Algae Oil: How Vegan DHA Is Actually Made

Your body builds DHA badly, and that is the whole point

Six young men were fed carbon-labelled alpha-linolenic acid and tracked for three weeks. Not one of them made a detectable molecule of DHA from it.

The companion study, in six young women, was kinder. About 21% of their labelled ALA reached EPA and roughly 9% reached DHA. Both papers ran in the British Journal of Nutrition in 2002, and both are small. But the direction has held up in every tracer study since.

This is why flaxseed oil and walnuts do not solve the problem. They deliver ALA. The enzymes that carry ALA the last two steps to DHA are slow, competitive with omega-6, and in men close to idle.

So if you do not eat fish, DHA has to arrive ready-made. There are only two realistic routes: extract it from an animal that already concentrated it, or grow the organism that made it in the first place.

Two organisms do almost all the work

Fish do not make DHA either. They accumulate it by eating microalgae, which sit at the bottom of the marine food chain and synthesise it directly. Algae oil skips the fish.

Two groups of single-celled marine organisms dominate commercial production. Crypthecodinium cohnii is a dinoflagellate, developed in the late 1980s for infant formula. Its oil runs roughly 40 to 50% DHA by weight of total fatty acids and contains essentially no EPA — which was the point, because formula makers wanted DHA on its own.

Schizochytrium and its relative Aurantiochytrium are thraustochytrids, not true algae at all. Their oils carry DHA alongside docosapentaenoic acid and a modest amount of EPA. That is why two vegan omega-3 bottles can list quite different fatty acid profiles.

The strain matters more than the marketing. If a label says "algal oil" without naming the organism, you cannot predict what is in it. Look for the genus on the pack or the specification sheet.

Sugar in, oil out: what happens inside the tank

Here is the part most people get wrong. These strains are not grown in sunlit ponds. They are heterotrophic — they feed on sugar rather than light — and they are grown in the dark.

Production starts from a frozen master cell bank. A pure culture goes into a test tube, then a shake flask, then a seed fermenter, then a production vessel. Each transfer is a step up in volume, and the whole chain is closed to the outside air.

Inside the vessel, temperature, pH, dissolved oxygen, pressure and agitation are held to set points and logged. The feed is glucose or glycerol plus nitrogen and mineral salts. The organism grows first, then switches to piling fat into itself once nitrogen runs short.

When cell density and fatty acid content hit target, the batch is harvested by centrifugation and usually spray-dried into a dry biomass. A run takes days, not a fishing season. Nothing about it depends on weather, quota or catch.

Getting the oil out of the cell

The DHA is inside the cells, packed into lipid droplets, so the wall has to come apart. Manufacturers do this mechanically, enzymatically, or with a solvent — most often hexane, which is then stripped off and recovered.

Solvent-free routes exist and get marketed hard. They are a genuine engineering achievement, but hexane residues in refined edible oils are tightly limited by law and routinely undetectable. It is not the thing that should decide your purchase.

What comes out is a crude oil. It is then refined, bleached, winterised and deodorised, in the same sequence used for any edible oil, before antioxidants such as mixed tocopherols or rosemary extract go in. The oil is handled under nitrogen because oxygen is the enemy from this point on.

Finally it is encapsulated, usually in a plant-based softgel made from starch or carrageenan rather than bovine gelatine. That last swap is the only step that is about veganism. Everything before it is about chemistry.

What a sealed tank leaves out

Methylmercury, dioxins and PCBs get into fish oil the same way they get into fish: by moving up a food chain in a polluted ocean over years. An organism grown for four days on food-grade sugar in a sealed vessel never enters that chain.

That is a structural argument, not a marketing one. Good fish oil refiners strip contaminants out with molecular distillation and their products test clean. The difference is that algae oil never has to.

Regulators have looked at the process itself. The EFSA panel assessing Schizochytrium limacinum oil in 2024 concluded the information on composition and production was sufficiently described and raised no safety concerns, and cleared the extended use. Schizochytrium oil has held authorised novel food status in Europe since the 2020 opinion, and the equivalent GB authorisations carry over.

Freshness is the honest caveat. DHA has six double bonds and will oxidise from any source. Fermentation shortens the cold chain; it does not repeal chemistry.

Does it actually reach your cells?

Three trials have put algal DHA up against a marine comparator, and the results are consistent.

A second study gave 31 adults 600 mg of DHA daily from algal or fish oil for two weeks. Final DHA levels did not differ between groups. Adjusted for body weight, the algal group's percentage change was actually the larger of the two — in a pilot that small, read that as reassurance rather than superiority.

One caveat you should have from us rather than from someone else: that 2025 trial was designed and funded by a company that sells algal oil. The finding is plausible and matches the older independent work. It is still industry data.

What to check before you buy

Start with the DHA number, not the oil weight. A 1,000 mg softgel of algal oil might carry 250 mg of DHA or 500 mg, and the front of the pack rarely makes that obvious. The authorised UK claims for maintenance of normal brain function and normal vision attach to 250 mg of DHA a day. Our UK buyer's guide works through the label maths in more detail.

Then ask for oxidation figures. Peroxide value, anisidine value and TOTOX are cheap to measure and should be on the certificate of analysis. The industry reference points are peroxide under 5, anisidine under 20 and TOTOX under 26.

Whether that matters is worth showing you honestly. In 2015, researchers bought 32 fish oil supplements off New Zealand shelves and tested them blind. Only three met their labelled EPA and DHA content, and most oxidation markers were over the line.

A follow-up analysis in 2016 tested 10 Australian and New Zealand products and found the opposite: every one met its label, averaging 109% of claimed EPA plus DHA, and none exceeded the peroxide limit. Both results are real. The lesson is that the category is variable, so ask for the paperwork rather than trusting the shelf.

Last, look at the packaging and the date. Dark glass or an opaque blister, a batch number, a best-before you can read, and storage away from the windowsill. Buy the size you will finish in three months.

Where the honest limits are

Knowing how the oil is made tells you what is in the capsule. It does not tell you what the capsule will do for you, and those are separate questions.

The evidence for DHA in healthy, active adults is uneven. The blood levels move reliably — every trial above shows that. Whether shifting your omega-3 index changes anything you can feel at 55 is a thinner literature. We went through the memory trials in healthy adults separately, including the two large ones that found nothing.

What the manufacturing route does settle is the sourcing question. If you are vegan, algae oil is the only ready-made DHA available. If you eat fish but dislike the contaminant load, the fermenter route removes it by design. If you already eat two portions of oily fish a week, you may not need a capsule at all.

Ask the boring questions. Which organism, how much DHA per capsule, what the TOTOX was at release, and when it was made. A manufacturer who can answer all four is telling you something about the rest of the operation.

References

1. Burdge, G.C. & Wootton, S.A. (2002). "Conversion of alpha-linolenic acid to eicosapentaenoic, docosapentaenoic and docosahexaenoic acids in young women." British Journal of Nutrition, 88(4), 411-420. PMID 12323090.
2. Burdge, G.C., Jones, A.E. & Wootton, S.A. (2002). "Eicosapentaenoic and docosapentaenoic acids are the principal products of alpha-linolenic acid metabolism in young men." British Journal of Nutrition, 88(4), 355-363. PMID 12323085.
3. Arterburn, L.M., Oken, H.A., Bailey Hall, E., Hamersley, J., Kuratko, C.N. & Hoffman, J.P. (2008). "Algal-oil capsules and cooked salmon: nutritionally equivalent sources of docosahexaenoic acid." Journal of the American Dietetic Association, 108(7), 1204-1209. PMID 18589030.
4. Bailey, E., Wojcik, J., Rahn, M., Roos, F., Spooren, A. & Koshibu, K. (2025). "Comparative Bioavailability of DHA and EPA from Microalgal and Fish Oil in Adults." International Journal of Molecular Sciences, 26(19), 9343. doi:10.3390/ijms26199343. PMID 41096614.
5. Ryan, L. & Symington, A.M. (2015). "Algal-oil supplements are a viable alternative to fish-oil supplements in terms of docosahexaenoic acid (22:6n-3; DHA)." Journal of Functional Foods, 19, 852-858. doi:10.1016/j.jff.2014.06.023.
6. Albert, B.B., Derraik, J.G.B., Cameron-Smith, D., Hofman, P.L., Tumanov, S., Villas-Boas, S.G., Garg, M.L. & Cutfield, W.S. (2015). "Fish oil supplements in New Zealand are highly oxidised and do not meet label content of n-3 PUFA." Scientific Reports, 5, 7928. doi:10.1038/srep07928.
7. Nichols, P.D., Dogan, L. & Sinclair, A. (2016). "Australian and New Zealand Fish Oil Products in 2016 Meet Label Omega-3 Claims and Are Not Oxidized." Nutrients, 8(11), 703. doi:10.3390/nu8110703.
8. EFSA Panel on Nutrition, Novel Foods and Food Allergens (2020). "Safety of Schizochytrium sp. oil as a novel food pursuant to Regulation (EU) 2015/2283." EFSA Journal, 18(10), 6242.
9. EFSA Panel on Nutrition, Novel Foods and Food Allergens (2024). "Safety of an extension of use of oil from Schizochytrium limacinum (strain FCC-3204) as a novel food pursuant to Regulation (EU) 2015/2283." EFSA Journal, 22(10), 9043.
10. Commission Regulation (EU) No 432/2012, retained in GB law (2012). Authorised health claims for DHA at 250 mg daily intake.

DHA from the tank, not the trawler

Our Omega-3 DHA is fermented algal oil — the same closed-system route described above, with the DHA per capsule printed on the label rather than the oil weight.

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