Omega-3 Fatty Acid Supplementation Review

Goal: To explore the use of fish oils and cod liver oil as a regular supplement to improve health.

Motivation: Everyone has heard of fish oil supplements and that they’re good for you. It’s a bit less well known why, and which kinds are best. I’m hoping, through this article, to bring some light and good ol’ education about the matter so when you talk about at the water cooler with your coworkers you can sound like a mindless zombie doing whatever the latest nutrition article says to do.

Executive Summary: Yeah. Omega-3 Fatty acids are good and you should probably be taking some.


So what are the main differences between fish oils, krill oil, and cod liver oils?

Fish oil: This oil is made from “oily fish”, which can include forage fish, sardines, herring, anchovies, salmon, trout, tuna, mackerel, etc… Basically, oily fish is non-whitefish. Their oils are also rich in EPA, DHA, (omega-3 fatty acids) as well as vitamins A and D.

Cod liver oil: This oil is made from cod fish and is known for containing high levels of the omega-3 fatty acids: eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), along with vitamins A and D. The concentrations of vitamin A and D are higher in cod liver oil when compared with fish oils. The omega-3 fatty acids are also associated with phospholipids in these supplements, which has been suggested to improve bioavailability. (a little)

Krill oil: This oil is made from crustaceans, not fatty fish. (Shrimp anyone?) They usually contain higher concentrations of EPA. It’s similar to cod liver oil in that it also has vitamins A and E. It also has the omega-3 fatty acids are also associated with phospholipids in these supplements. Despite the hype, the bioavailability argument isn’t that air tight with current research (reference below).


Well, right off the bat, cod liver oil and krill oil have higher concentrations of vitamins A and D, but more importantly, cod is classified by the Natural Resources Defense Council (NRDC) as having “moderate mercury” concentrations, when compared with anchovies, sardines, and salmon, which is the most common fish used for “fish oil”. An argument is made for krill oil containing fewer heavy metal contaminants because of it being at the bottom of the food chain. There may be some truth to that, but all these supplements are generally purified anyways, so the absolute concentration of the product should be the only concern. That being said, the purification isn’t perfect and if you start out with more mercury before purification you will likely end up with more afterwards. Even if the mercury levels were identical between cod, krill, and the other oily fish, the levels of vitamin A and D are significantly higher in cod liver oil and krill oil. Depending on your diet and what other vitamins you take, you may have to worry about taking in too much vitamin A or D. Make sure to check your labels and your amounts!

So what’s so good about these oils?

The most abundant components in krill oil, cod liver oil and fish oils are, EPA and DHA, (omega-3 fatty acids), vitamin A and vitamin D. Let’s take a look at each one:

EPA (eicosapentaenoic acid, an omega-3 fatty acid): EPA EPA is a precursor to another compound, prostaglandin-3, which has been shown to inhibit platelet aggregation, as well as a precursor to DHA.

DHA (docosahexaenoic acid, an omega-3 fatty acid): DHA DHA is one of the main structural components in the human brain in addition to skin, sperm, and retinas, so it merits some further looking into to see if taking extra can be beneficial.

Since omega-3 fatty acids are generally the primary component one hopes to get out of taking fish oil or cod liver oil, let’s take a look at what they do.

Why are Omega-3 fatty acids AMAZING?: Molecular mechanisms of action are usually hard to come by because the body has so many pathways and many different ways of using the same compound. Sometimes the best we can do is to figure out correlations of supplements with outcomes, such as improved cardiovascular health metrics or improved cholesterol levels, which is the case for omega-3 fatty acids. In a sense, that is really the only important outcome anyways. The study of omega-3 fatty acids all started out because there seemed to be correlations with people who eat fish and reduced mortality from various causes. Since omega-3s are a primary component in these fish, scientists started to look more closelyu at these types of compounds.

By this point, the literature on fish oil is pretty straight forward. It’s associated with many good outcomes. “Omega-3 fatty acids can ultimately increase arrhythmic thresholds, reduce blood pressure, improve arterial and endothelial function, reduce platelet aggregation, and favourably affect autonomic tone.” Omega 3 Fatty Acids Benefits Figure Abbreviations: GISSI-P and AOT: Different trials done on supplementation effects. CAD: Cotonary artery diseases. CVD: Cardiovascular diseases. (Kromhout et al., European Heart Journal doi:10.1093/eurheartj/ehr362, 2011) Its known mechanisms of action include acting as an anti-inflammatory( Calder PC. N-3 polyunsaturated fatty acids and inflammation: from molecular biology to the clinic. Lipids 2003;38:343–352), improved mitochondrial function and improved ATP generation efficiency (Swann PG, Venton DL, Le Breton GC. Eicosapentaenoic acid and docosahexaenoicacid are antagonists at the thromboxane A2/prostaglandin H2 receptor in human platelets. FEBS Lett 1989;243:244–246.), it inhibits platelet aggregation (good if you are at risk for heart attacks) (. Sampath H, Ntambi JM. Polyunsaturated fatty acid regulation of genes of lipid metabolism. Annu Rev Nutr 2005;25:317–340.), it lowers triglyceride levels, improves endothelial function ( Shimokawa H, Lam JYT, Chesebro JH, Bowie EJW, Vanhoutte PM. Effects of dietary supplementation with cod-liver oil on endothelium-dependent responses in porcine coronary arteries. Circulation 1987;76:898–905.), it helps to stabilize plaques, and has anti-arrhythmic effects. (Hallaq H, Smith TW, Leaf A. Modulation of dihydropyridine-sensitive calcium channels in heart cells by fish oil fatty acids. Proc Natl Acad Sci USA 1992;89:1760–1764)

How much fish oil should I take?

I like to use the natural amounts encountered evolution as a safe baseline for supplementation levels, but it’s not good for this case because the ratio of fatty acids (Omega-3 to Omega-6) is important, and our western diets skews what the “optimal amount” should be because of our increase Omega 6 fatty acid intake. As a result, the amount of supplementation may be very dependent on your individual diet. If you eat lots of Omega-6 Fatty acids, you may need to up your intake of Omega-3 Fatty acids to compensate. Common sources of Omega-6 fatty acids include: poultry, eggs, avocado, nuts, soybean oil, pumpkin seeds, etc…( It seems that elevated levels of Omega-6 relative to Omega-3 may lead to heart attacks, strokes, osteoporosis, obesity, and cancer. (Calder, Philip C. (1 June 2006), American Journal of Clinical Nutrition (American Society for Nutrition) 83 (6, supplement): 1505S–1519S.PMID 16841861.) It seems pretty safe that you won’t be overdosing on Omega-3 supplements since a good sized pill only contains about 300mgs of it.

However, people with an intake of ~0.6 grams per day were able to see a benefit compared with those with an intake of 0.07g per day in one study. (Alberto Ascherio et al., The New England Journal of Medicine, 1995) Additionally, intake of between 5g/day and 47g/day showed a positive correlation with DHA levels in beast milk in another study. (WS Harris et al., Am J Clin Nutr, 1984.) From this, it seems that taking “some” is better than taking none, and that the maximum allowable intake is fairly high. For reference, a 3 ounce portion of salmon has about 1.5g of omega-3’s.

Are all supplements made equal?

Yes and no. The chemical themselves, if accurately portrayed by the brands, are identical. That being said, brands are different and there are other chemicals in the supplements that may help facilitate transport and bioavailability. Krill Oil
in particular popular for being advertised for requiring lower doses in order to be effective, and one study think it may be because the Omega-3’s are found to phospholipids in those supplements vs fish oil. That particular study didn’t find a strong conclusion for that hypothesis, but it did show a slight increase in bioavailability from krill oil. (Schuchardt et al. Lipids in Health and Disease 2011, 10:145) What I gather from that is that there may be something to it, but it’s so small that it’s really not that important. If you’re worried, pop an extra pill of fish oil. As for cod liver oil, I would avoid that because of the higher concentrations of vitamin D and A. One may think of having “extra vitamins” as a good thing, but I would argue that overdosing on vitamins as a “side-effect” to increasing your Omega 3 intake isn’t a good compromise. Vitamins are cheap and can be bought separate. It’s better to control what you put in your body, if you can.

Additionally, since manufacturers get different fish sources and process them in different facilities, the amounts of heavy metals can vary between brands and likely between batches as well. This is a hard thing to monitor constantly, so you’ll just have to pick a trustworthy brand and go with it. I came across a few studies that did look at a few brands’ mercury levels back in 2003. (Arch Pathol Lab Med—Vol 127, December 2003), and the best brands as of then were Kirkland Fish Oil, Omega Brite (Doesn’t seem to be sold anymore), and Sundown Naturals Fish Oil I personally love Kirkland brands because they likely sell to the largest market. I find safety in numbers because those companies have more reputation to lose if they screw up. (Similar reason I would feel safest in a solid gold, solid diamond windowed airplane, because you KNOW they will find a way to keep that thing from crashing.) Additionally, even back in 2003, Kirkland was taking care of their business by keeping mercury levels as the lowest levels.

Conclusion! If you’ve got money to throw around and don’t mind having less control over your vitamin A and D intake, then go for Krill Oil. Personally, I’m using the Kirkland brand fish oils. Economic, and I can take a ton of them to make up for differences in bioavailability without affecting my vitamin A or D levels.