Marine Omega-3 Supplementation (EPA/DHA)

Scope of this entry

EPA and DHA from marine oils (capsules or functional foods). Alpha-linolenic acid (ALA) from plants appears in the same broad nutrient family but follows a different trial literature; large reviews often analyze LCn3 and ALA separately.

Lipids (high-certainty theme)

Major systematic reviews report lower fasting triglycerides with increased LCn3 intake—on the order of ~15% relative reduction versus control in pooled supplement trials, with dose-response patterns.

Mood / depression (RCT meta-analysis tier)

Liao et al. 2019 (Transl Psychiatry; PMID 31383846; liao-2019-omega3-depression-meta-transl-psychiatry) — 26 double-blind placebo-controlled trials (n = 2,160); pooled SMD −0.28 (P = 0.004) on depression symptom scales, with abstract-reported stronger signals for EPA-pure and EPA-major (≥60% EPA) formulations at ≤1 g/day—read as psychiatric adjunct literature distinct from hard MACE outcome trials.

Mortality and hard cardiovascular endpoints

Updated Cochrane-style syntheses pooling dozens of long-duration RCTs conclude there is little or no effect on all-cause mortality for LCn3 supplementation, while cardiovascular mortality and some coronary heart disease event estimates show small relative reductions with moderate-to-low certainty depending on the endpoint—consistent with heterogeneity across eras, baseline statin use, and trial design.

High-dose purified EPA (selected-risk trial; not OTC fish oil)

REDUCE-IT (Bhatt et al. 2019, N Engl J Med; PMID 30415628; source bhatt-2019-reduce-it-icosapent-ethyl-nejm) randomized statin-treated adults with persistent hypertriglyceridemia and ASCVD or diabetes plus risk factors to icosapent ethyl (2 g twice daily, highly purified EPA) versus placebo: primary ischemic composite HR ~0.75 over median ~4.9 years, with higher atrial fibrillation/flutter hospitalizations on active drug. Treat this as prescription-product, high-risk-population evidence—not interchangeable with typical mixed EPA/DHA capsules in Hooper-style broad LCn3 pools (formulation, dose, eligibility, and comparator debates differ).

High-dose omega-3 carboxylic acids vs corn oil (STRENGTH; null MACE)

Nicholls et al. 2020 (JAMA; PMID 33190147; nicholls-2020-strength-high-dose-omega3-carboxylic-mace-jama) randomised 13,078 statin-treated, high-risk adults to 4 g/day of an omega-3 carboxylic acid formulation (EPA+DHA) versus corn oil; the trial stopped early for futility with HR ~0.99 on the primary MACE composite (P = 0.84) and more GI adverse events on active drug. Use this row to calibrate “more omega-3 always helps hearts” claims—product, comparator, and population matter, and this result is not REDUCE-IT.

Moderate-dose marine n-3 in diabetes primary prevention (null vascular composite)

ASCEND n-3 fatty acid arm (ascend-2018-n3-fatty-acids-diabetes-nejm; PMID 30146932) randomised 15,480 adults with diabetes without known atherosclerotic CVD to 1 g/day n-3 fatty acid capsules vs matching olive-oil placebo (alongside the trial’s separate aspirin factorial). Over mean 7.4 years, a first serious vascular event occurred in 689 (8.9%) vs 712 (9.2%) participants (rate ratio 0.97, 95% CI 0.87 to 1.08; P = 0.55). Treat as primary-prevention null context for routine n-3 capsules in diabetes, distinct from high-dose prescription EPA trials such as REDUCE-IT.

Inflammation and specialized mediators

Narrative mechanistic work describes resolvins and protectins derived from EPA/DHA and links them to damped inflammatory signaling; read alongside triglyceride and CVD trial data rather than as a substitute.

Practice framing

Guidelines still emphasize dietary fish first; supplements are most clearly anchored for elevated triglycerides under clinician oversight and for populations matching positive trial definitions.

Tertiary map

Wikipedia: Fish oil covers EPA/DHA-rich oils as a consumer and prescription topic with outbound citations—navigation only; pooled RCT endpoints (lipids, mortality, CHD) belong to Hooper Cochrane and other PubMed rows linked here.

Related protocols

• Sunlight & bone health — vitamin D and UV exposure (do not merge with marine-oil evidence).
• Intermittent fasting / time-restricted eating — separate lever on insulin and liver fat.
• Magnesium supplementation (magnesium-supplementation) — different mineral axis (sleep/GABA-adjacent narratives); do not merge lipid evidence streams.
• Dietary nitrate (beetroot juice) (dietary-nitrate-supplementation) — nitrate–nitrite / BP RCT hub; distinct from EPA/DHA physiology.