Algae Omega-3 vs Fish Oil, Cod Liver Oil and Krill: Which Source?

Algal oil, fish oil, cod liver oil and krill oil all supply the same two omega-3 molecules, EPA and DHA: algal DHA raised blood DHA as much as the same amount from cooked salmon in a direct comparison. Flaxseed oil is the odd one out: ALA, the plant omega-3, and no EPA or DHA.^{1, 2}

• Same molecules: algal DHA is bioequivalent to fish DHA
• The differences: mg EPA+DHA per serving, vitamin A (cod liver oil only), fish or shellfish allergen, oxidation, cost, sustainability
• The yardsticks: 250 mg EPA+DHA, 250 mg DHA, 200 mg extra DHA in pregnancy, 2 g ALA

Sources checked on 29 October 2026.

Fish oil, cod liver oil, krill oil, algal oil and flaxseed oil: what each supplies

Typical figures for a 1,000 mg capsule; the label is the authority.

Is algae omega-3 as good as fish oil? (the equivalence trials)

For DHA, yes. In 32 adults given 600 mg of DHA a day for two weeks from algal-oil capsules or cooked salmon, plasma phospholipid DHA rose about 80% and red-cell DHA about 25% in both groups: nutritionally equivalent.¹ A systematic review found algal DHA raised blood DHA and the omega-3 index in vegetarians and vegans in every study, and in 46 vegans with an index below 4%, from a sample of 165, 254 mg of algal EPA and DHA a day for four months lifted it from 3.1% to 4.8%.^{3, 4}

Does algae oil contain EPA?

Some does. The first algal oils were DHA-rich with little EPA; newer ones supply both, typically 150 to 300 mg of EPA. The equivalence trials used DHA-only oils.

Cod liver oil vs fish oil: what is the difference?

Vitamin A, and less omega-3. Fish oil comes from the flesh of oily fish; cod liver oil from the liver, where fish store vitamins A and D, so a capsule carries roughly 200 mg of EPA and DHA plus retinol.⁵ The NHS says to avoid fish liver oil supplements when pregnant or trying for a baby, and to keep total vitamin A from food and supplements under 1.5 mg a day.^{5, 6} Cod liver oil plus a fish oil capsule is fine for the omega-3, which simply adds; count the vitamin A.

Krill oil vs fish oil: is krill better absorbed?

A little, perhaps. Krill's EPA and DHA are mainly phospholipids. In 113 adults over seven weeks, 3 g of krill oil (543 mg EPA+DHA) and 1.8 g of fish oil (864 mg) produced similar rises in plasma EPA and DHA and no differences in lipids: comparable sources at 63% of the dose.⁷ Across seven small trials and 662 people, krill oil lowered triglycerides by about 0.16 mmol/L and LDL cholesterol by about 0.4 mmol/L.⁸ A krill capsule holds perhaps half the EPA and DHA of a standard fish oil capsule, so "better absorbed" is settled by both labels.

Where does flaxseed oil fit?

As the ALA source. ALA is the strictly essential omega-3; most adults turn only about 5% of it into EPA and under 1% into DHA, so flaxseed raises blood EPA a little and DHA not at all.² Its register wording: ALA contributes to the maintenance of normal blood cholesterol levels at 2 g a day, which two tablespoons of ground flaxseed or a tablespoon of the oil supply.⁹ A flaxseed-oil omega 3-6-9 capsule supplies ALA alongside linoleic (omega-6) and oleic (omega-9) acid in flaxseed's own proportions, and contains no EPA or DHA.

How to read an omega-3 label (mg EPA and DHA, not mg oil)

"1,000 mg fish oil" is the weight of the oil; a standard capsule is about 18% EPA and 12% DHA, so about 300 mg of omega-3, and "500 mg algae oil" tells you nothing until you find the DHA line. Set the back-of-pack figures against the register yardsticks above and SACN's 450 mg a day food guideline.^{9, 10} Then stop: in the large trials the risk of new atrial fibrillation rose by about half above 1 g a day and about 12% at 1 g or less, and EFSA's 5 g a day is a ceiling, not a target.^{11, 12} Form: re-esterified triglyceride absorbed about a quarter better than natural fish oil and ethyl ester about a quarter worse, and absorption rises with a fat-containing meal, most of all for ethyl esters.^{13, 16} Freshness: half of 171 Canadian products and most of 32 New Zealand products exceeded the voluntary oxidation limits, and a strong fishy smell means an old oil.^{14, 15} How much omega 3-6-9 do I need daily has worked examples.

Omega-3 gummies vs capsules: what each supplies

A softgel can hold 250 to 500 mg of EPA and DHA; a gummy holds much less oil. A vegan omega-3 gummy typically supplies tens of milligrams of algal DHA per two-gummy serving, against the 250 mg of DHA at which the brain and vision wording applies, often with vitamin D3, which contributes to the maintenance of normal bones and teeth: preformed vegan DHA in a gelatine-free chew for a household that will not swallow a capsule or eat fish. Where a gummy also carries vitamin A, count it with other retinol sources against the 1.5 mg a day ceiling and keep the jar out of children's reach.

Who should choose which source?

• You eat oily fish most weeks: food supplies the SACN figure; any supplement is a top-up.¹⁰
• No fish, or vegan: algal oil for DHA (and EPA if the label has it), with ALA from flaxseed, chia and walnuts.^{1, 3}
• Pregnant, breastfeeding or trying: fish body oil or algal oil, not cod liver oil, with 200 mg extra DHA as the yardstick and no more than two portions of oily fish a week.^{5, 9}
• Fish allergy: algal oil; shellfish allergy: not krill.

What are the signs you need omega-3 covers who is likely to be low; the Wellgard omega-3 guide the whole subject. Why is fish oil no longer recommended covers the dose question for fish oils.

What we don't know

The large heart-outcome trials used fish oil or purified EPA, so algal oil's equivalence rests on blood levels over two weeks in 32 adults.¹ Krill oil has no outcome trial; its lipid effects come from seven small trials.⁸ No study has set an EPA-containing algal oil against fish oil.

Frequently asked questions

Is algae omega-3 safe? Who should not take algae oil?

Algal DHA at 600 mg a day was well tolerated in the equivalence trial; the usual cautions apply: tell your GP or anticoagulant clinic if you take an anticoagulant, and ask a cardiologist before exceeding 1 g a day with a heart rhythm condition.^{1, 11} Is there any danger when taking omega-3 has the bleeding evidence.

What are the side effects of algae omega-3?

The same as fish oil at the same dose: an aftertaste, belching and loose stools, commoner with an oxidised oil and eased by a meal.

Can I take algae oil every day?

Yes; the trials dosed daily for weeks to months.^{3, 4}

What are the cons of krill oil?

Less EPA and DHA per capsule, a higher price per milligram, a shellfish allergen, no outcome trials and a debated fishery.^{7, 8}

Should krill oil be taken at night or morning, and what should you not mix it with?

With a meal containing fat, morning or night: absorption rises with the fat in the meal, and no trial has compared times of day.¹⁶ Tell your clinic if you take an anticoagulant and keep the dose steady. When to take omega-3, 6 and 9 covers timing.

Sources

1. Arterburn LM, et al. Algal-oil capsules and cooked salmon: nutritionally equivalent sources of DHA. Journal of the American Dietetic Association, 2008. Randomised open-label trial, 32 adults, 2 weeks; lead author at a pharmaceutical company. PubMed 18589030.
2. Plourde M, Cunnane SC. Extremely limited synthesis of long chain polyunsaturates in adults. Applied Physiology, Nutrition, and Metabolism, 2007. Review; funding not stated on PubMed. PubMed 17622276.
3. Craddock JC, et al. Algal supplementation of vegetarian eating patterns improves DHA. Journal of Human Nutrition and Dietetics, 2017. Systematic review, 4 trials and 2 cohorts; funding not stated on PubMed. PubMed 28417511.
4. Sarter B, et al. Blood DHA and EPA in vegans and effects of an algal-derived omega-3 supplement. Clinical Nutrition, 2015. Survey of 165 vegans with a 46-person, 4-month supplement arm; funding not stated on PubMed. PubMed 24679552.
5. NHS. Fish and shellfish. nhs.uk. Page last reviewed 26 June 2026.
6. NHS. Vitamin A. nhs.uk. Page last reviewed 3 August 2020.
7. Ulven SM, et al. Metabolic effects of krill oil are essentially similar to those of fish oil. Lipids, 2011. Randomised trial, 113 adults, 7 weeks; funding not stated on PubMed. PubMed 21042875.
8. Ursoniu S, et al. Lipid-modifying effects of krill oil in humans. Nutrition Reviews, 2017. Meta-analysis, 7 trials, 662 people; funding not stated on PubMed. PubMed 28371906.
9. Great Britain nutrition and health claims (NHC) register. gov.uk. Last updated 19 May 2026.
10. SACN. Advice on fish consumption: benefits and risks. gov.uk. Published 1 December 2004.
11. Gencer B, et al. Marine omega-3 supplementation and the risk of atrial fibrillation. Circulation, 2021. Meta-analysis, 7 trials, 81,210 people; publicly funded (NIH). PubMed 34612056.
12. EFSA. EFSA assesses safety of long-chain omega-3 fatty acids. efsa.europa.eu. Published 27 July 2012.
13. Dyerberg J, et al. Bioavailability of marine n-3 fatty acid formulations. Prostaglandins, Leukotrienes and Essential Fatty Acids, 2010. Controlled trial, 72 volunteers, 2 weeks; funding not stated on PubMed. PubMed 20638827.
14. Albert BB, et al. Fish oil supplements in New Zealand are highly oxidised. Scientific Reports, 2015. Laboratory survey, 32 products; funding not stated on PubMed. PubMed 25604397.
15. Jackowski SA, et al. Oxidation levels of North American over-the-counter omega-3 supplements. Journal of Nutritional Science, 2015. Laboratory survey, 171 products; funding not stated on PubMed. PubMed 26688721.
16. Lawson LD, Hughes BG. Absorption of EPA and DHA from fish oil co-ingested with a high-fat meal. Biochemical and Biophysical Research Communications, 1988. Absorption study in male volunteers; authors at a pharmaceutical manufacturer. PubMed 2847723.

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This article is general information, not medical advice. If you are pregnant, have a fish or shellfish allergy, take an anticoagulant or have a heart rhythm condition, speak to your GP or pharmacist first.