Benefits
Healthy triglycerides
In a Cochrane review of 86 randomized trials, omega-3 supplements lowered blood triglycerides by about 15%, and the effect grew with dose (high-certainty evidence). In the EU, the claim that EPA and DHA help maintain normal triglyceride levels needs 2 g a day.
Normal brain function (DHA)
DHA is a major structural fat in the brain. EU regulators allow the claim that DHA contributes to normal brain function when a product supplies 250 mg of DHA a day. This is a claim about meeting the body's need, not evidence that extra omega-3 sharpens memory in people who already eat enough.
Healthy inflammation markers (CRP, IL-6)
A pooled analysis of 68 randomized trials with 4,601 people found that marine omega-3 supplements lowered the blood inflammation markers CRP, IL-6 and TNF-alpha in healthy people as well as in people with long-term illnesses. Longer use gave larger drops in IL-6, and in people with long-term illness the effect was weaker above a BMI of 30.
Mechanism of action
Membrane incorporation
EPA and DHA are built into the membranes of cells throughout the body, including the heart, brain and eyes, where they change membrane makeup and cell signaling.
Eicosanoid balance
Omega-3s are converted into signaling molecules, including resolvins, that help switch off inflammation. This is the usual explanation for the lower CRP, IL-6 and TNF-alpha seen in pooled trials.
Clinical trials
Cochrane systematic review and meta-analysis of 86 randomized trials (162,796 participants) of omega-3 fats for preventing heart and blood vessel disease, lasting 12 to 88 months. (Abdelhamid et al. 2020, Cochrane Database Syst Rev)
Adults at varying cardiovascular risk, mainly in high-income countries.
Omega-3 supplements lowered triglycerides by about 15% (high certainty). They had little or no effect on death from any cause (RR 0.97), cardiovascular death (RR 0.92, moderate certainty), cardiovascular events (RR 0.96, high certainty) or stroke, and may slightly reduce coronary heart disease events (RR 0.91, low certainty).
Meta-analysis of 68 randomized controlled trials (4,601 participants) of marine omega-3 supplements and fasting blood CRP, IL-6 and TNF-alpha. (Li et al. 2014, PLoS One)
Healthy people, people with long-term non-autoimmune illness and people with autoimmune illness.
Omega-3 supplements significantly lowered CRP, IL-6 and TNF-alpha in all three groups. Longer supplementation gave larger drops in TNF-alpha and IL-6 in people with long-term illness, and in that group the effect was weaker in people with a BMI over 30. Omega-3 from food alone lowered IL-6 but not CRP or TNF-alpha.