DHA for the brain

DHA is a 22-carbon omega-3 fatty acid and the single most abundant fatty acid in the grey matter of the brain and in the retina. It is a structural component — it sits inside neuronal cell membranes, where it keeps them fluid and supports how synapses signal. The body can make a little DHA from plant ALA (in flax, walnuts), but the conversion is poor, which is why oily fish or a direct DHA supplement matters. This is a genuinely different question from “does fish oil protect the heart” — here we care about DHA as a building block for the nervous system.

Age-related memory decline. The best single piece of evidence is the MIDAS trial: 485 healthy older adults (55+) with mild memory complaints took 900 mg/day of algal DHA or placebo for 24 weeks. The DHA group made significantly fewer errors on a learning-and-memory task, roughly equivalent to reversing a few years of age-related decline, and blood DHA doubled.¹

Correcting a real shortfall. DHA helps most when you start low — low dietary intake, little or no oily fish, or the ageing brain, where membrane DHA falls. If you already eat fish twice a week, you are likely replete and have less to gain.

Preventing dementia in healthy people. A Cochrane review pooling randomised trials in cognitively healthy older adults found omega-3 supplements gave no benefit over placebo for cognition and no protection against decline.² DHA is not a way to prevent Alzheimer’s, and once dementia is established the trials are largely disappointing too.

Pregnancy for a “smarter baby”. DHA is essential for building the fetal brain, but supplementing beyond a normal diet is oversold: the large DOMInO trial (800 mg/day DHA in pregnancy) did not improve children’s cognitive or language scores at 18 months.³ Adequate DHA in pregnancy matters; megadosing for cleverness is not supported.

Fish oil is a blend of two omega-3s. EPA is the one with the stronger cardiovascular and anti-inflammatory case; DHA is the structural, brain-and-eye one. So for cognition you specifically want a product with a high DHA figure on the label — not just a big “omega-3” number. Algal (algae-derived) DHA is a clean, vegan source that delivers DHA directly and was the exact form used in the memory trial above.

Everyday adequacy: ~250–500 mg combined EPA+DHA/day, or oily fish twice weekly. The cognitive trials in older adults used ~900 mg/day of DHA specifically for 6 months — a reasonable target if memory support is your goal. Effects build over weeks to months, not days.

DHA is well tolerated. High omega-3 doses can mildly thin the blood — take care before surgery or alongside anticoagulants. Choose a product with a stated DHA content and freshness/oxidation testing, since rancid fish oil is common. In pregnancy, stick to normal dietary or antenatal-recommended amounts.