Whilst EPA and DHA are both considered to be important regulators of immunity, platelet aggregation and inflammation, their health-influencing by-products arise from very different pathways and their effects in the body differ. DHA is the most abundant omega-3 fatty acid in cell membranes, present in all organs and most abundant in the brain and retina, playing an important structural role. EPA is present structurally only in minute quantities, always being utilised and under constant demand to be replaced. Whilst DHA provides mainly a structural role, it is becoming evident that EPA may be the dominant functional fatty acid out of the two in many areas of health and especially in inflammatory conditions.
Luo, J Rizkalla SW Vidal H Oppert JM Colas C Boussairi A Guerre-Millo M Chapuis AS Chevalier A Durand G Slama G. Moderate intake of n-3 fatty acids for 2 months has no detrimental effect on glucose metabolism and could ameliorate the lipid profile in type 2 diabetic men. Results of a controlled study. Diabetes Care. 1998;21(5):717-724. View abstract.
Evidence in the population generally does not support a beneficial role for omega−3 fatty acid supplementation in preventing cardiovascular disease (including myocardial infarction and sudden cardiac death) or stroke.[4][19][20][21] A 2018 meta-analysis found no support that daily intake of one gram of omega-3 fatty acid in individuals with a history of coronary heart disease prevents fatal coronary heart disease, nonfatal myocardial infarction or any other vascular event.[6] However, omega−3 fatty acid supplementation greater than one gram daily for at least a year may be protective against cardiac death, sudden death, and myocardial infarction in people who have a history of cardiovascular disease.[22] No protective effect against the development of stroke or all-cause mortality was seen in this population.[22] Eating a diet high in fish that contain long chain omega−3 fatty acids does appear to decrease the risk of stroke.[23] Fish oil supplementation has not been shown to benefit revascularization or abnormal heart rhythms and has no effect on heart failure hospital admission rates.[24] Furthermore, fish oil supplement studies have failed to support claims of preventing heart attacks or strokes.[7]
Several small studies have shown that combination therapy with fish oil and HMG CoA reductase inhibitors is safe.56–61 The largest trial to date, the JELIS trial,32 was an open label trial of 18,645 Japanese adults with hypercholesterolemia who were randomized to a standard statin regimen or a fish oil formulation containing 1.8 g of EPA added to a statin medication. The cohort was made up mostly of postmenopausal, nonobese women with a 15% to 20% incidence of diabetes, tobacco use, or CAD. The primary outcome of any major cardiovascular event, at a mean of 4.6 years, was moderately reduced by a relative risk reduction of 26%. Both unstable angina and nonfatal MI were reduced, but no change was seen in sudden death. Overall, the findings were remarkable because at baseline approximately 90% of Japanese consumed at least 900 mg of EPA and DHA per day.62 The rates of cancer, joint pain, lumbar pain, or muscle pain were similar in the 2 groups. There was a similar rate of increase in measures of creatine phosphokinase, but more patients had an increase in aspartate aminotransferase levels (0.6% vs. 0.4%) in the fish oil group. The rate of bleeding was 1.1% in the fish oil combination group versus 0.6% in the HMG–CoA reductase inhibitor group.
LCn3s are long chain fatty acids from fish, including eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). ALA is plant-based omega 3-alpha‐linolenic acid. Fatty acids are essentially chains of carbon atoms with an OOH group at one end. The available binding sites on the carbon atoms are filled with hydrogen atoms. If every binding site is occupied with a hydrogen, that is a saturated fatty acid. If instead of hydrogen atoms there is a double bond between two adjacent carbon atoms, that is an unsaturated fatty acid. If there are multiple double bonds, that is polyunsaturated. Omega 3 fatty acids are unsaturated, with a double bond between the third and fourth carbon atoms from the end opposite the OOH group.
A new Cochrane systematic review, published today in the Cochrane Library, combines the results of seventy-nine randomised trials involving 112,059 people. These studies assessed effects of consuming additional omega 3 fat, compared to usual or lower omega 3, on diseases of the heart and circulation. Twenty-five studies were assessed as highly trustworthy because they were well designed and conducted.
Kabir, M., Skurnik, G., Naour, N., Pechtner, V., Meugnier, E., Rome, S., Quignard-Boulange, A., Vidal, H., Slama, G., Clement, K., Guerre-Millo, M., and Rizkalla, S. W. Treatment for 2 mo with n 3 polyunsaturated fatty acids reduces adiposity and some atherogenic factors but does not improve insulin sensitivity in women with type 2 diabetes: a randomized controlled study. Am.J.Clin.Nutr. 2007;86(6):1670-1679. View abstract.
For patients without documented CAD, the American Heart Association 2006 Diet and Lifestyle Recommendations advise the consumption of at least 2 servings of fish per week, preferably fatty fish high in DHA and EPA.65 The guidelines also recommend a daily fish intake equivalent to 1 g/d of EPA and DHA for secondary prevention of CAD. Fish oil supplements containing EPA and DHA are suggested as an alternative to fatty fish consumption for secondary prevention.
Fish oil therapy is efficacious and safe for patients with severe to moderate hypertriglyceridemia. Combination therapy with HMG-CoA reductase inhibitors is also efficacious and has not been associated with any serious adverse reactions. Fish oil therapy added to fenofibrate in patients with severe hypertriglyceridemia is also effective and safe. Accordingly, it may be a safe and effective adjunct in the pharmacotherapy of the mixed lipid disorder that is frequently encountered in patients with the metabolic syndrome and/or type II diabetes mellitus.
Increased consumption of omega 3 fats is widely promoted globally because of a common belief that that it will protect against heart disease. There is more than one possible mechanism for how they might help prevent heart disease, including reducing blood pressure or reducing cholesterol. Omega 3 fats are readily available as over-the-counter supplements and they are widely bought and used.

There was a significantly greater association of treatment with reduced anxiety symptoms in participants receiving omega-3 PUFAs than in those not receiving omega-3 PUFAs in the subgroup with an EPA percentage less than 60% (k, 11; Hedges g, 0.485; 95% CI, 0.017-0.954; P = .04; Figure 4)35,49,52,54-61 but no significant difference in the association of treatment with reduced anxiety symptoms between participants receiving omega-3 PUFAs and those not receiving omega-3 PUFAs in the subgroup with an EPA percentage of at least 60% (k, 9; Hedges g, 0.092; 95% CI, –0.102 to 0.285; P = .35) (Figure 4).33,34,36,47,48,50,51,53,60 There were no significantly different estimated effect sizes between these 2 subgroups by the interaction test (P = .13).
Evidence linking fish oil and cancer has been all over the map. Some research suggests diets high in fatty fish or fish oil supplements might reduce the risk of certain cancers, including prostate cancer. Other research shows just the opposite, a  link between eating a lot of oily fish or taking potent fish oil supplements and a 43% increased risk for prostate cancer overall, and a 71% increased risk for aggressive prostate cancer.
Interestingly, the results are also consistent with our recent findings that somatic anxiety is associated with omega-3 PUFA deficits and the genetic risks of PUFA metabolic enzyme cytosolic phospholipase A2 in major depressive disorder62,63 and interferon α–induced neuropsychiatric syndrome.63,64 Brain membranes contain a high proportion of omega-3 PUFAs and their derivatives and most animal and human studies suggest that a lack of omega-3 PUFAs in the brain might induce various behavioral and neuropsychiatric disorders,16,65-70 including anxiety-related behaviors.12,18,19,32,49,71 Emerging evidence suggests that omega-3 PUFAs interfere with and possibly control several neurobiological processes, such as neurotransmitter systems, neuroplasticity, and inflammation,12,72 which is postulated to be the mechanism underlying anxiety and depression.
The omega-3 index is also important because it is inversely related to one’s omega-6 to omega-3 ratio — another important measurement (3). A lower omega-6/omega-3 ratio (meaning, you consume a balanced amount of these two fatty acid families) is associated with a reduced risk of many chronic diseases, including cardiovascular disease, cancer, and autoimmune disease, to name a few (4). Of course, most people get far too much omega-6 and too little omega-3, thanks to the plethora of highly processed foods in the Western diet.

To reach the required dose of EPA for treating certain conditions such as depression, CVD or CFS/ME you would need to take approximately 1-2 grams of ‘free EPA’ daily. Even with a concentrated omega-3 fish oil supplement, offering 180 mg excess EPA over DHA, this would require 10-20 capsules daily – significant in terms of volume and cost, and not efficient in terms of uptake in the body as our capacity for fat absorption is limited. The most effective and efficient way to ensure high EPA uptake in the body rapidly is to supplement with pure EPA for a minimum of 3-6 months.
Heart rate variability, a possible surrogate outcome for the risk of sudden death, was assessed in a randomized trial of myocardial infarction (MI) survivors with an ejection fraction of 40%. In the 49 patients that were randomized to either fish oil or olive oil, Holter monitor recordings showed an increase in heart rate variability in the fish oil group.31 In a larger cohort assessed in the Japan EPA Lipid Intervention Study (JELIS),32 however, no difference in heart rate variability could be attributed to fish oil.
What are the benefits of cod liver oil? This article provides detailed information on the health benefits associated with cod liver oil, and its potential therapeutic properties. This article looks at some of the claims that cod liver oil might improve cardiovascular health, ease joint stiffness caused by arthritis, and repair wounds. Read on to learn more. Read now
After the age of five, the development of the brain and CNS starts to reduce and the body’s need for DHA reduces. This is a good time to increase EPA in the diet, as studies show that EPA can help with childhood behaviour and academic performance, as well as focus, attention and reducing aggression. Dry skin conditions, asthma and allergies are also common in children and good levels of EPA at this time can help reduce the inflammation associated with these issues.
Of great clinical importance, EPA and DHA supplementation during pregnancy has been associated with longer gestation and increased concentrations of EPA and DHA in fetal tissues (21). In 2005, preterm births accounted for 12.7% of all births in the United States, increasing the likelihood of health complications (22). Carrying a baby to term is very important because prematurity is the cause of various infant diseases and can lead to death; preterm delivery is an underlying factor for 85% of the deaths of normally formed infants (23). One mechanism by which EPA and DHA may decrease the incidence of preterm birth is by decreasing prostaglandin E2 and prostaglandin F2α production, therefore reducing inflammation within the uterus, which could be associated with preterm labor (21, 24). Several studies investigated EPA and DHA intake during pregnancy and its correlation with longer gestation. Conclusions were that EPA+DHA supplementation during pregnancy delayed the onset of delivery to term or closer to term; however, supplementation did not delay delivery to the point of being post-term (20, 23, 25). This supports the evidence that EPA+DHA ingestion leads to optimal pregnancy length. EPA+DHA supplementation reduced the HR of preterm delivery by 44% (95% CI: 14–64%) in those who consumed relatively low amounts of fish and 39% (95% CI: 16–56%) in those who consumed medium amounts of fish; however, a level of statistical significance was not met (P = 0.10) (23). The Judge et al. (20) study found that women who had DHA supplementation from gestation week 24 until full-term delivery carried their infants significantly (P = 0.019) longer than did the women in the placebo group. One study found that DHA supplementation after gestation week 21 led to fewer preterm births (<34 wk of gestation) in the DHA group compared with the control group (1.09% vs. 2.25%; adjusted RR, 0.49; 95% CI: 0.25–0.94; P = 0.03). Also, mean birth weight was 68 g heavier (95% CI: 23–114 g; P = 0.003) and fewer infants were of low birth weight in the DHA group compared with the control group (3.41% vs. 5.27%; adjusted RR, 0.65; 95% CI: 0.44–0.96; P = 0.03) (25).

Meta-analyses (research that combines and analyzes results of multiple studies) generally suggest that the omega-3s are effective, but the findings are not unanimous because of variability between doses, ratios of EPA to DHA, and other study design issues. The most effective preparations appear to have at least 60% EPA relative to DHA. While DHA is thought to be less effective as an antidepressant, it may have protective effects against suicide. Recent work at Massachusetts General Hospital and Emory University suggests that depressed individuals who are overweight and have elevated inflammatory activity may be particularly good candidates for EPA treatment.
Pumps the Heart: Where to begin? Omega-3s reduce triglycerides, stabilize your heartbeat, make platelets "less sticky" and can even lower blood pressure. The EPA you get with your daily DHA dose helps prevent artery-blocking clots. In the Iowa Nurses Study (and 3 others), 1 ounce of nuts a day decreased the incidence of heart disease between 20 and 60 percent.
EPA is the precursor to DHA in the body and can be converted to DHA with the enzyme delta-6 desaturase, but this process is inefficient in many people (much like the inefficiency of short-chain omega-3s to long-chain). For those individuals taking pure EPA products as well as those taking our EPA-rich products, we still recommend eating oily fish at least once each week to provide a natural source of DHA. Fish provides a unique nutritional package, supplying the diet with important amino acids (the building blocks of proteins) and antioxidants, including vitamins and minerals needed to process fats, so eating fish will also support the natural enzyme-dependent EPA to DHA conversion.
Pay attention to the quality of fish oil when purchasing it. It is obtained from almost all fishes – fresh water, farm, ocean, deep sea and shallow sea fish. All these fishes can be contaminated with toxic compounds such as mercury, arsenic, lead, forms of calcium, furans, dioxins, PCBs, and methylmercury, and can negatively affect the human body. Therefore, the fish oil used must be pure. Many companies sell ultra refined or distilled fish oil, but you should always check if the standards have been followed and research on the company or the product before adding it to your diet.
The FDA recommends that consumers do not exceed more than three grams per day of EPA and DHA combined, with no more than 2 grams from a dietary supplement.[56] This is not the same as 3000 mg of fish oil. A 1000 mg pill typically has only 300 mg of omega-3; 10 such pills would equal 3000 mg of omega-3. According to the European Food Safety Authority's (EFSA) Panel on Dietetic Products, Nutrition and Allergies, supplementation of 5 grams of EPA and DHA combined does not pose a safety concern for adults.[57] Dyerberg studied healthy Greenland Inuit and found an average intake of 5.7 grams of omega-3 EPA per day; among other effects these people had prolonged bleeding times, i.e., slower blood clotting.[58]
An excessive dosage of fish oil can have adverse allergies and side effects on the body. Furthermore, fish oil can be problematic if you have certain conditions so it is necessary to consume fish oil supplements cautiously. Moreover, it can be consumed in various forms. These include eating the fish directly by baking, roasting, frying, grilling, broiling, or smoking it. It can also be consumed in the form of concentrated dietary supplements like liquid, tablet, capsule, pill, or soft gels. Also, there are various pharmaceutical grades of the oil. It is not necessary to constantly consume pharmaceutical-grade oil or even supplements. You should also consult your doctor to confirm the mode of consuming fish oil and the overall need for it in your diet.
2. Omega-3 normalizes and regulates your cholesterol triglyceride levels. Compared to a statin, both fish oil and krill oil are more efficient in doing this. According to a study comparing the efficiency of krill and fish oils in reducing triglyceride levels,7 both oils notably reduced the enzyme activity that causes the liver to metabolize fat, but krill had a more pronounced effects, reducing liver triglycerides significantly more.

Jatoi, A., Rowland, K., Loprinzi, C. L., Sloan, J. A., Dakhil, S. R., MacDonald, N., Gagnon, B., Novotny, P. J., Mailliard, J. A., Bushey, T. I., Nair, S., and Christensen, B. An eicosapentaenoic acid supplement versus megestrol acetate versus both for patients with cancer-associated wasting: a North Central Cancer Treatment Group and National Cancer Institute of Canada collaborative effort. J.Clin.Oncol. 6-15-2004;22(12):2469-2476. View abstract.

The chemical structures of EPA and DHA are very similar and they compete for uptake and processing resources. During digestion, the triglyceride molecules in standard fish oil are broken down into a mono glycerol and two free fatty acids, small enough to be absorbed into cells of the gut lining. More often than not, DHA is the fatty acid that remains attached to the glycerol backbone, meaning in essence that DHA gets a ‘free pass’ into the gut, while the remaining free fatty acids (more often EPA) must reattach onto a glycerol molecule or risk being oxidised and used as fuel. The implication of this is that DHA levels in our cells are often concentrated at the expense of EPA after absorption when taking EPA and DHA in the standard ratio of 1.5 to 1.
People used to believe that osteoporosis and osteoarthritis were the result of aging and reduced intake of calcium and milk products. Science has now shown that these bone and joint disorders are, in part, due to inflammation. Because of this, bones and joints are prime targets for the anti-inflammatory properties of omega-3 oils from both fish and krill.
Fish oil can be obtained from eating fish or by taking supplements. Fish that are especially rich in the beneficial oils known as omega-3 fatty acids include mackerel, herring, tuna, salmon, cod liver, whale blubber, and seal blubber. Two of the most important omega-3 fatty acids contained in fish oil are eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). Make sure to see separate listings on EPA and DHA, as well as Cod Liver Oil, and Shark Liver Oil.