Omega-3

Omega-3 fatty acids are among the most-studied supplements in modern medicine, with a literature spanning cardiovascular disease prevention, triglyceride reduction, pregnancy and infant outcomes (preterm birth, infant cognitive development), depression and other mood disorders, rheumatoid arthritis, dry eye disease, and (more recently) cognitive decline and inflammatory biomarkers. The marine forms (EPA and DHA from fish oil, krill oil, or algae) dominate the clinical literature; the plant-derived form (ALA from flaxseed and similar sources) converts to EPA/DHA inefficiently in humans, which is why most clinical evidence is from marine-sourced products.

The outcome dimensions covered most heavily are cardiovascular disease prevention (the longest-running research stream, including the major megatrials of the past decade), triglyceride reduction (one of the most-studied biochemical outcomes, with substantial meta-analytic synthesis), pregnancy outcomes including preterm birth prevention, inflammatory conditions including rheumatoid arthritis, depression and bipolar disorder (mixed but growing literature), and dry eye disease (where a large NIH-sponsored trial sits alongside several smaller studies). The cardiovascular evidence has been the subject of recent reanalysis as the megatrials produced results more nuanced than the earlier observational studies and small trials had suggested.

Demographically, the literature is unusually broad: cardiovascular trials enroll adults across a wide age range with varying baseline risk; pregnancy trials enroll pregnant women across many countries; older adults dominate the cognitive-decline research. Form, dose, and EPA-to-DHA ratio vary substantially between trials, which has complicated meta-analysis. Background diet (especially habitual fish intake) is a major modifier that earlier trials rarely accounted for: trials enrolling populations with low baseline fish intake tend to show larger effects than trials enrolling populations with high baseline intake.

Omega-3 is generally well-tolerated at typical supplemental doses (most capsules supply about 300 mg combined EPA+DHA; prescription products use up to 4 g/day). The most-common adverse effects are gastrointestinal: fishy aftertaste and burps, nausea, and loose stools, which improve with enteric-coated capsules or freezing the capsules. Bleeding risk has been a longstanding theoretical concern because omega-3 affects platelet function; rigorous systematic reviews have not found a clinically meaningful increase in bleeding risk at typical doses, though data in patients on anticoagulants are limited and prescription labels advise periodic monitoring. The FDA concluded in 2019 that supplements providing no more than 5 g/day combined EPA+DHA are safe when used as labeled. Drug interactions include theoretical additivity with anticoagulants (clinically less concerning than long-believed) and antihypertensives. Large trials using 4 g/day for several years have reported a slightly increased risk of atrial fibrillation in people with or at high risk of cardiovascular disease. People on anticoagulants or anticipating surgery should consult a clinician about timing.

This summary is informational and not medical advice. Consult a clinician before starting or changing any supplement, especially if you take prescription medications.