The short answer
DHA is an omega-3 fat your brain uses in its cell membranes. Getting it from food or algae oil gives brain nutrition a concrete place in your routine. Human studies have tested memory as well as long-term disease outcomes; those are different questions, with different results.
What DHA does in the brain
DHA (docosahexaenoic acid) is a long-chain omega-3 fatty acid and a structural building block of brain cell membranes, especially at the synapses where neurons communicate. The brain is unusually rich in it. That structural role is why low DHA has long been a suspect in cognitive aging, and why intake tends to track brain outcomes.
What the research shows
In the Framingham Offspring cohort, the group with the highest red-blood-cell DHA had about 49% lower relative incidence of Alzheimer’s than the group with the lowest. This was an association between measured DHA status and later diagnoses, not a 49% reduction caused by taking a supplement. Read the cohort study.
Human trials have produced mixed results. The 24-week MIDAS trial tested 900 mg DHA daily in 485 adults aged 55 and older with age-related cognitive concerns and reported an improvement on its learning outcome. That finding does not establish dementia prevention or a memory benefit from the 420 mg in Brain Longevity. Age, starting DHA intake, dose, and the outcome tested all matter. Read the MIDAS trial; explore DHA and lithium.
What this means for your routine
DHA from food, oily fish a couple of times a week, is part of a well-supported brain-and-heart-healthy pattern (it's also why the Mediterranean diet performs well). A supplement is a reasonable way to fill a gap if you eat little fish, but it should be understood as supportive, not a treatment that prevents dementia. The overall eating pattern matters alongside any supplement choice.
Semaine’s proposed Brain Longevity formula puts 420 mg algae-derived DHA and 1 mg elemental lithium from orotate in one vegetarian capsule. DHA supplies a component of brain-cell membranes; the lithium ingredient draws on a separate research rationale. The finished combination has not been shown to improve memory. Explore why we paired DHA and lithium.
When to see a clinician
Omega-3 supplements can interact with blood thinners and aren't right for everyone at high doses, so check with a clinician before starting, especially if you take medication. And supplements are an addition to, not a replacement for, the basics: sleep, exercise, and cardiovascular health.
Frequently asked questions
Is DHA good for your brain?
DHA is a component of brain-cell membranes. Some trials have reported improvements on selected memory or learning tests, while others have not. These results do not establish dementia prevention or a benefit from every DHA supplement. Read an example trial.
Does omega-3 prevent dementia?
No prevention claim is established. Cohort studies link higher DHA to lower risk, but randomized supplement trials have generally not confirmed a benefit. Association is not proof.
How much DHA should I get?
Most guidance points to oily fish a couple of times a week as the food-first approach. Supplement doses vary; discuss with a clinician, particularly if you eat little fish or take medication.
Does the APOE4 gene change how DHA works?
Possibly. Aging and APOE4 alter DHA metabolism, which may reduce the benefit of supplementation in some people and is one reason trial results are mixed (Hennebelle et al., 2013).
Is fish oil worth taking?
If your diet is low in oily fish, a supplement is a reasonable way to raise intake, understood as general support rather than a brain-disease treatment. Check with a clinician if you're on blood thinners.
Related reading
- Olive polyphenols and the brain
- DHA and lithium: reading the evidence
- Cognitive reserve: building a brain that ages well
References
- He, Huang, Wang et al. (2023). Circulating polyunsaturated fatty acids, fish oil supplementation, and risk of incident dementia: a prospective cohort study of 440,750 participants. GeroScience.
- Hennebelle, Plourde, Chouinard-Watkins et al. (2013). Ageing and apoE change DHA homeostasis: relevance to age-related cognitive decline. Proceedings of the Nutrition Society.
- Sala-Vila, Satizabal, Tintle et al. (2022). Red Blood Cell DHA Is Inversely Associated with Risk of Incident Alzheimer’s Disease and All-Cause Dementia: Framingham Offspring Study. Nutrients.
