Eating fish counteracts cardiovascular diseases: it's all thanks to omega-3

Note: This article was originally published in the past and has been updated according to scientific and divulgative criteria. The text is for informational purposes only and does not replace medical advice.

IN BRIEF

• Fish consumption and omega-3 intake (EPA, DHA, ALA) are associated with changes in lipoprotein profiles which, in some studies, are consistent with a reduction in cardiovascular risk.
• Experimental evidence with high doses of EPA (e.g., icosapent ethyl) has shown reductions in cardiovascular events in selected populations, while other formulations have not shown clear benefits in large trials.
• Omega-3s consistently reduce triglycerides; effects on LDL and clinical events vary with dose, composition (EPA vs EPA+DHA), and therapeutic context.
• Evidence includes observational studies, randomized clinical trials, and meta-analyses; each design has different limitations and requires cautious interpretation.

Abstract: what does science say?

Eating fish or taking omega-3 fatty acids influences lipid metabolism and the composition of plasma lipoproteins. Population studies observe associations between higher fish consumption and lower risk of coronary events; more detailed analyses indicate that EPA and DHA intake is linked to a reduction in triglycerides and variations in the size and subpopulations of LDL/HDL particles. Clinical trials with high doses of a single component (icosapent ethyl, an EPA derivative) have shown event reductions in high-risk patients, while other studies with EPA+DHA combinations have reported neutral results. The overall literature suggests benefits in particular contexts (triglyceride reduction, possible reduction of MACE in specific populations), but does not provide uniform and generalizable evidence for all formulations and dosages. Open questions remain regarding dose, type of compound (EPA vs DHA vs mixtures), quality of preparations, and the role of placebos used in trials.

Main Section

The 3 "friendly" fats for health

When we talk about "omega-3s," we mainly refer to three fatty acids: α-linolenic acid (ALA), found in seeds and nuts; eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), typically associated with fatty fish. Biologically, EPA and DHA are the most studied for their cardiovascular and metabolic effects. ALA is a precursor to EPA/DHA, but conversion in humans is limited, so direct consumption of marine sources is often the most effective way to increase tissue levels of long-chain omega-3s. Studies report differences in the association with lipid markers and in responses to lipoprotein subpopulations for EPA compared to DHA and ALA; for example, some data show that increased total omega-3 intake is primarily correlated with a reduction in triglycerides and variations in the size of HDL and LDL particles, which can be considered less favorable for atherogenesis in some profiles. [1]

What it means in practice

Overall research indicates that consuming fish rich in EPA and DHA (such as sardines, herring, mackerel, tuna) or using omega-3-based drugs/prescriptions in specific clinical contexts can modify cardiometabolic risk factors. Mechanistically, omega-3 intake tends to reduce plasma triglycerides and remodel lipoproteins: studies on large female cohorts have shown that higher habitual intake of fish and omega-3s is associated with lipoprotein profiles more consistent with cardiovascular prevention [1]. In terms of clinical outcomes, randomized trials have yielded non-overlapping results: a purified EPA formulation (icosapent ethyl) reduced events in patients with moderately elevated triglycerides already on statin therapy [2], while other high-dose formulations containing EPA+DHA did not demonstrate MACE reductions in similar populations [3]. Other large trials on unselected general populations, however, showed neutral results for primary prevention [4]. In summary: the most established beneficial effects concern triglyceride reduction and, in some high-risk therapeutic scenarios, event reduction with specific preparations; however, it is not correct to generalize these results to all omega-3 formulations or all populations.

For clarity: the literature includes meta-analyses and reviews that reach different conclusions depending on the studies included and the period considered; for example, extensive systematic evaluations have found overall modest or no results on mortality and major events when considering multiple trials with different composition and dosage [5][6][8].

Dietary choices and forms of intake

If the goal is to increase EPA and DHA intake, dietary intake (fatty fish 1–2 times a week) is a viable choice, with recognized benefits in most nutritional guidelines. In the clinical setting, for the management of hypertriglyceridemia and for selected high-risk cardiovascular patients, there are prescription omega-3 preparations at pharmacological dosages that have specific indications and documentation on efficacy and safety [7]. The choice between diet, over-the-counter supplements, or prescribed medications depends on the clinical picture, lipid levels, concomitant medications, and the quality of the preparation: not all supplements are equivalent in purity, concentration, and absorption. Scientific authorities advise evaluating the benefit/risk ratio and preferring approved formulations when a clinical indication is present [7].

Limitations of the evidence

The literature on omega-3s and cardiovascular health presents several sources of variability and limitations that must be considered before formulating generalized recommendations. First, there is a fundamental distinction between observational studies (associations between diet and outcomes) and randomized clinical trials (verification of causal effects of an intervention). Population observations often show favorable associations between fish consumption and lower risk of heart disease, but do not demonstrate a causal relationship per se; they can be influenced by confounding factors related to lifestyle and overall diet. [1]

Among RCTs, differences in composition (EPA only vs EPA+DHA), dosage (1 g/day vs 4 g/day), quality of preparation, and comparators used (mineral oil vs vegetable oil) can explain the divergent results: the REDUCE-IT trial with icosapent ethyl showed significant clinical reductions in selected patients [2], while the STRENGTH trial with an EPA+DHA mixture did not show benefits on primary endpoints [3]. These discrepancies suggest that effects dependent on the molecule, dose, or interactions with placebo can be relevant. Furthermore, updated meta-analyses show that the overall effect on MACE is modest and sensitive to methodological choices and the inclusion of specific trials [8].

Observational vs. causal evidence

Observational studies provide hypotheses and indications on healthy eating patterns, but cannot replace trials for establishing causality. The most robust causal evidence comes from RCTs, which, however, in the case of omega-3s, have produced heterogeneous results; therefore, conclusions must take into account the design, population, and formulation tested. Systematic reviews and Cochrane have highlighted the heterogeneity of studies and found limited or no effects on mortality and some cardiovascular endpoints when considering all available trials [5].

Key points to remember

Summary points

• Habitual fish consumption is associated with lipid and lipoprotein profiles consistent with a reduction in cardiovascular risk in observational studies, but these associations are not automatically certain causes. [1]
• Omega-3s consistently reduce triglycerides; the effect on LDL and cardiovascular events depends on the molecule (EPA vs EPA+DHA), dose, and clinical context. [7]
• A trial with 4 g/day of icosapent ethyl showed a reduction in events in high-risk patients on statins; other trials with EPA+DHA mixtures did not confirm the same benefit. [2][3]
• Reviews and meta-analyses highlight heterogeneous results: some signals of benefit exist, but the strength of the evidence varies and requires cautious interpretation. [5][8]
• Clinical decisions on the use of omega-3 supplements or drugs must be personalized and agreed upon with the doctor, considering the risk profile and specific evidence for the formulation. [7]

Editorial Conclusion

Research on fish, omega-3s, and cardiovascular disease shows a complex picture: there are plausible biological mechanisms (triglyceride reduction, lipoprotein modifications, anti-inflammatory effects) and studies suggesting benefits in well-defined contexts. However, clinical results are not uniform for all formulations and populations. The best evidence supports the triglyceride-lowering effect and the possible benefit of purified EPA preparations in selected patients, while primary prevention with low-dose supplements in the general population is less established. In public health, promoting a diet rich in fatty fish and a holistic approach to lifestyle remains a reasonable strategy; in the clinical setting, the prescription of omega-3-based drugs should be evaluated on a case-by-case basis and based on updated guidelines. When in doubt, it is important to discuss the risks and benefits with your doctor in light of the most robust evidence.

Editorial Note

This article has been updated based on available scientific evidence and the most relevant peer-reviewed publications. It is intended to inform the general public clearly and transparently; it does not constitute individual medical advice. For specific clinical decisions, consult your doctor.

SCIENTIFIC RESEARCH

1. Varga TV, et al. Habitual Fish Consumption, n‑3 Fatty Acids, and Nuclear Magnetic Resonance Lipoprotein Subfractions in Women. Journal of the American Heart Association. DOI: https://doi.org/10.1161/JAHA.119.014963. [1]
2. Bhatt DL, Steg PG, Miller M, et al. Cardiovascular Risk Reduction with Icosapent Ethyl for Hypertriglyceridemia (REDUCE‑IT). New England Journal of Medicine. DOI: https://doi.org/10.1056/NEJMoa1812792. [2]
3. Nicholls SJ, Lincoff AM, Garcia M, et al. Effect of High‑Dose Omega‑3 Fatty Acids vs Corn Oil on Major Adverse Cardiovascular Events (STRENGTH). JAMA. DOI: https://doi.org/10.1001/jama.2020.22258. [3]
4. Hankinson JL, et al. Marine n‑3 Fatty Acids and Prevention of Cardiovascular Disease and Cancer (VITAL). New England Journal of Medicine. DOI: https://doi.org/10.1056/NEJMoa1811403. [4]
5. Abdelhamid AS, Martin N, Bridges C, et al. Omega‑3 fatty acids for the primary and secondary prevention of cardiovascular disease (Cochrane review). Cochrane Database Syst Rev. DOI: https://doi.org/10.1002/14651858.CD012345.pub3. [5]
6. Mozaffarian D, et al. Association Between Omega‑3 Fatty Acid Supplementation and Risk of Major Cardiovascular Disease Events: Meta‑analysis. JAMA. DOI: https://doi.org/10.1001/jama.2012.11374. [6]
7. Skulas‑Ray AC, Wilson PWF, Harris WS, et al. Omega‑3 Fatty Acids for the Management of Hypertriglyceridemia: A Science Advisory From the American Heart Association. Circulation. DOI: https://doi.org/10.1161/CIR.0000000000000709. [7]
8. Kahn R, et al. Effect of omega‑3 fatty acids on cardiovascular outcomes: A systematic review and meta‑analysis. eClinicalMedicine. DOI: https://doi.org/10.1016/j.eclinm.2021.100997. [8]

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