Is Fish Oil Better Than Cod Liver Oil?

While cod liver oil might have gone out of fashion, omega 3 supplements, marine algae and krill oil are certainly popular now. Confused about how they differ and if you should be taking a supplement? What are the benefits of cod liver oil? Is fish oil better than cod liver oil? Or is krill oil better than fish oil? How do you choose between krill oil versus fish oil versus cod liver oil versus marine algae? And what about the whole food effect of oily fish? Read on to find out all you need to know about omega fatty acids and supplementation.

What Are Omega Fatty Acids?

There are two types of fats or fatty acids that are essential and can’t be produced in our bodies. These are omega 3 and omega 6. Omega 3 can be broken down into three main forms: alpha-linolenic acid (ALA), eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA).

Where Are Omega Fatty Acids Found?

ALA is found in plant oils, such as flaxseed, soybean, and canola oils. DHA and EPA are found in oily fish, fish oils, and krill oils. DHA and EPA are actually synthesised by micro algae, not by the fish, but accumulate in the tissue when they are eaten by fish and shellfish further up the food chain.

Alpha-linolenic Acid (ALA)

ALA can be converted via the liver into DHA and EPA, however this conversion is relatively inefficient, requiring a number of different enzymes, such that only about 15% is effectively converted. A number of different factors contribute to this rate of conversion including genetic background, the hormone oestrogen and nutrition status. Women are more able to convert ALA to EPA and DHA more efficiently, and is possibly an evolutionary adaptation to meet increased demands by the foetus during pregnancy.

This is why on a vegan diet, it is harder to get enough of EPA and DHA through diet alone, as only a small percentage of ALA is converted to these important compounds.

Why Are Omega Fatty Acids So Important?

Omega 3 and 6 fatty acids have an important structural role, needed for cell membranes. They are also energy sources, and are used to form signalling molecules called eicosanoids, comprised of prostaglandins, thromboxanes, and leukotrienes.

There are many different prostaglandins with wide ranging roles such as the sensation of pain, inflammation, regulation of pregnancy and birth, control of blood pressure, secretion of stomach acid, contraction and relaxation of smooth muscle.

Thromboxanes regulate blood clotting by causing constriction of blood vessels, and the aggregation of platelets (so they stick together), which are early steps in blood clotting.

Leukotrienes are involved in immune function by attracting immune cells such as neutrophils to sites of inflammation. They also constrict bronchioles in the lungs and make capillary walls permeable.

This is thought to be because the metabolic products of omega 3 fatty acids are less inflammatory than those produced from omega 6 fatty acids. Western diets are associated with an imbalance of omega 3/6 such that instead of levels of omega 3 being higher than 6, the reverse is more commonly seen. This is associated with an increased risk of chronic inflammation.

Omega 3 fatty acids have been shown to reduce blood pressure and can be incorporated into your diet by eating oily fish or seeds such as chia seeds, flaxseeds and nuts. 

What Are The Benefits of Omega 3 Supplementation?

A large review of 86 trials combined, totalling over 162,000 people looked to see what the effect of increased omega 3 had on cardiovascular risk (1). This was provided mostly by omega 3 supplements, while a few trials gave oily fish. Increasing ALA, made no significant difference to blood clots of the coronary arteries supplying the heart (coronary events), but slightly reduced cardiovascular events (diseases related to blood vessels such as clots and rhythm problems). While EPA and DHA reduced serum triglycerides, and also reduced the risk of coronary heart disease such as heart attacks.

They found that EPA and DHA decreased triglycerides (a type of fat) by about 15%, and reduced the risk of coronary artery death and coronary events, which are illness of arteries supplying the heart. However, they did not have an effect of cardiovascular events (for example strokes, heart irregularities).

While increasing ALA, made no significant difference to coronary events, but slightly reduced cardiovascular events.

This means that together omega 3 (ALA, EPA and DHA combined), may reduce the risk of coronary and cardiovascular disease, and triglyceride levels, but the effects are small.

One of the ways of decreasing your risk of cardiovascular disease is by lowering your cholesterol. Reducing saturated fats in your diet, and eating ALA omega 3 (for example from walnuts) (2).

Omega 3 supplements have been found to benefit clinical outcome of rheumatoid arthritis (3) and may even delay the need for medications (4). There is also limited evidence that omega 3 supplementation may benefit people with other types of autoimmune arthropathies such as systemic lupus erythematosus (SLE) as well, but more research is needed (3).

A grouped meta-analysis has not found there to be a link between omega 3 and dementia, but more information is needed to see if omega 3 can prevent cognitive decline.

What Are The Benefits Of Cod Liver Oil?

Cod liver oil is made from the liver of fish, and contains both DHA and EPA. Since the liver detoxifies toxins, there is the risk that it is more contaminated than other omega 3 supplements. If you are deficient in vitamin D, one of the benefits of cod liver oil is that it contains vitamin D and vitamin A. However, in order to take higher doses of omega 3 with cod liver oil, this does risk having too much vitamin D and in particular vitamin A. All vitamin A supplements should be avoided during pregnancy.

What Is Krill Oil?

Krill oil is extracted from the bodies of Antarctic krill, a tiny shrimp-like shellfish.

Like fish oil and cod liver oil, krill oil also contains DHA and EPA. 

Fish oil is extracted from the body of the fish and contains some vitamin A and vitamin D as well. Cod liver oil is extracted from the liver of the fish, and contains higher levels of vitamin A and D. High doses of vitamin A can be toxic as it is a fat soluble vitamin that is stored by your body. This is why omega 3 supplements that contain vitamin A are to be avoided in pregnancy, because high levels may damage the foetus.

Krill Oil Versus Fish Oil – Is Krill Oil Better Thank Fish Oil?

Evidence surrounding krill oil is limited compared with fish oils and cod liver oils.

A large portion of the EPA and DHA in krill comes in phospholipid form (whereas fish oil fatty acids are contained in triacylglycerols), which some claim has a higher rate of absorption in the body than fish oil.

Previously, it was thought that Krill oil was more bioavailable than fish oil, (5), but there were problems with this research with regards dosing. More recently, a randomised controlled trial in 66 people was performed to answer this question, and compared the bioavailability of krill oil compared with fish oil (6). It found that there was no difference between blood measurements of DHA and EPA (6). Therefore, evidence does not support krill oil being “better” or needing lower doses than fish oil.

How Does Krill Oil Compare With Cod Liver Oil?

Cod liver oil contains higher levels of vitamin D and vitamin A, which may be toxic in excess. If you want to take a high dose of omega 3, this means you will also end up having higher doses of vitamin A and D. Both of these are fat soluble vitamins that are stored by the body, and can become toxic. Vitamin A supplementation should be avoided during pregnancy due to risks for the baby. 

There is a risk that since the liver is used to filter out toxins, there is the possibility that cod liver oil contains more environmental contaminants than fish oil or krill oil.

Is Krill Oil Better Than Fish Oil For Cholesterol?

A study in animals looked at gene expression after supplementation with either krill oil or fish oil (7). They found that fish oil upregulated (increased gene expression) the cholesterol synthesis pathway more than krill oil (7). Krill oil was found to upregulate (increase gene expression) or more metabolic pathways than fish oil (7). This suggests that there might be different biological effects between krill and fish oil but more research is needed (7).

In group (meta) analysis of seven trials totalling 662 participants, Krill oil supplementation was found to reduce low-density lipoprotein cholesterol and triglycerides but not total cholesterol (8). Whether this translates to decreased risk of cardiovascular disease needs further research.

However, when directly compared, krill oil was not superior to fish oil supplementation, and had very similar effects on cholesterol (9).

Why is Krill Oil Red?

The deep red colour of krill oil, is due to a compound called astaxanthin found in krill. Astaxanthin is also found in other more sustainable sources such as red trout, crab, lobster and wild salmon. Astaxanthin is a carotenoid antioxidant compound that mops up harmful free radicals.

Are There Risks With Krill Oil?

Less research has been performed on krill oil and although no side effects have been reported, the safe maximum dose of natural astaxanthin has not been determined.

Krill make up a vital part of the Antarctic food chain and a huge number of species higher up the food chain depend on them. Fishing krill has the potential to catastrophically destabilise this important food-chain. Therefore, fish oils are more sustainable than krill oil.

What Are The Benefits Of Marine Algae

If krill oil isn’t sustainable, while cod liver oil and fish oil risk contamination from pollution, is marine algae the answer? What are the benefits of marine algae? Marine algae is the only plant-based source of DHA. There are some concerns that not all species contain EPA, but there are species that do produce both EPA and DHA. Marine algae can be made to be virtually tasteless, and is much more sustainable than krill, cod liver oil or fish oil. It is also suitable for people on a vegan or vegetarian diet. Since algae are right at the bottom of the food chain, there is a much lower risk of contamination as well. Fish and krill aren’t able to produce DHA and EPA themselves, instead they just concentrate what they ingest from algae. So while marine algae have so many benefits, it can still be hard to be sure that you are getting both DHA and EPA so buy from a reputable source and check the nutrient content.

Tips For Getting Enough Omega 3 in Your Diet

Aim to have oily fish twice a week if you aren’t pregnant, or once a week if you are, as the benefits of omega 3 have to be offset by risk of contamination with heavy metals.

Algae and seaweed are the only plant-based source of EPA and DHA, but ALA can be converted in your body into EPA and DHA.

Vegan sources of omega 3 are chia seeds, linseed, hemp seeds, walnuts and vegetable oils such as rapeseed. To meet the current guidance for omega 3, you would need to eat about a tablespoon of chia or ground linseeds, or two tablespoons of hemp seeds or six walnut halves a day.

Algae oil is an alternative to fish oil which makes it an attractive option for vegetarians. But while algae oils do contain large amounts of DHA, most don’t contain any EPA fatty acids at all.

Who Needs Omega 3 Supplements?

There are concerns that part of the benefit of omega 3 is from a whole food effect, that isn’t seen with taking a supplement instead. Research has shown that eating whole fish may have heart-protecting benefits, scientific studies have not yet proven that taking omega-3 supplements offers the same benefits as eating fish.

Overall, if you aren’t pregnant, or intending to get pregnant then omega 3 supplements are probably unlikely to do you harm and might benefit your long-term cardiovascular risk. It isn’t possible to tell the difference in general between eating enough omega 3 in your diet, versus supplementing, but whole foods have other benefits as well. Omega 3 supplements often have high levels of vitamin A, which can be harmful in pregnancy. Therefore, you should avoid supplementing or choose a pregnancy safe version.

If you are vegan, you may consider taking an omega 3 supplement made from algae or seaweed, but these are unregulated and can contain significant quantities of iodine, which can be harmful. Therefore, it is better where possible to optimise your diet.

Summary – Is Fish Oil Better Than Cod Liver Oil?

I hope from this article you know the dietary sources of omega 3, what EPA, DHA and ALA are, why they are important, and what the benefits of cod liver oil versus krill oil versus fish oil and marine algae are.

Krill oil supplements appear safe, and to be as effective as fish oil. They have the added bonus of containing the antioxidant astaxanthin, but harvesting krill is not sustainable, and risks destabilising the Antarctic food chain. Instead, aim to include foods rich in omega 3 in your diet to benefit from the “whole food effect”, and eat foods naturally rich in carotenoids such as vegetables, crab, and lobster. Avoid taking high doses of cod liver oil, and avoid completely during pregnancy due to the risk of vitamin A. Instead if you are vegan, or don’t like oily fish, consider taking fish oil supplements to get sufficient omega 3 in your diet.

References

1.     Abdelhamid AS, Brown TJ, Brainard JS, Biswas P, Thorpe GC, Moore HJ, et al. Omega-3 fatty acids for the primary and secondary prevention of cardiovascular disease. Cochrane Database Syst Rev. 2020 Feb 29;3(3):CD003177.

2.     Haghighatdoost F, Hariri M. Does alpha-lipoic acid affect lipid profile? A meta-analysis and systematic review on randomized controlled trials. Eur J Pharmacol. 2019 Mar 15;847:1–10.

3.     Akbar U, Yang M, Kurian D, Mohan C. Omega-3 Fatty Acids in Rheumatic Diseases: A Critical Review. J Clin Rheumatol. 2017 Sep;23(6):330–9.

4.     Petersson S, Philippou E, Rodomar C, Nikiphorou E. The Mediterranean diet, fish oil supplements and Rheumatoid arthritis outcomes: evidence from clinical trials. Autoimmun Rev. 2018 Nov;17(11):1105–14.

5.     Ulven SM, Kirkhus B, Lamglait A, Basu S, Elind E, Haider T, et al. Metabolic effects of krill oil are essentially similar to those of fish oil but at lower dose of EPA and DHA, in healthy volunteers. Lipids. 2011 Jan;46(1):37–46.

6.     Yurko-Mauro K, Kralovec J, Bailey-Hall E, Smeberg V, Stark JG, Salem N. 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 Sep 2;14(1):99–9.

7.     Ulven SM, Holven KB. Comparison of bioavailability of krill oil versus fish oil and health effect. Vasc Health Risk Manag. 2015;11:511–24.

8.     Ursoniu S, Sahebkar A, Serban M-C, Antal D, Mikhailidis DP, Cicero A, et al. Lipid-modifying effects of krill oil in humans: systematic review and meta-analysis of randomized controlled trials. Nutr Rev. 2017 May 1;75(5):361–73.

9.     Kim MG, Yang I, Lee HS, Lee J-Y, Kim K. Lipid-modifying effects of krill oil vs fish oil: a network meta-analysis. Nutr Rev. 2020 Sep 1;78(9):699–708.