Omega-3

Omega-3 is one of the most-studied supplements in cardiovascular and inflammatory contexts, and the trial evidence has shifted noticeably over the past decade. Marine omega-3 (EPA and DHA from fish or algae) is what the cardiovascular trials test, not plant-derived ALA, and the conversion of ALA to EPA in humans is poor enough that ALA cannot be assumed to substitute. The library entries on this page report what REDUCE-IT, STRENGTH, and the EPA-only icosapent ethyl trials actually showed, what the NHS, ESC, AHA, and SACN currently recommend, and where consumer marketing on triglyceride form, krill oil, and omega-6 ratio runs ahead of the evidence.

What this page covers

The omega-3 entries cover EPA vs DHA roles, triglyceride vs ethyl ester form bioavailability, the omega-3 index as a biomarker, dosing for cardiovascular vs mood vs general health contexts, oxidation and quality concerns, vegan algae-derived options, the 4 hour separation from blood thinners that some clinicians recommend perioperatively, the omega-6 to omega-3 ratio question, and pregnancy DHA dosing.

Where the guidance currently sits

The NHS recommends two portions of fish per week including one oily, which roughly approximates 250 to 500 mg per day of combined EPA plus DHA. The European Society of Cardiology and AHA have both recognised icosapent ethyl (a purified EPA ethyl ester at 4 g daily) as a Class IIa recommendation in patients with elevated triglycerides on a statin following the REDUCE-IT trial. The same trial design with mixed EPA plus DHA in STRENGTH did not show the same outcome benefit, which has informed the position that EPA is doing more of the work than DHA in cardiovascular contexts. SACN does not currently recommend supplementation for the general UK population beyond dietary fish, but acknowledges plausible benefit in specific clinical contexts.

Where the evidence and the marketing disagree

Krill oil is widely marketed as more bioavailable than fish oil on the basis of phospholipid-bound EPA and DHA. The clinical comparisons are mostly small and short, and the absolute EPA plus DHA content per gram of krill oil is typically lower than fish oil, so head-to-head dose-equivalent comparisons rarely favour krill once cost is factored in. The omega-6 to omega-3 ratio framing, which has driven a generation of seed oil discourse, has weaker evidence behind it than the discourse implies. Most of the cardiovascular and inflammatory data is on absolute EPA plus DHA intake, not the ratio. Triglyceride form is more consistently shown to be better absorbed than ethyl ester form when taken without a meal, but the difference shrinks substantially when either form is taken with a fat-containing meal. The library entries report which trials informed each position with sources visible.