Fish oil or algae oil? What really matters with omega-3
The origin is printed in large letters on the tin. The three numbers that actually say something about quality are almost never there. A look at amount, oxidation and purity.
Fish oil versus algae oil sounds like a question of principle. From where I sit, it is mostly a distraction. Two tins with identical labels can be further apart than fish and algae. What counts is not printed on the front.
I bet you know this situation. You are standing in front of the shelf. Twenty tins, all of them somehow omega-3. One says wild-caught, the next says vegan, the third says high-dose. The price ranges from eight to sixty euros. And you have no idea what the difference is supposed to be.
So you decide by feel. Fish sounds natural. Algae sounds modern. Or you take whatever happens to be on offer.
I understand that well. The packaging answers exactly the questions that barely matter, and says nothing about the three that do: How much EPA and DHA do I get per day? How fresh is the oil? And what else is in there?
That is what this text is about. Not fish versus algae. But amount, oxidation and purity.
The algae stands at the beginning, not the fish
Here is a point that rarely shows up in advertising, because it makes the story less romantic: fish do not produce EPA and DHA themselves. At least not in any meaningful amount.
The long-chain omega-3 fatty acids arise in the sea at one single place: in microalgae. They are the primary producers. Zooplankton eats the algae. Small fish eat the zooplankton. Bigger fish eat the small ones. And right at the end there is an oil that gets pressed out of that chain.
Microalga
Builds EPA and DHA from sunlight, carbon dioxide and nutrients. The actual manufacturer.
Zooplankton
Takes up the fatty acids and stores them. Does not build them anew, only moves them upwards.
Small schooling fish
Store EPA and DHA in their fatty tissue. And along with them everything else that is fat-soluble and floating in the water.
Large predatory fish
Each step concentrates the fat-soluble companions further. That applies to nutrients as much as to contaminants.
Fish oil in the capsule
Obtained at the end of a long chain, purified, concentrated. How well purified is up to the manufacturer.
Adarme-Vega and colleagues summarised in 2012 what has long been known in marine biology. Marine microalgae are the primary producers of EPA and DHA, fish is the detour through the food chain.
What this means for you: algae oil is not a substitute product for people who dislike fish. It is direct access to the original source.
Adarme-Vega TC et al. Microbial Cell Factories. 2012;11:96. DOI: 10.1186/1475-2859-11-96You may have thought: fish is the natural source, algae is the technical replacement. Turn that around for a moment.
The alga is the source. The fish is the warehouse. And over the years, warehouses collect more than just the things you want.
And now you know why the question fish versus algae is not really a biological question. Both routes lead to the same fatty acid. They differ in what else comes along for the ride.
Why EPA and DHA matter in the first place
Before we talk about quality, a quick word on the why. Because without the why, every number is just a number.
EPA and DHA are not vitamins in the classic sense. They are building material for cell membranes. Imagine the outer shell of a cell like a curtain. Saturated fats make it stiff like a roller blind. DHA makes it soft and mobile like silk. What passes through that curtain, and how quickly, depends on what it is woven from.
Nervous system
DHA is the most abundant polyunsaturated fatty acid in the brain and the retina. It sits preferentially in the membranes of the synapses, where it influences how mobile receptors are embedded.
Immune system
From EPA and DHA the body forms signalling molecules that are meant not only to slow inflammation down but to actively bring it to an end. If the raw material is missing, inflammation can last longer than necessary.
Metabolism
EPA and DHA can lower triglyceride levels in the blood. Membrane fatty acids also influence how well insulin receptors can work in their surroundings.
Hormonal system
Hormones need receptors, and receptors sit in membranes. A rigid membrane may make signal transmission harder, even when the hormone level looks unremarkable in the lab.
Harris and an international team analysed the data of 17 prospective studies together in 2021. Over a median of 16 years, 15,720 deaths occurred among 42,466 people.
What was observed: people in the top fifth of long-chain omega-3 blood levels had a 15 to 18 percent lower all-cause mortality than the bottom fifth. For plant-based alpha-linolenic acid this association did not appear.
What this means for you: it is about the level in your blood, not the capsule in your hand. And it is about EPA and DHA, not about linseed oil. These are observational data, they cannot prove a cause.
Harris WS et al. Nature Communications. 2021;12:2329. DOI: 10.1038/s41467-021-22370-2This is not about a capsule in the morning. It is about what the shell of every single one of your cells is built from. That is not a side note in your health. That is the building site itself.
Criterion 1: the amount of EPA and DHA per daily dose
May I ask you an uncomfortable question? Do you know how much EPA and DHA are in the tin you are currently using? Not how much oil. How much active substance.
This is the most common thinking error I see. The tin says 1000 mg. What nearly everyone reads as 1000 mg of omega-3 is in fact 1000 mg of oil. A classic fish oil concentrate contains around 18 percent EPA and 12 percent DHA. That works out at roughly 300 mg EPA plus DHA per capsule.
Bernasconi and colleagues pooled forty randomised trials on EPA and DHA and cardiovascular events in 2021.
What was observed: a 13 percent lower risk of myocardial infarction, relative risk 0.87 with a confidence interval of 0.80 to 0.96. For combined cardiovascular events the effect, at 0.95 with an interval of 0.90 to 1.00, was no longer clear-cut. Important for us: for myocardial infarction and cardiovascular events the effect was dose-dependent.
What this means for you: if you underdose, you can hardly expect an effect. The amount is not a detail, it is the whole topic.
Bernasconi AA et al. Mayo Clinic Proceedings. 2021;96(2):304-313. DOI: 10.1016/j.mayocp.2020.08.034Now comes the part that gets uncomfortable. Is what the label says actually in there?
Albert and a team from the University of Auckland analysed all fish oil capsules sold in New Zealand in 2015.
What was observed: only 3 of 32 products contained at least as much EPA and DHA as declared. The majority, 69 percent, came in under 67 percent of the label value. Price, country of origin and best-before date said nothing about quality.
What this means for you: a declaration is not a measurement. It is a statement.
Albert BB et al. Scientific Reports. 2015;5:7928. DOI: 10.1038/srep07928Two years later another laboratory network examined 47 products on the same market and came to a considerably friendlier result. 91 percent met their EPA and DHA declaration. The author group around Bannenberg discussed the differences openly and attributed them among other things to the analytical methods. Part of the picture is that several authors of that work were affiliated with the industry association GOED or with manufacturers.
My reading: both works are done cleanly. What they show in common is the enormous spread between products. Which is exactly why a blanket verdict on fish oil does not get you anywhere, only a look at your specific product does.
And now you know why comparing two tins by price per capsule can mislead you. The only comparison that makes sense is: price per gram of EPA plus DHA.
Criterion 2: TOTOX, the value that is almost never on the tin
Now we come to the point that occupies me most in this whole debate.
Omega-3 fatty acids are polyunsaturated. That is exactly what makes them so valuable biologically and so sensitive chemically. Every double bond is a breaking point for oxygen. An oil with six double bonds like DHA is about as relaxed on the shelf as a sliced avocado.
When an oil oxidises, it happens in two waves.
| Value | What it measures | Image for it | Limit in the industry standard |
|---|---|---|---|
| PV peroxide value | Primary oxidation. Freshly formed peroxides. | The smoke, just after something starts to burn. | maximum 5 meq/kg |
| AV anisidine value | Secondary oxidation. Aldehydes and ketones formed from the peroxides. | The ash, once it has already burned. | maximum 20 |
| TOTOX | Total oxidation, calculated as twice PV plus AV. | Smoke and ash together. The overall balance. | maximum 26 |
These limits come from the voluntary industry standard of the Global Organization for EPA and DHA Omega-3s. They are not law. But they are the yardstick the scientific market analyses use.
Hands and colleagues from George Washington University analysed 72 omega-3 products together with a testing laboratory over several years.
What was observed was a pattern that gave me pause: 68 percent of the flavoured products, that is 23 of 34, exceeded the TOTOX limit of 26. Among the unflavoured ones it was 13 percent, that is 5 of 38. The difference was clear for the peroxide value too, 65 versus 32 percent.
What this means for you: lemon or berry flavouring can mask a rancid taste without changing the chemistry. The taste test many people rely on can be silenced that way.
Hands JM et al. Journal of Dietary Supplements. 2024;21(2):195-206. DOI: 10.1080/19390211.2023.2252064The most common misunderstanding goes: if it does not taste of fish, it is good oil. According to these data, the opposite can be true.
A neutral taste can mean the oil is fresh. It can also mean that someone has laid a flavour over the top. From the outside you cannot tell the two apart. Only the number can.
How bad is it overall? Honestly: it depends on the market and on the study. And here the data diverge considerably.
Albert 2015 in New Zealand: 83 percent of products above the peroxide limit, 50 percent above the TOTOX limit, only 8 percent met all three values.
Bannenberg 2017, also New Zealand, different laboratory network: 72 percent met the peroxide limit, 77 percent the TOTOX limit. Almost the opposite picture.
Jairoun 2020 in the United Arab Emirates, 44 products: mean peroxide value 6.4 against a limit of 5, mean TOTOX value 23.8 against a limit of 26. Overall largely compliant.
Pasini 2022 on the French market, 20 unflavoured products: all met the peroxide value, the anisidine value and the TOTOX value.
What this means for you: a blanket claim that fish oil is rancid would be dishonest. What can be said: the spread is huge, and you cannot see it from the outside of the tin.
Albert BB et al. Sci Rep. 2015 DOI: 10.1038/srep07928 · Bannenberg G et al. Sci Rep. 2017 DOI: 10.1038/s41598-017-01470-4 · Jairoun AA et al. PLoS One. 2020 DOI: 10.1371/journal.pone.0244688 · Pasini F et al. Biomolecules. 2022 DOI: 10.3390/biom12101361De Boer and colleagues analysed a large testing-laboratory database of fish oil samples collected worldwide in 2018.
What was observed: 13.9 percent exceeded the peroxide limit of 5, and 8.8 percent the TOTOX limit of 26. Interesting for our question: the mean peroxide value of fish oil was at the same level as that of algae oil and sunflower oil, and clearly below that of extra virgin olive oil.
What this means for you: algae oil is not a magic oil that cannot oxidise. There too, the processing decides. Part of the picture is that authors from the industry association GOED and from a manufacturer were involved in this work.
De Boer AA et al. Food Chemistry. 2018;254:249-255. DOI: 10.1016/j.foodchem.2018.01.180And does oxidised oil actually do anything?
This is where what large human studies can show for certain comes to an end. Robust investigations into what heavily oxidised fish oil might do in humans over years are missing. What does exist is an animal model, and its result is clear enough to be worth naming.
Albert and a team from Auckland gave pregnant rats either water, fresh fish oil or heavily oxidised fish oil throughout the pregnancy.
What was observed: under the oxidised oil, markedly more newborns died on the second day of life. The odds of a death were raised by a factor of 8.26 compared with the control group and by a factor of 13.70 compared with the fresh fish oil group. At weaning, the mother animals showed higher insulin resistance, HOMA-IR 2.64 versus 1.42.
What this means for you: shown in the animal model, not yet conclusively investigated in humans. I still consider it a good reason to insist on freshness in a preparation you take daily over years.
Albert BB et al. Am J Physiol Regul Integr Comp Physiol. 2016;311(3):R497-504. DOI: 10.1152/ajpregu.00005.2016A rancid oil does not give you less benefit. It gives you something extra that you never ordered.
And now you know why, with omega-3, I ask for a number that appears on no package in Europe. Not out of pedantry. But because otherwise you have nothing to hold on to.
Criterion 3: what else ends up in the capsule
Let us come back to the food chain. Fat-soluble contaminants behave like EPA and DHA: they gather in fatty tissue. And with every step of the chain they become more concentrated. That applies to dioxins, to dioxin-like PCBs and, in a somewhat different way, to methylmercury.
Tsutsumi and colleagues from the national institute of health sciences examined dietary supplements based on animal oils between 2007 and 2014.
What was observed: dioxins were detectable in 43 of 46 products, in a range from 0.00015 to 67 picograms of toxic equivalent per gram. The outlier at the top was a shark liver oil product, whose consumption used up 58 to 70 percent of the Japanese tolerable daily intake. For most other products the contribution was under 5 percent.
What this means for you: the majority of preparations were unremarkable. But the range across a factor of several hundred thousand shows how strongly the choice of raw material comes through.
Tsutsumi T et al. Chemosphere. 2017;191:514-519. DOI: 10.1016/j.chemosphere.2017.10.046Vejrup and a team from the Norwegian institute of public health analysed data from the mother and child cohort MoBa. Methylmercury intake was calculated from fish consumption during pregnancy.
What was observed: children of mothers above the 90th percentile of exposure, that is above 2.6 micrograms per day, more often had speech that was hard to understand, odds ratio 2.22 with an interval of 1.31 to 3.72, and weaker communication skills, odds ratio 1.33. Additionally accounting for PCBs and dietary omega-3 changed little.
What this means for you: this is an observational study, it cannot prove a cause. But it does show that methylmercury can be a relevant factor even in a population with overall low exposure.
Vejrup K et al. Environment International. 2016;92-93:63-69. DOI: 10.1016/j.envint.2016.03.029Now the interesting flip side. If the exposure comes from the food chain, what happens when you shorten the chain?
Zatti and colleagues replaced the fish oil in aquaculture feed entirely with algae oil from Schizochytrium and then examined the fillet.
What was observed: dioxin levels in the fillet fell by 70 percent, dioxin-like PCBs by 79 percent. Growth, gut health and flesh quality remained unchanged.
What this means for you: this is a fish farming study, not a human study. But it shows the principle very cleanly. The closer you are to the alga, the less food chain you carry with you.
Zatti K et al. Aquaculture. 2023;574:739653. DOI: 10.1016/j.aquaculture.2023.739653And now you know why, on the question of fish oil or algae oil, I do not argue with dietary philosophy but with the route the molecule has taken.
Is algae oil really equivalent? What the studies show
This is the question where many people become suspicious. Understandably. Fish oil has been around for decades, algae oil feels new. So: what do the comparison studies say?
Arterburn and colleagues directly compared algae oil capsules with cooked salmon in 2008. Both groups received 600 mg DHA per day for two weeks, the salmon group through analysed portions.
What was observed: in both groups DHA in the plasma phospholipids rose by around 80 percent and in the red blood cells by around 25 percent. The differences between the groups were not meaningful.
What this means for you: at the same amount of DHA, just as much arrives in the blood from the alga as from the fish.
Arterburn LM et al. J Am Diet Assoc. 2008;108(7):1204-1209. DOI: 10.1016/j.jada.2008.04.020Bailey and colleagues tested microalgal oil and fish oil directly against each other for the first time in 2025, with measurements after 6 and after 14 weeks.
What was observed: the availability of DHA and EPA in the plasma phospholipids was statistically not inferior under microalgal oil, despite different production and composition.
What this means for you: the most recent direct comparison study supports equivalence. For context: the study was conducted by a manufacturer that produces both types of oil.
Bailey E et al. Int J Mol Sci. 2025;26(19):9343. DOI: 10.3390/ijms26199343Bernstein and colleagues from the Harvard School of Public Health and the Cleveland Clinic analysed all studies on algal DHA and cardiovascular risk factors in 2012. The mean dose was 1.68 g DHA per day.
What was observed: triglycerides fell by 0.20 mmol/l, HDL cholesterol rose by 0.07 mmol/l, LDL cholesterol rose by 0.23 mmol/l.
What this means for you: algal DHA can show the same metabolic patterns that are described for fish oil. The rise in LDL is known, it occurs under DHA from any source and its significance is still being discussed among experts.
Bernstein AM et al. J Nutr. 2012;142(1):99-104. DOI: 10.3945/jn.111.148973But algae oil has no EPA, does it?
That was true for a long time and is only partly true today. The first algae oils delivered almost exclusively DHA. Modern oils from Schizochytrium also contain EPA, depending on the strain and the process. And there is a second route that is often overlooked.
Conquer and Holub from the University of Guelph gave 1.62 g of pure algal DHA per day for six weeks, with no EPA at all.
What was observed: DHA in the serum phospholipids rose by 246 percent. And although no EPA was given, EPA rose by 117 percent as well. The body converts part of the DHA back into EPA, with an estimated retroconversion of 11.3 percent in serum and 12.0 percent in platelets.
What this means for you: a pure DHA preparation can raise EPA status too. If EPA matters to you in particular, still pay attention to the declared amount rather than hoping for retroconversion.
Conquer JA, Holub BJ. J Nutr. 1996;126(12):3032-3039. DOI: 10.1093/jn/126.12.3032Strengths and limits
- Decades of study data, including for hard endpoints
- Usually EPA-weighted, often cheaper per gram
- Quality varies widely, oxidation is the core issue
- Contaminants depend on raw material and purification
- Burdens wild stocks, the raw material is limited
Strengths and limits
- Original source of the fatty acid, short chain
- Bioavailability equivalent in comparison studies
- Fermenter instead of ocean, therefore well controllable
- Often DHA-weighted, check the EPA content closely
- Usually pricier, long-term endpoint studies are still missing
I want to stay honest here. The large endpoint studies on myocardial infarction and mortality were done with fish oil, not with algae oil. What we have for algae oil are bioavailability and risk factor studies. Inferring the same long-term benefit from the same blood concentration is biologically very plausible, but it is an inference, not proof.
Put differently: I see no solid reason to assume that DHA from the alga works differently in the body than DHA from the fish. It is the same molecule. But I would not sell it as proven.
Yurko-Mauro and colleagues compared fish oil as ethyl ester, fish oil as triglyceride and krill oil over four weeks. Unlike in earlier comparisons, the dose was matched exactly, at around 816 mg EPA and 522 mg DHA per day in each case.
What was observed: no meaningful difference in plasma levels, p equal to 0.052, with the deviation between groups under 24 percent. The omega-3 index in the red blood cells was comparable too.
What this means for you: when the dose is held equal, the great difference in form disappears. Which is exactly why I consider dose and freshness more important than the label on the front.
Yurko-Mauro K et al. Lipids Health Dis. 2015;14:99. DOI: 10.1186/s12944-015-0109-zI know this pattern very well
People come to me and say they have been taking omega-3 for years. And then the omega-3 index in the blood is low all the same.
In my observation there are usually two reasons behind it. First, the amount of EPA plus DHA actually taken in was smaller than the person thought, because they mixed up oil weight with active substance. Second, the preparation simply was not what the tin said it was.
What I am describing here is an observation from my everyday work, not a study. It may be distorted by selection effects, because the people who come to me tend to be those for whom something is not adding up. What I take from it is nonetheless simple: measuring is more honest than guessing.
Three levers you can pull right away
Enough theory. What will you do differently tomorrow?
The practical check before your next purchase
- Convert to EPA plus DHA per day. Take the declared milligrams of the two fatty acids, add them up, multiply by the daily portion. Only that number makes products comparable. And only that number can be related to studies.
- Ask for the batch-specific certificate of analysis. It should list the peroxide value, the anisidine value and the TOTOX value. The industry limits of maximum 5, maximum 20 and maximum 26 serve as orientation. A manufacturer who dodges this question has already given you an answer.
- Measure your omega-3 index instead of guessing. The value describes the share of EPA and DHA in the membrane of your red blood cells. It shows you whether your dose is arriving where it should. More on this in our article measuring the omega-3 index.
Small things that make a big difference
- Buy unflavoured. According to the available market data, flavoured products are more often oxidised, and the flavour also takes away the one piece of feedback your sense of taste could give you.
- Small containers rather than a year's supply. Oxygen, light and heat are the three drivers of oxidation. A bulk pack on special offer spends many months in the cupboard.
- Store cool and dark once opened. Liquid oils belong in the fridge and should be used up within a few weeks.
- Look for vitamin E in the product. An antioxidant in the oil can slow oxidation down. It does not replace a proper analysis, though.
- Take it with a meal containing fat. That can improve absorption and reduces burping.
You may have started this article with the question: which is better, fish oil or algae oil?
The more useful question is: how much EPA and DHA arrive in me, how fresh are they, and what do they bring along? Anyone who can answer those three questions has settled the origin question along the way. Anyone who cannot has gained nothing, even with the noblest label.
And now you know why, with omega-3, I do not debate fish or algae but three numbers. This is not about worldview. It is about you actually getting building material for your cells for your money, and not its breakdown products.
Frequently asked questions
Is algae oil just as good as fish oil?
Based on the evidence so far, yes, provided the amount of EPA and DHA is the same. Randomised comparison studies found comparable increases in blood DHA and EPA for algae oil and fish oil.
Arterburn and colleagues showed in 2008 in 32 adults that algae oil capsules with 600 mg DHA per day and cooked salmon raised DHA levels in plasma and red blood cells to the same degree. A randomised double-blind study in 74 adults from 2025 reached the same result for microalgal oil compared with fish oil. What matters is the dose, not the origin.
What remains open: the large long-term studies on myocardial infarction and mortality were carried out with fish oil. For algae oil they are still missing.
What is the TOTOX value in omega-3?
TOTOX stands for Total Oxidation Value and describes how far an oil has already gone rancid.
It is calculated from twice the peroxide value plus the anisidine value, so it combines fresh and advanced oxidation. The voluntary industry standard of the Global Organization for EPA and DHA Omega-3s names upper limits of a peroxide value of 5, an anisidine value of 20 and a TOTOX value of 26.
The value is practically never printed on the pack. Reputable manufacturers will name it on request in the batch-specific certificate of analysis. I consider that question the most useful quality test you can run without a laboratory.
How can I tell whether fish oil has gone rancid?
Reliably only from the laboratory value, not from the taste. That is exactly where the problem lies.
In an analysis of 72 omega-3 products from the United States, 68 percent of the flavoured products exceeded the TOTOX limit of 26. Among the unflavoured ones it was 13 percent. Lemon or berry flavouring can mask a rancid taste without affecting the oxidation.
A fishy burp is a hint, but not proof, and a neutral taste is not an all-clear. Ask for the certificate of analysis for the batch.
How much EPA and DHA do I need per day?
Professional societies usually name 250 to 500 mg EPA plus DHA per day for adults as baseline coverage.
A meta-analysis of 40 randomised trials with 135,267 participants found a 13 percent lower risk of myocardial infarction for EPA and DHA, and the effect increased with the dose. In studies on triglycerides the amounts used are considerably higher.
How much makes sense for you depends on your starting level, your diet and your situation. That is why I consider the omega-3 index in the blood a more honest basis than a blanket number. Please discuss higher amounts with your doctor, particularly if you are taking anticoagulant medication.
Does algae oil contain EPA as well, or only DHA?
Both are possible. The first algae oils on the market delivered almost exclusively DHA. Today's oils from Schizochytrium also contain relevant amounts of EPA, depending on the strain and the production process.
On top of that there is a detour the body takes itself. In a study in 24 vegetarians, serum EPA rose by 117 percent under pure algal DHA, because the body converts part of the DHA back into EPA. The estimated retroconversion was around 11 to 12 percent.
If EPA matters to you, for instance because of inflammatory complaints, check the declared EPA amount anyway instead of relying on retroconversion.
Is algae oil lower in contaminants than fish oil?
That is biologically plausible and supported by environmental data, but it is not automatic.
Fat-soluble contaminants such as dioxins, dioxin-like PCBs and methylmercury accumulate along the food chain. Algae stand at the beginning of that chain, and edible oil from microalgae is produced in closed fermenters. In a feeding study in Atlantic salmon, fully replacing fish oil with algae oil lowered dioxin levels in the fillet by 70 percent and dioxin-like PCBs by 79 percent.
Well-purified fish oil can also reach very low values. The spread between individual products is large, however, as a Japanese analysis of 46 preparations with a range across several orders of magnitude has shown.
Why does the tin say 1000 mg but only 300 mg omega-3?
Because the 1000 mg refer to the total weight of the oil, not to the active substance.
A classic fish oil concentrate contains around 18 percent EPA and 12 percent DHA, so roughly 300 mg EPA plus DHA per capsule. Anyone aiming for 1000 mg EPA plus DHA would need a good three of those capsules per day.
So always convert to EPA plus DHA per daily dose before you compare prices. A seemingly expensive preparation with a high concentration can be cheaper per gram of active substance than a cheap one with a low concentration.
Can oxidised fish oil do harm?
For humans this is not conclusively settled, but there are signals from the animal model that deserve to be taken seriously.
In a study in pregnant rats, heavily oxidised fish oil led to markedly higher mortality of the newborns on the second day of life and to higher insulin resistance in the mother animals. Comparable data in humans are not available.
Mechanistically it is plausible that breakdown products such as aldehydes create a burden rather than a benefit. Since you may be taking such a preparation daily over years, I consider the cautious conclusion appropriate: prefer fresh oil.
Is krill oil better than fish oil or algae oil?
At the same dose, probably not by much.
In a randomised study in 66 adults with 1.3 g EPA plus DHA per day over four weeks, fish oil as ethyl ester, fish oil as triglyceride and krill oil did not differ meaningfully in plasma levels. Krill oil delivers omega-3 in phospholipid form, which has theoretical advantages but in practice mainly raises the price and delivers less EPA and DHA per capsule.
There is also an ecological question: krill forms the basis of the Antarctic food web. That is not a medical statement, but it is a point that belongs in the decision.
How do I store omega-3 capsules correctly?
Cool, dark and airtight, and once opened preferably in the fridge.
Oxygen, light and heat are the three drivers of oxidation. Those three factors are exactly what turns a fresh oil into a rancid one over months.
Buy small containers you will use up within a few weeks rather than the year's supply on special offer. Liquid oils always belong in the fridge once opened and should be used up within a few weeks. The bathroom shelf is the worst storage place imaginable.
Further reading in the Supplements guide
Related articles from this cluster
- Measuring the omega-3 index: the one blood value hardly any doctor orders
- ALA, EPA and DHA: why linseed oil is not the omega-3 you need
- Omega-3 from plants, animals or algae: where EPA and DHA come from
- Which magnesium is the best? The forms compared
- Taking vitamin D properly: why you go in circles without magnesium and K2
- All articles in the Supplements guide
Related topics
Supplements
Dose, quality and what the blood value says about it
This articleHeavy metals
Mercury, the food chain and routes of exposure
Nutrition
Fats, oils and what ends up on the plate
Sport
Recovery, inflammation and membrane quality
Sources
- Adarme-Vega TC, Lim DKY, Timmins M et al. Microalgal biofactories: a promising approach towards sustainable omega-3 fatty acid production. Microb Cell Fact. 2012;11:96. DOI: 10.1186/1475-2859-11-96 [Review]
- Harris WS, Tintle NL, Imamura F et al. Blood n-3 fatty acid levels and total and cause-specific mortality from 17 prospective studies. Nat Commun. 2021;12:2329. DOI: 10.1038/s41467-021-22370-2 [Real-world, pooled cohort analysis, n=42,466]
- Bernasconi AA, Wiest MM, Lavie CJ et al. Effect of Omega-3 Dosage on Cardiovascular Outcomes: An Updated Meta-Analysis and Meta-Regression of Interventional Trials. Mayo Clin Proc. 2021;96(2):304-313. DOI: 10.1016/j.mayocp.2020.08.034 [Meta-analysis, k=40, n=135,267]
- Albert BB, Derraik JGB, Cameron-Smith D et al. Fish oil supplements in New Zealand are highly oxidised and do not meet label content of n-3 PUFA. Sci Rep. 2015;5:7928. DOI: 10.1038/srep07928 [Real-world, market analysis, n=32 products]
- Bannenberg G, Mallon C, Edwards H et al. Omega-3 Long-Chain Polyunsaturated Fatty Acid Content and Oxidation State of Fish Oil Supplements in New Zealand. Sci Rep. 2017;7:1488. DOI: 10.1038/s41598-017-01470-4 [Real-world, market analysis, n=47 products]
- Hands JM, Anderson ML, Cooperman T, Frame LA. A Multi-Year Rancidity Analysis of 72 Marine and Microalgal Oil Omega-3 Supplements. J Diet Suppl. 2024;21(2):195-206. DOI: 10.1080/19390211.2023.2252064 [Real-world, market analysis, n=72 products]
- Jairoun AA, Shahwan M, Zyoud SH. Fish oil supplements, oxidative status, and compliance behaviour: Regulatory challenges and opportunities. PLoS One. 2020;15(12):e0244688. DOI: 10.1371/journal.pone.0244688 [Real-world, market analysis, n=44 products]
- Pasini F, Gómez-Caravaca AM, Blasco T et al. Assessment of Lipid Quality in Commercial Omega-3 Supplements Sold in the French Market. Biomolecules. 2022;12(10):1361. DOI: 10.3390/biom12101361 [In vitro, laboratory analysis, n=20 products]
- De Boer AA, Ismail A, Marshall K et al. Examination of marine and vegetable oil oxidation data from a multi-year, third-party database. Food Chem. 2018;254:249-255. DOI: 10.1016/j.foodchem.2018.01.180 [Real-world, database analysis, n over 1,900 samples]
- Albert BB, Vickers MH, Gray C et al. Oxidized fish oil in rat pregnancy causes high newborn mortality and increases maternal insulin resistance. Am J Physiol Regul Integr Comp Physiol. 2016;311(3):R497-504. DOI: 10.1152/ajpregu.00005.2016 [In vivo, rat]
- Arterburn LM, Oken HA, Bailey Hall E et al. Algal-oil capsules and cooked salmon: nutritionally equivalent sources of docosahexaenoic acid. J Am Diet Assoc. 2008;108(7):1204-1209. DOI: 10.1016/j.jada.2008.04.020 [RCT, n=32]
- Arterburn LM, Oken HA, Hoffman JP et al. Bioequivalence of Docosahexaenoic acid from different algal oils in capsules and in a DHA-fortified food. Lipids. 2007;42(11):1011-1024. DOI: 10.1007/s11745-007-3098-5 [RCT, dose-response design]
- Bailey E, Wojcik J, Rahn M et al. Comparative Bioavailability of DHA and EPA from Microalgal and Fish Oil in Adults. Int J Mol Sci. 2025;26(19):9343. DOI: 10.3390/ijms26199343 [RCT, equivalence study, n=74]
- Bernstein AM, Ding EL, Willett WC, Rimm EB. A meta-analysis shows that docosahexaenoic acid from algal oil reduces serum triglycerides and increases HDL-cholesterol and LDL-cholesterol in persons without coronary heart disease. J Nutr. 2012;142(1):99-104. DOI: 10.3945/jn.111.148973 [Meta-analysis, k=11, n=485]
- Conquer JA, Holub BJ. Supplementation with an algae source of docosahexaenoic acid increases (n-3) fatty acid status and alters selected risk factors for heart disease in vegetarian subjects. J Nutr. 1996;126(12):3032-3039. DOI: 10.1093/jn/126.12.3032 [RCT, double-blind, n=24]
- Yurko-Mauro K, Kralovec J, Bailey-Hall E et al. Similar eicosapentaenoic acid and docosahexaenoic acid plasma levels achieved with fish oil or krill oil in a randomized double-blind four-week bioavailability study. Lipids Health Dis. 2015;14:99. DOI: 10.1186/s12944-015-0109-z [RCT, n=66]
- Tsutsumi T, Takatsuki S, Teshima R et al. Dioxin concentrations in dietary supplements containing animal oil on the Japanese market between 2007 and 2014. Chemosphere. 2017;191:514-519. DOI: 10.1016/j.chemosphere.2017.10.046 [In vitro, laboratory analysis, n=46 products]
- Vejrup K, Schjølberg S, Knutsen HK et al. Prenatal methylmercury exposure and language delay at three years of age in the Norwegian Mother and Child Cohort Study. Environ Int. 2016;92-93:63-69. DOI: 10.1016/j.envint.2016.03.029 [Real-world, cohort study, n=46,750]
- Zatti K et al. Full replacement of fish oil with algae oil in farmed Atlantic salmon (Salmo salar): debottlenecking omega 3. Aquaculture. 2023;574:739653. DOI: 10.1016/j.aquaculture.2023.739653 [In vivo, feeding study, Atlantic salmon]