Like fish oil, krill oil contains the omega-3 fatty acids eicosapentaenoic acid (EPA) and docosa-hexaenoic acid (DHA), famous for their heart-healthy and brain-boosting properties. But these fats are supposedly better absorbed from krill oil. Krill oil also contains potent antioxidants that, proponents claim, give it the edge over fish oil. Other purported advantages of krill oil are that it's pollution-free and comes with no fishy aftertaste. Numerous websites are now promoting krill oil as the 'ultimate' source of omega-3s.
Let's take a closer look at krill oil and see if the claims really do stack up.
The research into krill oil is still in its infancy but, so far, studies suggest that it may well be a superior source of omega-3 fatty acids.
For starters, while fish oil contains omega-3 fats in triglyceride form, a significant proportion of the omega-3 found in krill oil is in the form of phospholipids-fat-like molecules that deliver the fatty acids directly to the body's cells. Animal and human studies show that phospholipid-bound fatty acids have better absorption and delivery to the brain compared with triglyceride-bound fatty acids.
In one primate study, twice as many phospho-lipid-bound fatty acids accumulated in the brain compared with triglyceride-bound fatty acids (Pediatr Res, 2002; 51: 265-72). In another animal (pig) study, phospholipid-bound fatty acids increased brain DHA levels more than did fish oil (Lipids, 1999; 34: 5-16).
In a human trial, daily doses of 216 mg EPA and 90 mg DHA from krill oil provided greater fatty-acid increases than did daily doses of 212 mg EPA and 178 mg DHA derived from fish oil. At the end of the four-week study, average blood levels of EPA were 377 umol/L in the krill-oil group and 293 umol/L in the fish-oil group. And although the krill oil supplement provided just half as much DHA as the fish oil, average blood levels of DHA were around the same in both groups-476 umol/L in the krill-oil group and 478 umol/L in the fish-oil group (Nutr Res, 2009; 29: 609-15).
Another study in humans compared the bioavailability of omega-3s from krill and fish oils providing almost identical doses of EPA and DHA. Although the results were not statistically significant, the study found that krill oil consump-tion was associated with the highest levels of EPA and DHA in the blood, again suggesting better bioavailablity compared with fish oil (Lipids Health Dis, 2011; 10: 145).
Krill-oil proponents point out that, because omega-3s from krill oil are better absorbed, less is needed for a beneficial effect.
Another difference between krill and fish oils is that krill oil is naturally rich in antioxidants, including vitamins A and E, and the carotenoid astaxanthin (Altern Med Rev, 2003; 8: 171-9). These free-radical fighters provide the omega-3 fatty acids with natural protection against oxidation, so no additives are needed to maintain krill oil's stability. In contrast, fish oil commonly contains added antioxidants to prevent it from going rancid during production and on the shelf.
The natural antioxidants in krill oil may also offer additional health benefits. Astaxanthin, for example, has a potency more than 100-fold higher than vitamin E, and is showing promise for dementia, infertility, vision problems and ageing skin (for more information, see WDDTY vol 22 no 4).
Krill oil's antioxidant content might explain why the supplement has outperformed fish oil in terms of health effects in a couple of preliminary trials.
One particular brand of krill oil-Neptune Krill Oil (NKO)-has been put to the test in a handful of clinical trials. One, a double-blind randomized controlled trial, compared the effects of NKO and fish oil in 70 healthy women suffering from premenstrual syndrome (PMS). For 30 days, half the women took 2 g/day of krill oil while the other half took 2 g/day of fish oil. Following this, they took the supplements for just 10 days per month over the next two months. Over this period, the women tracked their mental and physical symptoms on a questionnaire developed by the American College of Obstetrics and Gynecology.
At the end of the study, the results revealed that both groups improved in weight, abdominal discomfort and swelling, but only the krill-oil group saw statistically significant improvements in breast tenderness, feelings of inadequacy, stress, irritability, depression, joint discomfort and bloating. Moreover, the krill-oil group reported greater improvements in alert-ness, energy and well-being, and took significantly less analgesic medication around the time of their period compared with the fish-oil group. The researchers also noted that "[p]atients taking NKO did not experience any gastrointestinal difficulties such as regurgitation, while 64 per cent of the women in the fish oil group complained of unpleasant reflux" (Altern Med Rev, 2003; 8: 171-9).
Another randomized controlled trial compared the effects of NKO, fish oil and a placebo on blood lipids (fats) in 120 patients with hyperlipidaemia (abnormally high levels of blood lipids). In this 90-day trial, two groups received krill oil at either 1-1.5 g/day or 2-3 g/day, depending on their body mass index (BMI), while another group received 3 g/day of fish oil and a fourth group received a placebo.
At the lowest dosage, krill oil significantly lowered total and LDL ('bad') cholesterol, and raised HDL ('good') cholesterol compared with the starting-out (baseline) levels as well as vs the fish-oil and placebo groups. At 2 g/day, krill oil also significantly lowered triglyceride levels in addition to cholesterol, but 3 g/day failed to provide any additional benefit vs 2 g/day. In contrast, the fish oil lowered cholesterol only marginally and failed to reduce triglycerides below baseline values (Altern Med Rev, 2004; 9: 420-8).
In another trial, NKO was tested against placebo for its anti-inflammatory effects. Ninety patients with cardiovascular disease, rheumatoid arthritis and/or osteoarthritis, along with high levels of C-reactive protein (CRP)-a marker of systemic inflammation-were given either 300 mg/day of krill oil or a placebo for 30 days. By day 7, krill oil had significantly reduced CRP (by 19 per cent) compared with placebo (increased by 15.7 per cent). By day 30, krill oil had further reduced CRP by 30 per cent. The researchers also reported reduced arthritic symptoms in the krill-oil group, including less pain, stiffness and functional impairment (J Am Coll Nutr, 2007; 26: 39-48).
Although the study didn't compare krill and fish oils, fish oil has failed to lower CRP in at least four separate studies (Altern Med Rev, 2007; 12: 207-27).
The bottom line
Unlike many much-hyped supplements, krill oil actually has a reasonable amount of science behind it, including studies that appear to support the impressive claims being made for it. However, it's still early days, and it would be useful to have some independent, non-manufacturer-led clinical studies of krill oil to rule out any potential biases.
Also lacking is any research on pollution levels in krill oil. Although proponents claim that krill oil is free of the contaminants that are sometimes associated with low-quality fish oil, such as mercury and polychlorinated biphenyls (PCBs), there don't appear to be any scientific studies of the subject. According to the NKO website, the fact that krill is at the bottom of the food chain means that it doesn't accumulate as many toxins and heavy metals as fish do. "This results in a safer and purer product than the standard fish oils on the market" (http://neptunekrilloil.com/ en/faq.aspx).
Ultimately, more research is needed to settle the krill oil/fish oil debate. But the evidence so far, not to mention many happy customers, suggests that this may be one of the few hyped supplements that actually delivers.
WDDTY 22 no 7, October 2011