Her conclusion is that the diet-derived DHA is in a phospholipid form which is able to cross the blood brain barrier much better than free DHA (as found in most supplements) in ApoE4 people.FASEB J. 2018 Oct 5:fj201801412R. doi: 10.1096/fj.201801412R. [Epub ahead of print]
Role of phosphatidylcholine-DHA in preventing APOE4-associated Alzheimer's disease.
Dietary and supplemental intake of the ω-3 fatty acid docosahexaenoic acid (DHA) reduces risk of Alzheimer's disease (AD) and ameliorates symptoms. The apolipoprotein E ( APOE) 4 allele is the strongest risk factor for sporadic AD, exclusive of age. APOE4 carriers respond well to the DHA present in fish but do not respond as well to dietary supplements. The mechanisms behind this varied response remain unknown. I posit that the difference is that fish contain DHA in phospholipid form, whereas fish oil supplements do not. This influences whether DHA is metabolized to nonesterified DHA (free DHA) or a phospholipid form called lysophosphatidylcholine DHA (DHA-lysoPC). Free DHA is transported across the outer membrane leaflet of the blood-brain barrier (BBB) via passive diffusion, and DHA-lysoPC is transported across the inner membrane leaflet of the BBB via the major facilitator superfamily domain-containing protein 2A. I propose that APOE4 carriers have impaired brain transport of free DHA but not of DHA-lysoPC, as a consequence of a breakdown in the outer membrane leaflet of the BBB, putting them at increased risk for AD. Dietary sources of DHA in phospholipid form may provide a means to increase plasma levels of DHA-lysoPC, thereby decreasing the risk of AD.-Patrick, R. P. Role of phosphatidylcholine-DHA in preventing APOE4-associated Alzheimer's disease.
Does this mean we should just be eating fish and dumping our omega 3 supplements? Actually I found that you can find supplements that contain DHA in the phospholipid form (at least that's what is claimed), and it appears that any omega 3 that comes from Krill oil should be high in phospholipid form DHA. The author even hints at that in the final sentence of her paper:
"There is a pressing need for clinical trials evaluating the effects of omega-3 in phospholipid form, either from fish roe oil or krill oil, on cognitive function in APOE4 carriers with AD."
Personally I just bought some krill oil based supplements. I will not post a link to any products, as I don't want to appear to be promoting anything. They're pretty easy to find.