Walk into a supplement store and most marine oils get grouped into one category:

Omega-3s.

Fish oil.

Krill oil.

Cod liver oil.

They all contain marine omega-3 fatty acids, but that does not make them nutritionally identical.

Conventional fish oil is typically used primarily as a concentrated source of EPA and DHA.

Cod liver oil provides EPA and DHA too, but it also naturally contains the fat-soluble vitamins A and D because the oil comes from the liver of the fish.

Krill oil takes another approach. A significant portion of its EPA and DHA is associated with phospholipids rather than being carried primarily as triglycerides, and krill naturally contains astaxanthin and choline-containing phospholipids.

Those differences matter.

At Formula IQ, this is why we generally favor cod liver oil and krill oil rather than treating all marine oils as interchangeable.

One provides a broader whole-food source of naturally occurring fat-soluble vitamins alongside marine lipids.

The other provides omega-3 fatty acids within a phospholipid-rich marine matrix.

Neither should be evaluated simply by looking for the largest number of milligrams on the front of a bottle.

Key Takeaways

• Conventional fish oil, cod liver oil, and krill oil all contain marine omega-3s, but their nutritional profiles are different.

• Cod liver oil naturally provides vitamins A and D in addition to EPA and DHA.

• Krill oil contains a high concentration of phospholipids, including phosphatidylcholine, and naturally contains astaxanthin.

• A significant portion of EPA and DHA in krill oil is associated with phospholipids rather than triglycerides or ethyl esters.

• Several human studies have found favorable absorption or tissue incorporation of phospholipid-bound omega-3s from krill oil, although long-term evidence does not establish universal superiority in every circumstance.

• Conventional concentrated fish oil can provide large amounts of EPA and DHA, but concentration alone does not determine nutritional quality.

• EPA and DHA are vulnerable to oxidation, making processing, freshness, storage, and testing important.

• Cod liver oil and krill oil serve different nutritional purposes and can be viewed as complementary rather than interchangeable.

• Formula IQ uses Cod Liver IQ primarily as a whole-food source of naturally occurring vitamins A and D with omega-3s, while Krill IQ is our preferred concentrated marine omega-3 option.

Start With the Goal

Before comparing marine oils, it helps to ask why someone is taking one.

If the only goal is to consume a very large dose of EPA and DHA, a highly concentrated fish oil can accomplish that efficiently.

But EPA and DHA concentration is not the only reason to use a marine oil.

Someone may want:

• Naturally occurring vitamin A

• Naturally occurring vitamin D

• EPA and DHA

• Phospholipids

• Choline-containing phospholipids

• Astaxanthin

• A less processed marine lipid source

• A broader nutritional profile

Once the goal changes, the best choice can change too.

This is why we prefer to evaluate cod liver oil, krill oil, and conventional fish oil as different nutritional tools rather than three versions of the same ingredient.

Conventional Fish Oil: Primarily an EPA and DHA Delivery System

Most conventional fish oils are derived from fatty fish tissues.

The oil naturally contains triglycerides, which can then be purified, concentrated, or chemically modified during manufacturing.

A typical fish oil supplement might contain 1,000 mg of total fish oil but only around 180 mg of EPA and 120 mg of DHA. Actual commercial formulas vary dramatically.¹

More concentrated products can provide substantially higher amounts of EPA and DHA.

This is useful if high-dose omega-3 delivery is the objective.

But the number:

1,000 mg Fish Oil

does not mean:

1,000 mg EPA + DHA.

Consumers need to turn the bottle around and look at the actual fatty-acid composition.

Cod Liver Oil Is a Different Food

Cod liver oil is technically a fish oil, but nutritionally it deserves its own category.

The oil comes from the liver of cod rather than primarily from the fatty tissues of the fish.

That changes what is naturally present.

The NIH specifically notes that cod liver oil provides **vitamins A and D in addition to EPA and DHA.**¹

That makes cod liver oil fundamentally different from a standard concentrated omega-3 product.

Vitamin A in cod liver oil is present as preformed vitamin A, or retinol.

Vitamin D occurs naturally within the oil as well.

These nutrients are fat soluble, meaning their natural presence in a marine lipid matrix makes biological sense.

Cod liver oil has also been consumed as a traditional nutritional food for generations, long before purified EPA and DHA concentrates became available.

Cod Liver Oil Is Not About Winning the EPA/DHA Contest

This point is important.

Cod liver oil is sometimes compared unfavorably with concentrated fish oil because it usually provides less EPA and DHA per capsule.

That comparison misunderstands why someone chooses cod liver oil.

If the goal is simply:

How much EPA and DHA can we fit into one softgel?

then concentrated fish oil will usually win.

That is not the nutritional purpose of cod liver oil.

Cod liver oil provides a combination of:

• Retinol

• Vitamin D

• EPA

• DHA

• Other naturally occurring fatty acids

within the same marine oil.

The nutritional value is in that broader profile.

This is much closer to the food-first philosophy that guides many of our Formula IQ formulations.

We are not trying to isolate one compound and maximize it at the expense of everything else naturally present.

Why Retinol Matters

Vitamin A exists in several dietary forms.

Plant foods provide provitamin A carotenoids such as beta-carotene.

Animal foods provide preformed vitamin A, including retinol and retinyl esters.

These are not metabolically identical.

The body must convert beta-carotene into active vitamin A, and the efficiency of that conversion varies substantially between individuals.²

Retinol does not require the same conversion pathway.

Vitamin A contributes to:

• Normal vision

• Immune function

• Cellular differentiation

• Reproduction

• Epithelial tissue health

• Gene regulation

Cod liver oil provides preformed vitamin A naturally within the oil rather than requiring it to be added as a separate synthetic vitamin.

Vitamin D Is Part of the Same Marine Matrix

Cod liver oil also naturally contains vitamin D.

Vitamin D is widely known for its role in calcium and bone metabolism, but vitamin D receptors are present throughout numerous tissues.

Again, the point here is not to turn cod liver oil into a high-dose vitamin D product.

Its value lies in providing naturally occurring vitamin D alongside retinol, EPA, DHA, and the rest of the marine lipid matrix.

At Formula IQ, we deliberately do not fortify Cod Liver IQ with synthetic vitamin A or vitamin D simply to produce larger numbers on the Supplement Facts panel.

We want the nutrients naturally present in the cod liver oil.

Krill Oil Is Not Fish Oil

Krill are tiny marine crustaceans, primarily harvested from Antarctic waters.

Like fish, they accumulate EPA and DHA from the marine food chain.

But the way those fatty acids are packaged is different.

In conventional fish oil, EPA and DHA are commonly carried largely as triglycerides or, after concentration, as ethyl esters or re-esterified triglycerides.

In krill oil, a substantial proportion of the fatty acids are associated with phospholipids.³,⁴

Reviews of Antarctic krill oil have reported phospholipid concentrations ranging broadly from approximately 30% to over 60% depending on the oil and extraction method.³

This phospholipid-rich structure is one of the defining characteristics of krill oil.

Why Phospholipids Are Interesting

Phospholipids are major structural components of cell membranes.

Unlike triglycerides, which primarily serve as energy-storage lipids, phospholipids contain both water-compatible and fat-compatible regions.

That structure makes them fundamental components of biological membranes.

A large portion of the phospholipids in krill oil consists of phosphatidylcholine, a choline-containing phospholipid.⁵

Researchers analyzing Antarctic krill oil identified dozens of choline-containing phospholipid species, many containing long-chain omega-3 fatty acids.⁵

This means krill oil is not simply EPA and DHA floating in another type of oil.

It provides marine omega-3s within a phospholipid-rich matrix.

Krill Oil and Choline

Choline is an essential nutrient involved in:

• Cell membrane structure

• Phospholipid synthesis

• Acetylcholine production

• Methyl-group metabolism

• Normal liver function

Phosphatidylcholine is one of the body's major choline-containing phospholipids.

Krill oil naturally contains substantial phosphatidylcholine.⁵

In a small human pilot study, 28 days of krill oil supplementation increased fasting plasma concentrations of choline and several downstream choline metabolites.⁶

That does not make krill oil equivalent to a standardized choline supplement.

The amount of choline can vary between oils and may not be listed as a quantified nutrient on every Supplement Facts panel.

It does show that krill oil provides more nutritional complexity than isolated EPA and DHA alone.

Krill Oil Naturally Contains Astaxanthin

Krill's characteristic red color comes partly from astaxanthin, a carotenoid naturally accumulated from the marine food chain.

Astaxanthin has antioxidant properties and helps protect biological lipids from oxidation.

Krill oil naturally packages astaxanthin alongside its highly unsaturated fatty acids and phospholipids.³

That does not make oxidation impossible.

EPA and DHA remain chemically vulnerable fats.

But astaxanthin adds another naturally occurring component that distinguishes krill oil from most conventional fish oils.

Is Krill Oil Better Absorbed?

This is where supplement marketing can get ahead of the research, so the wording matters.

There is legitimate evidence suggesting an absorption advantage for phospholipid-rich krill oil under certain conditions.

In a randomized crossover study, researchers compared equal amounts of EPA and DHA delivered as krill oil, re-esterified triglyceride fish oil, and ethyl esters.

Krill oil produced the highest numerical incorporation of EPA and DHA into plasma phospholipids over 72 hours, although not all differences reached statistical significance.⁷

Another randomized crossover study found significantly greater 72-hour incorporation of EPA and DHA into plasma phospholipids from krill oil than from fish oil when similar amounts were consumed.⁸

Longer studies have also demonstrated differences in how omega-3s from krill oil and fish oil are incorporated into circulating lipid species.⁹

A recent comprehensive review of human omega-3 bioavailability generally ranked phospholipid-bound omega-3s highly among the available molecular forms.¹⁰

But there is an important qualifier.

Not every trial shows krill oil outperforming every type of fish oil.

A 2023 randomized crossover study comparing krill oil with a phospholipid-enhanced fish-oil formulation found similar overall EPA+DHA absorption over 24 hours.¹¹

The current evidence therefore supports this conclusion:

Phospholipid-bound omega-3s in krill oil have favorable bioavailability and can be efficiently incorporated into human lipid pools, but the evidence does not justify claiming that every krill oil product will always outperform every fish oil product.

That is still a strong nutritional case for krill.

Acute Absorption Is Not the Entire Story

There is another important point when comparing omega-3 supplements.

Most people do not take them once.

They take them for months or years.

A 2024 comprehensive review of EPA and DHA bioavailability found differences among molecular forms, with phospholipids performing favorably in acute absorption studies.

The authors also noted that short-term differences do not always translate into major differences during chronic supplementation.¹⁰

That does not make molecular form irrelevant.

It means quality should be evaluated as a whole.

Form.

Dose.

Consistency.

Food intake.

Product quality.

And long-term use all matter.

Cod Liver Oil and Krill Oil Solve Different Problems

This is the most important distinction in the article.

At Formula IQ, we do not see Cod Liver IQ and Krill IQ as competing products.

They serve different purposes.

Cod Liver Oil

Cod liver oil is primarily valuable because it provides:

• Naturally occurring retinol

• Naturally occurring vitamin D

• EPA

• DHA

• A traditional whole-food marine lipid matrix

Krill Oil

Krill oil is primarily valuable because it provides:

• EPA

• DHA

• Phospholipids

• Phosphatidylcholine

• Choline-containing compounds

• Naturally occurring astaxanthin

One is not simply a stronger version of the other.

They provide different nutritional profiles.

Why We Prefer These Over Generic Fish Oil

Conventional fish oil can be an effective way to increase EPA and DHA intake.

There is nothing inherently wrong with it.

Our preference for cod liver oil and krill oil comes from a broader formulation philosophy.

We generally prefer nutrients that arrive with useful compounds naturally associated with their food source.

Cod liver oil gives us omega-3s plus naturally occurring vitamins A and D.

Krill oil gives us omega-3s within a phospholipid-rich matrix, along with phosphatidylcholine and astaxanthin.

A highly concentrated fish-oil ethyl ester may deliver more EPA and DHA per capsule.

That may be exactly what someone wants.

It is simply a different nutritional approach.

For foundational daily nutrition, we place greater value on the broader marine nutrient matrix.

What About Oxidation?

Regardless of whether the oil comes from cod, krill, sardines, anchovies, or another marine source, EPA and DHA remain highly unsaturated fats.

EPA contains five double bonds.

DHA contains six.

Those structures make them vulnerable to oxidation.

Heat, oxygen, light, storage time, and manufacturing conditions can all accelerate oxidative deterioration.¹²,¹³

Oxidation can produce hydroperoxides, aldehydes, and other breakdown products.

This is why marine oil quality depends on more than the label.

Extraction matters.

Processing matters.

Packaging matters.

Storage matters.

And testing matters.

Krill Oil Has Some Natural Oxidative Protection

Krill oil's naturally occurring astaxanthin is particularly interesting in this context.

Astaxanthin is a lipid-soluble carotenoid with antioxidant activity.

Krill oil also contains phospholipids and other lipid-soluble compounds that contribute to its unique oxidative characteristics.³

This does not mean krill oil cannot oxidize.

It can.

It means the natural composition of the oil includes antioxidant compounds alongside the omega-3 fatty acids.

That fits the same nutritional pattern we value in cod liver oil.

The oil is more than one isolated nutrient.

Purity Still Matters

Marine products can potentially be exposed to environmental contaminants.

High-quality manufacturing should therefore include appropriate contaminant testing.

Krill occupy a relatively low position in the Antarctic marine food chain and have short life cycles, limiting the opportunity for some contaminants to bioaccumulate compared with larger predatory fish.

Fish-oil purification can also remove contaminants effectively.

NIH notes that commercial omega-3 supplements generally have not been found to contain methylmercury because mercury is removed during processing and purification.¹

Source does not eliminate the need for testing.

Testing verifies the source.

How Formula IQ Uses the Two Oils

Formula IQ offers both because they serve distinct purposes.

Cod Liver IQ

Cod Liver IQ is made from Atlantic cod caught off the coast of Iceland.

Each softgel provides:

• 415 mg cod liver oil

• 375 mcg vitamin A as naturally occurring retinol

• 3.4 mcg vitamin D

• 37 mg EPA

• 36 mg DHA

• 17 mg other omega-3 fatty acids

No synthetic vitamin A or vitamin D is added to inflate those numbers.¹⁴

The oil is processed using a proprietary low-heat extraction method intended to preserve the naturally occurring nutrients in the cod liver oil.¹⁴

Cod Liver IQ is not designed to win a contest for the most EPA and DHA per softgel.

Its purpose is to provide the naturally occurring nutritional profile of cod liver oil.

Krill IQ

When the primary goal is omega-3 supplementation, Krill IQ is our preferred marine omega-3 product.

A two-softgel serving provides:

• 1,000 mg Antarctic krill oil

• 200 mg total phospholipids

• 120 mg EPA

• 80 mg DHA

• 200 mcg naturally occurring astaxanthin

The omega-3s are provided within krill oil's phospholipid-rich structure rather than as a conventional concentrated ethyl-ester fish oil.¹⁵

Krill oil also naturally contains choline-containing phospholipids, particularly phosphatidylcholine.⁵

This gives Krill IQ a nutritional profile that extends beyond EPA and DHA alone.

Which One Should You Choose?

The answer depends on the goal.

Choose cod liver oil when the priority is:

• Naturally occurring retinol

• Naturally occurring vitamin D

• Whole-food marine nutrition

• Modest EPA and DHA alongside fat-soluble vitamins

Choose krill oil when the priority is:

• Marine omega-3 supplementation

• Phospholipid-bound EPA and DHA

• Phosphatidylcholine

• Naturally occurring astaxanthin

• A broader alternative to conventional concentrated fish oil

Some people may use both as part of their nutritional approach because they are serving different purposes.

They should not be viewed simply as duplicate omega-3 products.

Frequently Asked Questions

Is cod liver oil just another fish oil?

Technically it is a marine fish oil, but its nutritional profile is different.

Cod liver oil naturally contains vitamins A and D in addition to EPA and DHA.¹

Is krill oil fish oil?

No.

Krill are marine crustaceans. Krill oil provides EPA and DHA, but much of its fatty-acid content is associated with phospholipids rather than the triglycerides or ethyl esters common in fish oils.³

Which is better, cod liver oil or krill oil?

They serve different purposes.

Cod liver oil is particularly valuable for its naturally occurring vitamins A and D.

Krill oil is an excellent option when the primary goal is marine omega-3 supplementation within a phospholipid-rich matrix.

Does krill oil contain choline?

Krill oil is rich in phosphatidylcholine, a choline-containing phospholipid. Analytical research has identified numerous phosphatidylcholine species in Antarctic krill oil.⁵

Does krill oil contain astaxanthin?

Yes.

Astaxanthin is a naturally occurring carotenoid responsible for much of krill's reddish color. The amount varies among krill oils.

Is krill oil more bioavailable than fish oil?

Several studies have found favorable EPA and DHA absorption or incorporation from krill oil, and phospholipid omega-3s generally show strong bioavailability.⁷⁻¹⁰

However, results differ according to the fish-oil formulation, dose, study design, and whether acute or long-term absorption is being measured. It is more accurate to say krill oil offers a highly bioavailable phospholipid form of marine omega-3 than to claim it always outperforms every fish oil.

Why doesn't Cod Liver IQ contain extremely high EPA and DHA?

Because concentrated EPA and DHA is not its primary nutritional purpose.

Cod Liver IQ is intended to provide naturally occurring vitamin A and vitamin D alongside the omega-3s naturally present in cod liver oil.

Why use both Cod Liver IQ and Krill IQ?

They provide different nutritional profiles.

Cod Liver IQ emphasizes naturally occurring vitamins A and D within cod liver oil.

Krill IQ emphasizes phospholipid-rich marine omega-3s, phosphatidylcholine, and astaxanthin.

The Bottom Line

The term omega-3 supplement covers products that can be very different from one another.

Conventional fish oil is primarily a vehicle for EPA and DHA.

Cod liver oil provides EPA and DHA within a marine oil naturally containing retinol and vitamin D.

Krill oil provides EPA and DHA within a phospholipid-rich structure alongside phosphatidylcholine and naturally occurring astaxanthin.

That is why we do not judge these products simply by asking which one contains the largest amount of fish oil or even the largest EPA/DHA number.

We look at the whole nutritional profile.

For foundational marine nutrition, cod liver oil and krill oil are the two forms we prefer at Formula IQ.

Cod liver oil gives us the naturally occurring fat-soluble vitamins that make cod liver oil unique.

Krill oil gives us a phospholipid-based source of marine omega-3s with additional compounds that ordinary concentrated fish oil does not provide.

Different source.

Different structure.

Different nutritional purpose.

The best choice starts by understanding what is actually inside the oil.

References

1. National Institutes of Health, Office of Dietary Supplements. Omega-3 Fatty Acids: Fact Sheet for Health Professionals. National Institutes of Health. Accessed September 2026.

2. Haskell MJ. The challenge to reach nutritional adequacy for vitamin A: beta-carotene bioavailability and conversion. American Journal of Clinical Nutrition. 2012;96(5):1193S-1203S.

3. Xie D, Gong M, Wei W, et al. Antarctic krill (Euphausia superba) oil: a comprehensive review of chemical composition, extraction technologies, health benefits, and current applications. Comprehensive Reviews in Food Science and Food Safety. 2019;18(2):514-534. doi:10.1111/1541-4337.12427.

4. Recent reviews of krill oil composition describe approximately 30% to 65% or more of krill lipid fatty acids as associated with phospholipids depending on extraction and product composition.

5. Winther B, Hoem N, Berge K, Reubsaet L. Elucidation of phosphatidylcholine composition in krill oil extracted from Euphausia superba. Lipids. 2011;46(1):25-36. doi:10.1007/s11745-010-3472-6.

6. Berge K, et al. Plasma choline, homocysteine and vitamin status in healthy adults supplemented with krill oil: a pilot study. 2018. PMID: 30261756.

7. Schuchardt JP, Schneider I, Meyer H, Neubronner J, von Schacky C, Hahn A. Incorporation of EPA and DHA into plasma phospholipids in response to different omega-3 fatty acid formulations: a comparative bioavailability study of fish oil vs. krill oil. Lipids in Health and Disease. 2011;10:145. doi:10.1186/1476-511X-10-145.

8. Köhler A, Sarkkinen E, Tapola N, Niskanen T, Bruheim I. Bioavailability of fatty acids from krill oil, krill meal and fish oil in healthy subjects: a randomized, single-dose, cross-over trial. Lipids in Health and Disease. 2015;14:19.

9. Sung MM, et al. Krill oil has different effects on the plasma lipidome compared with fish oil following 30 days of supplementation in healthy women: a randomized controlled and crossover study. Nutrients. 2020.

10. Schuchardt JP, et al. Bioavailability of EPA and DHA in humans: a comprehensive review. Progress in Lipid Research. 2024/2025; doi:10.1016/j.plipres.2024.101318.

11. Guarneiri LL, Wilcox ML, Maki KC. Comparison of the effects of a phospholipid-enhanced fish oil versus krill oil product on plasma levels of eicosapentaenoic and docosahexaenoic acids after acute administration: a randomized, double-blind, crossover study. Nutrition. 2023;114:112090. doi:10.1016/j.nut.2023.112090.

12. Shahidi F, Ambigaipalan P. Omega-3 polyunsaturated fatty acids and their oxidation products: chemistry and biological properties. Reviews of marine lipid oxidation.

13. Albert BB, et al. Oxidation of marine omega-3 supplements and human health. BioMed Research International. 2013.

14. Formula IQ. Cod Liver IQ Supplement Facts and Product Information. Accessed September 2026.

15. Formula IQ. Krill IQ Supplement Facts and Product Information. Accessed September 2026.

Disclaimer

This article is intended for educational purposes only and is not medical advice. Marine oil needs vary according to diet, health status, medications, pregnancy, seafood intake, and other individual circumstances. Consult a qualified healthcare professional before making significant changes to your supplement routine.