Recognition of the nutritional utility and conditional essentiality of omega-3 fatty acids such as eicosapentaenoic (EPA) and docosahexaenoic acids (DHA) has had a transforming effect on both global food innovation and dietary supplement formulations. The advent of microbial/algal sources of DHA had a revolutionary impact, providing a concentrated single-celled organism source of DHA. However, to date there appears to be no commercial microbial source of EPA or EPA + DHA.
In the icy waters of the South Atlantic reside shelled, shrimp-like organisms that weigh one gram. They are known as krill, with the genus Euphausia superba the primary commercial krill species of the 100 or so species described. Krill harbours appreciable quantities of EPA + DHA, incorporated primarily into phospholipids rather than as triglycerides as found in fatty fish.
These highly polyunsaturated fatty acids (PUFAs) serve as a ?biological anti-freeze? constituent in these hardy organisms, preserving the fluidity of cell membranes. Thirty to 40 per cent of the fatty acids found in krill oil are comprised of EPA + DHA.1,2
Surprisingly, despite the high concentration of PUFAs, which renders fish oil susceptible to oxidative rancidity, krill oil appears to be remarkably stable.2 This may be due to the presence of lipid-soluble antioxidants, including the carotenoid astaxanthin.3 Astaxanthin in krill oil is largely esterified to saturated and monounsaturated fatty acids.3 Krill also boasts an appreciable quantity of alpha-tocopherol and a unique derivative known as marine-derived tocopherol.4,5 This latter vitamin E entity may function as a more effective antioxidant in the freezing conditions of krill?s habitat than alpha-tocopherol.
Human studies with krill are limited. One review describes a seven-day feeding study with 25g krill meat, resulting in favourable, ?aspirin-like? changes in blood platelet function and significant increases in blood EPA + DHA concentrations.6
Unpublished work funded by, and conducted in part with, Neptune Technologies and Bioressources (Canada) claims superior blood lipid-modifying effects to an equal dose of fish oil. Neptune markets a patented krill oil obtained through solvent extraction, wherein a derivative of the flavonoid luteolin has also been identified, perhaps explaining in part the exceptional shelf stability of krill oil in general.
Additionally, a double-blind clinical trial conducted among 70 women with premenstrual syndrome assigned women to receive either 2g Neptune krill oil or 30 per cent omega-3 fish oil for three months.7 At 45 and 90 days into the study, the krill oil group showed superior improvements in most of the self-reported symptom scores and also in the use of analgesic medications during the eight days preceding and two days following the onset of menstruation in each cycle.
This study?s findings need to be interpreted with caution. First, the use of archaic diagnostic criteria and the absence of a prospective daily symptom diary invites misdiagnosis of PMS.8,9 Second, the study design did not exclude subjects who display a high placebo response, a common finding in studies that measure a large number of symptoms of mild to moderate severity (as did this study). Thirdly, conflict of interest issues are prominent, as the lead author of the study is the vice president of research and development at Neptune.
Clearly, independent confirmation of krill oil?s effects and peer review scrutiny are warranted to assess the true promise of this tiny crustacean?s role in human nutrition.
References1. Kolakowska A, et al. Winter season krill (Euphausia superba Dana) as a source of n-3 polyunsaturated fatty acids. Nahrung 1994;38:128-34.
2. Bustos R, et al. Oxidative stability of carotenoid pigments and polyunsaturated fatty acids in microparticulate diets containing krill oil for nutrition of marine fish larvae. J Food Engin 2003;56:289?93.
3. Takaichi S, et al. Fatty acids of astaxanthin esters in krill determined by mild mass spectrometry. Comp Biochem Physiol B 2003;136:317?22.
4. Dunlap WC, et al. Notothenioid fish, krill and phytoplankton from Antarctica contain a vitamin E constituent (alpha-tocomonoenol) functionally associated with cold-water adaptation. Comp Biochem Physiol B 2002;133:299?305.
5. Yamamoto Y, et al. An unusual vitamin E constituent provides antioxidant protection in marine organisms adapted to coldwater environments. Proc Natl Acad Sci USA 2001;98:13144?8.
6. Anon. Nutritional value of Antarctic krill. Bull World Health Org 1995;73:551.
7. Sampalis F, et al. Evaluation of the effects of Neptune Krill Oil on the management of premenstrual syndrome and dysmenorrheal. Altern Med Rev 2003;8:171-9.
8. Rapkin AJ, et al. Comparison of retrospective and prospective assessment of premenstrual symptoms. Psychol Rep 1988;62:55?60.
9. ACOG (American College of Obstetricians and Gynecologists). Premenstrual Syndrome. ACOG Practice Bulletin No. 15, 2000 April.