Chuckles; caveat; I am not a scientist, and I'm not qualified to express a scientific opinion. I'm more like a reporter / librarian . What I can say is what I observe from the literature.
Both DHA and EPA are metabolically active and essential to "normal" body functions. DHA oriented studies consistently point to its primary activity as being utilized in the brain, especially during early development . That's because DHA is found in larger amounts in the brain vs EPA, there but even at that , there are questions of which fatty acid is utilized by the brain because some postulate that EPA isn't seen in the brain as much because it is being utilized more than DHA. Literature also suggests EPA has an anti depressant like effect (& confirmed by many here) so we know its biologically active in the brain. So DHA is net beneficial for your body in dietary levels (from foods). And in low dose it's hard to tell the difference between the two
But what we are focused on is very high dose of either. 4 grams of either EPA / DHA is a lot to take daily , roughly same as taking 20-30 OTC supplements daily. And that is where EPA clearly pulls away from DHA. In high dose, both are effective in lowering TGs other lipds, but in high Doses, EPA perform much better than DHA such as not raising LDL-C. In addition there are fewer side effects of pure EPA vs DHA in high doses. So I believe Vascepa is highly differentiated , and more so than any other O3 formulated drug including Lovaza and up and coming Epanova.
Then remember this, No other O3 drug is as far along in an outcomes trials like Reduce It. If Vascepa performs close to JELIS cohort, why would any doc mess around with anything less than pure EPA -when it becomes proven to reduce CVD risk? Layer on patent protection til 2030 and you have a very valuable asset . BTW they have patents to cover DHA along with EPA to 20%. So they built a nice "fire-wall"
Lastly, an area of O3 science that is emerging deals with discovery those specific metabolites of EPA that are responsible for its heart benefits. Thsi recently came to light in a JAMA article last month (EPA Metabolite 18-HEPE) http://jama.jamanetwork.com/article.aspx?articleid=1900498
Now imagine a day when, instead of taking 4 large capsules of Vascepa, you can take 1 pill contain the active EPA metabolites? Imagine after Reduce It, Amarin (under protection of its combo patents) comes out with statin drug combined with a few of these metabolites in a single daily dose?
Now that would be something wouldn't it? Hard to call lit "fish Oil" at that point... and any comparison with DHA becomes moot
Your questions must be addressed depending on what population you are asking about - older adults with CV risk? Yes, EPA cream of the crop. Developing children need both - DHA is needed for the brain, and is frequently added to formula for that purpose.
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