Omega-3: EPA, DHA, fish and algae

You're standing in front of two bottles. One says "1000 mg fish oil" in large friendly letters. The other says "algae oil" and a number about a third of the size. Which one has more omega-3? Surprisingly, neither front label tells you.

The number that counts is the EPA plus DHA in one daily portion, printed in the small print. Fish, krill and algae are three ways of getting there. On blood levels, one re-evaluation of a trial found algal oil non-inferior to fish oil once the results were adjusted for how much supplement people took. The outcome trials further down mostly tested fish-derived omega-3, so what algal oil does for heart events hasn't been tested the same way. Choosing a source is mostly a matter of diet, allergies and values. What the supplements do depends heavily on the outcome: a dependable effect on triglycerides, a small and uncertain one for coronary events, and, for some groups, real reasons to talk to a professional first.

EPA and DHA: the two letters that matter

Omega-3 is a family of fats. The two that supplements are sold for are EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid), both "long-chain" omega-3s. Oily fish are the richest dietary source, according to the NHS, which advises at least two portions of fish a week, one of them oily. Fish get their EPA and DHA from the algae they eat, which is why algae can supply the same fats directly. The Consumentenbond makes the same point in its explainer on algae oil (updated October 2025).

Plant omega-3 (ALA, from flax or walnuts) is a different molecule. When the Cochrane reviewers pooled trials, they analysed long-chain omega-3 and ALA separately, with different results (Abdelhamid et al., 2020), so this page is about EPA and DHA.

Fish, krill or algae: where the oil comes from

• Source: Fish oil; What the NCCIH says: Contains EPA and DHA; Worth knowing: The EPA-to-DHA split varies by product.
• Source: Cod liver oil; What the NCCIH says: Contains EPA and DHA, and also vitamins A and D "in amounts that vary from product to product"; Worth knowing: Vitamin A matters in pregnancy (see below).
• Source: Krill oil; What the NCCIH says: Omega-3s "in the form of phospholipids"; Worth knowing: The phospholipid form is a difference in chemistry; no head-to-head human trial of krill against fish oil on health outcomes is cited here, so the table makes no comparison.
• Source: Algal oil; What the NCCIH says: "a vegetarian source of DHA; some also contain EPA"; Worth knowing: Contents depend on the product: some are DHA-only, some include EPA.

Source for the second column: NCCIH, Omega-3 Supplements: What You Need To Know (last updated November 2024).

So "algae oil" doesn't mean "DHA only", and "fish oil" doesn't mean "EPA-heavy". The label decides.

Algae versus fish: does the source change what reaches your blood?

One study compared the two directly. Bailey and colleagues (2025, International Journal of Molecular Sciences) re-evaluated plasma data from an earlier randomised, double-blind, placebo-controlled trial by Maki and colleagues, in which 74 adults (analysed) took a microalgal oil, a fish oil or a placebo, four capsules a day. After 6 and 14 weeks, once the EPA and DHA levels in plasma phospholipids were normalised to the amount of supplement taken, the algal oil was statistically non-inferior to the fish oil. The capsules differed: the algal capsule held 164 mg EPA and 443 mg DHA, the fish capsule 289 mg EPA and 205 mg DHA, so the authors themselves note that different EPA-to-DHA ratios complicate strict equivalence claims.

Two limits matter. First, it measured blood levels, not heart attacks or memory. Second, five of the authors are employed by dsm-firmenich, which supplied the algal oil, and the statistician was contracted by the company; the paper reports no external funding. Independent repeats would show whether the result holds.

An older study (Arterburn et al., 2008, 32 healthy adults, two weeks) compared 600 mg DHA a day from algal-oil capsules with the same DHA from cooked salmon. DHA in plasma phospholipids rose by around 80% and in red blood cells by around 25% in both groups, and the authors called the two equivalent for delivering DHA. That was DHA only, with salmon as the comparator, and a small, short, open-label design.

Reading the label: a worked example

The front of the pack describes the oil. The research is about EPA and DHA, which are only part of it. In the trial above, one fish-oil capsule delivered 289 mg EPA plus 205 mg DHA, so 494 mg of omega-3 that counts, and the algal capsule 164 mg plus 443 mg, so 607 mg. Same shelf, different arithmetic.

Here's the method, using one real algae-oil listing. On 8 October 2026 the PLNKTN omega-3 page said (supplier information, not our measurement):

• each capsule contains at least ("minimaal") 125 mg EPA and 250 mg DHA, so at least 375 mg EPA + DHA per capsule, which we treat as the daily portion in this example;
• the oil comes from the microalga Schizochytrium sp.;
• 60 capsules cost €29.95 as a one-off purchase, or €25.46 on the two-monthly subscription.

The arithmetic, taking the listed minimum: 60 capsules × 375 mg = 22,500 mg EPA + DHA, or 45 units of 500 mg. €29.95 ÷ 45 ≈ €0.67 per 500 mg; at €25.46 it is about €0.57. Prices move, so treat these as a dated example of the method rather than a ranking. Do the same sum for any product you're weighing, using the daily portion on the pack, not the number of capsules in the bottle.

The EU labelling rules point the same way: supplements must state a recommended daily dose and a warning not to exceed it (Your Europe). Our supplement label guide covers the other checks.

What the research shows, outcome by outcome

Heart and circulation. The biggest synthesis is the 2020 Cochrane review: 86 randomised trials, 162,796 participants, lasting 12 to 88 months, with doses from 0.5 g to over 5 g a day of long-chain omega-3, mostly as capsules. Raising omega-3 made little or no difference to all-cause mortality (high-certainty evidence) or to cardiovascular events (RR 0.96, 95% CI 0.92 to 1.01; high certainty). It may slightly reduce coronary heart disease events (RR 0.91, 95% CI 0.85 to 0.97) and coronary deaths, both rated low-certainty. It probably also slightly lowers cardiovascular deaths (RR 0.92, 95% CI 0.86 to 0.99, moderate certainty). Arrhythmia and stroke showed no clear change (Abdelhamid et al., 2020).

Triglycerides. The same review found long-chain omega-3 lowered blood triglycerides by about 15%, in a dose-dependent way, and rated this high-certainty. A lower triglyceride number is a lab result, not the same thing as fewer heart attacks.

Atrial fibrillation. A 2021 meta-analysis of seven large trials (81,210 patients, mean age 65) found marine omega-3 supplements were associated with more atrial fibrillation (HR 1.25, 95% CI 1.07 to 1.46). The hazard ratio was 1.49 (95% CI 1.04 to 2.15) in trials testing more than 1 g a day and 1.12 (1.03 to 1.22) at 1 g a day or less (Gencer et al., 2021, Circulation). These were trials of cardiovascular outcomes in older adults, and they tested marine omega-3, so we don't know whether the finding carries over to younger readers or to algal oil.

Pregnancy. The 2018 Cochrane review (70 trials, 19,927 women, supplements and food) found preterm birth before 37 weeks was lower with omega-3 (13.4% versus 11.9%; RR 0.89, 95% CI 0.81 to 0.97) and so was birth before 34 weeks (4.6% versus 2.7%; RR 0.58), both rated high-quality evidence, while prolonged pregnancy beyond 42 weeks was probably more common (1.6% versus 2.6%) (Middleton et al., 2018). That is a population finding, not a personal instruction; see the pregnancy section below.

Dementia. The 2016 Cochrane review pooled three placebo-controlled trials in 632 people with mild to moderate Alzheimer's disease and found no benefit on cognitive function at six months (Burckhardt et al., 2016). That says nothing about preventing memory problems in healthy people.

Dry eye. The DREAM trial gave 3,000 mg a day of fish-derived EPA and DHA or an olive-oil placebo to 535 people with moderate-to-severe dry eye disease. After 12 months, symptom scores had improved by 13.9 points on omega-3 and 12.5 on placebo, a difference that wasn't statistically significant (Asbell et al., 2018, NEJM).

The pattern is easy to spot once it's laid out. The strongest finding is about a blood fat; the rest is small, uncertain or null for the people studied. Omega-3 has a clear job in triglyceride numbers and a much smaller footprint everywhere else, which is worth knowing before you picture it as all-round cover.

Safety: who should ask first

Most side effects are mild: unpleasant taste, bad breath, headache, heartburn, nausea or diarrhoea (NCCIH). These groups should check with a pharmacist, GP or prescriber before buying:

• Blood thinners, bleeding disorders and upcoming surgery. Omega-3 affects platelets, so bleeding is a standard question. A 2007 expert opinion judged clinically significant bleeding with prescription-strength omega-3 to be an unfounded concern (Harris, 2007), and a small retrospective study of 95 spinal-surgery patients (16 had taken omega-3 until about two days before) found no extra blood loss (Kepler et al., 2012). The Dutch Voedingscentrum is more cautious about high doses: it says supplements with high doses of EPA and DHA raise the chance of bleeding, and of heart-rhythm disturbance in people with cardiovascular disease (Voedingscentrum, read 8 October 2026). If you take blood thinners, the Voedingscentrum says to see a doctor if you take a supplement with more than 1 g of EPA and DHA a day, and it puts the risk as greatest at 4 g a day. Tell the prescriber and the surgical team what you take; they decide. Our interactions guide explains how to run a medicine check.
• Heart-rhythm conditions. See the atrial fibrillation finding above.
• Fish or shellfish allergy. Many fish-oil labels carry a warning for fish-allergic people. A pilot study of six people with finned-fish allergy found they tolerated two fish-oil supplements in skin tests and oral challenges (Mark et al., 2008). Six people is far too few to call fish oil safe for allergic readers, so ask an allergist and read the allergen statement. "Algae" has its own allergy question, which we found no reliable data on.
• Pregnancy and breastfeeding. The NHS says to avoid fish liver oil supplements such as cod liver oil in pregnancy unless a GP advises otherwise, because they are high in vitamin A, and that you may be advised to avoid supplements containing vitamin A more generally (NHS). The Consumentenbond says the Dutch Health Council advises a supplement for pregnant women who eat too little fish, and itself suggests 250 to 450 mg DHA a day (Consumentenbond, updated October 2025). Ask a midwife or GP; this is not dosing advice from us.
• Prescribed omega-3 medicines. A retail capsule is a different product. Don't swap one for the other yourself.

How much is too much?

EFSA's 2012 opinion did not set a tolerable upper intake level, because the data were insufficient. It concluded that supplemental EPA and DHA combined up to 5 g a day, and EPA alone up to 1.8 g a day, raised no safety concerns for adults, and that long-term intakes up to about 5 g a day did not appear to increase spontaneous bleeding, provided the oils' oxidative stability is guaranteed (EFSA NDA Panel, 2012). It also described dietary recommendations for European adults of 250 to 500 mg a day of EPA and DHA.

Hold two things together. Five grams is a ceiling, not a target. And the atrial fibrillation data suggest more caution at higher doses in people with cardiovascular risk. The two sources answer different questions, so we don't merge them into one number.

On a Dutch shelf: what the rules and advice say (8 October 2026)

Start with how much. The Voedingscentrum says that if you choose an EPA and DHA supplement, 200 mg a day is enough. EFSA (2012) mentions 250 to 500 mg a day for cardiovascular considerations. Neither is a personal recommendation, and they don't agree, which tells you how soft the "right" number is.

On the label, a supplement sold in the EU must carry a recommended daily dose and a warning not to exceed it, and may not claim to prevent, treat or cure a disease (Your Europe). Product pages often quote claims such as "EPA and DHA contribute to the normal function of the heart"; EU rules allow EPA and DHA heart-function claims only under set conditions, which we don't list here, so check the Commission's health-claims register.

As an ingredient, a 2023 review of EU microalgae law lists several Schizochytrium oils among the EU's authorised novel foods (Foods, 2023). Authorisation depends on the specific strain and oil, so check the species on the label and the supplier's documentation; we haven't verified the authorisation of any individual product. Law and guidance change; check the current rules.

So, which bottle?

If you eat oily fish regularly, the research above doesn't show a case for a capsule on top; food brings other nutrients as well. If you avoid fish, algal oil is a reasonable route to EPA and DHA, judged on the same terms as any oil: declared EPA and DHA per daily portion, price per 500 mg, and what the label says about species and allergens. A medical reason, such as a high triglyceride level, is a conversation with your prescriber, who may talk about prescription products. And if you take blood thinners, have a heart-rhythm condition, are pregnant or have surgery planned, ask first.

Where next

• How to read supplement labels
• Supplement and drug interactions

Written by Smart Supplements with AI assistance from the sources linked in the text. It has not been reviewed by a clinician.

Last updated: 12 October 2026

This article is for informational purposes only and is not intended as medical advice. Always consult a healthcare professional before starting any new supplement, especially if you take prescription medication.