Celebrated for about two decades as an extraordinary means of preventing cardiovascular disease (to the point of being prescribed as a true prophylactic therapy after a heart attack) and as a potential defense against several types of cancer, in recent months the role of the omega-3 is seeing substantial retrenchment on both fronts.
After the results of the study ASCEND (A Study of Cardiovascular Events in Diabetes.) published during 2018, had questioned the real utility of these essential fatty acids as protection against acute cardiovascular events in people with diabetes, the findings of the double-blind randomized controlled trial VITAL (Vitamin D Omega-3 Trial), recently published in the New England Journal of Medicine, deal a further blow to their use for preventive purposes in the general population, which lacks specific risk factors.
Contrary to past inferences from observational studies, which seemed to indicate a lower incidence of cardiovascular disease and cancer among people who consumed larger amounts of fatty fish from the North Seas (salmon, mackerel, tuna, herring, sardines, etc.) known to be rich in omega-3, fish oil or targeted supplements, the results of the VITAL study showed no difference in incidence for either group of diseases between those taking omega-3 (at a dosage of 1 mg/day) and vitamin D3 (at a dosage of 2,000 IU/day) and those taking preparations similar in appearance but completely inert biologically (placebo).
Even deepening the analysis and focusing on individual aspects, supplementation with omega-3 and vitamin D3 resulted in effects entirely superimposed on placebo, with comparable rates of overall cardiovascular events, stroke, death from cardiovascular causes, death from oncological causes, and death from all causes. The only favorable data concerned myocardial infarction rates, which were slightly lower among those taking omega-3, and side effects, which were similar for omega-3 and placebo (indicative of the harmlessness and good tolerability of supplementation, but not sufficient to justify its use).
But how is it possible that what seemed useful until yesterday is no longer useful today? As mentioned, until now, the benefits associated with omega-3 supplementation for primary prevention had been highlighted mainly in observational studies, that is, comparing the incidence of cardiovascular disease and cancer in populations that were or were not taking these essential fatty acids for various reasons, but without prior patient selection criteria or standardization of administration for timing, mode and dosage.
Studies of this kind can provide insights into the potential effects of a substance or drug in the body, which must, however, be confirmed in the context of double-blind randomized controlled trials, in which two groups of patients with overlapping characteristics and exposed to comparable conditions are randomly assigned to take either the active treatment or the inactive placebo and monitored for a predefined period of time. Only such studies, such as the VITAL study, can provide reliable information about the effects of a drug or other preventive or therapeutic intervention.
The outcomes of the VITAL study deserve special attention because they were obtained on a very large population (nearly 26 thousand people) and of different ethnicities (although all of them are residents of the United States), being, therefore, decidedly robust.
On the other hand, the new data are not inconsistent with those obtained in the late 1990s as part of the GISSI – Prevention study, conducted by the Italian Group for the Study of Survival in Myocardial Infarction. This “landmark” trial had, in fact, clearly demonstrated the preventive benefits of omega-3 supplementation in patients who had already had a first heart attack and were, therefore, at increased risk of experiencing a second one (secondary prevention).
Source
- Manson JE et al. Marine n-3 Fatty Acids and Prevention of Cardiovascular Disease and Cancer. N Engl J Med 2019;380:23-32
- Keaney JF, Rosen CJ. VITAL Signs for Dietary Supplementation to Prevent Cancer and Heart Disease. N Engl J Med 2019;380:91-92
- Italian Group for the Study of Survival in Myocardial Infarction. Dietary supplementation with n-3 polyunsaturated fatty acids and vitamin E after myocardial infarction: results of the GISSI-Prevenzione trial. Lancet 1999;354(9177):447-55.
