the accumulation of EPA in serum phospholipids is significantly attenuated in postmenopausal women receiving HRT compared with that in women not receiving HRT. DHA supplementation can also favorably influence selected cardiovascular disease risk factors in postmenopausal women.

Antiarrhythmic effects of n-3 fatty acids: evidence from human studies

PURPOSE OF REVIEW

N-3 fatty acids from fish reduce cardiovascular mortality including sudden cardiac death. In this paper, the authors discuss the results of human studies with regard to the hypothesis that n-3 fatty acids reduce the risk of fatal coronary heart disease through antiarrhythmic effects.

RECENT FINDINGS

Results from two recent clinical trials do not support a protective effect of n-3 fatty acids. In light of the earlier published bulk of evidence that n-3 fatty acids reduce cardiovascular mortality and sudden cardiac death, it is hard to explain these findings. Two recent observational studies confirmed that intake of n-3 fatty acids from fish is associated with less cardiovascular disease in the general population. They indicated that the protective effect of a fish meal may depend on the n-3 fatty acid content or preparation method and suggested a protective effect on arrhythmia rather than on atherosclerosis. Intervention studies on electrophysiological predictors of arrhythmia do not clearly confirm a beneficial effect of n-3 fatty acids. However, most of these studies were small or performed in healthy populations.

SUMMARY

The available evidence still suggests that n-3 fatty acids may prevent fatal cardiac arrhythmia, but more conclusive studies are urgently needed.

Effect of altered dietary n-3 fatty acid intake upon plasma lipid fatty acid composition, conversion of [13C]alpha-linolenic acid to longer-chain fatty acids and partitioning towards beta-oxidation in older men

The effect of increased dietary intakes of alpha-linolenic acid (ALNA) or eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) for 2 months upon plasma lipid composition and capacity for conversion of ALNA to longer-chain metabolites was investigated in healthy men (52 (SD 12) years). After a 4-week baseline period when the subjects substituted a control spread, a test meal containing [U-(13)C]ALNA (700 mg) was consumed to measure conversion to EPA, docosapentaenoic acid (DPA) and DHA over 48 h. Subjects were then randomised to one of three groups for 8 weeks before repeating the tracer study: (1) continued on same intake (control, n 5); (2) increased ALNA intake (10 g/d, n 4); (3) increased EPA+DHA intake (1.5 g/d, n 5). At baseline, apparent fractional conversion of labelled ALNA was: EPA 2.80, DPA 1.20 and DHA 0.04 %. After 8 weeks on the control diet, plasma lipid composition and [(13)C]ALNA conversion remained unchanged compared with baseline. The high-ALNA diet resulted in raised plasma triacylglycerol-EPA and -DPA concentrations and phosphatidylcholine-EPA concentration, whilst [(13)C]ALNA conversion was similar to baseline. The high-(EPA+DHA) diet raised plasma phosphatidylcholine-EPA and -DHA concentrations, decreased [(13)C]ALNA conversion to EPA (2-fold) and DPA (4-fold), whilst [(13)C]ALNA conversion to DHA was unchanged. The dietary interventions did not alter partitioning of ALNA towards beta-oxidation. The present results indicate ALNA conversion was down-regulated by increased product (EPA+DHA) availability, but was not up-regulated by increased substrate (ALNA) consumption. This suggests regulation of ALNA conversion may limit the influence of variations in dietary n-3 fatty acid intake on plasma lipid compositions.

The role of omega-3 fatty acids in the secondary prevention of cardiovascular disease

It has long been recognized from epidemiological studies that Greenland Eskimos have substantially reduced rates of acute myocardial infarction (MI) compared with Western controls. From these epidemiological observations, the benefits of fatty fish consumption have been explored in cell culture and animal studies, as well as randomized controlled trials investigating the cardioprotective effects of omega-3 fatty acids. Dietary omega-3 fatty acids seem to stabilize the myocardium electrically, resulting in reduced susceptibility to ventricular arrhythmias, thereby reducing the risk of sudden death. These fatty acids also have potent anti-inflammatory effects, and may also be antithrombotic and anti-atherogenic. Furthermore, the recent GISSI-Prevention study of 11 324 patients showed a marked decrease in risk of sudden cardiac death as well as a reduction in all-cause mortality in the group taking a highly purified form of omega-3 fatty acids, despite the use of other secondary prevention drugs, including beta-blockers and lipid-lowering therapy. The use of omega-3 fatty acids should be considered as part of a comprehensive secondary prevention strategy post-myocardial infarction.

Cardiac benefits of fish consumption may depend on the type of fish meal consumed: the Cardiovascular Health Study

BACKGROUND

Few studies have examined associations of fish consumption with ischemic heart disease (IHD) risk among older adults or how different types of fish meals relate to IHD risk.

METHODS AND RESULTS

In a population-based prospective cohort study, usual fish consumption was ascertained at baseline among 3910 adults aged > or =65 years and free of known cardiovascular disease in 1989 and 1990. Consumption of tuna and other broiled or baked fish correlated with plasma phospholipid long-chain n-3 fatty acids, whereas consumption of fried fish or fish sandwiches (fish burgers) did not. Over 9.3 years' mean follow-up, there were 247 IHD deaths (including 148 arrhythmic deaths) and 363 incident nonfatal myocardial infarctions (MIs). After adjustment for potential confounders, consumption of tuna or other broiled or baked fish was associated with lower risk of total IHD death (P for trend=0.001) and arrhythmic IHD death (P=0.001) but not nonfatal MI (P=0.44), with 49% lower risk of total IHD death and 58% lower risk of arrhythmic IHD death among persons consuming tuna/other fish 3 or more times per week compared with less than once per month. In similar analyses, fried fish/fish sandwich consumption was not associated with lower risk of total IHD death, arrhythmic IHD death, or nonfatal MI but rather with trends toward higher risk.

CONCLUSIONS

Among adults aged > or =65 years, modest consumption of tuna or other broiled or baked fish, but not fried fish or fish sandwiches, is associated with lower risk of IHD death, especially arrhythmic IHD death. Cardiac benefits of fish consumption may vary depending on the type of fish meal consumed.

The role of omega-3 fatty acids in cardiovascular disease

Plant-derived alpha-linolenic acid has been studied in a limited number of investigations. So far, some epidemiologic and a few mechanistic studies suggest a potential of protection from cardiovascular disease, but this potential remains to be proven in intervention studies. In contrast, eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), which are prevalent in fish and fish oils, have been studied in thousands of investigations. A consistent body of evidence has been elaborated in various types of investigations, ultimately demonstrating reduction in total mortality, cardiovascular mortality, and morbidity by ingestion of roughly 1 g/d of EPA plus DHA. Current guidelines, however, do not discern between the omega-3 fatty acids mentioned; in fact, most even do not differentiate polyunsaturated fatty acids at all. Unfortunately, this complicates efficient implementation of an effective means of prophylaxis of atherosclerosis.