A new study has shown that, after a four-week daily high dose intervention, fish oils, fish oil ethyl esters and krill oil have almost the same bioavailability in red blood cells and plasma when levels of EPA and DHA are matched. There was no evidence that the high phospholipid content or antioxidant content of krill oil improved the bioavailability of EPA and DHA.
A new, double-blind, randomized controlled trial (n=66) involving an intervention of 1.3 g/day eicosapentaenoic and docosahexaenoic acid (approx. 61% EPA:39% DHA) over a period of four weeks has demonstrated that accrued levels of EPA and DHA in red blood cells and plasma were comparable regardless of whether the dose was received from fish oil, fish oil ethyl esters or krill oil.
Krill oil has been widely marketed as having greatly superior bioavailability of EPA and DHA because the latter are predominantly found in the phospholipid form (rather than the triglyceride form found in fish oil), and because this oil contains a potent natural antioxidant in the form of astaxanthin.
However, prior to the present study, former trials looking at the bioavailability of krill oil did not use comparable doses of EPA and DHA (on an individual basis) and tended to be carried out over a relatively short time period (i.e., insufficient to allow tissue to accumulate (2)).
Previously, a small-scale, double-blind crossover study from 2013, involving a much lower daily intervention of 600 mg total omega-3s over four weeks, had appeared to show an approximate doubling of EPA in tissues for krill oil compared to fish oil, whereas there was minimal difference in DHA levels between the two (3). The problem with this study is that tissue accumulation of EPA is very low in any event, and EPA:DHA ratios for krill oil and fish oil were not matched.
An open-label study by Ulven et al., in which adults were supplemented for seven weeks, used non-equivalent doses of 3 g krill oil and 1.8 g fish oil triglycerides (4).
Arterburn et al. demonstrated that a four-week intervention of omega-3 fatty acids was necessary to achieve “steady state” plasma levels (5).
A recent trial by Kohler et al., in which the impact of a single intervention dose was measured after 72 hours, failed to show a difference in bioavailability between matched EPA and DHA content in krill meal and fish oil (6).
The Yurko-Mauro study (1) had the advantage of using commercial preparations. The krill oil used contained 840 μg astaxanthin per capsule, and approx. 44% of the omega fatty acids were bound as phospholipids. The fish oils contained 0.1% mixed tocopherols as an antioxidant. After four weeks of the intervention, the tissue accumulation of EPA and DHA between krill oil, fish oil, and fish oil ethyl esters varied by a maximum of 24%. Overall, there was a trend toward krill oil being slightly more effective than fish oil, which in turn was slightly more effective than fish oil ethyl esters – but these differences did not achieve statistical significance.