What is different about krill oil
Both oils supply the two long-chain omega-3 fatty acids that matter most, EPA and DHA. Fish get them from the algae at the bottom of the food chain; krill, small shrimp-like crustaceans, eat those algae directly.
| Fish oil | Krill oil | |
|---|---|---|
| Main omega-3 form | Triglycerides (or ethyl esters in some concentrates) | Mostly phospholipids |
| EPA to DHA ratio | Roughly 1 to 1 in many products, varies widely | About 2 to 1, more EPA |
| EPA plus DHA per gram of oil | About 300 mg in a typical 1,000 mg softgel; concentrates carry more | About 150 to 180 mg in the doses studied |
| Other content | Varies by product | Contains astaxanthin, a red antioxidant pigment |
Absorption: what the studies show
The NIH Office of Dietary Supplements sums it up: some studies suggest krill's phospholipids are somewhat better absorbed than the omega-3s in fish oil, and others do not. All forms, including fish oil triglycerides and ethyl esters, significantly raise EPA and DHA in the blood.
In one 7-week randomized trial, 3 g a day of krill oil (543 mg EPA plus DHA) raised blood omega-3 levels about as much as 1.8 g of fish oil (864 mg EPA plus DHA). A 2015 review said the studies are limited and hard to compare, and that more human trials are needed before a firm conclusion can be made.
Evidence strength: low and mixed for a small absorption edge, and no good evidence yet that krill oil leads to better health outcomes than fish oil.
What omega-3 supplements can and can't do
Most large trials used fish oil, not krill oil. The picture so far:
- Heart: At about 1 g a day, omega-3 supplements did not significantly lower combined heart attacks, strokes and cardiovascular deaths in large trials of people without heart disease. A 2020 review found a slight reduction in coronary events. A high-dose prescription EPA product lowered events in people with heart disease or high risk who already took statins, but that is a medicine, not a supplement.
- High triglycerides: NIH notes some evidence that people with heart disease or high triglycerides may benefit from omega-3 supplements.
- Stroke: Little or no effect in reviews.
- Atrial fibrillation: Two large trials found 4 g a day slightly raised the risk of atrial fibrillation in people with or at high risk of heart disease.
Cost per gram of EPA plus DHA
Price per bottle tells you little. Compare the cost per gram of EPA plus DHA instead:
- Find EPA plus DHA per serving on the label (not total fish oil or krill oil).
- Multiply by servings per bottle to get total EPA plus DHA, then divide by 1,000 to get grams.
- Divide the price by that number.
Using the figures above, getting 1 g of EPA plus DHA takes about 3.3 g of typical fish oil, about 2 g of the concentrated fish oil in that 7-week trial, and about 5.5 to 6.5 g of krill oil. So unless a krill oil costs far less per gram of oil, it will cost more per gram of omega-3.
A free Gabriel account pays cost-plus prices on supplements, and with Gabriel Core or Plus member prices are lower still. For example, omega-3 fish oil, 60 softgels, is $47.30 for Plus members (list price $86.99). Check the label for its EPA plus DHA per softgel to work out your cost per gram.
Side effects and who should be careful
- Blood thinners. Fish oil may lengthen clotting time in people on warfarin. Most research finds 3 to 6 g a day does not significantly change anticoagulation, but prescribing information for omega-3 drugs advises monitoring. If you take warfarin or another blood thinner, ask your clinician before starting.
- Shellfish allergy. Krill are crustaceans, so ask a clinician before trying krill oil if you have a shellfish or other seafood allergy.
- Dose. FDA has concluded that supplements providing up to 5 g a day of EPA plus DHA are safe when used as recommended.
- Common side effects are mild: fishy aftertaste, bad breath, heartburn, nausea, loose stools and headache.
Get care right away for unusual bleeding or bruising, or for a racing, fluttering or irregular heartbeat while taking omega-3 supplements.
Common questions
Is krill oil better than fish oil?
Not clearly. Some studies suggest krill's phospholipid omega-3s are absorbed a bit better, others find no difference, and krill oil usually supplies less EPA and DHA per gram, so it often costs more per gram of omega-3.
How much krill oil equals fish oil?
In one trial, 3 g of krill oil with 543 mg EPA plus DHA raised blood omega-3 levels about as much as 1.8 g of fish oil with 864 mg. Compare products by EPA plus DHA per serving.
Does krill oil cause fishy burps?
Any omega-3 oil can. NIH lists an unpleasant taste, bad breath, heartburn and stomach upset among the usual mild side effects of omega-3 supplements, whatever the source.
Can I take fish oil with blood thinners?
Ask your clinician first. Typical doses usually don't change warfarin control much, but omega-3s can lengthen clotting time, so your clinician may want to monitor you.
Is fish oil safe every day?
For most adults, yes at usual doses. FDA considers up to 5 g a day of EPA plus DHA from supplements safe, though 4 g a day for several years was linked to a slightly higher risk of atrial fibrillation in people with or at high risk of heart disease.
Sources
- Omega-3 Fatty Acids: Fact Sheet for Health Professionals NIH Office of Dietary Supplements
- Omega-3 Supplements: What You Need To Know National Center for Complementary and Integrative Health (NIH)
- Comparison of bioavailability of krill oil versus fish oil and health effects (Ulven and Holven, 2015) Vascular Health and Risk Management
- A Look at Krill Oil's Benefits Cleveland Clinic Health Essentials
This guide is general information, not medical advice. It does not replace a visit with a licensed clinician. Gabriel membership is not health insurance.