Cardiovascular diseases have become a public health concern and are among the diseases for which the most spectacular progress has been achieved in recent years. Of course, this progress involves improvements in the care of myocardial infarction and its new therapies, but also active prevention of the various risk factors, as well as the progressive accumulation of proof of the benefits of an appropriate diet.
According to the WHO, 30% of cardiovascular diseases would be prevented by a good diet.
The very low incidence of cardiovascular diseases among Eskimo populations in Greenland (10 to 30% lower than Denmark) has been attributed to their diet rich in omega-3 and is the starting point for research conducted on long-chain omega-3 fatty acids (Kromann N et al, 1980 ; Bjerregaard P et al, 1988).
Several epidemiological studies have associated the regular consumption of fish with a halving of the mortality rate from cardiovascular diseases (Kromhout D et al, 1985 ; Siscovick D et al, 1995).
These studies have thus highlighted a protective effect of omega-3s in reducing cardiovascular morbidity-mortality without necessarily reducing cholesterolemia. The cardioprotective effect has been confirmed in various controlled intervention studies (clinical studies) described below.
Two primary prevention studies (the Physician's Health Study and the MRFIT study) respectively showed that subjects with a higher serum concentration of omega-3 benefit from an 81% reduction in the risk of sudden death, and that consumption of more than 0.7 g of omega-3 per day permits a 40% reduction in the heart attack risk (Albert CM et al, 2002 ; Dolecek TA et al, 1991).
A secondary prevention study (the GISSI study on survivors of a first cardiovascular accident) conducted in Italy on more than 11,000 subjects showed that, in infarct survivors, supplementation with omega-3 associated with a Mediterranean diet led to a 23% reduction in the risk of sudden death over a period of 3.5 years. The GISSI study thus confirms the results of the DART trial conducted on more than 2,000 men which showed that fish eaters had a 29% lower mortality risk compared to non-fish eaters (GISSI Prevention, 1999 ; Burr et al, 1989).
All of these studies suggest that long-chain omega-3s, due to their metabolism, have a preventive action on certain risk factors involved in cardiovascular diseases.
Coagulation and platelet aggregation
The long-chain omega-3s (EPA, DHA) inhibit platelet aggregation and promote blood vessel dilation. They have an antihemostatic and antithrombotic action. Any substance modulating the platelet function has an important influence on the severity of a myocardial infarction. These antithrombotic and antihemostatic properties of omega-3s remain within a physiological limit and do not lead to an increase haemorrhage risk at daily doses of between 1 and 3.5 g of DHA and EPA (von Schacky, Fischer et al.; von Schacky and Weber 1985; Gerster 1995).
Arterial hypertension represents one of the principal risk factors for cardiovascular disease. The long-chain omega-3s have a hypotensive effect in patients suffering from hypertension. (Knapp et al, 1989; Morris, Sacks et al. 1993). The hypotensive effect of omega-3s is correlated with the plasma composition of phospholipids rich in long-chain omega-3s.
An elevated plasma triglyceride level is now recognized as a cardiovascular risk factor (Stampfer, Kraus et al. 1996; Miller, Seidler et al, 1998). All nutritional factors capable of regulating high plasma concentrations of triglycerides are therefore potentially interesting from a cardiovascular prevention viewpoint. Long-chain omega-3s reduce the level of plasma triglycerides (Nenseter, Rustan et al. 1991; Lu, Windsor et al. 1999) both in normal subjects and those suffering from hyperlipidemia.
All of these effects were observed for omega-3 doses of between 1 and 7 g per day.
Cardiac rhythm disorders are characterized by an irregular electrical activity of the myocardium. They are potentially fatal and are often a cause of sudden death.
The incidence of death by cardiac arrest is lower in subjects whose cardiac cell membranes contain a higher level of long-chain omega-3s (Siscovick, Raghunathan et al. 1995).
Studies have shown that ventricular arrhythmias decrease from 2.4 g per day of omega-3 (Christensen, Gustenhoff et al. 1996; Christensen, Christensen et al. 1996). The severity of arrhythmias can be correlated with the omega-3 content of the cardiac membranes.
An anti-arrhythmic effect is observed when DHA represents 20% of the lipid content of the cardiac membranes. Only a direct dietary source of DHA (and not its precursors) permits this omega-3 content to be attained (Durot, Athias et al. 1997; Kang and Leaf 2000; Leaf 2002).
|The omega-3s have a beneficial influence on cardiovascular risk factors of dietary origin, such as the level of triglycerides, arrhythmias and arterial hypertension. In adults, omega-3 fatty acids permit a reduction in mortality of 20 to 45% in studies of patients suffering from cardiovascular pathologies (myocardial infarction, rhythm disorders and mortality from all causes).
Dietary intake to reestablish the omega-3/omega-6 balance in people in good health and supplementation with nutritional doses of omega-3, combined with appropriate therapies, in at-risk subjects, represents a genuine hope for prevention of cardiovascular diseases.
The efficacy of omega-3s in this field is such that, to this day, no medication devoted to the prevention of cardiovascular diseases exists which achieves better results (GISSI, 1999; Singh et al, 2002; de Lorgeril et al, 2002).