What are EPA and DHA, and can my body make enough?

EPA and DHA are long-chain polyunsaturated fatty acids, each with distinct biological roles. While both belong to the omega-3 family, they serve different functions at the cellular level¹.

EPA (eicosapentaenoic acid) is a 20-carbon fatty acid that serves as a precursor to a class of signaling molecules called eicosanoids. These include prostaglandins and resolvins that help regulate the inflammatory response. When your body has adequate EPA, it produces more anti-inflammatory signals and fewer pro-inflammatory ones^1,2.

DHA (docosahexaenoic acid) is a 22-carbon fatty acid that is a structural component of cell membranes, particularly in the brain and retina. DHA makes up roughly 40% of the polyunsaturated fatty acids in the brain and about 60% of those in the retina⁴. Its accumulation in the fetal brain takes place mainly during the last trimester of pregnancy and continues at very high rates up to the end of the second year of life⁴.

Your body can technically convert ALA (alpha-linolenic acid, found in flaxseed and walnuts) into EPA and DHA, but the conversion rate is extremely low -- typically less than 5% for EPA and less than 0.5% for DHA³. This is why dietary intake of preformed EPA and DHA is considered important.

The biological essentiality of EPA and DHA is well-established across decades of research. Swanson et al. (2012) conducted a comprehensive review demonstrating that EPA and DHA exert health benefits across the entire lifespan, from fetal development through aging, with mechanisms including anti-inflammatory eicosanoid production, cell membrane structural support, and gene expression modulation¹.

The distinct roles of EPA and DHA arise from their differing chain lengths and double-bond configurations. EPA (20:5n-3) is the primary substrate for Series-3 prostaglandins and Series-5 leukotrienes, which are substantially less inflammatory than their arachidonic acid-derived counterparts. EPA also gives rise to E-series resolvins, specialized pro-resolving mediators that actively terminate inflammatory responses rather than merely suppressing them².

DHA (22:6n-3) plays an irreplaceable structural role: it is a structural constituent of membranes specifically in the central nervous system, and its accumulation in the fetal brain takes place mainly during the last trimester of pregnancy and continues at very high rates up to the end of the second year of life⁴. Innis (2008) reviewed the role of dietary omega-3 fatty acids in providing DHA for nervous tissue growth and function⁵. Inadequate intakes of omega-3 fatty acids decrease DHA and increase omega-6 fatty acids in the brain, and decreased DHA in the developing brain leads to deficits in neurogenesis, neurotransmitter metabolism, and altered learning and visual function in animals; epidemiological studies have linked low maternal DHA to an increased risk of poor child neural development⁵. Most of the human data on DHA concern its contribution to optimal visual acuity development⁴.

The NIH Office of Dietary Supplements notes that while ALA-to-DHA conversion exists as a metabolic pathway, it is insufficient to meet physiological demands in most individuals. Stable isotope tracer studies show conversion rates of ALA to EPA at approximately 0.2-8% and ALA to DHA at less than 0.05-4%, with considerable interindividual variability influenced by sex, genetics, and background diet³. This evidence underpins the recommendation for direct dietary intake of preformed EPA and DHA.