DHA

Docosahexaenoic acid is the most abundant omega-3 fatty acid in neural tissue. Its molecule has a 22-carbon backbone carrying six cis double bonds, and its older trivial name, cervonic acid, reflects a long-recognized link with the brain ^[2]. DHA makes up a large share of the polyunsaturated fatty acids found in the grey matter of the brain and in the retina, where it concentrates in the membranes of neurons and photoreceptor cells ^[1][2].

Preformed DHA reaches people mainly through marine foods such as salmon, herring, mackerel, and anchovies, as well as through fish oil and, for those who avoid animal products, oils pressed from marine microalgae ^[1]. Although the body can lengthen and desaturate plant-derived alpha-linolenic acid into DHA, that conversion is inefficient, so dietary or supplemental intake is generally regarded as the practical way to keep tissue levels up ^[2]. Microalgae are the original biological producers of the fatty acid, and fish accumulate it as it moves up the marine food chain.

Within cell membranes, DHA supports the formation and buildup of phosphatidylserine, an anionic phospholipid that is especially enriched in neurons and that participates in survival signaling and neurotransmitter release ^[3]. Much of the interest in the fatty acid centers on the developing brain, since DHA is deposited rapidly during pregnancy and early infancy, and the amount transferred from maternal stores shapes how much accumulates in fetal and infant neural tissue ^[5].

Reviews spanning the lifespan connect adequate DHA status with aspects of learning and memory and note associations between low intake and steeper cognitive decline in older age, although supplementation trials have given mixed results ^[1][2]. A placebo-controlled trial in older adults reported that supplementation raised DHA and EPA concentrations in cerebrospinal fluid, with a smaller increase among carriers of the APOE4 gene variant, which suggests that delivery of the fatty acid to the brain depends partly on genetics ^[4]. Marine omega-3 fatty acids have also been examined for cardiovascular endpoints, and in 2019 the U.S. Food and Drug Administration permitted qualified health claims relating them to reduced risk of high blood pressure and coronary heart disease.

In commerce, DHA is treated as a food ingredient and dietary supplement rather than a drug, and purified forms are recognized as safe for addition to foods and infant formulas. It is sold as fish oil, as concentrated triglyceride or ethyl ester preparations, and as vegetarian algal oil, often alongside the related omega-3 eicosapentaenoic acid.

DHA is very safe for most people; high doses can cause a fishy aftertaste, mild GI upset, or a slight blood-thinning effect. People on anticoagulants should mention high-dose fish oil to their doctor. Choosing a purified product limits concerns about mercury and other contaminants.

Most interaction data on DHA comes from fish oil preparations that also contain EPA, so attributing an effect to DHA alone is difficult; the honest summary is that the interactions are real but modest.

The one that gets attention is bleeding. DHA incorporates into platelet membranes, shifts eicosanoid production away from thromboxane A2 and reduces platelet aggregation slightly. Case reports describe raised INR and serious bleeding in people taking warfarin alongside fish oil, including a fatal case after head trauma in which the coagulopathy could not be reversed. Controlled studies at ordinary supplemental doses have generally found little change in INR, so the risk appears to sit with high intakes and with people already on an anticoagulant or antiplatelet drug.

DHA is fat soluble, so orlistat and other lipase inhibitors reduce how much of it is absorbed. A small blood pressure lowering effect can add to antihypertensives. There is no meaningful effect on cytochrome P450 enzymes.

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