Benefits · Brain, eyes & skin
Brain, eyes & skin
Group these together because they share a mechanism. In each case DHA isn’t doing something to the tissue — it is part of what the tissue is made of. That’s a different kind of claim from most supplement marketing, and a more defensible one.
The brain is structurally fatty
Well established
By dry weight, the human brain is roughly 60% lipid, and DHA is the most abundant long-chain polyunsaturated fatty acid in it. It concentrates in synaptic membranes — the junctions where neurons pass signals — where its unusually flexible shape keeps the membrane fluid enough for receptors and channels to work properly.
That DHA is structurally essential to the brain is not in dispute. It is why DHA requirements are highest during foetal development and infancy, when the brain is being built fastest, and why it is added to infant formula.
Does supplementing improve cognition in healthy adults?
Early or mixed
Here the evidence gets much weaker, and we’d rather say so. Trials of omega-3 supplementation for memory and cognitive performance in healthy adults have produced inconsistent results. Some found small improvements on specific measures; many found nothing distinguishable from placebo.
The pattern that does recur is that benefits show up more often in people who started with low omega-3 intake, and in older adults, than in well-nourished younger ones. This is the sensible reading of a structural nutrient: topping up a shortfall helps, and adding more on top of sufficiency mostly doesn’t.
Eyes
Reasonably supported
The retina is the most DHA-dense tissue in the body. Photoreceptor cells rebuild their outer segments continuously and need DHA to do it, and the membrane fluidity DHA provides is directly involved in how efficiently light gets converted into a nerve signal.
Omega-3 has also been studied for dry eye, on the reasoning that it influences the quality of the oily layer of the tear film. Results have been mixed — some trials positive, at least one large well-run trial finding no advantage over placebo. Adequate DHA supports normal retinal structure; anything stronger than that overstates the evidence.
Skin
Early or mixed
Skin claims are where omega-3 marketing tends to get loosest, so here is the careful version. The outermost layer of skin is a lipid barrier, and the fatty acids you eat do end up in it, influencing how well it holds water. Omega-3s also feed into the same inflammation-resolution pathways described on the joints page, which is the mechanism behind interest in them for irritated skin.
What’s reasonable to say: dietary fats contribute to the composition of the skin barrier. What isn’t: that a krill oil softgel will visibly change how your skin looks. Trials in this area are small, short and inconsistent, and topical and lifestyle factors dominate.
Why phospholipid form gets mentioned here
The transporter that moves DHA across the blood-brain barrier — MFSD2A — preferentially carries DHA that is attached to a phospholipid rather than free DHA. That’s a real and interesting piece of biology, and it’s often cited as evidence that krill oil is better for the brain specifically.
Our honest read: the transporter finding is solid, but the leap from it to “krill oil measurably improves brain outcomes in humans” has not been made by the clinical evidence. It is a plausible mechanism awaiting a trial, and we’d rather present it as that than as a proven advantage.