What it is
EPA and DHA are long-chain omega-3s found in fatty fish and built into cell membranes, including those of the brain and retina. The body makes very little of them from plant ALA. People buy them mostly for the heart, the brain and the joints.
What the label does not say
- The number to read is the sum of EPA + DHA per capsule, not the weight of oil. A capsule showing 1,000 mg of fish oil typically provides 300 mg according to the NIH. The claims in the Health Canada monograph are calculated in EPA + DHA: 200 mg per day for cardiovascular health, 1,000 mg for triglycerides, 2,800 mg for rheumatoid arthritis pain.
- The oil oxidizes. Health Canada caps the peroxide value at 5 mEq/kg, the anisidine value at 20 and the TOTOX at 26. In an analysis of 36 supplements sold in New Zealand, 83% exceeded the peroxide limit, only 8% met all three thresholds, and the average EPA + DHA content reached 68% of the label, with no relation to the expiry date.
- On the cardiovascular side, the 2020 Cochrane review (86 trials, 162,796 participants) concludes that EPA and DHA supplements have little or no effect on mortality and cardiovascular events. The REDUCE-IT trial, often invoked on store shelves, covered 4 g per day of prescription icosapent ethyl in 8,179 at-risk patients on a statin, against a mineral oil placebo whose neutrality is disputed. That is not a 300 mg capsule.
- In people with or at high risk of cardiovascular disease, the NIH reports that 4 g per day for several years slightly increased the risk of atrial fibrillation in two large trials.
The forms on the shelf
- Standard fish oil: the NIH describes a typical 1,000 mg capsule of oil containing 180 mg of EPA and 120 mg of DHA, or 300 mg of omega-3 per 1,000 mg of oil.
- Ethyl esters (concentrates) versus natural or re-esterified triglycerides: the NIH indicates that triglycerides, free fatty acids and re-esterified triglycerides have a slightly higher bioavailability than ethyl esters, and the ethyl ester-based medication was given with meals in its trials.
- Krill oil: omega-3 mostly in phospholipid form, with bioavailability sometimes higher, sometimes equal to that of fish oil according to the studies cited by the NIH. The United States Pharmacopeia requires krill oil to contain only a minimum of 10% EPA and 5% DHA, versus 18% and 12% in the NIH's typical fish oil.
- Algal oil: 100 to 300 mg of DHA per serving according to the NIH, sometimes with EPA, in triglyceride form. It is the source for a vegan diet.
Published reference values
- No recommended intake exists for EPA and DHA. The adequate intake for ALA is 1.6 g per day for men and 1.1 g for women.
- The NIH reports that the FDA considers supplements providing no more than 5 g per day of EPA + DHA to be safe; the Health Canada monograph sets the same ceiling of 5,000 mg.
- Reported effects: aftertaste, fishy breath, heartburn, nausea, diarrhea. From 2 to 15 g per day, the NIH flags a possible lengthening of bleeding time.
- On blood triglycerides, the data are solid: a dose-dependent drop of about 15% in the Cochrane review, and a 44.9% drop with 4 g per day of prescription ethyl esters in patients above 500 mg/dL, with a median rise in LDL of 44.5%.
When
With a meal, especially for ethyl esters. The NIH points out that the major organizations recommend one to two servings of fish per week, which a standard capsule does not replace.
Keep apart from
- Warfarin and other anticoagulants or antiplatelets: the NIH indicates that fish oil could lengthen clotting time, even though most data at 3 to 6 g per day show no significant effect, and advises periodic INR monitoring. Monitoring, not spacing doses by the hour.
To mention to a professional
- Use of anticoagulants or antiplatelets, atrial fibrillation, planned surgery, allergy to fish or shellfish (krill), pregnancy and breastfeeding: check with a health care professional.
From the plate first
According to the NIH: farmed salmon 1.24 g of DHA and 0.59 g of EPA per 3 ounces; Atlantic herring 0.94 g and 0.77 g; canned sardines 0.74 g and 0.45 g; Atlantic mackerel 0.59 g and 0.43 g. Health Canada lists salmon, rainbow trout, herring, Atlantic mackerel and char among fish rich in omega-3 and low in mercury.
Sources
- NIH Office of Dietary Supplements, Omega-3 Fatty Acids (Health Professional)
- Cochrane, Omega-3 fatty acids for the primary and secondary prevention of cardiovascular disease (Abdelhamid et al., 2020), plain language summary
- Health Canada, natural health product monograph, Fish Oil
- Albert et al., Fish oil supplements in New Zealand are highly oxidised and do not meet label content of n-3 PUFA, Scientific Reports, 2015
- DailyMed (NIH), drug monograph for omega-3-acid ethyl esters
- USP-NF, Krill Oil monograph (minimum EPA and DHA content)
- Health Canada, Mercury in Fish (fish rich in omega-3 and low in mercury)
Educational information, drawn from the sources above. It does not replace the advice of a health professional, who remains the reference for your situation, your medications, pregnancy or breastfeeding.