Benefits
Knee joint comfort, stiffness and function
In 235 adults with mild to moderate knee osteoarthritis, 4 g a day for 6 months improved knee pain, stiffness and function slightly more than placebo, below published thresholds for a meaningful change. A 30 day trial of 2 g a day in 50 adults with mild knee pain favored krill oil on some items, not on overall pain scores. The largest trial, 2 g a day for 24 weeks in 262 people, found no pain benefit. Industry funded or supplied all three.
Muscle strength and size in older adults
In a 6 month trial in 102 healthy adults over 65 who exercised little, 4 g a day of Superba Boost krill oil (Aker BioMarine) raised knee extensor strength 9.3 percent, grip strength 10.9 percent and thigh muscle thickness 3.5 percent relative to a vegetable oil control, without changing a physical performance battery or quality of life. This is a single trial; the authors declared no conflicts of interest.
Omega-3 index in one comparison with fish oil
In a double-blind crossover trial in 24 healthy volunteers, krill oil and fish oil each gave 600 mg omega-3 a day for 4 weeks, and the omega-3 index rose more with krill oil. The krill oil was supplied by its maker, Enzymotec, whose employees designed the study. This is a blood marker in one small trial; no health outcome, taste or tolerability was compared.
Blood triglycerides and cholesterol, lipid markers
In 300 adults with raised triglycerides, 0.5 to 4 g a day for 12 weeks lowered triglycerides 10.2 percent versus olive oil only after all doses were pooled, in a maker-sponsored trial. An older 90 day trial of a maker-supplied krill oil reported large lipid changes. In other trials, lipids did not differ from placebo or cholesterol rose. These are blood markers, not heart outcomes.
Choline and astaxanthin content
Krill oil carries choline as phosphatidylcholine: a single 8 g dose of one krill oil supplied 572 mg choline and raised blood choline about as much as choline bitartrate, in a 12 person study sponsored by the maker. One knee trial product held 0.11 mg astaxanthin per 1 g capsule. No study cited here linked either to a health outcome.
Mechanism of action
EPA and DHA bound to phospholipids
In krill oil much of the EPA and DHA is attached to phospholipids, mainly phosphatidylcholine, rather than to the triglycerides of fish oil: 73 percent in one knee trial product. In one small crossover trial, the omega-3 index rose more than with fish oil at the same omega-3 dose. Why phospholipid omega-3s might be taken up differently is proposed, not shown, by the studies cited here.
Choline from phosphatidylcholine
Phosphatidylcholine in krill oil is a source of choline. After a single 8 g dose of one krill oil, free choline in blood reached a similar level to choline bitartrate, peaked later, and produced higher betaine and much lower TMAO. This was a small study sponsored by the maker, and no trial has linked this choline to a health outcome.
Omega-3 effects on joints and muscle are proposed
Once absorbed, EPA and DHA enter cell membranes, which the omega-3 index tracks. They are proposed to ease joint discomfort through inflammatory signaling and to support muscle through membrane effects, but in the 6 month knee trial inflammatory markers did not differ from placebo, and in the muscle trial C-reactive protein did not change.
Astaxanthin
Krill oil contains a small amount of astaxanthin, the red carotenoid that colors krill: 0.11 mg per 1 g capsule in one knee trial product. No study cited here measured antioxidant status or any health effect of astaxanthin in people taking krill oil.
Clinical trials
Multicenter, randomized, double-blind, placebo-controlled parallel trial; 4 g a day of Swisse High Strength Deep Sea Krill Oil made with Superba Boost (Aker BioMarine), giving 0.60 g EPA and 0.28 g DHA a day, versus a vegetable oil blend placebo; supported by Swisse Wellness, which helped design the study; registered NCT03483090 (Stonehouse et al. 2022, Am J Clin Nutr)
235 adults aged 40 to 65 with clinically diagnosed mild to moderate knee osteoarthritis, regular knee pain and low omega-3 intake (117 krill oil, 118 placebo).
Knee pain improved in both groups, more with krill oil (adjusted between-group difference at 6 months -5.18 on a 0 to 100 WOMAC scale, p = 0.04); stiffness (-6.45) and physical function (-4.67) also improved more (p < 0.05). The authors note these differences were below published minimal clinically important improvement values. NSAID use, serum lipids, inflammatory and safety markers did not differ, and the omega-3 index rose from 6.0 to 8.9 percent versus 5.5 to 5.4 percent on placebo.
Multicenter, randomized, double-blind, placebo-controlled trial in five Australian cities in people with knee osteoarthritis, significant knee pain and effusion-synovitis on MRI; 2 g a day of krill oil versus matching placebo for 24 weeks; funded by the National Health and Medical Research Council of Australia, with krill oil and placebo softgels and omega-3 index testing provided in kind by Aker BioMarine, the study funders had no role in design, analysis or reporting (Laslett et al. 2024, JAMA)
262 adults (mean age 61.6, 53 percent women) with significant pain and effusion-synovitis on MRI; 130 krill oil, 132 placebo; 222 completed.
Pain on a 0 to 100 visual analog scale, the primary outcome, fell about 20 points in both groups with no difference between them (-19.9 versus -20.2; between-group difference -0.3, 95 percent CI -6.9 to 6.4). One or more adverse events were reported by 51 percent on krill oil and 54 percent on placebo.
Randomized, double-blind, parallel-group, placebo-controlled trial; 2 g a day of Superba Krill Oil (Aker BioMarine) in eight 250 mg capsules versus safflower oil; capsules prepared and the study funded by Sunsho Pharmaceutical, a Japanese company, which planned the study with the investigators; registered UMIN000014413 (Suzuki et al. 2016, PLoS One)
50 adults aged 38 to 85 with mild knee pain at an orthopedic clinic in Japan.
Both groups improved on the Japanese knee questionnaires. After adjustment, the krill oil group improved more than placebo on knee pain while sleeping and standing (both p < 0.001) and on knee range of motion (p = 0.011), and on two pain and stiffness questions; two other questionnaire items favored placebo. The knee pain visual analog scale and the total knee questionnaire score did not differ between groups. Plasma EPA rose with krill oil.
Randomized, double-blind, controlled trial; 4 g a day of SuperbaBoost krill oil (Aker BioMarine; each 1 g capsule 193 mg EPA, 96 mg DHA, 79 mg choline, as described in the secondary analysis; listed as Aker Biomarine Superba Krill Oil in the registry) versus a vegetable oil blend control for 6 months, with knee extensor (quadriceps) maximal torque as the primary outcome; registered NCT04048096; the authors declared no conflicts of interest (Alkhedhairi et al. 2022, Clin Nutr)
102 healthy adults over 65 with a BMI under 35 who did less than 1 hour a week of structured exercise; 94 completed (49 krill oil, 45 control), mean age 71.
Relative to control, quadriceps maximal torque, the primary outcome, rose 9.3 percent, grip strength 10.9 percent and thigh muscle thickness 3.5 percent (p < 0.05), and the omega-3 index rose 61 percent. The short physical performance battery, quality of life and most neuromuscular measures did not differ.
Double-blind, randomized, placebo-controlled crossover trial with three 4 week phases separated by 8 week washouts: krill oil (K-REAL, supplied by Enzymotec) or fish oil, each giving 600 mg n-3 PUFA a day, or a corn oil control; two authors were Enzymotec employees who designed the study and wrote the protocol; registered NCT01323036 (Ramprasath et al. 2013, Lipids Health Dis)
24 healthy volunteers.
The omega-3 index, a blood marker of omega-3 status, rose more after krill oil than after fish oil (p = 0.0143) or control (p < 0.0001). Serum triglycerides and HDL cholesterol did not change with any treatment, while total and LDL cholesterol rose after both krill and fish oil compared with control. No treatment-related adverse events were reported.
Multicenter, randomized, double-blind, placebo-controlled trial with five groups (olive oil placebo or 0.5, 1, 2 or 4 g a day of krill oil, named Superba Krill Oil in the registry entry NCT01415388) for 12 weeks; sponsored by Aker BioMarine, which employed four of the five authors, the fifth being from the consultancy Intertek Cantox (Berge et al. 2014, Nutr Res)
300 adults with low habitual fish intake and fasting triglycerides of 150 to 499 mg/dL.
Because triglycerides varied widely within individuals, the four krill oil groups were pooled; pooled krill oil lowered serum triglycerides by a calculated 10.2 percent relative to placebo, and LDL cholesterol did not rise. The abstract does not report a dose response, and the authors said a study with more measurements per group was needed to raise confidence in the result.