Dietary sources of EPA and DHA include fatty fish (salmon, mackerel, sardines, anchovies, herring), shellfish, and algae-based products. Supplements (fish oil capsules, krill oil, and algae-based products) are widely used, and algae oil supplies preformed EPA and DHA without fish: the DO-HEALTH trial’s omega-3 arm used 1 g/day providing 330 mg EPA plus 660 mg DHA from marine algae. Examine notes that total EPA and DHA intake should come from a mix of food and supplements, and that the more the diet provides, the less supplementation is required. The sources cited on this page do not establish that a particular EPA:DHA ratio suits particular applications.
Triglyceride reduction is the best-supported effect of fish oil. Examine’s evidence summary states plainly that fish oil reduces triglycerides, and triglycerides is one of only two outcomes on the entire fish oil page to earn Examine’s top evidence grade of A — against 20 outcomes at B, 38 at C, 76 at D, and 1 at F. The supporting literature is correspondingly deep: Examine’s database covers High Cholesterol across 30 outcomes and 128 studies, and triglyceride trials dominate its reference list for this supplement, including prescription omega-3 ethyl ester studies in hypertriglyceridemic and dyslipidemic patients. What the sources cited here do not supply is a magnitude: none of them states the percentage reduction, the dose–response relationship, or the mechanism, so this page claims direction and evidential strength but not effect size.
Examine’s summary credits fish oil with improving some painful, inflammatory conditions, and TNF-α is the named representative of the 20 outcomes it grades B — a tier below triglycerides. A review of n-3 fatty acids in the brain likewise attributes anti-oxidative-stress, anti-inflammatory, and anti-apoptotic properties to ALA, EPA, and DHA. Two limits are worth stating outright. First, the sources cited on this page establish no eicosanoid mechanism: resolvins, protectins, competition with arachidonic acid, and shifts in the pro- to anti-inflammatory signaling ratio are absent from all of them. Second, they give no pooled effect on systemic inflammatory markers such as hs-CRP or IL-6, and no evidence that the effect is larger in populations with elevated baseline inflammation. Indeed, one of the trials in Examine’s own reference list for this page reports that n-3 intake from fish did not lower serum C-reactive protein in healthy subjects.
ALA, EPA, and DHA are highly concentrated in the brain. A review of n-3 fatty acids in neurogenesis and neuroplasticity describes their effects on the dentate gyrus of the hippocampus — one of the two regions where adult neurogenesis occurs, and a region implicated in both cognition and mood regulation. Exposure to n-3 fatty acids enhances adult hippocampal neurogenesis, promotes synaptic plasticity by increasing long-term potentiation, and modulates synaptic protein expression in a way that stimulates dendritic arborization and the formation of new spines. That review is a mechanistic narrative review rather than a trial synthesis, and the sources cited here neither quantify DHA as a fraction of brain fatty acid content nor demonstrate a cognitive benefit in humans: Examine’s database covers Cognitive Improvement across 16 outcomes in 8 studies and age-associated memory impairment and cognitive decline across 2 outcomes in 2 studies, but cognition does not appear among the benefits Examine summarizes for fish oil.
Examine’s evidence summary states that fish oil appears to reduce the symptoms of depression, and the page carries a standing FAQ asking whether fish oil really helps depression. Its database covers Depression (2 outcomes across 4 studies), Perinatal Depression (2 outcomes across 12 studies), Peripartum Depression (2 outcomes across 11 studies), Bipolar Disorder (2 outcomes across 5 studies), and Mood Improvement (12 outcomes across 4 studies). No source cited on this page quantifies the size of that effect, isolates major depressive disorder as a distinct population, establishes that EPA outperforms DHA, or identifies a threshold EPA fraction — so omega-3 belongs in the well-tolerated adjunct column rather than as a substitute for first-line treatment.
The cardiovascular story for omega-3 supplements is a negative one. A 2012 JAMA systematic review and meta-analysis (Rizos et al.) pooled 20 randomized trials of 68,680 patients reporting 7,044 deaths and found no statistically significant association between omega-3 supplementation and all-cause mortality (RR 0.96; 95% CI 0.91–1.02), cardiac death (RR 0.91; 0.85–0.98), sudden death (RR 0.87; 0.75–1.01), myocardial infarction (RR 0.89; 0.76–1.04), or stroke (RR 1.05; 0.93–1.18), on both relative and absolute measures. Examine reaches the same conclusion in its summary: fish oil does not seem to affect the rate of cardiovascular events. Claims that dietary fish is clearly protective where supplements are not, or that high-dose trials such as REDUCE-IT overturn this picture, are not supported by any source cited on this page.
Blood omega-3 status behaves as a mortality biomarker. A 2021 analysis of 2,240 Framingham Offspring Cohort participants without prevalent cardiovascular disease, followed for 11 years from a baseline age in their mid-60s, screened 28 red-blood-cell fatty acid metrics against 8 standard risk factors. The Omega-3 Index (RBC EPA + DHA) was one of four fatty acid metrics that repeatedly survived model selection as a significant predictor of all-cause mortality, and a four-metric fatty acid model predicted death at least as well as the remaining six standard risk factors (C-statistic 0.778 versus 0.777). The headline life-expectancy figure needs care. The Omega-3 Index hazard ratio was 0.86 per quintile, and the years-of-life number is a theoretical conversion the authors label as such: dividing that coefficient by the per-year age coefficient yields 1.18 years per quintile, or 4.74 years across four quintiles — set beside the 4.73 years the same table attributes to not smoking. The paper separately observes, as an ecological aside, that Japan’s mean Omega-3 Index exceeds 8% against roughly 5% in the United States, where life expectancy is about 5 years shorter. The authors state that predictions should be confined to ages roughly 65 to 76 and that extrapolating further is unwarranted, that other highly correlated fatty acids could substitute for the Omega-3 Index with similar results, and that replication in other cohorts is needed.
A post hoc analysis of the DO-HEALTH randomized trial, published in Nature Aging in 2025, examined 777 Swiss participants aged 70 and older who provided blood samples at baseline and at three years. In this 2×2×2 factorial design testing 2,000 IU/day vitamin D, 1 g/day omega-3, and a home strength-training program, omega-3 alone slowed three of four next-generation DNA methylation clocks — PhenoAge, GrimAge2, and DunedinPACE — and all three treatments showed additive benefit on PhenoAge. Standardized effects from baseline to year 3 ranged from 0.16 to 0.32 units, or 2.9 to 3.8 months, which the authors characterize as a small protective effect. Subgroup analyses suggested a stronger benefit in participants who started with lower baseline omega-3 blood levels. The sample was preselected for health and mobility and is not representative of adults over 70 generally.
Examine gives 250 mg of combined EPA and DHA per day as the minimum dose for general health, obtainable through fish intake, and notes that the American Heart Association recommends 1 g daily. Fish oil can be taken at any time of day; taking it with meals minimizes the “fish burp” aftertaste. Pregnant women should increase DHA intake by at least 200 mg a day provided there is no risk of elevated mercury exposure. The sources cited on this page support no condition-specific dose — not for triglycerides, not for depression — and no storage or formulation guidance. Examine flags bleeding risk and atrial fibrillation risk as open questions in its FAQs; this page makes no claim either way.